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Summary: The effect of hydrogen addition on the ignition delay time of methyl butanoate was studied using a rapid compression machine experiment and ANSYS CHEMKIN‐PRO 19.0 numerical analysis. The ignition delay was measured under engine‐relevant conditions by varying equivalence ratios (0.5 and 1.0), compression pressures (15 and 30 bar), compression temperatures (860‐1060 K), and hydrogen mole fractions in the methyl butanoate/hydrogen mixture (0%, 25%, 50%, and 75%). The kinetic mechanism was modified by adding the methyl butanoate mechanism to the NUIG Aramco 3.0 mechanism and modifying the rate parameters of the H‐atom abstraction reactions of methyl butanoate. The numerical results obtained using the modified mechanism were in good agreement with the experimental results. The methyl butanoate/hydrogen mixture did not show a negative temperature coefficient characteristic. With hydrogen addition, the ignition delay increased at low temperatures but decreased at high temperatures. The results of the chemical and dilution effect analysis using the imaginary inert H2 showed that the chemical effects differ depending on the temperature. Most added hydrogen molecules participate in the chain propagation reactions to produce H radicals and consume OH by the reaction H2 + OH → H + H2O. This, in turn, changes the reactions of other species, such as HO2 and H2O2. The results of the reaction path analysis for the related species showed that the addition of hydrogen reduced radical reactions at low temperatures, while increasing them at high temperatures. [ABSTRACT FROM AUTHOR]

Hydrogen addition effectively reduces the fuel consumption of spark ignition engines. We propose a new on-board reformer that produces hydrogen at high concentrations and enables multi-mode operations. For the proposed reformer, we employ a catalytic fuel decomposition reaction via a commercial NiO–CaAl 2 O 4 catalyst. We explore the physical and chemical aspects of the reforming process using a fixed bed micro-reactor operating at temperatures of 550–700 °C. During reduction, methane is decomposed to form hydrogen and carbon. Carbon formation is critical to hydrogen production, and free space for carbon growth is essential at low temperatures (≤600 °C). We define a new accumulated conversion ratio that quantitatively measures highly transient catalytic decomposition. The free space of the coated monolith clearly aided low-temperature decomposition with negligible pressure drop. The coated substrate is therefore suitable for on-board applications considering that our reformer concept also utilizes the catalytic fuel decomposition reaction. Image 1 • A new concept of an on-board reformer enabling multi-mode operation. • Producing high level hydrogen by catalytic fuel decomposition on NiO–CaAl 2 O 4 catalyst. • Introducing the accumulated conversion ratio to quantitate the transient phenomena. • Coated monolith showed the improved performance suitable for an on-board reformer. [ABSTRACT FROM AUTHOR]

The use of alternative energy is increasing with the concerns about global warming and the dwindling reserves of fossil fuels. Biodiesel and hydrogen are promising alternative fuels, and engine research has investigated the use of biodiesel/hydrogen mixtures. However, no study has examined the chemical kinetics of biodiesel and hydrogen mixtures. This study investigated the effects of hydrogen on the ignition delay of a methyl butanoate/ n -heptane mixture. An experiment was conducted using a rapid compression machine (RCM) at 15 bar while varying the temperature (716–858 K) and hydrogen fraction in the fuel mixture (0, 25, 50, and 75%), and a numerical analysis was performed using CHEMKIN-PRO software to understand how the combustion process changes. The experimental and numerical analyses showed that, with hydrogen addition, the ignition delay increased. [ABSTRACT FROM AUTHOR]

The performance and knock-resistance characteristics of a homogeneous charge compression ignition (HCCI) engine fueled by methane and blends with hydrogen were investigated numerically using a one-dimensional cycle simulation. Parameters that affect combustion, such as intake temperature, intake pressure, excess air ratio (EAR), and mass fraction of hydrogen additive were selected as independent variables. The engine model was based on a Hyundai D6BT engine and the HCCI operation range was determined before the simulation. Modeling was performed based on the ranges found: intake temperatures of 443–493 K, intake pressures of 130–160 kPa, and EARs of 2.0–2.6. Within the operational ranges, the mass fraction of hydrogen added to the fuel was varied from 0 to 3%. The model was validated and calibrated by several sets of experimental data, under conditions of 0% and 1% hydrogen addition for various intake temperatures, pressures, and EARs. The results show that added hydrogen improved knock resistance under given conditions, and also slightly improved torque output, engine efficiency, and emissions. The peak of in-cylinder pressure decreased and was retarded, with slower combustion and heat release rates. That is, a wider operation range with a decreased risk of heavy knocking and enhanced ignition capabilities was achieved with hydrogen addition. [ABSTRACT FROM AUTHOR]

A proposed dual-loop exhaust-gas recirculation (EGR) system that combines the features of high-pressure (HP) and low-pressure (LP) systems is considered a key technology for improving the combustion behavior of diesel engines. The fraction of HP and LP flows, known as the EGR split, for a given dual-loop EGR rate play an important role in determining the engine performance and emission characteristics. Therefore, identifying the proper EGR split is important for the engine optimization and calibration processes, which affect the EGR response and deNO X efficiencies. The objective of this research was to develop a dual-loop EGR split strategy using numerical analysis and one-dimensional (1D) cycle simulation. A control system was modeled by coupling the 1D cycle simulation and the control logic. An EGR split index was developed to investigate the HP/LP split effects on the engine performance and emissions. Using the model-based control system, a multi-objective Pareto (MOP) analysis was used to minimize the NO X formation and fuel consumption through optimized engine operating parameters. The MOP analysis was performed using a response surface model extracted from Latin hypercube sampling as a fractional factorial design of experiment. By using an LP rich dual-loop EGR, a high EGR rate was attained at low, medium, and high engine speeds, increasing the applicable load ranges compared to base conditions. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of an engine generator fueled with methane-based biogas and its blend with hydrogen (H2) were numerically investigated using a one-dimensional cycle simulation and the fractional factorial design of experiment method. Based on the experimental results, the numerical model was validated and calibrated under various excess air ratio (EAR), boost pressure, spark timing, and biogas composition conditions. The conventional and current optimization methods, maximum brake torque (MBT), and minimum input fuel (MIF) conditions, were compared in terms of engine performance, NO x emission, and generating efficiency. Under MBT conditions, although higher torque and mass fraction burned (MFB) could be achieved, boosting degradation was evident at the optimum MBT timing. On the contrary, under MIF conditions with down-boosting, reduced NO x formation and improved generating efficiency could be achieved, but was accompanied by an MFB decrease. Moreover, the reduced MFB could be enhanced by H2 addition and spark-timing control. Compared to MBT, MIF optimization had advantages in terms of generating efficiency, NO x emission reduction, and spark-timing control, and could avoid boosting degradation over the entire operating range for various fuel compositions. [Copyright &y& Elsevier]

