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International audience; The reduction of pollutant emissions from internal combustion engines, and in particular greenhouse gases, must be achieved by optimizing the combustion process and choosing fuels with a low carbon impact. Heterogeneous mixture combustions such as Diesel induce a difficulty in managing of the pollutants formation even if in its principle the output efficiency remains favorable. Therefore, it is necessary to distinguish this last point, which refers to the compression ratio, in order to move towards homogeneous combustion with a high compression ratio. We then speak generically of HCCI combustion (Homogeneous Charge Compression Ignition), whose process takes place in the context of auto ignition.An important challenge of this combustion is the control of the ignition timing. This paper presents a concept to control the initiation of combustion of a reactive gas mixture with low susceptibility to auto-ignition, which meets the expectation of high efficiency, via the introduction of biomass particles. From a schematic point of view, these particles will play the role of spark plugs distributed throughout the combustion chamber, and should have an auto ignition time much lower than that of the fuel.For this purpose, a particle injector was conceived to directly inject a controlled quantity of biomass powder into the reactive mixture directly. This part is a challenging point. The reproducibility and viability of the particle injector were qualitatively validated by image analysis acquired at high frequency and high resolution. Thus, the system was integrated into an RCM (Rapid Compression Machine) chamber, allowing diphasic gas/solid biomass combustion study. This preliminary test was investigated by high-speed video on a lean diluted biomass enriched with hydrogen mixture (CH4/CO2/H2) at low fuel-air equivalence ratio (Φ = 0.6), with different auto-ignition delays in the condition of experimentation. It was shown that the direct injection of a small amount of biomass particles was able to promote its reactivity and initiate the combustion process. This study highlights the promising effects of the injection of powder to control the beginning of homogeneous combustion, by bringing locally a spot of energy, distributed in the whole chamber. The control given by a global contribution of weak energy is distinguished from the process of combustion by auto-ignition of the fuel mixture whose properties of equivalence air-fuel ratio or dilution will complete the optimization of the process.

The development of alternative fuels is important in the fight against climate change. Both hydrogen and ammonia are renewable energy sources and are carbon-free combustible fuels. In a recent experimental study, the performance and emission characteristics of a spark-ignition engine burning a premixed hydrogen/ammonia/air mixture were evaluated. The manifold absolute pressure was adjusted to 61 kPa and the engine speed was stabilized at 1300 rpm. The difference between a mixture with a 2.2% volume fraction of ammonia and a pure hydrogen fuel was analyzed in comparison. Specifically, the addition of ammonia increased the ignition delay and flame development periods and reduced the rate of in-cylinder pressure rise. In conjunction with the ignition timing strategy, the addition of ammonia did not affect the engine performance. Nitrogen oxides emissions are increased due to the addition of ammonia. The experimental results suggest that ammonia can be used as a combustion inhibitor, which provides a new reference for the development of hydrogen-fuelled engines.

In the present study, the countermeasures are proposed to minimize the problem on torque and power output performance and exhaust gas emissions of natural gas engine with use of lower calorific gas. An experiment was conducted to identify thermal efficiency and harmful exhaust gas emission characteristics under partial load conditions in order to improve efficient fuel use in engines affected by the introduction of low calorific gases. A countermeasure for coping with emission gas regulations and preventing thermal efficiency deterioration under rated power operating conditions was then presented. An 11 L six-cylinder turbo-charged engine for city buses compliant with the EURO 6 regulation was used in the experiment, and the results obtained using the reference natural gas fuel were compared with those obtained using simulated low calorific gases. Pure methane (CH 4) was also used to investigate the effects of gas composition changes on thermal efficiency and exhaust gas emissions. When N 2 is added or pure CH 4 is used under partial load operating conditions, the combustion rate decreases; consequently, the optimum ignition timing is additionally advanced relative to that obtained when the reference natural gas fuel is used. If the N 2 mixing ratio is increased to a minimum of 4.7% under rated power operating conditions, combustion becomes unstable. Stable operation can be secured by increasing the set base fuel amount, 2.35% and 9.41% for pure CH 4 and 8% N 2 , respectively; however, torque decreases in proportion to the combustion speed of the gas fuel. The strategy of boost pressure control for the torque compensation can minimize the decrease in thermal efficiency.

