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The secondary combustion between unburnt fuel in rocket plume and ambient air significantly affects the stealth characteristics of rocket motors. In order to reveal the effect of secondary boundary layer combustion of hydrogen on rocket plume heat release characteristics, a two-dimensional axisymmetric model for boundary layer combustion between the rocket plume and air is established. The results identifies significant exothermic effect due to secondary combustion reaction between the plume and air. Compared to the nozzle plume without considering secondary combustion, the average temperature of the plume with secondary combustion increases by 47%. As hydrogen content in the nozzle plume increases from 2.7% to 4.2%, the average temperature of the nozzle plume increases by 17.2% due to enhanced combustion heat release. The secondary combustion process is weakened with the increase of flight altitude. The average temperature of the nozzle plume decreases by 11.8% from 2 km to 8 km of flight altitude. This is because both the pressure and temperature of the ambient air decrease when the flying altitude rises, which leads to lower secondary combustion reaction and heat release rate. Moreover, as the ambient pressure decreases, the hydrogen concentration in the plume decreases due to plume expansion effect. The results indicate that hydrogen content and flight altitude affect secondary combustion by different mechanisms. The hydrogen content directly affects the concentration term of the reaction rate of secondary combustion. However, the flight altitude affects the kinetic rate of secondary combustion by changing both the temperature and partial pressure of oxygen. The present study provides better insight into the interaction mechanism between nozzle plume and ambient air. • Established numerical model for secondary combustion of rocket plume. • Higher hydrogen content enhances secondary combustion process. • Secondary combustion heat release is weakened as flight altitude increases. • Secondary combustion is controlled by shear mixing and heat transfer. [ABSTRACT FROM AUTHOR]

This study explores the transition in combustion technologies from dry micro-mix hydrogen-air to wet micro-mix hydrogen-oxygen configurations. The investigation involves a comprehensive analysis of the combustion processes currently being considered for converting methane gas turbines to methane-hydrogen mixtures and hydrogen, including wet premixed, dry low emission, sequential combustion, and micro-mix, examining key parameters such as efficiency, emissions, and overall performance. Then, the work considers the shift from utilizing air as an oxidizer to oxygen. Wet micro-mix hydrogen-oxygen combustion is then discussed for its impact on combustion dynamics and the potential for achieving zero emissions, cancelling NOx emissions in addition to CO 2 emissions. The findings contribute valuable insights into the feasibility and advantages of transitioning from conventional hydrogen-air combustion to innovative wet hydrogen-oxygen combustion, paving the way for more sustainable and environmentally friendly combustion technologies. Scheme of a hydrogen energy storage system comprising one electrolyser, two tanks for the hydrogen and the oxygen, and an O 2 /H 2 /H 2 O gas turbine power system. The system could be able to receive non-dispatchable electricity and release dispatchable electricity working as a battery but without any limitation on the amount of energy storable, or the time of the storage. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study focuses on the removal of ineffective hydroxyl surface (B–OH) of the shell of pristine boron (B) particles, followed by its modification using a low-cost, eco-friendly, and non-hazardous ethylene glycol (EG). Subsequently, very small-sized titanium dioxide (TiO 2) particles are coated onto the boron surface by adding titanium tetraisopropoxide (TTIP) precursors at room temperature. Characterization techniques were employed to investigate the structure and morphology of these materials. FTIR, XPS, and TEM analysis reveal that EG effectively removes ineffective boron hydroxyl surfaces and modifies the surface through passivation by its surface functionalities. Furthermore, EG assists in the coating very small-sized TiO 2 particles on the boron surface. Thermal stability tests show that the modified boron surface and TiO 2 -coated boron surface exhibit earlier oxidation of the core boron compared to pristine boron. This enhanced capability for earlier oxidation of core boron was further investigated in the shock tube and bomb calorimeter for measurement of ignition delay time and heat of combustion. The findings demonstrate that room temperature synthesized TiO 2 -coated B particles (ignition delay time of ∼181 μs and heat of combustion of ∼17.3 kJ/g) outperform pristine B particles (ignition delay time of ∼284 μs and heat of combustion of ∼13.2 kJ/g). This improvement is attributed to the removal of ineffective boron hydroxyl surfaces, surface modification, uniform coating with very small TiO 2 particles, the catalytic effect of TiO 2 on oxygen diffusion, and effective oxidation of core boron. This study suggests that efficient energetic material can be achieved at room temperature with no potential harm to the environment. [ABSTRACT FROM AUTHOR]

Metastable intermolecular composites (MICs) are often used in military and aerospace applications because of their high energy density. However, the traditional preparation methods are either complicated and unsafe, or the prepared composites have incomplete combustion and low energy release rates. In this paper, a series of aluminum/metal oxide/nitrocellulose (AM x N) composite microspheres were prepared by spray drying technique. The field emission scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) results show that the prepared AM x N composite microspheres have regular morphology and uniform particle size, and nitrocellulose (NC) is successfully coated between fuel (Al) and oxidizers (CuO, MoO 3 , and Bi 2 O 3). The thermal reactivity, energy, and combustion properties of AM x N were investigated and compared with physically mixed aluminum/metal oxide (AM x). The explosion heat of AM x N is higher than AM x , while the thermal reaction exothermic peak temperature is lower. Among them, the composite containing copper oxide has the highest explosive heat value (5034 J/g), and the composite containing bismuth oxide has the shortest burning time (2.8 ms). These results prove that NC as a binder shortens the reaction distance between the oxidizer and the fuel in the presence of spray drying. Different oxidizers can modulate the energy release rate of AM x N composites, which is beneficial for applying MICs in energetic materials. [ABSTRACT FROM AUTHOR]

This study examined the influence of various chemical reaction mechanisms and heat loss conditions on the prediction of longitudinal combustion instability in the Continuous Variable Resonance Combustor (CVRC). To assess the impact of chemical reaction mechanisms on the prediction of longitudinal combustion instability modes, both global and skeletal mechanisms were used, while adiabatic wall conditions were employed to eliminate the effects of heat loss. To evaluate the effect of heat loss conditions on the prediction of combustion instability modes, investigations were conducted under three different conditions: adiabatic wall, isothermal wall, and considering thermal radiation using the simple P1 model and the gray gas model. Radiative heat loss was calculated using a radiative convection boundary condition, while heat loss through wall convection was ignored. The dominant frequency, temperature field, pressure field, and combustion instability development mechanism were analyzed based on the numerical results and compared with experimental data and previous numerical studies. The use of a skeletal mechanism and the consideration of heat loss were found to reduce the difference in combustion instability mode frequency compared to experimental data. The results showed that maintaining an isothermal wall temperature effectively decreased the difference in the dominant frequency compared to experiments, but had limitations in reducing pressure fluctuation amplitudes. Additionally, incorporating thermal radiation did not significantly decrease the difference in the first mode frequency compared to experimental data, although it kept the range of pressure fluctuations within a reasonable level. Therefore, this study underscores the importance of accurate temperature prediction for evaluating thermal-acoustic instability frequencies and highlights the necessity of using a chemical reaction mechanism that accurately predicts the adiabatic flame temperature and heat loss conditions. • We investigated the impact of modeling choices on the prediction of instability. • Global and skeletal reaction mechanisms overestimated instability frequencies. • Radiative heat loss was found negligible for temperatures under 2500 K. [ABSTRACT FROM AUTHOR]

• The flammability limits of R13I1 + R152a/R600a/R1270 binary mixtures were measured. • The critical flammable volumetric ratios of R13I1 + R152a/R600a/R1270 were obtained. • A generalized equation for the LFL of R13I1 mixtures was provided. • F -number and HOC were calculated and the inhibitory effects of R13I1 were analyzed. Trifluoroiodomethane (R13I1) is a flame retardant with an extremely low global warming potential (GWP) and can be used as a component to improve the flammable characteristics of most promising low-GWP refrigerants. In this paper, the flammability limits of R13I1 + 1,1-Difluoroethane (R152a), R13I1 + isobutane (R600a) and R13I1 + propylene (R1270) binary mixtures were measured at 60 °C and atmospheric pressure with a 12 L flask according to ASHRAE standards. The critical suppression ratios of R13I1 + R152a, R13I1 + R600a and R13I1 + R1270 are 0.45, 2.24 and 0.99, respectively. A generalized equation for the lower flammability limit (LFL) of R13I1 mixtures was provided. With the LFL of the fuel gas in air and the ratio of R13I1 to the fuel gas, the developed generalized equation can calculated the LFL of R13I1 mixtures with a reasonable accuracy. The influence of R13I1 on the flammability of R152a, R600a and R1270 were studied. The LFL increases and heat of combustion (HOC) decreases significantly with the increase of the R13I1 concentration. The flammability inhibition effects of R13I1 decrease in the order: R152a > R1270 > R600a. [ABSTRACT FROM AUTHOR]