Abstract: We investigated the effects of H2 on the number concentration of particulate matter (PM) emissions from a diesel engine fitted with a low-pressure loop exhaust gas recirculation system. We used a 2.2-L four-cylinder direct-injection diesel engine satisfying EURO V regulations, and converted this engine to include an H2 feed. The air/fuel (A/F) ratio was varied in the range of 21.9–45.5 and the brake mean effective pressure was varied in the range of 2–6 bars to control the O2 concentration and in-cylinder temperature, both of which are significant for PM emissions. The number concentration of the emitted PM was measured using a scanning mobility particle sizer. We found that the emitted PM decreased by the addition of H2 which caused the unburned gas temperature increased. Furthermore, the degree of reduction was larger as the A/F ratio, load, and H2 energy fraction increased. However, with A/F ratios of less than 21.9, the addition of H2 increased the number concentration of emitted PM which was attributed to the small O2 concentration at these A/F ratios. [Copyright &y& Elsevier]

Abstract: In this study, we examined H2 effects on the combustion and emissions of a diesel engine with low-pressure loop (LPL) exhaust gas recirculation (EGR). We converted a 2.2-L four-cylinder direct-injection diesel engine satisfying Euro5 for H2 supply. An LPL-EGR system replaced the high-pressure loop (HPL) EGR system. For all tests, the brake mean effective pressure (BMEP) was kept at 4 bar and the EGR ratio was varied from 9 to 42%. The H2 energy percentage was varied from 0 to 7.4% independently to evaluate the H2 effects and EGR effects separately. The heat release rate was calculated from the measured cylinder pressure. We found that substitution of H2 for diesel fuel made the premixed burn fraction larger, and reduced the nitrous oxide (NOx) and particulate matter (PM) emissions simultaneously. For example, the NOx emissions were reduced by 36% for an EGR of 42% and an H2 percentage of 7.4%. PM emissions were reduced by 18% for an EGR of 35% and an H2 percentage of 7.4% compared with diesel fuel only cases. [Copyright &y& Elsevier]

Abstract: A newly developed microwave plasma system for fuel reforming was tested for three different hydrocarbon fuels. The microwave plasma system was powered by a low cost commercial magnetron and power supply. The microwave power was delivered to the nozzle from the magnetron via a coaxial cable, which offers tremendous flexibility for system design and applications. A non-premixed configuration was achieved by delivering a separate stream of fuel to the plasma plume, which is composed of diluted oxygen only. The feasibility of syn-gas production capability of the microwave plasma system was demonstrated and the reforming characteristics of methane, iso-octane and gasoline were compared. The effects of input power, injected fuel amount, total flow rate and O/C ratio were evaluated. The production rates of both hydrogen and carbon monoxide were proportional to the input power and the inverse of the total flow rate. As a result, the maximum efficiency of 3.12% was obtained with iso-octane for power consumption of 28.8W, O/C ratio of 1, and 0.1g/min of fuel supply. Liquid fuels produced more syn-gas and showed better efficiency than methane for the same input powers and O/C ratios. [Copyright &y& Elsevier]

• The effects of hydrogen addition on n-butane ignition delay were investigated. • The ignition delay of n-butane increases upon hydrogen addition. • Added hydrogen affects the levels of various radicals through related reactions. Hydrogen effects on the ignition delay of n-butane were investigated through a rapid compression machine (RCM) experiment and numerical analysis. The experiment was done by varying compression pressures (20 and 25 bar), equivalence ratios (0.5, 1.0, and 1.5), compression temperatures (722–987 K), and molar ratios of hydrogen in the fuel mixture (0, 25, 50, and 75%). Heat transfer model was developed based on adiabatic core assumption with volume expansion, and NUIG Aramco 2.0 mechanism was used for kinetic modeling. The experimental and numerical results of this study were in good agreement with those of previous studies. The negative temperature coefficient (NTC) trend of n-butane was identified, and the ignition delay decreased as the pressure or equivalence ratio increased. The ignition delay increased upon addition of hydrogen, attributable to both chemical and dilution effects. Sensitivity and reaction path analysis were performed at 750 K, 830 K, and 910 K. Most added hydrogen was consumed via the reaction H 2 + OH = H + H 2 O, reducing the level of OH radicals and increasing that of H radicals. The change also affected the levels of other radicals such as HO 2 ; all changes eventually affect an ignition delay. [ABSTRACT FROM AUTHOR]

Aluminum is added to solid propellant to increase specific impulse of solid propellant, but tends to stick together and so agglomerate into large particle. Such an agglomeration has a detrimental effect on the propellant performance due to incomplete combustion. There are so many factors that cause agglomeration. In this study, we assume the distance between aluminum particles as one of the most important factors affecting agglomeration. Microstructure was reflected through 3D random packing and X-ray micro-CT scanning. And agglomeration model was developed to predict the sizes of agglomerates. As a result of applying the model to the random packing and Xray micro-CT data, the volume distributions of agglomerates was similar in most of the ranges. [ABSTRACT FROM AUTHOR]