Natural gas with H2 is widely used for lean-burn combustion, which leads to NOx emission as the main problem for it. For decreasing NOx emission and increasing thermal efficiency, the investigation on seeking the influence of H2 fractions on the mixture of CH4 and CO2 was conducted. Firstly, the ignition timing was decided through thermal efficiency and brake mean effective pressure (BMEP) for CH4 only. Then, combustion characteristics of CH4, CH4+CO2 and CH4+CO2+H2 were compared with volume percentage of H2 changing from 5% to 30%. Finally, the H2 injection strategy was checked between closed and open valve injections. Among these discussions, thermal efficiency, power output, BMEP and fuel consumption were evaluated. Results show that CO2 addition decreases power output and BMEP, leading to much more fuel consumption and lower thermal efficiency. When H2 is added, at the rich mixture conditions (λ＜1.0), power output and thermal efficiency decrease sharply as the mixture is enriched. However, at the lean-burn conditions (λ＞1.0), the decrease in flow rate of lower heating value (LHV) and increase in power output finally result in the higher efficiency with H2 addition. Moreover, when λ＞1.0, both low fuel consumption and high efficiency can be obtained with H2 addition to achieve the high BMEP. Furthermore, the open valve injection could obtain higher thermal efficiency, power output and BMEP with lower fuel consumption, suggesting that the H2 injection strategy should be well controlled with the ignition timing.

To investigate the property of the promising and eco-friendly hydrogen-fueled rotary engine, the effect of excess air ratio on the combustion and emission characteristic of it was explored by experiment. The test was conducted under 1500 rpm and 5 CAD ADTC ignition timing. The test results demonstrated that with the decrease of excess air ratio from 2 to 0.85, the thermal efficiency of the hydrogen-fueled rotary engine increases first and then decreases. Besides, increasing MAP is beneficial to improve thermal efficiency. Among the tested condition, the highest brake thermal efficiency is realized when the rotary engine operates at 1.4 excess air ratio and 88 kPa MAP, about 18.34%. And the excellent HC and NO emissions can be obtained at the highest efficiency point. Besides, with the decrease of excess air ratio and the increase of load, the stability and flame development period gradually decrease. With a decreased excess air ratio, the flame propagation period decrease first and then increases, whereas work capacity and thermal efficiency increase first and then decrease. For NO emission, it will increase sharply near the equivalent ratio and gradually decrease after rich combustion. Also, according to the analytical model, it is found that the power performance of the rotary engine depends on the trade-off relationship of in-cylinder pressure and its angle of action.

Hydrogen has become an ideal alternative fuel for internal combustion engines. However, with an increase in the equivalence ratio and compression ratio, knock combustion is more likely to occur, which limits its engineering application. In this study, the effects of the equivalence ratio on the knock under different compression ratios were studied through numerical simulation. The signal energy ratio (SER) were used to evaluate the knock onset (KO). The knock intensity (KI) and engine performance were compared and analyzed under different equivalence ratios and compression ratios. The results revealed that a high compression ratio can significantly amplify the effect of the equivalence ratio on combustion and knock. Under the compression ratio of 17.5, KI increases more quickly, with the constant equivalence ratio rise and is more sensitive to ignition timing with equivalence ratio increasing. For the compression ratio of 11, the ignition timing limited by knock is about 4°CA earlier than that of compression ratio of 17.5, and the engine performance is more stable in the low-knock zone. However, when KI exceeds 1 MPa, the power and ITE decreases 20.6% and 20.9% respectively.