Chemical reaction is the major source of combustion irreversibility in premixed conditions, and revealing the details of exergy destruction can provide a more essential perspective on exploring high-efficiency combustion strategies. The present study focuses on the homogeneous combustion process of CH 4 /H 2 /air mixtures, aiming to reveal the exergy destruction behavior of chemical reactions from the viewpoint of different combustion stages and oxidation paths. Results indicate that exergy destruction is mainly accumulated in the ignition delay stage, and the exergy destruction caused by different elementary reactions depends on the temperature at which the reaction takes place and the resulting change of free energy. By dividing the chemical reactions into four groups, the main reaction channels that contribute to the change in exergy destruction with combustion boundaries have been identified. Global reaction flux analysis reveals the effect mechanism of different oxidation paths on exergy destruction. Furthermore, the staged combustion concept with endothermic reactions reacting firstly at lower temperatures followed by dilute combustion in the high-temperature heat release stage is discussed from the point of the exergy destruction evolution, which offers the potential to simultaneously reduce exergy destruction and suppress NO x formation. • Exergy destruction depends on the reaction temperature and free energy change. • The chemical reactions are classified into four groups. • Exergy destruction is significantly affected by the reaction paths. • H 2 addition effectively broadens the area of low exergy destruction. • A staged combustion concept for reducing combustion irreversibility is explored. [ABSTRACT FROM AUTHOR]

The development of net-zero emission fuels is a priority area of modern research due to the imminent reduction of fossil fuel reserves and environmental problems caused by their combustion. One of the promising fuels is hydrogen, which has a high heat of combustion and is eco-friendly, forms water as the only byproduct. Recently, methods of hydrogen production by microorganisms, which use directly the solar energy or utilize the organic waste during fermentation, have been intensively developed and applied. In this review, the basic principles of the main light-dependent (biophotolysis, photofermentation) and light-independent (dark fermentation and microbial electrolysis) methods of biological hydrogen production are discussed. Particular attention is paid to the advantages and disadvantages of these methods, the possibility of combining them into a single system, as well as various strategies for improving biohydrogen production aimed at transition from laboratory research to full-scale application. [ABSTRACT FROM AUTHOR]

Gas-centered swirl coaxial (GCSC) injectors, a type used in the combustion chamber of liquid rocket engines, have been widely investigated because their characteristics are key parameters for the performance of the engine. This study investigated the spray and combustion characteristics of GCSC injectors used in the combustion chamber of oxidizer-rich staged-combustion cycle engines. When the propellant mass flow rate and oxidizer-to-fuel mass flow ratio (O/F ratio) were identical, the diameter of the gas nozzle was changed such that the ratio of the gas-to-liquid momentum could be changed; thus, the swirl strength of the liquid also changed because of the increase in the injector diameter. In the spray experiments, the spray characteristics were identified in accordance with changes in the diameter of the gas nozzle through the spray angle, droplet mean velocity, and droplet size by using backlight photography and the ParticleMaster imaging system. For combustion tests, four types of reduced combustion chambers were designed to spray propellants through the same two injectors used in the spray experiments. To generate an oxidizer-rich combustion gas, combustion tests were performed using a pre-burner. The changes in combustion characteristics according to the change in the injector shape under the same combustion chamber shape, propellant flow rate, and O/F ratio were identified through the characteristic velocity and heat flux of the combustion chamber. As the gas–liquid momentum flux ratio increased in accordance with the change in diameter of the gas nozzle, the characteristic velocity increased from at least 1700 m/s to a maximum of 1721 m/s, which was related to the decrease in the Sauter mean diameter observed in the spray experiments. Few studies have investigated GCSC shape variables by simultaneously conducting atmospheric spray experiments and high-pressure combustion tests on GCSC injectors using kerosene and oxidizer-rich combustion gases as propellants. This study observed the changes in spray characteristics according to the change in the diameter of the injector gas nozzle through atmospheric spray experiments of the GCSC injector and compared and analyzed the combustion characteristics through combustion tests using the same injector. The results of this study will potentially aid the design optimization of GCSC injectors and facilitate future developments. • Gas-centered swirl coaxial (GCSC) injector spray, combustion characteristics studied. • These are used in oxidizer-rich staged combustion cycle engine combustion chambers. • Atmospheric spray experiments and combustion performed. • Results can aid design optimization of GCSC injectors and future developments. [ABSTRACT FROM AUTHOR]

The current works aim is performance improvement of different integrated energy systems towards net-zero energy which is driven by a set of Internal Combustion Engine (ICE) through adding some components like fuel cell and thermoelectric generator (TEG) in new arrangements introduced and analyzed. The novelty of the present work is the proposal of the new arrangement of energy conversion systems. In this study the basic cycle (cycle 1) is including an ICE, Kalina cycle, Humidification and Dehumidification (HDH) unit, in cycle 2, the HDH is eliminated while a fuel cell is added to the system and in the cycle 3, in addition to fuel cell and having HDH unit in the system, a thermoelectric generator (TEG) has been used instead of condenser to recover more wasted thermal energy. The performance of all proposed systems is analyzed from energy, exergy, and exergo-economic aspects. It is demonstrated that from an energetic viewpoint, cycle 3 has the better performance with an energy efficiency, and net output power of 37% and 391.7 kW, respectively. That is while from an exergetic viewpoint cycle 2 with exergy destruction of 257.1 kW has superior exergetic performance. The results of current work can provide a precise basis for designing an efficient energy system with a higher thermal performance. • Performance of different integrated energy systems towards net-zero energy. • Cycle components are ICE, HDH unit, Fuel cell, Thermoelectric generator. • From energetic viewpoint, cycle 3 has the better performance. • From exergetic viewpoint, cycle 2 has superior exergetic performance. [ABSTRACT FROM AUTHOR]

Jet obstacles can quickly induce the deflagration to detonation transition (DDT) process and reduce the thrust loss of an engine. However, there are few studies on the use of combustible premixed gases as the reactive jet obstacle. Based on the OpenFOAM platform, a detailed numerical investigation of the flame acceleration and DDT process is carried out with different initial jet velocities and the number of jet obstacles. The results show that, although the stronger flame generated by the reactive jet obstacles will reduce the virtual blockage ratio to a greater extent, the turbulence and combustion heat release effect generated by them still significantly promote the flame acceleration. In terms of flame acceleration, initially, increasing the initial jet velocity has no obvious effect on the flame acceleration. Later, turbulence and combustion heat release begin to dominate the flame acceleration and significantly promote the flame acceleration. Since the jets in this study adopt the same combustible premixed gases, increasing the number of reactive jet obstacles downstream does not improve the upstream flame acceleration. In DDT, increasing the initial velocity of the reactive jet can improve the detonation initiation, but the effect of the obstacle number on DDT is greatly affected by the initial jet velocity. Specifically, at a low initial jet velocity, more jet obstacles can significantly promote the detonation initiation, while at a high initial jet velocity, the enhanced turbulence caused by the jet is the dominant factor for the flame acceleration. Therefore, compared with the number of jet obstacles, the detonation initiation process of the premixed gases is more sensitive to the change in the initial jet velocity. • Reactive jet enhances turbulence effect and provide extra heat for DDT. • Jet velocity variations have different influences in different stages. • The number of downstream jets barely affects the upstream flame evolution. • The DDT process is more sensitive to the change in the initial jet velocity. [ABSTRACT FROM AUTHOR]

This paper presents a study to optimize biogas feed distribution ratio between the reformer and the burner for hydrogen production. The objective is to improve operational and economic efficiency by optimizing the process and minimizing calorific deficits due to CO 2 in direct biogas reforming. The results showed that increasing burner distribution ratio increased energy demand, and decreasing the reformer distribution ratio decreased the energy conversion efficiency. Therefore, an optimized distribution ratio is important. Computational fluid dynamics analysis and experimental investigations show that a 5:5 feed distribution at temperatures above 750 °C facilitates efficient heat transfer to the outer wall of the reforming tube. We believe that this study highlights the importance of optimizing combustion energy and hydrogen production through the distribution ratio while ensuring temperature uniformity in the reformer. • Direct biogas reforming is a way to reduce process costs. • Optimized biogas ratio is vital for efficient H 2 production and minimal heat loss. • Decreasing reformer distribution ratio lowers energy conversion efficiency. • 5:5 feed distribution at 750 °C is ideal for heat transfer in reforming gas. • Study contributes to design and operation of biogas-fed hydrogen production systems. [ABSTRACT FROM AUTHOR]

To improve the energy conversion and efficiency of hydrogen-fueled combustion, a micro recuperative planar with porous media is proposed. Numerical simulation model of premixed H 2 /air combustion is verified by experimental test, then orthogonal analysis of multi-factors, i.e., porous media setting and flow rate, on the combustion characteristics and heat transmission are compared and analyzed. The results indicate that combustion characteristics and heat release are strongly impacted by porous media, that is, preheating of unburnt reactants and heat transmission of gases and gas-solid are improved via the heat recirculation in/around porous media. For instance, the difference of mean wall temperatures of the combustor with/without porous media reaches 4.5% at m f = 6.67 × 10−7 kg/s. So, the inserted porous media boosts the burner radiation temperature, and porous media dimensions and porosity affect the thermal performance of the burner, reducing exhaust gas temperature and improving energy efficiency. Besides, orthogonal analysis is also employed to understand the coupling effects of multi-factors on burning and heat transmission, the effect degree on T m is ranked by m f , L , H and φ. Hence, an optimal burning setting is obtained, i.e., combustor C4.8–6.8, where T m is increased by 4.6% compared to the combustor C3-3 at m f = 9.17 × 10−7 kg/s. It achieves the maximum radiation efficiency 35.26% at m f = 6.34 × 10−7 kg/s. • A micro combustor with porous media is proposed for thermophotovoltaic. • Effects of porous media setting and flow rates on combustion are investigated. • A higher radiation performance can be obtained in the burner with porosity 0.7. • Comprehensive analysis and grey correlation of multi-factors are conducted. • Optimal burner setting is achieved with the maximum radiation efficiency 35.26%. [ABSTRACT FROM AUTHOR]