Highlights • H 2 effects on performance of T-GDI engine with various air/fuel ratios are studied. • Spark timing could be retarded on MBT zone and could be advanced on knock zone. • With H 2 , CA0-50 was improved on all, but CA50-90 worsened on BMEP 8 to 16 bar. • Variations of cylinder-to-cylinder and cycle-to-cycle are reduced by H 2 addition. • Thermal efficiency is improved by H 2 addition but optimum conditions differed. Abstract Lean combustion has been identified as a way of improving the thermal efficiency of gasoline engines. However, it is difficult to operate gasoline engines in lean conditions, because the stability of the combustion deteriorates. Hydrogen has properties that can be exploited to improve the combustion stability, and hence solve the combustion instability problem. In this paper, we describe an experimental study into the effects of hydrogen on the combustion stability, performance, and emissions at various air/fuel ratios using a four-cylinder 2.0-L turbo gasoline direct-ignition engine. The engine speed was fixed at 2000 RPM with a brake mean effective pressure of 2–18 bar. The results of these experiments indicate that combustion is improved, thermal efficiency enhanced, and emissions reduced except for NO X. Especially, in terms of combustion stability, the cycle-to-cycle variation and cylinder-to-cylinder variation decreased when hydrogen was added. This was caused by two effects. First, when the brake mean effective pressure was 10 bar or below, the burn duration was reduced by the fast flame speed, high adiabatic temperature, and high diffusion coefficient of hydrogen. This led to an increase in the combustion stability and thermal efficiency. Second, when the brake mean effective pressure was above 10 bar, knock resistance was enhanced by hydrogen: spark timing could be advanced upon hydrogen addition. Therefore, the combustion stability and performance improved. Additionally, the improvements to the combustion, especially in terms of combustion stability, became more pronounced as the in-cylinder air–fuel mixture became leaner: the lean limit was thus extended. [ABSTRACT FROM AUTHOR]

We study shock behavior of single crystalline nickel (Ni) using molecular dynamics (MD) simulations. Five different embedded-atom method (EAM) potential models were tested to select a suitable potential for shock simulation by comparing Grüneisen parameter, a key parameter in the equation of state describing energy change before and after shock load. We conducted shock propagation simulations along <100> direction of Ni and extracted (1) pressure-volume Hugoniot curve and (2) shock velocity (Us) vs particle velocity (up) relation with selected potential models by Grüneisen parameter. Although the Hugoniot p-V curve calculated by the MD simulations is slightly higher than the experimental data, its trend is overall in good comparison, considering that the experimental data is obtained from polycrystalline Ni sample containing many internal defects. The Us-up curve shows deviation especially for low up, since the sound speed c0 along <100> direction acts as the lower bound for shock velocity (Us ≥ c0). [ABSTRACT FROM AUTHOR]

The effects of hydrogen on the combustion characteristics, thermal efficiency, and emissions of a turbo gasoline direct-injection engine with exhaust gas recirculation (EGR) were investigated experimentally at brake mean effective pressures of 4, 6, and 8 bar at 2000 rpm. Four cases of hydrogen energy fraction (0%, 1%, 3% and 5%) of total fuel energy were studied. Hydrogen energy fraction of total fuel energy was hydrogen energy in the sum of energy of consumed gasoline and added hydrogen. The test results demonstrated that hydrogen addition improved the combustion speed and reduced cycle-to-cycle variation. In particular, cylinder-to-cylinder variation dramatically decreased with hydrogen addition at high EGR rates. This suggests that the operable EGR rate can be widened for a turbo gasoline direct-injection engine. The improved combustion and wider operable EGR rate resulted in enhanced thermal efficiency. However, the turbocharging effect acted in opposition to the thermal efficiency with respect to the EGR rate. Therefore, a different strategy to improve the thermal efficiency with EGR was required for the turbo gasoline direct-injection engine. HC and CO 2 emissions were reduced but NO X emissions increased with hydrogen addition. The CO emissions as a function of engine load followed different trends that depended on the level of hydrogen addition. [ABSTRACT FROM AUTHOR]

Hydrocarbon-selective catalytic reduction (HC-SCR) is a deNO x system for diesel engines, which uses onboard fuel as the reductant to simplify the system. However, HC-SCR is relatively inefficient at reducing NO x , especially at low temperatures. Here we investigate improvements in the efficiency resulting from the addition of hydrogen. We investigated the effects of adding hydrogen on the efficiency of NO x reduction via HC-SCR using various reductants. Tests were carried out using both laboratory experiments and an engine test-bench at temperatures below 315 °C, with a 2.5 wt.% high-dispersion Ag/Al 2 O 3 catalyst. The hydrogen was introduced to maximize the efficiency of NO x reduction at low temperatures (245–315 °C). In the laboratory tests, propene, heptane, and dodecane were used as reductants to determine the effects of different chain lengths and chemical structures. The effects of hydrogen addition on the gas-phase reaction of HC-SCR were also examined. The efficiency of NO x reduction increased significantly following the addition of hydrogen. In particular, the effects of hydrogen addition were significantly influenced by characteristics of the fuel, including the chain length and the structure, and longer chains and a higher degree of saturation were found to be advantageous. Engine tests were carried out to verify the effects of longer hydrocarbons in the presence of hydrogen; we found a maximum NO x reduction efficiency of 79% at 315 °C and 74% at 245 °C using diesel fuel as a reductant. [ABSTRACT FROM AUTHOR]

The performance and NO x (nitrous oxide) emissions of a biogas-fueled turbocharged internal combustion engine were investigated using one-dimensional cycle simulation. Analyses were carried out using the design of experiment method, and the results were verified by comparison with experimentally measured data. The combustion behaviors were improved as the CH 4 content in the biogas increased. The brake power, brake thermal efficiency, and NO x emissions increased as the CH 4 content or the boost pressure increased. Appropriate boost pressures to produce the same brake power at a given relative air/fuel ratio of 1.1 without boost were determined for each relative air/fuel ratio or each biogas composition considering brake power. In general, the lean operation limit was extended up to a relative air/fuel ratio of 1.5 with various biogas compositions and up to a relative air/fuel ratio of 1.7 for CH 4 :CO 2 volume ratios of 65%:35% and 70%:30% without knocking. The maximum brake thermal efficiency was 35.9%, which was observed with a relative air/fuel ratio of 1.7 and a boost pressure of 1.44 bar at CH 4 :CO 2 = 70%:30%. The NO x emissions were reduced by more than 90% via a reduction in the combustion temperature, which was achieved as a result of the lean combustion. [ABSTRACT FROM AUTHOR]