High power density of opposed rotary piston (ORP) engines provides a possibility for the applications to hybrid vehicles. Under real driving conditions, internal combustion engines as the power sources of hybrid vehicles run under part load conditions in majorities of operation time. Hydrogen applications in internal combustion engines will promote zero-carbon travel, contributing to alleviating global warming. In this investigation, 3D numerical simulations were conducted to explore the performance of an ORP engine fuelled with hydrogen under part load and various ignition timing conditions. The results indicated that peak in-cylinder pressure and corresponding crank angle (CA) changed slightly within the early ignition range of −20.85o CA~ −14.23o CA; peak in-cylinder pressure was decreased significantly by late ignition. Heat release rates were more sensitive to late ignition than early ignition. Start of combustion, combustion phase, and combustion durations presented minor impacts by early ignition and engine loads. Ignition timing of −20.85o CA~ −11.06o CA showed limited impacts on indicated mean effective pressure and indicated power over individual intake manifold pressure. Indicated thermal efficiency was around 40% for the ignition timing of −20.85o CA~ −11.06o CA over the intake manifold pressure of 0.8 bar; indicated thermal efficiency drop caused by ignition timing of −8.33o CA was higher than 7% compared with optimal conditions. Heat loss by cylinder walls in proportions of fuel energy was lower than 25%, 20%, 18% for the intake manifold pressure of 0.4 bar, 0.6 bar, 0.8 bar respectively. Energy loss by the exhaust was higher than 41% for all the scenarios, with the maximum value being approximately 57%. Nitrogen oxides (NOx) emission factors were higher than 11 g (kW h)−1, and they were increased significantly by early ignition.

The purpose of the present paper is to investigate the hydrogen injection strategy on the combustion performance of a natural gas/hydrogen rotary engine. Considering that apex seal leakage (ASL) is an inevitable problem in the actual working process of a rotary engine, the action of ASL cannot be ignored for an in-depth study of its combustion performance. Therefore, in this paper, a 3D dynamic simulation model that put the effect of ASL into consideration was established. Furthermore, based on the established 3D model, the combustion process of a natural gas/hydrogen rotary engine under various hydrogen injection angle (HIA) and hydrogen injection timing (HIT) was investigated. The results indicated that the hydrogen jet flow first impacted on the rotor wall after entering the cylinder, and then diffused under the action of the vortexes in the cylinder. Therefore, the HIA and HIT could change the hydrogen distribution by changing the hydrogen impact location and the intensities of the vortexes in the cylinder. In addition, the ideal hydrogen distribution at the ignition timing which could improve the combustion efficiency was given. That is, under the premise of ensuring minimized hydrogen leakage, the hydrogen should mainly distribute in the middle and the front of the cylinder, and a high hydrogen concentration is maintained near the spark plug.

Pre-ignition is an undesirable ignition event that affects chemical kinetic measurements in chemical reactors. Meanwhile, it appears randomly in engineering systems and is highly relevant to the soft knock or much stronger and detrimental super-knock in modern downsized engines. Currently its origins are still not fully understood. In this study, the role of turbulence in pre-ignition phenomena was experimentally investigated using a novel rapid compression machine. Different turbulent flow fields were achieved through calibrated orifice plates. Stoichiometric isooctane/air mixtures were tested under engine-relevant conditions in a target pressure range of 15–50 bar and a temperature range of 720–860 K. Useful insights into pre-ignition mechanism were obtained by combining instantaneous pressure acquisition with simultaneously recorded high-speed imaging. The experimental results demonstrate that owning to turbulent mixing with colder boundary layers, ignition timing is delayed when compared to ideal homogeneous compression ignition scenarios. However, pre-ignition phenomena can still be observed and become pronounced at lower target pressures with longer ignition delays. Moreover, pre-ignition formation can be characterized by single or multiple spherical flame kernels, distributed discretely inside core mixture or at near-wall regions. Different from the auto-ignition scenarios dominated by the chemical reactivity of test mixture, these pre-ignition flame kernels feature standard deflagration propagation. Finally, a dimensionless scaling analysis shows that pre-ignition formation is closely associated with turbulent length scale and laminar flame thickness.