The cold start-up time is crucial for an on-line methanol reformer. The light-off temperatures of methanol, H 2 and CO catalytic combustion, the light-off temperatures of methanol decomposition and methanol steam reforming, and the light-off temperatures reducing oxidative copper-based catalysts/oxygen carriers (CCOCs) with methanol, H 2 and CO were measured. According to these results, a novel cold start-up method with combining chemical-looping combustion and catalytic combustion (CLC&CC) over CCOCs was proposed in this paper. Firstly, the air is introduced into the reformer and the reformer is heated from the ambient temperature to the light-off temperatures of methanol catalytic combustion with the oxidation reaction heat of the reductive CCOCs, here a part of reductive CCOCs is transformed to oxidative CCOCs. Then, air and methanol are introduced into the reformer and the reformer is further heated to the required temperature with the heat of methanol catalytic combustion and the reduction heat of oxidative CCOCs. By decreasing the end temperature of the air oxidation step as low as its light-off temperature, the oxidation amount of reductive CCOCs, that is, the metallic Cu is greatly decreased, thus, the influence of a cold start-up on CCOCs is limited. Through 200 times cold start-up based on this method, the methanol steam reforming conversion was kept near 100%, while the cold start-up time decreased from 65 s to 62 s. This was in accordance with the characterization results that the dispersion of active substance of metallic Cu in CCOCs was significantly improved through the cold start-up. [Display omitted] • A novel cold start-up method for a methanol reformer was proposed. • Methanol chemical-looping combustion and catalytic combustion were employed. • The cold start-up time of the reformer was about 1 min. • The performance of the CCOCs was improved in this cold start-up method. [ABSTRACT FROM AUTHOR]

A modification in the ramjet engine, known as the Supersonic Ramjet Combustion, completes the combustion at supersonic speeds. Inside the combustion chamber, the mixing of fuels and the entire combustion procedure completes in milliseconds. So, the combustion chamber's flow physics is highly complicated. Through this study, the target is to improve the combustion efficiency inside the combustion chamber, thereby improving the performance of the scramjet engine. For this study, the performance of a strut-based flame stabilizer was analyzed in various positions, and the impact on energy efficiency and combustion performance is evaluated. SST k-ω model of turbulence is used to work out the Navier-stokes equation. To validate data from the experiment, a single strut configuration was considered for the next step, i.e., the comparison of the available data with a three-strut configuration. While considering the three-strut layout, in the x and y directions, secondary struts are placed, while the position of the primary strut remains constant. Only the flow from the primary strut is considered for the analysis of combustion performance out of three struts. From the obtained results, it is clear that the significant factor in improving energy efficiency is positioning the secondary strut in the present three-strut layout. The experiment results state that the combustion efficiency is boosted by 33.86% compared to a single strut combustor. It was also found that there was a considerable decrease in the level of unburned fuel, which makes the configuration more economical. The placement of struts plays a vital role, as any fault in the configuration makes it less efficient than a single strut layout. Other elements that boost combustion efficiency are expansion fans and shock reflection inside the primary zone of combustion and the secondary strut region. With the inclusion of secondary struts, the static wall pressure also escalated. A discrete flow was also observed on the combustion walls for some particular strut layouts. An increase in combustion efficiency was seen when both primary and secondary struts were placed near each other and also for reacting flow from the primary strut alone. There arises no need to supply fuel to secondary struts. So, overall fuel efficiency is improved, making the whole system energy-efficient. • Primary strut is considered for the analysis of combustion performance out of three struts. • The significant factor in improving energy efficiency is positioning the secondary strut in the present three-strut layout. • The combustion efficiency is boosted by 33.86% compared to a single strut combustor. • The intensity of combustion also increased which is evident from static temperature plots. • Shear shock layer enhances the mixing rate by intensifying turbulence phenomena. [ABSTRACT FROM AUTHOR]

Agricultural food grains have been involved in various large fires, but little is known about the fire parameters for many varieties required to evaluate their fire hazard. This research experimentally studied various food grains, with an emphasis on African food grains to obtain their important fire parameters. Oven-dried cowpea, lentils, millet, soybean, flax (linseed), unshelled peanuts, sunflower, shelled peanuts, and sesame were subjected to heat fluxes of 25 kW/m2, 35 kW/m2, and 50 kW/m2 in a cone calorimeter. Heat release rate, effective heat of combustion, mass loss, critical heat flux, time to ignition, peak heat release rate, total heat release, and time to peak heat release rate were obtained. Thermal fire hazard indices derived from these primary parameters, such as flashover potential, fire growth rate, and percentage mass loss were determined and compared with wood pellets. Under a 50 kW/m2 heat flux, the peak heat release rate ranged from 230 to 608 kW/m2 for millet and sunflower respectively. The correlation of materials characteristics and fire parameters shows that the oil content is the dominant determinant of the thermal fire hazard level in the food grains tested. These grains were also found to have a higher fire hazard compared to wood pellets. [ABSTRACT FROM AUTHOR]

This review presents the latest and representative seawater electrolysis systems at both fundamental research and pilot-scale reactor levels. Experimental details including seawater treatment, product detection, electrode assembly, reactors, electrolyte feeding modes, etc. are emphasized. We systematically analyze truly useful strategies/materials designs as well as whether the electrodes are genuinely stable as two main quests to find out truly nice electrode engineering. Gas release behaviors/kinetics at high reaction rates are highlighted. We conclude by taking a look at research directions/opportunities for encouraging practical applications of seawater electrolysis systems/technologies. [Display omitted] • Latest/representative lab-/pilot-scale seawater electrolysis works are summarized. • Vital details overlooked in earlier reviews are stressed like seawater treatments. • Strategies like local reaction micro-environment engineering are distinguished. • Ideas on research like electrolyzer design and gas release are discussed. • Suggested research protocols, critical insights and future perspectives are offered. H 2 has a sufficiently high energy density and a combustion process that emits no carbon, therefore being an appealing storable alternative to fossil fuels. With evident advantages of seawater resources available worldwide, electrochemically making H 2 from seawater holds a great development prospect towards the global deployment of H 2 -based energy plants. However, with current water splitting technologies, this is not an easy task, and the primary obstacle is impurities in natural seawater including halide salts, magnesium salts, organic matter, etc. , which readily cause the electrocatalysis systems to shut down. We herein present a timely review of seawater electrolysis systems at both lab-scale fundamental research and pilot-scale reactor level on the basis of most representative studies. We analyze some of the crucial experimental details that are frequently ignored, such as seawater treatments, product detection, electrode assembly, reactors, electrolyte feeding modes, etc. We then systematically emphasize the latest and representative strategies and catalytic materials designs as well as whether corresponding electrodes are genuinely stable as two key quests to find out truly reliable and exploitable electrode engineering. Gas release behaviors/kinetics at high reaction rates are highlighted as well. In addition, we introduce valuable contents like how to learn from ocean life for electrocatalytic system design. We conclude by taking a look at the future research directions and opportunities for encouraging more practical applications of seawater electrolysis systems/technologies. [ABSTRACT FROM AUTHOR]

The development of hydrogen gas turbine is one of the most important ways to achieve energy conversion, but hydrogen fuel affects the combustion temperature and gas composition, which in turn affects the radiative heat transfer of the combustor. In this paper, two global gas models, the weighted sum of grey gas radiation (WSGG) model and the Planck-mean based on the line-by-line (LBL-PM) method, were used to investigate the effect of different gas models on the heat radiation transfer in the combustion chamber of a DLN hydrogen heavy-duty gas turbine. And the Realizable k − ε model, transported probability density function (PDF) combustion model, and Discrete Ordinates (DO) radiation model were used to establish the whole three-dimensional compressible combustion flow radiative heat transfer process. The results show that in the low temperature and low gas concentration region of the combustor, there is a great difference between the radiative heat flux values calculated by the two gas models, while in the latter half of the combustor and near the wall of the combustor where the high temperature and high concentration region, the relative error between the two models remains within 20%. The relative error fluctuation range of radiant heat flux calculated by the two models is related to the fluctuation degree of temperature and gas concentration. The results also showed that the LBL-PM model is more sensitive to changes in temperature and gas composition than the WSGG model. The enhancement of the radiative heat flux by temperature in hydrogen gas turbine is greater than its suppression by the gas absorption coefficient, and the high temperature and high concentration regions, where the large radiative heat flux may be influenced by both the high temperature and the large H 2 O content with weaker absorption properties. • The gas radiation characteristics of hydrogen heavy duty gas turbine was considered. • Differences of WSGG and LBL-PM models are influenced by the degree of temperature and gas concentration fluctuations. • The relative errors of the WSGG and LBL-PM models in high temperature and concentration region are kept within about 20%. • LBL-PM model is more sensitive to changes in temperature and gas concentration compared to WSGG model. [ABSTRACT FROM AUTHOR]