The filtration characteristics of a metal fiber filter on dry soot particles have been investigated empirically as a function of the filter pore size and fiber diameter. Six types of metal fiber filters, having various pore sizes and fiber diameters, were examined experimentally, with a focus on the pressure drop, deposited mass, and filtration efficiency. Filtration efficiency was calculated based on the particle number concentration and expressed as a function of the electrical mobility diameter and time. Dry soot particles were generated by a soot generator (mode diameter: 100 nm; total number concentration: 3.48×10 10 /cm 3 ). The deposition temperature, total flow rate, and deposition time were set to 250 °C (equivalent to a particle approach velocity of 1.7 m/s), 29.2 sLPM, and 1 h, respectively. Our results showed that the pressure drop, mass, and particle number concentration-based filtration efficiency exhibited the same tendencies. Specifically, the filter pore size influenced the initial and final filtration efficiencies, while the fiber diameter had a significant effect on the rate of increase of the filtration efficiency. [ABSTRACT FROM AUTHOR]

A metal foam filter is a porous metal DPF (Diesel Particulate Filter) that has different deposition characteristics to wall-flow-based filters. In this study, the soot particle deposition characteristics of a metal foam filter were examined using a 450 μm pore size filter. The pressure drop and the deposited mass were measured and filtration efficiency was derived by measuring the soot particle number concentration at the front and rear side the filter, using a scanning mobility particle sizer. The temperature range under which deposition occurred was set as 150 °C, 250 °C, and 400 °C. The total flow rate was about 30 sLPM (Standard liter per minute), and deposition time was 1 h. The mode diameter and number concentration of generated particles was 41 nm, 4.39 × 10 9 /cm 3 ; 128 nm, 3.12 × 10 9 /cm 3 ; and 190 nm, 9.24 × 10 8 /cm 3 . The filtration efficiency was derived and expressed as a function of the particle diameter and the total number concentration. Mode diameters of 128 nm and 190 nm were selected for the quantitative measurement of number concentration. The results indicated that the filtration efficiency of a metal foam filter is determined predominantly by the particle mode diameter, but is also affected by the deposition temperature. [ABSTRACT FROM AUTHOR]

We propose a gas sensor operable over a wide temperature range and using suspended GaN nanowires functionalized with Pt–Pd. The sensor is batch-fabricated by directly integrating the GaN nanowires onto batch-processed silicon microelectrodes in parallel. The high thermal stability of the sensor originates from a large band gap of GaN nanowires that enables the detection of NO2 gas at an elevated temperature of up to 350 °C without a decrease in responsiveness. Exposed to NO2 at 100–1000 ppm at 350 °C, the sensor shows a linear increment in relative response with respect to the change in gas concentration. The sensor results in a two- to four-fold increase in responsiveness to NO2 at 100 ppm compared to NH3 at 100 ppm and CO2 at 1000 ppm. The nanowires suspended over a substrate provide increased surface area that could interact with gas molecules for enhanced responsiveness, and prevent any unnecessary interactions between the nanowires and the substrate. [ABSTRACT FROM AUTHOR]

Abstract: Recent diesel engine technologies, developed for enhanced regulation of exhaust emissions, are characterized by high exhaust gas recirculation (EGR) rates and high-pressure fuel injection. The use of high EGR rates, by which high temperatures can be avoided in a cylinder, is an effective method for reduction of nitrogen oxide (NO x ) emissions. High-pressure fuel injection leads to smaller soot particles, which decreases mass-based soot emission. These technologies, however, also have effects on particulate matter (PM) characteristics that are closely related to EGR cooler fouling. High-pressure fuel injection, which makes smaller soot particles, increases the concentration of soot particles, and a high EGR rate, which lowers the temperature in the cylinder, increases the soluble organic fraction (SOF). In this study, we evaluated the effects of these changes in PM characteristics on EGR cooler fouling. Instead of an engine-based experiment, in which a parametric study is nearly impossible, a laboratory experiment was performed to separate variables. A soot generator was used to make model exhaust gas because the variables could be controlled separately (e.g., mean particle size and concentration of soot particles) and this improved the reproducibility of the experiments. Additionally, n-dodecane, a model compound representing diesel fuel, was vaporized and injected into the exhaust gas to test the effects of SOF on cooler fouling. For particle sizes ranging from 41 to 190 nm in diameter, the deposition fraction was inversely proportional to particle size. Thus, smaller soot particles in the exhaust gas were more likely to cause formation of thermophoretic deposits on the wall of the EGR cooler. At an EGR gas temperature of 350 °C, the deposition fraction was greatest (84%) for the smallest particle size of 41 nm, whereas the deposition fraction was least (7%) for the largest particle size, 190 nm. The performance degradation of the EGR cooler showed a similar trend to the measured deposit mass. As coolant temperature decreased, the effect of n-dodecane injection on the growth of PM deposits increased, which significantly reduced the overall thermal conductivity of the EGR cooler. This result showed that ‘wet soot’ caused greater contamination of the EGR cooler. [Copyright &y& Elsevier]

Abstract: Recently, the diesel engine particulate matter (PM) emission standard was changed from being based on mass to being based on both number and mass. However, it is difficult to determine the mass- and number-weighted distributions simultaneously because of the complex shapes of PM. We studied a new method to determine the mass-weighted distribution of PM using the primary particle density, and compared it with two conventional PM measurement methods using effective density and gravimetric filtration. In the method developed, the primary particle size was measured using transmission electron microscopy (TEM)-calibrated laser-induced incandescence (LII) to detect changes in the primary particle size in real-time. The number-weighted distribution of aggregates was measured with a scanning mobility particle sizer (SMPS). The mass–mobility exponent and the effective density were determined with an impactor and the SMPS. The differences in the mass concentrations for each technique were between 3.1% and 29.9%. [Copyright &y& Elsevier]

Abstract: Conventional fossil fuels for combustion systems, such as gasoline and diesel, have a number of problems related to energy security and emissions. Alternative fuels, such as methane, hydrogen, and mixtures of these two gases, are being promoted as clean energy substitutes for primary fossil fuels. Natural gas (which consists mainly of methane) is one of the most promising of these fuels, providing lower cost, cleaner emissions and is direct applicable to existing combustion systems. However, the use of natural gas as fuel can adversely affect engine performance. Therefore, hydrogen is sometimes used as an additive, as its higher burning rate often leads to enhanced combustion. In this study, cycle simulation was used to numerically investigate the performance and emission characteristics of an engine employed primarily to power a generator, and fueled with methane and methane – hydrogen blends. Dominant parameters such as excess air ratio, spark timing, and volume percent of hydrogen content, were investigated as independent variables. The fundamental effect of hydrogen on methane combustion was investigated for a fixed excess air ratio of 1.2 and a spark timing of 14CA(Crank Angle) BTDC (Before Top Dead Center), with an accompanying reduction in ignition delay. By varying the excess air ratio, hydrogen was demonstrated to play an important role in extending the lean operating limit. The DOE (Design of Experiment) method was applied to study MBT (Maximum Brake Torque) spark timing for various excess air ratios and hydrogen contents. When MBT spark timing was employed, maximum brake torque could be achieved under leaner burning conditions by increasing the hydrogen content. [Copyright &y& Elsevier]