Accurate prediction of in-cylinder heat transfer processes within internal combustion engines (ICEs) requires a comprehensive understanding of the boundary layer effects in the near-wall region (NWR). This study investigates near-wall temperature fluctuations of an optical reciprocating engine using a combined approach of planar laser-induced fluorescence (PLIF) thermometry and numerical conjugate heat transfer modeling. Single-line excitation of toluene and subsequent one-color emission detection is employed for PLIF thermometry, while large-eddy simulations (LES) using commercial CFD software (CONVERGE v2.4.18) is utilized for modeling. The PLIF signal is calibrated to predicted in-cylinder temperatures from a GT-POWER simulation, and precision uncertainty of temperature is found to be ±1.5 K within the calibration region. Near-wall temperature fluctuations are determined about the multi-cycle mean, and the development of thermal stratification is captured in the NWR under motored and fired conditions during the compression stroke. Regions of the largest cycle-to-cycle temperature fluctuations are identified closer to the in-cylinder head surface indicating the unsteadiness of the thermal boundary layer. Analysis includes an assessment of cyclic variability of near-wall temperature fluctuation, and the effects of compression on temperature fluctuations. Additionally, thermal stratification is found to be similar under motored and fired conditions before ignition timing. Lastly, spatial correlation analysis of temperature fluctuations is performed in the wall-normal direction, and it reveals higher correlations under fired conditions. Spatial correlations experience an initial drop outside of the buffer layer in the NWR, and the location of the drop is well captured in the simulations. Analysis of fluctuating temperatures needs to be extended to fluctuations about the spatial average temperature which directly affects the spatial thermal gradients relevant to engine heat transfer.

The spark ignition engines are universally used for automobile applications as a result of their consistent performance and economy. Regarding SI engine utilization in such applications global issues are concerned like NOx, HC, CO. Alternative fuels are the fuels of present and future. More and more vehicles are switching to alternative fuels worldwide. Usage of different fuels also reduces emissions which has further pushed demand for eco-friendly fuels. during this direction interest is concentrated on reducing formation of NOx & PM.Exhaust Gas Recirculation (EGR) may be a technique to attenuate NOx and smoke emission. the foremost reliable alternative possibility to deal with critical emissions is to use oxygenated fuels like ethanol, butanol and ether etc. which are renewable. Experimental investigations are performed out on one cylinder four stroke petrol engine producing an influence output of 5.2 kw In this experiment ethanol blends are used alongsideconventional gasoline. The blends used are 75% Ethanol 25% petrol, 50% Ethanol 50% petrol, 75% petrol 25% Ethanol alongsidethis performance parameters like ignition timing, Brake thermal efficiency and Emissions like HC, CO, NOx are monitored.

Two stroke spark ignition engines are characterized by simplicity in construction, a higher power and lower maintenance cost. However, the main, disadvantages are high specific fuel consumption, excessive exhaust emission of hydrocarbon monoxide. Great deal of research work is going all over the world to find an effective solution to the growing problem of environmental pollution and fuel conservation of gasoline powered 2-stroke S.I. Engine. Fuel conservation and environmental pollution are directly influenced by the characteristics of the combustion process. For an S.I. Engine spark is the source of ignition and combustion of the air fuel mixture inside the cylinder. Hence, the spark timings of an S.I. Engines have a significant effect on the fuel consumption and exhaust pollution. In the present work, the electronic spark timing unit was employed to vary the spark ignition timing and the engine performance was investigated.

Spark-assisted compression ignition (SACI) has a promising potential to substantially improve engine's fuel efficiency. To this end, two exothermic stages in SACI combustion, flame propagation and auto-ignition, need to be well organized to increase control authority of bulk ignition timing especially in lean burn. In this study, three gasoline surrogates, namely EPRF, ETPRF and TPRF, formulated through blending ethanol/toluene with primary reference fuel (PRF) and having the same research octane number (RON) and octane sensitivity (S), were used to conduct experiments in a rapid compression machine (RCM) under lean engine-relevant conditions (10–30 bar and 722–862 K). Under different ethanol blending ratios, both ethanol's synergistic effect during auto-ignition and its stronger pressure dependence of flame speed (S_(Flame)) than toluene were observed. The ethanol's synergistic effect is mainly attributed to its more HO₂ production and then faster consumption by benzyl which results in more OH radical production. As for the stronger pressure dependence of S_(Flame) of ethanol, at 722 K, it is primarily determined by the stronger pressure dependence of H radical in EPRF's flame structure rather than the promotion effect from critical reactions on S_(Flame); while at 862 K, these two factors influence the pressure dependence of S_(Flame) simultaneously. Whatever the temperature is, third-body reactions have larger impacts on ethanol's S_(Flame) than on toluene's. In this study, the relative magnitude of S_(Flame)’s pressure dependence between ethanol and toluene shows rationality at lower φ and higher T, which is in line with the pressure exponents extracted from the existing high-p laminar burning velocities of ethanol and toluene. Further verification was made in a spark-ignition engine, which showed that low-carbon alcohols, exhibited stronger pressure dependence of S_(Flame) than monophenyl aromatics in commercial gasoline, represented by toluene. The aforementioned characteristics of ethanol can be utilized under different engine loads and provide a reference in fuel design for lean SACI combustion.