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases. • Combustion. • Heat flux; detonation. • Heat distribution. • Heat transfer. • Intake temperature. [ABSTRACT FROM AUTHOR]

One of the most effective ways to realize multi-mode and high-performance matching operation of rocket-based combined cycle (RBCC) engine is to adopt a variable geometry combustor. In this study, direct-connect experiments and three-dimensional numerical simulations were used to investigate the matching characteristics between the isolator and the geometric throat of the variable geometry rocket-based combined cycle combustor under Ma 6 condition. The influences of equivalence ratio and geometric throat height variations on the combustor matching characteristics were obtained. The study results show that: (1) The pressure in the combustor and the outlet pressure of the isolator increase gradually with the increase of equivalence ratio, which causes the pre-combustion shock train position in the isolator to move forward gradually. Meanwhile, the combined injection of secondary fuel with the isolator and the pylon is beneficial to the improvement of combustor pressure, thus further improving the engine performance. (2) Different geometric throat heights have a substantial impact on the isolator and combustor matching when the equivalent ratio of the combustor is fixed. Under the conditions of Ma 6 operating at an altitude of 24 km inflow, the starting position of the pre-combustion shock train in the isolator is precisely at the isolator entrance, and the corresponding geometric throat height is 2.10H. The isolator and the combustor can complete matching operation at this point which the geometric throat height is the minimal throat height for Equivalent ratio = 1.0. (3) The reduction in geometric throat height can result in an increase in combustor pressure but a loss in combustor heat release and combustion efficiency of fuel combustion, which are reduced by 21.1% and 7.2% respectively. (4) The heat release and combustion efficiency in the combustor will decrease with a decrease in equivalent ratio at the minimal throat height condition where the isolator and the combustor can complete matching operation. This happens when the equivalent ratio and the geometric throat height change synergistically. • The influencing factors on performance were investigated by experiment. • The effects of geometric throat height on heat release were studied numerically. • The matching characteristics of equivalent ratio and throat height wer. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical simulation of the gasification process in a downdraft gasifier to produce syngas with high hydrogen content. For the first time, the possibility of using dark fermentation digestate as a feedstock for thermochemical conversion using air as an oxidizer at equivalence ratio (ER) of 0.45, 0.55 and 0.65 was investigated. Modeling of the gasification process was carried out in the software package Comsol Multiphysics. As a result of numerical studies, the concentrations of the main components of the syngas were obtained. The syngas yield at air gasification was 1.8 m3/kg. At the same time, the combustion heat of the generated gas varied from 3.1 to 3.9 MJ/m3 with the molar ratio (MR) being in the range from 3.1 to 3.9. The maximum content of hydrogen (26.94%) in syngas was achieved at an ER of 0.45. The hydrogen production efficiency HPE ranged from 23.8 to 27.3%. The thermal power that can be obtained from the syngas ranges from 47 to 59 kW. Carbon conversion efficiency coefficient (CCE) was 23.6–28.8%. Based on the design calculation, the main geometric parameters of a downdraft gasifier for the production of syngas from anaerobic digestates were obtained. [ABSTRACT FROM AUTHOR]

Waste biomass pelletization is a suitable process for obtaining energy dense solid fuel. If the pellets are further processed by torrefaction, both their qualitative and energy parameters are changed. Therefore, the objective of this study is to investigate the effect of the torrefaction process on pellets made from coffee grounds, garden chaff and rapeseed straw. Mechanical parameters, such as the pellet durability index, the wettability index of the pellets, their water moisture resistance, hardness, or specific and bulk density were determined for evaluation. Furthermore, pellet energy parameters such as the heat of combustion, calorific value, or elemental analysis were compared. Pelletization of the above-mentioned waste biomass and the torrefaction of the pellets were carried out in pilot plants. The first results showed that the torrefaction process for all samples increased the values of the heat of combustion or the values of the carbon content. The energy value of the pellets increases. The higher heating value of torrefied coffee ground pellets reached 26 MJ kg−1. The ash content also increases with these values. A simple energy balance has been carried out. Therefore, the study shows an insight into the energy use of coffee grounds and chaff from the garden compared to the results of the rapeseed straw pellets for the pelletization and torrefication process. [Display omitted] [ABSTRACT FROM AUTHOR]

To characterize the impact of thermal nonequilibrium conditions in shock-induced combustion in high Mach number scramjet engines, a comparative numerical investigation has been performed. The combustor configuration was based on the HyShot II scramjet while the total enthalpy is 3.3 MJ/kg which resembles Mach 8 flight condition. The improved delay detached eddy simulation with Park two-temperature approach in combination with the vibration-chemical coupling model was employed in the nonequilibrium simulations. It is shown that under thermal nonequilibrium inflow conditions, noticeable stratification in the thermal state exists in the circumferential direction both in the combustor section and exhaust nozzle. In the inner core where the fuel mixes with the mainstream, flow deceleration caused by the heat release leads to a sufficient transformation of energy between the vibrational and translational-rotational modes approaching the thermal equilibrium state. However, the τ v , m i x is quite large in the supersonic mainstream, whereby the thermal nonequilibrium dominates. For the case with higher T v in the inflow, the fuel jet's penetration height is lower while the local viscosity is higher which results in poor mixing between the fuel and air stream. Nevertheless, a 400 K increase in inflow T v gives a higher effective temperature, which promotes the dissociation reactions, shortens the ignition distance and yields an 8% increase in the overall combustion efficiency. With better combustion performance, an additional 6% deceleration in the supersonic mainstream and the energy exchange rate between vibrational and translational-rotational modes becomes almost four times faster at the combustor outlet, which promotes the restoration of the thermal equilibrium state. Furthermore, under higher inflow vibrational temperature, the shock-induced combustion in supersonic crossflow becomes less stable with noticeable fluctuations in combustion heat release and local static pressure. • Combustion dynamics for the Hyshot II scramjet engine under different thermal nonequilibrium inflow conditions were investigated numerically. • Noticeable stratification in thermal state in the circumferential direction was observed when vibrational nonequilibrium effect was considered. • Increase in vibrational temperature at combustor inlet by 400 K resulted in an 8% increase in the overall combustion efficiency. • The instability of shock-induced combustion was enhanced under higher inlet vibrational temperature. [ABSTRACT FROM AUTHOR]

• Developed a Third-order model for optimization of D-FVHP. • NSGA-II is used to optimize dynamic and thermodynamic performances. • Eight structure parameters for dynamic performance are optimized simultaneously. • Nine structure parameters for thermodynamic performance are optimized simultaneously. • free stroke is improved by 78% and electromagnetic work is reduced by 87.72%. Free-piston Vuilleumier heat pump (FVHP) is a heat pump driven by thermal energy such as the combustion of natural gas. Thus, it is a more energy-efficient way for heating than boilers. In this work, one dimensional computational fluid dynamic model is developed for FVHP with dwell motion. Structural design parameters of FVHP are optimized for higher C O P t o t a l based on the coupling of developed model and NSGA-II (Non-dominated Sorting Genetic Algorithm-II) under the condition of given heating capacity. 8 structural parameters are optimized for dynamic performance. The results show that free stroke is improved by 78% and C O P t o t a l is improved by 2.61%. Then, based on the obtained optimal 8 structural parameters, 9 structural parameters for thermodynamic performance are further optimized. The results show C O P h is increased by 3.04% while the heating output power is only reduced by 3.15% [ABSTRACT FROM AUTHOR]

Plastic waste elimination is more important for environmental pollution. Alternate fuel is essential for future IC engine applications because of fossil fuel availability. This study focuses on both challenges by creating combustion energy for direct injection CI engines from the wastes with lesser NOx emissions. Plastic wastes of low-density polyethylene (LDPE) have the most negligible recycling value based on their collection point of view from municipal wastes. Conversion of this LDPE plastic waste into alternate fuel for CI engines by pyrolysis will provide value for that waste. The combustion, emission, and performance of neat pyrolyzed oil of LDPE plastic wastes (POLPW) were studied with exhaust gas recirculation (EGR; 0%, 10%, and 20%) in a 1500 rpm 5.2 kW engine on different loads. 20% of EGR used POLPW fuel produced 31.63% of brake thermal efficiency and 62.28% reduction in NOx (596 ppm) than diesel at maximum load. Pyrolyzed oil of low-density polyethylene plastic wastes can be utilized as a 100% substitute fuel in CI engines with an EGR of 20%. This will provide alternate fuel and low-value plastic waste downcycling, initiating environmental pollution reduction. [Display omitted] • Using one time used plastic waste to generate combustion energy for engine. • Downcycling of low-density polyethylene environment waste by pyrolysis with 80% yield. • Neat pyrolyzed LDPE oil usage is possible with all loads in the engine. • Neat oil with 20% exhaust recirculation have 31.36% brake thermal efficiency. • Compared to diesel, 62.82% of NOx emissions were reduced. [ABSTRACT FROM AUTHOR]