Abstract: The National Institute of Standards and Technology (NIST) detailed reaction mechanism of methane combustion was optimized based on a flow reactor experiment to obtain syngas (H2 + CO). The experimental methane partial oxidation was conducted with pre-mixed gas in a flow reactor. Specifically, 0.2% methane and 0.1% oxygen were diluted with 99.7% argon, restraining the exothermic effect. The experiment was conducted from 1223 K to 1523 K under pressure. Through a comparison of the experimental results with calculated values, the NIST mechanism was selected as a starting point. Rate coefficients of O + OH = O2 + H, CH3 + O2 = CH3O + O, and C2H2 + O2 = HCCO + OH were replaced with results from other studies. The replaced rate coefficient for CH3 + O2 = CH3O + O was again optimized, within its reported uncertainty of 3.16, based on the experimental results of this study. The revised value of the rate coefficient for CH3 + O2 = CH3O + O was k 37 = 7.92 × 1013 × e(−31400/RT). The optimized mechanism showed better performance in predicting the results of other studies, as well as this study. The optimization reduced the RMS error for the results of this study from 6.7 to 1.18. [ABSTRACT FROM AUTHOR]

Abstract: The emission regulations for diesel particulate matter (PM) are becoming increasingly strict. The focus of regulations is turning to reducing the number of nanosized particles as well as the total mass. A more precise measurement technique for particle numbers and mass must be developed to meet these new regulations. In this study, a new method for estimating the mass weighted size distribution of diesel PM was investigated by measuring the size of primary particles and the number concentration distribution of particle aggregates. Time-resolved laser-induced incandescence was used for primary particle size measurement and a scanning-mobility particle sizer was used to quantify the number concentration of aggregates. The results from these two conventional measurement techniques were combined using fractal analysis formulas to relate the electrical mobility diameter, the number of primary particles per aggregate, primary particle size, and fractal dimension. This method, applied to single-cylinder diesel engine exhaust with various engine loads and injection pressures, successfully estimated the mass weighted size distribution of particle aggregates. The procedure is very simple and the estimations are comparable with those based on effective density, making this method a useful and reliable tool for estimating mass weighted size distribution of fractal particles such as diesel PM. [Copyright &y& Elsevier]

• Steam addition reforming effects on performance of a range extender are studied. • Steam was generated from heat energy of exhaust gas. • Steam addition improved the H 2 fuel conversion efficiency of the reformer. • Thermal efficiency was improved by reforming, but steam addition did not have a strong effect. • Reforming with steam addition decreased NO X emissions while maintaining thermal efficiency. Electric vehicles (EVs) are becoming increasingly popular in the global automobile industry. A range extender is a generator that increases the mileage of EVs. The engine for a range extender operates in a steady state. Steady conditions are suitable for catalyst-based on-board fuel reforming operations. Hydrogen has unique properties that improve combustion performance, such as fast burning, short quenching distance, and increased flammability. We carried out experiments and analyses to improve the thermal efficiency of a range extender that uses catalyst-based on-board fuel reforming with steam addition. For this study, steam was generated from exhaust-waste heat. Based on a previous study, the power requirement for the range extender of a medium-sized city bus was calculated. Accordingly, the range extender was operated at a brake mean effective pressure (BMEP) of 10 bar and speed of 2000 rpm. The results indicate that reformed H 2 has positive effects on the combustion performance and thermal efficiency of the range extender. Steam addition to the reformer improves the reforming performance and greatly influences the reduction in NO x emissions. Moreover, steam addition to the reformer leads to an increase in thermal efficiency. However, steam addition cannot affect the thermal efficiency as much as it affects the reforming performance. [ABSTRACT FROM AUTHOR]

Experimental research was conducted to study the combustion characteristics of clouds composed of micrometer-sized aluminum particles with an oxidizer blend of oxygen and superheated steam. Both ignition and combustion of an aluminum particle are difficult because it is enveloped by an oxide layer that has a high melting point (above 2300 K). To overcome the problem, we induced a particular shape of the combustor that can keep a stable flame of aluminum dust clouds at a lower feeding-rate. The combustion characteristics were examined using a system applied combustor involving a variety of parameters affecting the burning of the dust clouds. Based on these attempts, the aluminum dust clouds had an upper flammability limit above the equivalence ratio (Ф) 1.9 for oxygen diluted by air. Varying the lower limit of flammability, we found, crucially, that the feeding-rate and velocity of the particles are more effective than the equivalence ratio or combustor length. Furthermore, we could confirm the changing of the lower limit from 0.3 to 0.26 because the steam was additionally fed in the combustion of aluminum-oxygen. • Designed Combustor that Al dust can be terminated the burning without depositing. • Variation of the lower limit of flammability depending on Al dust feeding conditions. • Confirming the changing of a lower limit owing to feeding steam in Al–O 2 flame. [ABSTRACT FROM AUTHOR]

• Combined reforming effects on performance of T-GDI engine are studied. • PFI effects of the reformer have no negative influence on T-GDI engine at 4 and 6 bar BMEP. • Combined reforming improves H 2 fuel conversion efficiency significantly near the light-off level. • Combined reforming has a strong effect on BTE when R-CAT temperature is near the light-off level. • Combined reforming has a little effect on CO 2 emissions due to improvement in reformed CO. Hydrogen (H 2) addition is known to have features of increasing the laminar burning velocity (Di Sarli and Di Benedetto, 2007), the resistance of the flame to strain-induced extinction (Di Sarli and Di Benedetto, 2012, 2013), and also enlarging the operating window of stable combustion (Di Sarli, 2014). We experimentally investigated how to improve the thermal efficiency of a turbo gasoline direct injection (T-GDI) engine using H 2 from combined steam and partial oxidation exhaust gas gasoline reforming under low-load stoichiometric conditions. During real driving, 4 and 6 bar brake mean effective pressure (BMEP) at 2,000 rpm are frequently used. Our experimental results show that reformed H 2 improves the brake thermal efficiency (BTE) of T-GDI engines operating at 4 and 6 bar BMEP. Furthermore, the combustion speed (increasing heat release rate) and stability (reducing cyclic variation) were enhanced by reformed H 2 , making more heavy exhaust gas recirculation (EGR) operation. Combining steam and partial oxidation exhaust gas gasoline reforming with extra air injection to a reformer had a large effect on the fuel conversion efficiency of the reformer as the engine load decreased. Therefore, the BTE of the T-GDI engine with combined steam and partial oxidation reforming achieved further improvement over steam reforming only at 4 bar BMEP. Nitrogen oxide (NO X) emissions increased with reformed H 2. However, on the basis of the improved combustion stability achieved using reformed H 2 , NO X emissions could be reduced further by using a higher EGR rate while enhancing the BTE. [ABSTRACT FROM AUTHOR]