The propagation of combustion wave, which is formed as a result of impact of a filamentary pulsed periodic non-equilibrium discharge on a mixture that is not ignited by only compression in the HCCI engine, has been simulated. The discharge for a short time locally activated the mixture in the engine cylinder at a certain crankshaft rotation angle at the compression stage. The approach to evaluation of the temperature and composition in the region activated by high-frequency corona discharge has been proposed. Multi-pulse and multi-channel nature of discharge was accounted for in our model. The densities of chemically active species produced during streamer propagation were found using two-dimensional axially symmetric fluid model. The obtained composition and temperature in the activated zone were the initial conditions for modeling the propagation of combustion wave along the cylinder radius in 1D approximation. Special terms were included in equations responsible for the compression along the axis of cylinder to mimic the real change in pressure in cylinder. The calculations were performed for a lean C3H8-air mixture, which is characterized by the presence of low-temperature heat release (LTHR) stage, and intermediate and high temperatures heat release (ITHR and HTHR) stages. It was shown that the ignition timing in activated zone depends on the specific energy input into the streamer channel, the radius of activated region coupled with the volume fraction of activated region treated by discharge, and the moment of discharge initiation relative to the top dead center (TDC). The speed of combustion wave, the occurrence of auto-ignition in the end gas and transition to combustion, accompanied by “knocking” or strong pressure fluctuations are largely determined by the moment of discharge initiation and the specific energy input. The significant effect of discharge is explained by the stimulation of oxidation kinetic mechanisms at LTHR and ITHR stages.

In the current investigation, a four stroke, variable speed, single cylinder, variable compression ratio (VCR) SI engine is operated with raw biogas at wide open throttle (WOT) condition and at five different CRs ranging from CR 10 to CR 14 over the operating speed range of the engine. The ignition timing (IT) of the engine is also varied from 23○CA to 47○CA before top dead centre (bTDC) at each operating CR. The optimized operating CR and IT of the engine are obtained through series of experiments and its effects on the performance, combustion and emission characteristic are analysed herein. The rise in operating CR from CR 10 to CR 12 enhanced the power output and efficiency of the biogas fueled SI engine by 12.72% and 5.68%, respectively and reduced fuel consumption by 5.42% at 1400 rpm. Enhancing the CR from CR 10 to CR 12, limited the intensification of NOx and unburnt hydrocarbon emission by 10.17% and 15.6%, respectively at 1400 rpm. Hence, CR 12 is recommended as the optimum CR and its combination with 1400 rpm and WOT setting is recommended as the best operating condition of the engine.

This paper includes the experimental test data of an SI engine fuelled with simulated LCV gas (Low Calorific Value), which resembles synthesis gas in composition. The LCV gas was simulated by a mixture of carbon monoxide, hydrogen and nitrogen. During the experiment, the lower heating value of the LCV gas was altered by dilution with nitrogen. A single-cylinder Honda GX270 engine was adopted in the experiment to assess the impact of LCV gas on the system performance. This engine is typically used to power various machines and for electrical energy production in small generator sets. A modified engine was connected to an electric generator, which was loaded with an electric resistor. Engine operation was controlled using a microprocessor controller. All tests were performed at constant engine speed (3000 rpm). The engine was working at wide-open throttle for all mixtures. All mixtures were burned at stoichiometric conditions and with fixed value of ignition timing (30 deg bTDC). The indicated performance of the SI engine was evaluated based on the in-cylinder pressure measurements. No significant impact on the main internal parameters of the tested SI engine fuelled with simulated LCV gas diluted by nitrogen was observed. The experimental tests showed that the combustion duration increased for the mixtures with higher content of inert gas. Increase in the LHV raised the specific emissions of NOx and decreased specific emissions of CO and HC.