Under the background of the international energy crisis, it is urgent to develop a micro-thermophotovoltaic system using hydrogen as combustion energy. In order to optimize the micro-combustor in the system, the nozzle micro-combustors with five different channels are designed. All nozzle micro-combustors are numerically studied by using the mechanism of 9 components and 19 elementary reactions within the ANSYS Fluent 20.0, and their advantages and disadvantages in thermal performance, flame performance and chemical reaction are compared. It is concluded that the nozzle micro-combustor with constriction-expansion channel has the best performance among the five micro-combustors because of its reasonable segmented structure. Then, a new type of nozzle micro-combustor with segmented channel is designed, and the numerical study of segmented micro-burners and non-segmented micro-combustors with different inlet velocities and hydrogen/air equivalence ratios shows that the thermal performance of segmented micro-combustors is much better than that of non-segmented micro-burners. Therefore, compared with non-segmented nozzle micro-combustors, segmented nozzle micro-combustors have better application potential in micro-thermophotovoltaic applications. • The nozzle micro-combustors with five different channels are investigated. • Thermal, flame and chemical reaction in nozzle micro-combustors are compared. • A new type of nozzle micro-combustor with segmented channel is designed. • Some parameters for influencing the performance enhancement are obtained. [ABSTRACT FROM AUTHOR]

Renewable Energy Sources (RES) represent an attractive way to save natural resources and improve the overall impact of power systems on the environment. A continuous increase of share of RES in national energy mixes is observed, and due to the energy policy of the European Union and many other countries, further increase is expected. A disadvantage of RES is their random, weather-dependent availability, which requires energy storage. A promising method of integrating RES with the energy system is the use of hydrogen as an energy carrier (e.g. coupling RES with electrolyzers in order to directly use the renewable electricity for production of hydrogen). In the present work, a simulation of cooperation of a photovoltaic power plant with a gas piston engine fueled by hydrogen was performed, with and without the presence of energy storage. The aim of the analysis is twofold. First, the "compensation losses" due to forced part-load operation of the engine coupled with RES are evaluated and compared with "storage losses" resulting from the thermodynamic imperfectness of the storage; this allows to calculate the minimum round-trip efficiency of storage required for positive energy effect. The "compensation losses" have been determined to be of the order of magnitude of 2%, and the minimum round-trip efficiency of storage to be at the level of 85%. Second, a thermo-ecological analysis was carried out to determine the impact of the source of hydrogen on the overall ecological effectiveness of the system. Contrary to the commonly used measure of "energy efficiency" describing a local balance boundary, thermo-ecological cost (TEC) evaluates the consumption of non-renewable exergy within a global balance boundary. The analysis confirmed that comparing various hydrogen production methods (especially renewable and non-renewable) in terms of local energy efficiency is inadequate, because it does not tell much about their sustainability. For a hydrogen energy system basing on the water electrolysis – hydrogen transport/storage – combustion in a gas piston engine pathway to be considered sustainable, the input electricity to the electrolysis process should be characterized by TEC lower than ∼0.15 J∗/J, a value which even some renewable energy sources fail to achieve. • H 2 engine cooperating with intermittent photovoltaics achieves lower efficiency. • The "compensation losses" in the engine can be avoided if energy storage is used. • High efficiency of storage is required to achieve energy savings. • Thermo-ecological analysis highlights the benefits of "renewable" hydrogen. [ABSTRACT FROM AUTHOR]

In this study, we successfully synthesized PrFeO 3 /CeO 2 -based nanocomposites with different mass contents of СeO 2 (0–18 wt%) via solution combustion with subsequent heat treatment in air. The results of EDXS and PXRD confirmed the presence of two phases in nanocomposites: a PrFeO 3 orthorhombic phase with an average crystallite size of 13.6–36.6 nm and a СeO 2 cubic phase in the form of an ultradisperse phase with an average particle size of 7.4–11.5 nm depending on the mass content of СeO 2. We characterized the morphology, porosity, and specific surface structure of the powders by scanning electron microscopy, transmission electron microscopy, and adsorption–structural analysis, which established the foam-like morphology of nanopowders with a predominantly mesoporous structure. The specific surface area varied in the range of 8.8–19.4 m2/g for different СeO 2 contents. We studied the optoelectronic properties of the nanocomposites with UV–visible diffuse reflection spectroscopy, which determined the values of the band gap of the PrFeO 3 phase actively absorbing radiation in the visible region (2.07–2.13 eV). Based on the adsorption–photocatalytic properties of the obtained nanocomposites, we established the presence of a synergistic effect from the addition of CeO 2 to PrFeO 3. We studied the adsorption capacity of the samples during the adsorption of methyl violet, and we analyzed the resulting adsorption isotherm in accordance with the Freundlich model. The obtained results indicated increased dye adsorption in the presence of CeO 2 , with the maximum value of K f = 45.7 observed at 15 wt%. We studied the photocatalytic Fenton-like activity of nanopowders during the degradation of methyl violet under the influence of visible light. We established he presence of a positive effect of CeO 2 additive. At 9 wt% content, the maximum photocatalytic reaction rate constant was reached at 0.056 min−1, which was previously unavailable for analogical Fenton-like photocatalysts based on REE orthoferrites. Based on the conducted studies, we propose a possible mechanism of the photo-Fenton-like decomposition of organic pollutants in the presence of PrFeO 3 /CeO 2 under the influence of visible light. The obtained nanocomposite materials were also characterized by high cyclic stability and the potential for magnetically controlled separation from the reaction solution, showing their potential as a basis for photocatalysts in wastewater treatment from dyes and other organic pollutants. [Display omitted] [ABSTRACT FROM AUTHOR]

With the growing installation of electrochemical energy storage systems, the safety issues of lithium-ion batteries have attracted extensive attention. To identify the development of thermal failure in energy storage systems, horizontal and vertical thermal runaway (TR) propagation characteristics of lithium-iron-phosphate battery modules with different connections are systematically investigated herein. Once TR occurs in the initial battery, it initially propagates to subsequent batteries along the horizontal direction, followed by vertical propagation to the upper batteries. Particularly, the almost simultaneous occurrences of TRs in the upper batteries accompanied by extreme combustion are observed during vertical propagation, exhibiting huge thermal hazards. The maximum temperature and heat release of upper batteries are 548.3 °C and 490.7 kJ, much higher than that of lower batteries with values of 423.2 °C and 217.7 kJ, demonstrating upper batteries experience severer TR. Moreover, the heat generated by the combustion of the individual battery can increase temperatures of upper batteries by 30 °C–40 °C, which is insufficient to cause vertical TR propagation, while TRs of upper batteries will eventually be triggered with the proceeding of horizontal TR propagation. The results provide valuable information for TR propagation between battery modules and benefit the safety application of energy storage systems. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of ethanol-gasoline-hydrogen in a lean-burn SI engine with different proportions such as E5, E10, E20, E30, and E40 at compression ratio 10.5:1. The results infer that the E10 blend is the optimized one. Further, E10 mixture investigates for 5% and 10% hydrogen addition on energy basis. Overall, this study establishes that the addition of ethanol enhances brake power by 9% and brake thermal efficiency by about 7%. Hydrogen enrichment to E10 mixture shows a significant enhancement in brake power and brake thermal efficiency at a lower equivalence ratio. Further, it observes that the lean limit had extended to a 0.47 equivalence ratio compared to a 0.5 equivalence ratio with the E10, and 0.54 with pure gasoline. The addition of hydrogen to E10, improves the combustion process and heat release rate while it reduces cycle-by-cycle variations and hydrocarbon emissions. • Study of ethanol-gasoline blend and hydrogen addition on lean burn SI engine. • Investigation on the effect of high compression ratio on ethanol-gasoline blend. • Ethanol-gasoline blend improves brake power output and brake thermal efficiency. • Hydrogen addition to ethanol-gasoline leads to lower HC and NO emissions. • Stable combustion of hydrogen reduces CCV variations and extends lean misfire limit. [ABSTRACT FROM AUTHOR]

• Field emission characteristics covering the entire combustion process were investigated. • Promoted heating stoves have the risk of increasing PM 2.5 and NO X emissions. • Household coal consumption was more than three times lower than official report. • The adoption is unlikely to be successful on a large scale due to over reliance on subsidies. Straw pellets are widely promoted and expected to be a cleaner alternative fuel to unprocessed crop residues and raw coal in rural China. However, the effectiveness of these dissemination programs is not well evaluated. In this field study, emission characteristics of burning straw pellets, raw coal, and unprocessed corn cobs in heating stoves were investigated in a pilot village in Northeast China. Emission measurements covering the whole combustion cycle (ignition, flaming, and smoldering phases) shows the promotion of improved heating stoves and straw pellets could reduce pollutant emissions (e.g., SO 2 and CO), but increase NO X and PM 2.5 emissions compared to the initial stove-fuel use pattern in the studied area. There is a significant variance in emission characteristics between different combustion phases. The normalized emission concentrations of the different stove-fuel combinations were higher than the limits in the Chinese national standard for heating stoves, indicating that the standard is not met for real-world emissions. Coal consumption was lower than official data. Household surveys were conducted to identify the barriers to fuel and stove access associated with existing promotion strategies, management, and policies. The pilot program was of the typical "subsidy-and-policy-dependence" pattern and was unlikely to be implemented on a large scale. Technological innovation, operational optimization, and proper policies considering the local socioeconomic factors are needed to sustain the promotion of biomass straw pellets and stoves. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to ensure the safety of hydrogen energy system, a robust and reliable hydrogen sensor device with an optical fiber Bragg grating (FBG) has been developed. The sensing mechanism is based on temperature changes in the device induced by the heat of the catalytic reaction of hydrogen on platinum-loaded fumed silica catalyst powder. Through optimization of the preparation conditions for the catalyst, which is a hydrogen-sensitive substance, a large degree of heat generation in the presence of hydrogen could be obtained, and good stability was also achieved. A sensor device in which a column filled with the obtained catalyst powder was attached to a commercially available robust FBG for temperature measurement, and integrated with another FBG as a temperature reference via a heat shielding plate, was fabricated and evaluated. A stable baseline was demonstrated even in an environment where the ambient temperature severely fluctuated, and a sensor output proportional to the hydrogen concentration could be obtained. The detection limit was about 0.2 vol%, and the long-term stability of the device was good. • Platinum-loaded fumed silica catalyst was prepared as hydrogen sensing materials. • Large amount of catalytic combustion heat of hydrogen on the catalyst was obtained. • The catalyst was immobilized on robust fiber Bragg grating temperature sensor device. • The sensor integrated with temperature compensation device showed good responses. • The detection limit was about 0.2 vol% and the long-term stability was good. [ABSTRACT FROM AUTHOR]