The fundamental combustion characteristics and engine performance of a dual-fuel engine, fueled with diesel and natural gas, were investigated using a commercial 1D simulation program (GT-Power). Furthermore, the effects of air-fuel ratio under dual-fuel combustion conditions were studied, and optimized design points that minimize brake-specific fuel consumption (BSFC) and nitrogen oxides (NO X) emissions simultaneously were determined using a multi-objective Pareto optimization method. The engine model was validated based on experimental results and previous work under various engine loads. The thermal efficiency of the engine, which was modified from a diesel to a dual-fuel engine, showed a decreasing tendency as the natural gas substitution ratio (NSR) increased due to changes in the combustion characteristics. The decline in thermal efficiency in dual-fuel combustion could be improved somewhat by optimizing the injection strategy. Under dual-fuel combustion conditions, an optimum air-fuel ratio value for BSFC could be determined, especially for higher NSR conditions. However, NO X emissions showed a tendency to increase with increasing air-fuel ratio. The relationship between the trends was more than a simple tradeoff, so multi-objective Pareto optimization was conducted to minimize both BSFC and NO X emissions, with start of injection timing and air-fuel ratio as variables. Ultimately, optimal design points were determined. • The large stationary engine was modeled and modified to dual-fuel engine. • The characteristics of dual-fuel combustion were investigated. • The effect of air-fuel ratio under dual-fuel combustion condition are investigated. • The optimal design points for improving fuel economy and NOx emission are suggested. • Helpful methodology for conceptual design of virtual engine system was suggested. [ABSTRACT FROM AUTHOR]

Multi-functional energetic structural material (MESM) is a mixture of metals, metal oxides and binders, which improves the insensitivity and maintains explosion power of the explosives. MESM during explosion reaction undergoes various changes in thermal, mechanical, and chemical characteristics caused by shock wave propagation in time scale of nanoseconds. It is hard to study impact characteristics of MESM through various experiments due to short impact reaction, high cost and safety problem. Therefore, analysis using mesoscale simulation is important in studying impact characteristics such as Hugoniot relation and pressure data. In this study, meso-scale simulations of shock wave propagation were conducted for Al, Ni, W, Al-W and Al-Ni mixture, under the conditions of impact velocities ranging from 0.5 km/s to 5 km/s. Simulation data of Al, W and Ni using Mie-Gruneisen EOS were used to confirm the accuracy of analysis, and the results correlated reasonably well with the corresponding data (Los Alamos explosive experiment). Based on this single metal simulation results, simulations for Al-W and Al-Ni mixture were performed at various volume fractions and propagation distances of shock. The results of these simulations could be useful information to predict impact characteristics of mixtures. [ABSTRACT FROM AUTHOR]

The purpose of this work is to investigate proper hydrogen production methods from methane through the parametric study for the highly active and stable nanofibrous perovskite catalyst. A ruthenium doped lanthanide chromate (LaCr 0.8 Ru 0.2 O 3 ) micro-fibrous perovskite catalyst is prepared and fixed to focus on the effect of reaction environments such as steam, partial oxidation and autothermal conditions. Temperatures, H 2 O/C and O 2 /C ratios were occasionally changed for the investigation of the effects and the optimization conditions. At the same perovskite catalyst system, the reaction at the autothermal atmosphere is the most effective conditions in terms of both CH 4 conversion and H 2 production, which was comparable to the theoretical calculations. It is found that conversion increases with oxygen at even low temperature while the H 2 productivity increases with much stable behavior at steam condition. These are more obvious at the elevated temperature with each optimized H 2 O and O 2 amounts for high activity by low activation energy. Time-on-stream runs conducted on these three reactions with each optimized conditions of 50 h at 800 °C, H 2 O/C = 3 and O 2 /C = 0.5. The perovskite micro-fiber catalyst at autothermal condition shows excellent CH 4 conversion of over 95%, H 2 production of around 70%, and even H 2 /CO of over 4. On the other hand, the reactivity at the steam condition is lower and even slow. The durability at the partial oxidation condition starts to decrease after 10 h due to the instability of the perovskite at the extremely oxidative concentration which causes a relatively high coke formation. Therefore, it is worthwhile in suggesting proper autothermal reaction conditions for the highly active and stable perovskite catalyst like LaCr 0.8 Ru 0.2 O 3 micro-fibers. [ABSTRACT FROM AUTHOR]

The effect of methanol addition on the performance and NO x emission of a diesel engine was investigated using one-dimensional engine cycle simulation. The methanol component was injected into the intake manifold of a diesel engine at a certain energy fraction (0, 5, 10, or 15%) of the fuel. The in-cylinder pressure and temperature decreased as the methanol content increased due to the lower cetane number and lower heating value of methanol. The resulting decrease in the combustion efficiency lowered the NO x emission and brake thermal efficiency of the engine, and consequently deteriorated the brake specific fuel consumption (BSFC). The BSFC decreased but the NO x emission increased with advanced injection timing under dual-fuel operating conditions. Response surface plots of the BSFC and NO x emission as a function of the injection timing and exhaust gas recirculation (EGR) rate were obtained using a design of experiment method. The optimal Pareto fronts that improved both the BSFC and NO x emission were found. The EGR rate had a greater influence on the optimal Pareto front than the injection timing, which suggested that design parameters such as the injection timing and EGR rate could be used to control the performance and emission under various duel-fuel conditions. [ABSTRACT FROM AUTHOR]