The article considers the possibility of applying the concept of a "transition link" from hydrocarbon to "green" energy. The entire world industry uses hydrocarbons as fuel. The share of "green" energy is growing, but it cannot completely replace oil, gas and coal at this stage. In many production processes, due to technology, a significant amount of heat is lost. Thus, the anthropogenic impact is doubled both due to fuel combustion and due to heat losses into the environment. Traditional methods of reducing harmful emissions, as a rule, are focused only on a specific type of treatment and are capital treatment facilities. The authors' approach to the problem differs from the generally accepted one. The developed method makes it possible to obtain an additional product due to waste heat, while reducing emissions of carbon monoxide into the atmosphere. The authors have chosen Combined heat power plant (CHPP), thermal power plant (TPP) as the object of research. Their role as a source of heat, light and hot water supply can hardly be overestimated. But thermal power plants and thermal power plants are also sources of greenhouse gases generated during fuel combustion, sources of heat loss with exhaust gases and thermal pollution of water bodies with cooling liquid. Thermal pollution of water bodies leads to their overgrowth with algae, and as a result, deterioration of water quality. The method presented by the authors is based on the integrated use of waste heat generated in large volumes in algae cooling ponds and the production of bioethanol. Studies were carried out on a mass spectrometer of the chemical composition of algae formed in various media (sea, tap and purified water). During the experiments, legumes were grown on purified water, tap water, and distilled water. According to the calculations, the cost of 1 L of the resulting bioethanol will be about 28 rubles/l, which is 3 times cheaper than what is currently produced. It is concluded that the polluted water of a thermal power plant or thermal power plant has a negligible effect on the bioethanol yield. A 17.8-fold decrease in sodium was shown due to the use of biofilters. During the experiments, legumes were grown on purified water, tap water, and distilled water. The conclusion is made about the significant adsorption capacity of Zn, Mg, Fe, Al, Si, Pb ions. The resulting water after passing through the algae was tested according to SanPiN 2.1.4.1074-01, and fully complied with the standard, which allows it to be used for technological and technical purposes and, moreover, to be returned to the natural environment without consequences. The work is planned within the framework of an international project to create devices and industrial technology that provides for the production of synthesis gas in a fuel processor and hydrogen for generating electrical energy using a fuel cell. [ABSTRACT FROM AUTHOR]

The problem of flight safety of high-speed aircrafts is primarily related to the reliability of engines, which, in turn, depends on the correct understanding of the processes of ignition and combustion of fuel in the combustion chambers of engines during their design. In this work, a new method for registration the ignition of shock heated gaseous fuels using a thermoelectric detector is proposed. The detector well measures the ignition delay time of fuels in the microsecond range, which is characteristic of detonation processes in the combustion chambers of promising aircraft engines operating on detonation combustion. The efficiency of the detector is demonstrated by the ignition of a propane-air mixture behind a reflected shock wave as an example. During the experiments, the thermoelectric detector showed such properties as the ability to register high heat flux values, low inertia, high signal-to-noise ratio, and high temporal resolution. The data obtained are compared with the measurement data of the ignition delay time by optical and piezoelectric methods obtained in this work, as well as in the studies of other authors. • Clarification the ignition delay time of fuels in microseconds and less. • Application of thermoelectric detector under conditions of high pressure and temperature. • New data about heat fluxes during self-ignition and combustion of shock heated gaseous fuels. • High heat flux value registration with low inertia, high signal-to-noise ratio, and high temporal resolution. [ABSTRACT FROM AUTHOR]

The distributed power generation of methanol steam reforming reactor combined with solid oxide fuel cell (SOFC) has the characteristics of outstanding economic advantages. In this paper, a methanol steam reforming reactor was designed which integrates catalyst combustion, vaporization and reforming. By catalyst combustion, it can achieve stable operation to supply fuel for kW-class SOFC in real time without additional heating equipment. The optimal operating condition of the reforming reactor is 523–553 K, and the steam to carbon ratio (S/C) is 1.2. To study the reforming performance, methanol steam reforming (MSR), methanol decomposition (MD), water-gas shift (WGS) were considered. Operating temperature is the greatest factor affecting reforming performance. The higher the reaction temperature, the lower the H 2 and CO 2 , the higher the CO and the methanol conversion rate. The methanol conversion rate is up to 95.03%. The higher the liquid space velocity (LHSV), the lower the methanol conversion rate, the lowest is 90.7%. The temperature changes of the reforming reactor caused by the load change of stack takes about 30 min to reach new balance. Local hotspots within the reforming reactor lead to an excessive local temperature to test a small amount of CH 4 in the reforming gas. The methanation reaction cannot be ignored at the operating temperature. The reforming gas contains 70–75% H 2 , 3–8% CO, 18–22% CO 2 and 0.0004–0.3% CH 4. Trace amounts of C 2 H 6 and C 2 H 4 are also found in some experiments. The reforming reactor can stably supply the fuel for up to 1125 W SOFC. • The reforming reactor can operation to supply fuel for kW-class SOFC without additional heating equipment. • The reforming reactor integrates catalyst combustion, vaporization and methanol steam reforming. • Reaction temperature has the greatest impact on reforming performance than LHSV and S/C. • In the reforming reactor, the methanation reaction should not be neglected, and trace amounts of C 2 H 6 and C 2 H 4 are found. • The reforming reactor is verified to meet the operating of SOFC by experiments, which is available for up to 1125 W SOFC. [ABSTRACT FROM AUTHOR]

The article presents the results of the experimental studies carried out to analyze the connections between the configuration of the particles and the delay time of their ignition. The results of the experimental studies of the ignition processes of woody biomass particles of various shapes and sizes, but identical volumes, as applied to the heating conditions in the combustion chambers of the typical boiler units, are obtained. Three shapes of wood particles were studied: a rectangular parallelepiped, a cube, and a plate. Quite non-obvious (based on traditional concepts) dependences of the ignition delay times on the characteristic sizes of wood particles have also been established: under conditions of relatively low ambient temperatures (T g = 873K), the characteristic size and shape have a significant effect on the characteristics and conditions of ignition. In the case of ignition of plates, the dependence t ign (δ) is linear; in the case of ignition of cubic particles, the dependence t ign (δ) is nonmonotonic with a local minimum; in the case of ignition of biomass particles in the form of parallelepipeds, the function t ign (δ) has a nonmonotonic character with a local maximum of the value of t ign. [ABSTRACT FROM AUTHOR]

Five components of heat flux, viz: conduction, q c o n d ″ , sensible mass diffusion, q d i f f ″ (s) , formation mass diffusion, q d i f f ″ (o) , sensible convection, q c o n v ″ (s) , and formation convection, q c o n v ″ (o) have been analyzed extensively in this paper for the unwrapped model of the rotating detonation engine (RDE), using an explicit large-eddy simulation (LES) approach with a kinetic mechanism consisting of eight reaction steps and seven chemical species. The results shown are from averaged fields obtained after the attainment of the quasi-steady state condition. The maximum static pressure occurs at the transverse detonation wave, with a value that is one order of magnitude higher than the relatively uniform values that are found in most part of the domain. By y ≈ 0.0044 m , which is roughly one-tenth of the axial distance in the domain with (x , y) ε [ 0,0.1 ] × [ 0,0.04 ] m, most of the reacting species (H 2 , O 2) have been depleted at all transverse locations. From the mass averaged magnitudes of the heat flux components, it has been found that q c o n v ″ (o) , has the largest contribution, followed very closely by its sensible counterpart, q c o n v ″ (s) , whose magnitude is roughly half of that for the formation enthalpy heat flux. This is followed (in magnitude) by q d i f f ″ (o) and q d i f f ″ (s) , which are of comparable values and are over three orders of magnitude smaller than the convective heat flux components. The conductive heat flux q c o n d ″ is roughly an order of magnitude smaller than the mass diffusion values. The Nusselt number and heat transfer coefficient for the present problem are significantly higher than those encountered in low-speed, non-reacting flow fields. • Five components of heat flux in a model of the rotating detonation engine (RDE) were extensively investigated in this study using the large-eddy simulation (LES) approach within the context of combustion and detonation. • The critical structures in the RDE combustor (shock waves, slip lines, contact discontinuities, etc.) significantly determine the magnitudes and distributions of the three heat flux components that are based on molecular diffusion. • The formation convective heat flux has the largest contribution, followed very closely by its sensible counterpart, whose magnitude is roughly half of that for the formation enthalpy heat flux. The conductive heat flux has the smallest magnitude, which is roughly one order smaller than the mass diffusion values. • The maximum static pressure occurs at the transverse detonation wave, with a value that is one order of magnitude higher than the relatively uniform values that are found in most part of the domain. • The axial distance at which a significant amount of the reactions occur was determined. [ABSTRACT FROM AUTHOR]

Methane is an ideal alternative to other fossil fuels but requires great bond strength to bond dissociation, which leads to poor ignition performance. Hydrogen, as a promising and environmental-friendly fuel, has a very high calorific value, the addition of which is considered as an effective approach to enhance the methane combustion. In this study, the ReaxFF reactive force field molecular dynamics (ReaxFF-MD) simulation is used to study the process of methane/hydrogen blended combustion with various amounts of hydrogen addition. The results show that the addition of hydrogen can promote the methane combustion by accelerating the consumption of methane. In addition, the instant when methane starts to participate in the reaction is advanced. However, with the increase of hydrogen content, the promoting effect of methane combustion weakens as the temperature increases. It is found that the enhanced OH production resulted from the hydrogen addition not only promotes the initiation but also affects the intermediate and final products of methane combustion. Furthermore, compared with pure methane combustion, the addition of hydrogen significantly lowers the activation energy by up to 50% but the enhancement is becoming weaker with the increasing amount of hydrogen addition. This research provides atomistic insights into the methane/hydrogen blended combustion that could potentially benefit its practical application. • ReaxFF-MD simulation is employed to study the CH 4 /H 2 blended combustion. • Initial reaction pathways of CH 4 are changed in the presence of H 2. • Enhancement of CH 4 combustion becomes weaker with the increase of H 2 addition. • Hydrogen addition lowers the activation energy of methane combustion. [ABSTRACT FROM AUTHOR]

Non-carbon nature and higher hydrogen energy density of ammonia have gained a lot of interest as an energy asset and green fuel. In this work, the effects of ammonia fuel share and engine operating load on the combustion stability and engine characteristics (combustion and performance) of gaseous (NH 3 /CH 4) fuelled SI engine have been reported. The lower heating value and flame propagation speed of fuel mixture reduce with the increase in ammonia share (0–60% at 8 Nm engine load) and thus results in detrimental engine performance and higher cycle-to-cycle combustion variations (1.36%–14.9% COV of IMEP). A rise in operating load from 8 Nm to 16 Nm increases the flame propagation speed of the fuel mixture (60% ammonia share) and improves engine performance and combustion stability (14.9%–4.3% COV of IMEP). The results of this study indicate that the substitution of methane with ammonia could be maximized at higher engine operating loads to get the benefit of clean fuel utilization. [Display omitted] • Green ammonia as a hydrogen energy carrier and potential fuel for IC engines. • Study on the effect of ammonia addition in methane fuelled Spark Ignition engine. • Increasing share of NH 3 in fuel mixture at lower loads reduced combustion stability. • Enhancement of operating limits at higher engine loads in methane fuelled engines by NH 3 addition. [ABSTRACT FROM AUTHOR]

Yttrium aluminum garnet (YAG) is a well-known high-temperature ceramic material that is used in a plethora of applications such as solid-state laser materials, cathode-ray tubes, field emission displays, scintillators, phosphors, electro-luminescent devices, etc. In recent years, plasma-sprayed yttrium aluminum garnet (YAG) has been explored as an alternative ceramic topcoat for thermal barrier coatings (TBCs) as it is known to prevent the oxidation of the bond coat. Also, it possesses high resistance to calcium magnesium aluminosilicate (CMAS) attack compared to conventional yttria-stabilized zirconia (YSZ) TBC topcoat material. In the current investigation, an attempt is made to fabricate plasma-sprayed YAG coating. The flowable powders required for plasma spraying are synthesized by the versatile solution combustion method after optimizing the process with two different fuels. The powders synthesized using hexamine fuel possess blocky angular-shaped particles and very good flowability. The flowability of the powders is correlated to the heat of combustion, adiabatic flame temperature and shape of the particles. The YAG powder synthesized from hexamine fuel is used for plasma spray application as the process results in higher yield and better flowability. The influence of different plasma spray powers (20, 30 and 40 kW) on the phase purity and crystallinity of the YAG coatings is studied using X-ray diffractometry. The influence of three different plasma powers on the microhardness and microstructure of the coatings is explored. The YAG coating plasma-sprayed at 30 kW is relatively a dense coating and exhibits a higher microhardness value of 1342 ± 9 HV at a load of 100 mN. The CMAS resistance of the YAG coatings is also reported. [ABSTRACT FROM AUTHOR]

Torrefaction in partially oxidative atmospheres is a non-traditional approach to the thermal pre-treatment of biomass. Despite the potential benefits arising from this compared to traditional torrefaction undertaken under costly inert atmospheres, the literature lacks data on the combustion and kinetic analyses of densified biomass torrefied under partially oxidative conditions comparable to those of (reusing) combustion flue gases. This paper, therefore, investigates the effects of partially oxidative atmosphere on the chemical functionality, combustion kinetics and thermodynamics of densified (Australian) woody biomass. Torrefaction was conducted at 250, 275, 300 °C for 30min under both inert and partially oxidative atmosphere (O 2 : 5 vol%, N 2 balance). The kinetic parameters were derived from iso-conversional method over the entire conversion range. Results show that solid biofuel torrefied under partially oxidative atmospheres has superior chemical functionality (e.g., less oxygenates and higher thermal stability), but comparable physical properties to inert atmospheres. In addition, improved thermodynamic features and lower combustion activation energy for partially oxidative torrefied biomass was observed. Overall, the results suggest that the use of partially oxidative atmospheres for torrefaction not only produce a high quality solid biofuel but can also improve process efficiency by using waste heat and flue gases from other combustion processes to thermally pre-treat biomass. [ABSTRACT FROM AUTHOR]

[Display omitted] • The physical and chemical properties of PS and PC were studied systematically. • The reactivity of PC combustion reaction was significantly affected by PS. • PC:PS = 4:1 has the lowest combustion activation energy. • The Kissinger Akahira Sunose model shows a good fitting effect. The co-combustion reactivity and kinetics of petroleum coke (PC) and paper sludge-derived hydrochar (PS) were investigated via thermogravimetric analysis. The physical and chemical structure features were also systematically tested. The results show that the combustion process of PS could be divided into three stages, while for PC only one stage could be clarified. Due to high volatile content, developed pore structure and low carbon-order degree, the combustion reactivity of PS was higher than that of PC. Although the ignition property of the blends could be significantly improved by addition of PS, it changed little for the burnout temperature and as a result the combustion intensity was deteriorated. For the samples with addition of PS from 20 % to 80 %, the comprehensive combustion index decreased from 3.69 × 10-15 to 2.12 × 10-15. The Kissinger AkahiraSunose model-free method was used in the co-combustion reaction of PC and PS, and good fitting results were obtained. For different samples with varying addition of PS, the activation energies were in the range of 107.51–198.44 kJ/mol, with the lowest value obtained at 20 % of PS, which was also the optimum proportion for co-combustion of PC and PS. [ABSTRACT FROM AUTHOR]

Integrated Vehicle Fluid (IVF) system is a promised energy management system for cryogenic upper stage. The power unit of IVF is hydrogen-oxygen internal combustion engine (ICE) whose energy utilization is close to 100% in IVF system. The oxygen concentration of intake gas was gradually raised during ICE tests as a preliminary study. The power of hydrogen-oxygen ICE reaches 4 kW at 3000 r/min, which satisfies the power requirement of IVF system. At this time, the exhaust loss reaches 41.6%, the heat transfer loss is 35.9%, and the output power only accounts for 21.9%. The heat transfer loss shows a parabolic trend which first rises and then falls with increasing oxygen concentration. But the exhaust loss keeps growing with the increases in oxygen concentration and engine speed. It is significant for the design of regenerative cooling system and other subsystems in IVF system at specific engine speed. • Engine tests under 21%, 30% and 40% oxygen concentration were performed. • Laminar burning velocities of hydrogen under high oxygen concentration were studied. • One-dimensional simulation of engine was performed under higher oxygen concentration. • Energy of each part under different oxygen concentration were analyzed in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] The syntheses and characterization of novel propargyl ethers of N -(hydroxymethyl)nitramines that contain from one to four nitramine units are reported. All nitramine-functionalized ethers were well characterized by IR and multinuclear NMR spectroscopy as well as CHN analysis, and the X-ray crystal structures of two of them are described. For ethers bearing two or three nitramine units, the standard molar enthalpies of formation at 298.15 K were determined from the experimental standard molar energies of combustion in oxygen measured by static bomb combustion calorimetry [ABSTRACT FROM AUTHOR]