Iso-octane-based surrogates have been widely used to represent gasoline fuel combustion. The surrogate's autoignition characteristics have been of particular interest due to combustion issues associated with spark-ignition engine knocking or controlled autoignition. In this study, the autoignition of several hydrocarbons was measured and analyzed using a rapid compression machine. The two-stage ignition characteristics of gasoline and iso-octane were compared and the differences analyzed from the viewpoint of the effect of the fuels' chemical structure on low-temperature oxidation processes and internal isomerization. Finally, the reliability of iso-octane as a gasoline surrogate was examined, and other surrogates were suggested. Our results indicated that surrogates containing ∼20% cyclic alkenes were better able to simulate gasoline autoignition, including two-stage ignition characteristics. [ABSTRACT FROM AUTHOR]

The fractal particle concept was applied to the real-time light transmission spectroscopy (RTLTS), an in-situ particle-size distribution measurement technique. The number of fractal-shaped particles in diesel engine exhaust gases was measured under transient conditions using RTLTS. The engine operated at a fixed speed and under different loads. One-second resolution RTLTS detected instantaneous changes in the particle emission under rapidly decreasing load conditions. The particle size determined with RTLTS was compared with values obtained using commercial analysis systems, such as a differential mobility analyzer (DMA) and condensation particle counter (CPC). The fractal reflected Mie-scattering database was applied to RTLTS to reduce multi-scattering error due to the fractal shape of the aggregates. The single-mode particle size distribution was obtained using reflective fractal analysis. Using a particle shape reflected light-scattering database can enhance the reliability of RTLTS measurements. [ABSTRACT FROM AUTHOR]

The ignition delay time with mixtures of primary reference fuels (PRFs) and hydrogen were measured using a rapid compression machine (RCM), where the concentration of hydrogen was systematically varied. The experiments were performed for compressed temperatures in the range 735–847 K. The fuel/air equivalence ratio was varied to investigate its effects on the ignition delay of n -heptane and iso-octane. Hydrogen was added with hydrogen-energy-share ratios in the range of 0–10%, meaning that the energy of the hydrogen replaced 0–10% of that of either n -heptane or iso-octane. When hydrogen was added to n -heptane, there was a significant increase in the ignition delay, especially during the first-stage reaction region. This was explained using the chemical kinetic analysis software package CHEMKIN PRO; hydrogen consumed radical species related to the ignition of hydrocarbon fuels. With iso-octane, there was a significant increase in the ignition delay not only in the fist-stage reaction region, but also in second-stage reaction region. The effects of the hydrogen concentration were found to depend on the equivalence ratio and temperature for both fuels. [ABSTRACT FROM AUTHOR]

• Analysis of the atomization characteristics of slurry fuels containing aluminum particles using a swirl atomizer for the first time. • Microscopic shadowgraph image capture of ligaments and droplets and Sauter mean diameter of droplets. • Confirmation of ligament and droplet formation, breakup characteristics, and slurry fuel atomization characteristics. Slurry fuel, which has a high energy density, is a mixture of liquid or gel and metal fuels (Al, B, Mg) in powder form. Such slurry fuels have non-Newtonian fluid characteristics in the form of shear thinning based on cohesion, inertia, and friction among the metal particles present in the fuel. Additionally, the atomization characteristics of slurry fuels differ from those of conventional fuels and vary according to the metal particle content, mean particle diameter, and injection parameters. In this study, the effects of aluminum particles on slurry fuels were experimentally investigated. To determine the effects of the content and mean diameter of aluminum particles in a slurry on ligament and droplet formation and breakup, microscopic shadowgraph images were captured, and the Sauter mean diameter (SMD) of the droplets was measured. In particular, the breakup mechanisms of liquid films and ligaments, and the impact of an increase in mean particle diameter are discussed. Additionally, for the first time, the effects of shear and elongation rheological characteristics on the atomization performance of a slurry swirl spray are described. When the mean diameter of the aluminum particles contained in the slurry increases from 10 to 21 μm, the breakup length and number of ligaments that cannot be broken up into droplets increase. On the contrary, when the particle size is the largest (54 μm), the breakup length is the shortest and the number of ligaments is the smallest as a result of the effects of elongation rheological characteristics. However, the SMD increases monotonically according to particle content and particle size increases under the effects of shear rheological characteristics. [ABSTRACT FROM AUTHOR]

We developed an improved particle measurement spectroscopic technique, real-time laser transmission spectroscopy (RTLTS), to detect the number-weighted distribution of particles in real time. The measurement system used a deuterium–tungsten lamp for the light source and a spectrometer as the detector. The operating wavelength range was 300–810 nm. To obtain a physically reasonable number concentration from the experimental results, a sequential regularization method was used during the calculations. To verify the feasibility and reliability of RTLTS, the number-weighted distribution of polystyrene particle suspensions was determined over diameters ranging from 0.005 to 2.000 μm in 0.005-μm increments. The measured concentration error was 0.67–32.67%. A mean diameter of the smallest particle we had detected was 0.09 μm, with a 16% oversizing. The measurable concentration range was ∼108#/cc to ∼1011#/cc for 0.895-μm-diameter particles. The measurable concentration range could be adjusted simply by changing the system configuration. This technique is available for both waterborne and airborne particles. Copyright 2013 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Abstract: The distinctive properties of hydrogen have initiated considerable applied research related to the internal combustion engine. Recently, it has been reported that NO x emissions were reduced by using hydrogen in a diesel engine at low temperature and heavy EGR conditions. As the continuing study, cylinder pressure was also investigated to determine the combustion characteristics and their relationship to NO x emissions. The test engine was operated at constant speed and fixed diesel fuel injection rate (1500 rpm, 2.5 kg/h). Diesel fuel was injected in a split pattern into a 2-L diesel engine. The cylinder pressure was measured for different hydrogen flow rates and EGR ratios. The intake manifold temperature was controlled to be the same to avoid the gas intake temperature variations under the widely differing levels (2%–31%) of EGR. The measured cylinder pressure was analyzed for characteristic combustion values, such as mass burn fraction and combustion duration. The rising crank angle of the heat release rate was unaffected by the presence of hydrogen. However, supplying hydrogen extended the main combustion duration. This longer main combustion duration was particularly noticeable at the heavy EGR condition. It correlated well with the reduced NO x emissions. [Copyright &y& Elsevier]

Abstract: Cooled and heavy exhaust gas recirculation (EGR) has been used to control NOx emissions from diesel engines, but its application has been limited by low thermal efficiency or high unburned hydrocarbon emissions. In this study, hydrogen was added into the intake manifold of a diesel engine to investigate its effect on NOx emissions and thermal efficiency under low-temperature and heavy-EGR conditions. The energy content of the introduced hydrogen was varied from an equivalent of 2–10% of the total fuel’s lower heating value. A test engine was operated at a constant diesel fuel injection rate and engine speed to maintain the same engine control unit (ECU) parameters, such as injection time, while observing changes in the carbon dioxide produced due to variations in the hydrogen supply. Additionally, the EGR system was modified to control the EGR ratio. The temperature of the intake gas manifold was controlled by both the EGR cooler and the inter-cooling devices to maintain a temperature of 25 °C. Exhaust NOx emissions were measured for different hydrogen flow rates at a constant EGR ratio. The test results demonstrated that the supplied hydrogen reduced the specific NOx emissions at a given EGR ratio while increasing the brake thermal efficiency. This behavior was observed over constant EGR ratios of 2, 16, and 31%. The rate of NOx reduction due to hydrogen addition increased at higher EGR ratios compared with pure diesel combustion at the same EGR ratio. At an EGR ratio of 31%, when the hydrogen equivalent to 10% of the total fuel’s lower heating value was supplied, the specific NOx was lowered by 25%, and there was a slight increase in the brake thermal efficiency. This behavior was investigated by measuring and analyzing changes in the exhaust gas composition, including oxygen, carbon dioxide, and water vapor. [Copyright &y& Elsevier]

Abstract: This paper investigates the generating efficiency and NO x emissions of a gas engine generator with a low-pressure loop exhaust gas recirculation system, fueled by a model biogas. Experiments for improving the generating efficiency and reducing NO x emissions were conducted, utilizing optimum spark timings based on the maximum generating efficiencies with varying exhaust gas recirculation (EGR) rates. The test results show that both the NO x emissions and the generating efficiency generally decrease when the EGR rate is increased. Also, by utilizing optimum spark timings with varying EGR rates, the addition of hydrogen to the biogas increases the generating efficiency of the engine. In particular, the generating efficiency of the biogas–hydrogen test increased by about 1.5% in comparison with the model biogas test for the optimum spark timing at 15% EGR. Accordingly, comprehensive techniques, such as the use of a biogas–hydrogen fuel mixture and optimum spark timings with respect to EGR rates, should be employed to efficiently generate electricity with a biogas engine. [Copyright &y& Elsevier]

Abstract: We investigated the generating efficiency and pollutant emissions of a four-stroke spark-ignition gas engine generator operating on biogas–hydrogen blends of varying excess air ratios and hydrogen concentrations. Experiments were carried out at a constant engine speed of 1200 rpm and a constant electric power output of 10 kW. The experimental results showed that the peak values of generating efficiency, maximum cylinder pressure, and NO x emissions were elevated at an excess air ratio of around 1.2 as the hydrogen concentration was increased. CO2 emissions decreased as the excess air ratio and hydrogen concentration increased, due to lean-burn conditions and hydrogen combustion. An efficiency per NO x emissions ratio (EPN) was defined to consider the relationship between the generating efficiency and NO x emissions. A maximum EPN value of 0.7502 was obtained with a hydrogen concentration of 15%, for an excess air ratio of 2.0. At this EPN value, the NO x and CO2 emissions were 39 ppm and 1678.32 g/kWh, respectively, and the generating efficiency was 29.26%. These results demonstrated that the addition of hydrogen to biogas enabled the effective generation of electricity using a gas engine generator through lean-burn combustion. [Copyright &y& Elsevier]

Abstract: Based on tunable diode laser spectroscopy with direct absorption measurement, we developed a reliable measurement scheme which can precisely detect water vapor concentration independent of the scattering (attenuation) caused by the non-water dust particles inside the observed humidity chamber. The relative water vapor concentration was measured at water vapor transition band by 938nm distributed feed-back diode laser at different temperatures using the tunable diode laser spectroscopy technique. These relative water vapor concentrations are converted into the absolute water vapor concentrations and we confirmed that the experimental results at different temperatures are consistently independent of the attenuation. Our measurement system gives the consistent water vapor concentrations without regard to either high or low scattering caused by the non-water dust particles inside the observed humidity chamber. [Copyright &y& Elsevier]

• Simulating IR signatures and flow structure of plume at the rear of solid rocket motor. • Using HTPB (weak afterburning) and NEPE (strong afterburning) propellants. • Confirming the effect of altitude, flight Mach number, and motor size. In this study, radiation signatures of rocket plumes based on HTPB and NEPE propellants are simulated under varying altitudes, flight Mach numbers, and motor size. The flow field of plume is calculated by computational fluid dynamics, and the infrared signature is predicted using a Ludwig model. To verify the numerical method, experiments were conducted using small rocket motors and radiometric FTIR. The acceptable agreement between numerical calculation and the experiment was obtained in 2 – 5 μm wavelength region. The total radiance decreases with increasing altitude whether afterburning exists or not. A decreasing rate in the radiance of the plume with strong afterburning is larger than that of the plume with weak afterburning. The change in total intensity according to altitude depends on the afterburning and is directly affected by the radiating area. As the flight Mach number increases, total radiance, total intensity, and radiating area decrease. The motor size makes radiation intensity increase exponentially; exponent value is from 2.6 to 2.7. As the motor size increases, the effect of altitude increases, while the effect of flight Mach number decreases. [ABSTRACT FROM AUTHOR]

Abstract: A semiconductor gas sensor based on WO3 doped TiO2 having a rutile phase was fabricated on an Al2O3 substrate. The sensing film of the sensor was deposited by using screen printing. In order to enhance the sensitivity of the sensor, the sensing film was fabricated with a porous shape by high temperature heat treatment and the TiO2 layer was doped with WO3 to improve the gas selectivity. The surface topography and inner morphological properties of the sensing film were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The gas sensing properties of the fabricated sensor were evaluated by detecting NO2 and other oxidizing gases (CO, O2 and CO2) at high operating temperature (600°C). [Copyright &y& Elsevier]