Burning of hydrogen produces high-grade heat, which can be used for zero-carbon power generation and/or heating and in heat-intensive industries. In combination with water electrolysis, hydrogen combustion provides efficient energy storage method for variable renewables. Hydrogen combustion systems are compact, powerful and highly maneuverable in comparison with fuel cells. We present experimental results of fire tests of a water-cooled hydrogen-oxygen steam generator (HOSG). This fast-response device has start-up time less than 15 s to thermal capacity of 147 kW. Temperature of generated steam is within 1173–1273 K, parameters of steam and energy conversion efficiency can be adjusted the water-to-hydrogen ratio. The maximum efficiency of conversion of chemical energy of hydrogen into enthalpy of steam is 98.7%. [Display omitted] • Experimental results on hydrogen-oxygen steam generator (HOSG). • High temperature steam (900–1000 °C). • Start-up time to capacity of 147 kW is less than 15 s. • Water cooling absorbs combustion heat and protects the device. • 98.7% efficiency of hydrogen HHV conversion to steam enthalpy. [ABSTRACT FROM AUTHOR]

This paper presents the application of a multidisciplinary approach for the preliminary design and evaluation of the potential improvements in performance and environmental impact through the utilization of compressed (CGH2) and liquefied (LH2) hydrogen fuel for a civil tilt-rotor modelled after the NASA XV-15. The methodology deployed comprises models for rotorcraft flight dynamics, engine performance, flight path analysis, hydrogen tank and thermal management system sizing. Trade-offs between gravimetric efficiency, energy consumption, fuel burn, CO 2 emissions, and cost are quantified and compared to the kerosene-fuelled rotorcraft. The analysis carried out suggests that for these vehicle scales, gravimetric efficiencies of the order of 13% and 30% can be attained for compressed and liquid hydrogen storage, respectively leading to reduced range capability relative to the baseline tilt-rotor by at least 40%. At mission level, it is shown that the hydrogen-fuelled configurations result in increased energy consumption by at least 12% (LH2) and 5% (CGH2) but at the same time, significantly reduced life-cycle carbon emissions compared to the kerosene counterpart. Although LH2 storage at cryogenic conditions has a higher gravimetric efficiency than CGH2 (at 700 bar), it is shown that for this class of rotorcraft, the latter is more energy efficient when the thermal management system for fuel pressurization and heating prior to combustion is accounted for. [Display omitted] • A civil tilt-rotor is retrofitted for liquid and gaseous hydrogen fuel. • The hydrogen-fuelled rotorcraft are compared against the kerosene-fuelled counterpart. • Performance and environmental assessment is conducted at payload-range and mission level. • Liquid hydrogen offers higher gravimetric densities but its requirement for heating penalizes performance. [ABSTRACT FROM AUTHOR]

To investigate the relationship between fuel properties and pyrolysis heating rates (PHRs) of molded charcoals (MCs), biomass briquettes (manufactured by 70% bamboo and 30% wood blends) were pyrolyzed using various PHRs based on industrial production stages (preheating, primary pyrolysis, and carbonization stage). Proximate and ultimate analyses, as well as thermogravimetric and kinetics analyses, were performed for MCs. Results showed that PHRs had a significant effect on the quality and yield of MCs at the primary pyrolysis stage. Based on the production efficiency and energy performances, the PHRs were suggested to 5 °C/min, 1 °C/min, and 5 °C/min for preheating, primary pyrolysis, and carbonization stages. The higher heating value, energy enrichment factor, calorific value improvement, energy yield, and fuel ratio of optimal MCs were 34.02 MJ/kg, 1.777, 1.716, 71.65%, 55.27, and 11.51, respectively. The MCs had a minimum activation energy of 98.57 kJ/mol. The findings of this study will be useful in understanding and standardizing the manufacturing process of MCs. [Display omitted] • The industrial production process of molded charcoal has been imitated. • Pyrolysis heating rate influences the preheating and carbonization stages slightly. • High pyrolysis heating rate affects the primary pyrolysis stage primarily. • High combustion heating rate decreases the activation energy. • Combustion heating rate has a greater effect on E a than pyrolysis heating rate. [ABSTRACT FROM AUTHOR]

• The process of the plasma-assisted combustion of the low calorific gases showed that combustion efficiency of low-calorific gases is increasing. • CO emissions decreased by 90–97 % (depends on excess air ratio) for high (120 kHz) plasma parametes for biogas, containing 60 % of methane. • Energy density of the discharge at 80 kHz plasma assistance regime was the highest observed for both studied biogases, being ahead of the other frequencies in terms of volume density by 20–50 % • Plasma assistance decrease flame lift-off by 3.33–51.28% depending on excess air ratio, frequency and biogas composition. This study explores the impact of plasma driving frequency on diverse biogas compositions, emphasizing flame behaviour by analysing spatial emissions of OH*, C 2 *, and CH* from plasma-assisted flames. Experimental investigation performed combusting mixtures with 25 % and 60 % CH 4 in CO 2 under lean combustion conditions with the varying fuel equivalence ratios from 0.71 to 0.83 and plasma discharge frequencies from 60 to 120 kHz resulting in higher energy density. Obtained results indicate that the plasma assistance notably enhances flame stability under lean fuel conditions with increasing frequency from 80 to 120 kHz. The discharge frequency of 60 kHz indicates insufficient energy to enhance combustion of low calorific value mixtures as the flame lift-off height increases approximately by 0.43–1.5 % for the mixture of 25 vol% CH 4 in CO 2 and by 0.26–7.7 % for the mixture of 60 vol% CH 4 in CO 2. Changing the plasma frequency from 80 to 120 kHz, the flame position is shifted closer to the burner nozzle for both mixtures and the highest effect is determined at 120 kHz. The flame lift-off height is reduced by 2.43–16.34 % for the mixture with 25 vol% of CH 4 and by 3.57–51.28 % for the mixture with 60 % of CH 4. The plasma-assisted combustion leads to improved combustion efficiency as CO emissions are reduced from 1550 ppm to 45 ppm for biogas mixture, but in the case of low calorific value gas, the CO emissions increase linearly with the frequency increase even the flame curvature and stability is improved. [ABSTRACT FROM AUTHOR]

Co-combustion of anthracite and hydrochar derived from hydrothermal carbonization with process water recirculation was proposed as an effective way to achieve a transition to low-carbon energy in industries that rely heavily on coal combustion. In this study, thermogravimetric analysis and model-free methods were employed to investigate the co-combustion characteristics and kinetics of anthracite and hydrochar. The results demonstrate that the carbon content of hydrochar is lower than that of anthracite, but the volatile content is higher than that of anthracite, indicating that hydrochar has better combustion performance. There is a synergistic effect in the co-combustion reaction of hydrochar and anthracite. With the increase of the hydrochar addition ratio, the ignition and burnout temperatures of anthracite decrease gradually. With the increase of temperature rise rate, the combustion reaction is enhanced and the combustion performance of anthracite is improved under the fixed mixing ratio. According to the calculation of combustion activation energy by Flynn-Wall-Ozawa and Kissenger-Akahira-Sunose methods, the apparent activation energy of the mixed samples gradually decreases with the increase of combustion conversion rate. When the addition of hydrochar is 60 %, the average apparent activation energy of the mixed sample is the lowest, which is 66.51 kJ mol−1 and 54.62 kJ mol−1, respectively. • Rice husk hydrochar burns more easily than anthracite. • Adding hydrochar improves the combustion characteristics of anthracite. • There is a synergistic effect in the co-combustion of hydrochar and anthracite. • Increasing the heating rate can improve the combustion characteristics of blends. • When the hydrochar addition ratio is 60 %, the combustion performance is optimal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inserting the semiconductor materials g-C 3 N 4 nanosheet into Al/CuO can improve its safety and precisely regulate the combustion. • More active sites in reaction interface and easier adsorption between metals Al and CuO are induced by polymer polyvinylpyrrolidone (PVP). • The one-step sol-freeze-drying technology is a facile and safety strategy for the preparation of nanothermites. • This work will provide a fresh strategy for extending applications of nanothermites. Nanothermites are presenting competitive advantage potential in military and civilian applications, but high electrostatic discharge (ESD) sensitivity severely hinders their preparation, storage and usage. Aiming to improve the safety and combustion properties of energetic materials (EMs), the two-dimensional semiconductor materials graphite carbon nitride (g-C 3 N 4 also abbreviated as CN) was inserted into the Al/CuO mixture via the one-step sol-freeze-drying method. The successful preparation of samples was confirmed by morphological and chemical bond characterization. Then DFT calculation and BET tests prove that more active sites exist in reaction interface, and the adsorption between Al atoms and CuO unit cells are easier due to polyvinylpyrrolidone (PVP) and g-C 3 N 4 functioning, thereby improving the combustion of Al/CuO and ESD safety. The Al/CuO/CN nanocomposite with 2.5 wt% CN has an ESD ignition threshold of 3.2 mJ and realizes maximal reaction energy and constant volume heat of combustion (Q v) of 1400.4 J·g−1 and 5896 J·g−1, respectively. As the CN content grows to 10.0 wt%, the ESD ignition threshold keeps decreasing to 8.45 mJ. Additionally, PVP and CN show superior advantages in regulating the combustion of Al/CuO, and the possible effect mechanism is investigated. This work will provide a fresh strategy for extending applications of nanothermites. [ABSTRACT FROM AUTHOR]