Spark assistance for homogeneous charge compression ignition (HCCI) can control combustion phasing, improve thermal efficiency, and reduce emissions in gasoline engines. As the characteristics of flame propagation determine the control authority of ignition timing, it is important and necessary to investigate pressure dependence of flame speed in the lean-premixed mixture relative to engine operating conditions. Experimental study in an optical rapid compression machine (RCM) and simulation work were carried out using two fuels comprising n-heptane/iso-octane/ethanol with varied octane sensitivity (S). The effective pressure ranged from 10 to 35 bar, temperature from 715 to 860 K, and equivalence ratios between 0.3 and 0.7 to cover the region of lean flammability limits of low and high S fuels with ethanol blended. Based on pressure profiles, flame speed extracted from images, and sensitivity analysis of flame speed, the dependence of flame speed on the effective pressure in low and high S fuels was discovered and the fundamental mechanism behind this phenomena became to be understood in the negative temperature coefficient (NTC) and non-NTC regions, respectively. In the studied temperature conditions, the flame speed of high S fuel has stronger dependence on the pressure than that of low S fuel does. In the NTC region, this phenomenon is attributed to the dependence of H radical concentration on pressure in the unburned mixture and flame structure. In the non-NTC region, promoting effect of dominant reactions varied with pressure can significantly influence pressure dependence of flame speed. Although quite limited data of laminar burning velocity for studied fuels were obtained in high pressures (>15 bar), the trend of flame speed's dependence on pressure was well predicted by two models with different but well-accepted core mechanisms, showing consistent results with the experimental ones in the RCM.

Engine performance parameters, including fuel conversion efficiency (FCE), power, torque and specific fuel consumption (SFC), can be affected by variables such as ignition timing (IGT), injection timing (IT) and hydrogen volume fraction (H2%). In this paper an engine fueled with different H2/CNG blend rations from 0 to 50% volume under ignition and injection timing at different speeds were investigated. For model validation, the engine operating conditions were simulated using the AVL fire software and compared with experimental results. The statistical comparison showed that there was no significant difference between them. Also, a support vector machine (SVM) was used to study the engine's behavior according to the variables studied. The SVM model predicted the FCE, power, torque, SFC and CO with error of less than 4%. The Genetic Algorithm (GA) was used to find optimal IGT, IT and H2% values to achieve optimum engine performance. Therefore, the results showed that the optimum engine operating conditions depend on the engine speed. Also, the results showed that independent variables (IT, IGT and H2%) maximize the engine performance and minimize SFC and CO emission. So that the optimum use of hydrogen in this research at different engine speeds was between 20% and 30%.

This work presents an analysis of a diesel power generator converted to operate in Otto cycle using ethanol as fuel. This conversion was done without changing the compression ratio of 17:1, with the build-up of adequate control for intake air mass flow rate, fuel injection, and ignition timing when operating with ethanol. The new conversion approach allows for simplicity of reversion to the original configuration. In Diesel cycle, the engine was fuelled with diesel oil containing 7% biodiesel injected directly into the combustion chamber. The in-cylinder pressure, emissions of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOX), unburned hydrocarbons (THC), as well as fuel conversion efficiency, when operating with pure hydrous ethanol, were evaluated. The results showed no significant changes on THC emissions in Otto cycle configuration, in comparison with engine operation in Diesel cycle configuration. The emissions of CO2, CO, and NOX were increased when operating in Otto cycle with ethanol.

The combustion process in Homogeneous Charge Compression Ignition Engines (HCCI) is one of the new methods of futuristic combustion technologies. Since there is no direct operator for the start of the combustion (SOC) of these engines, air-fuel mixture properties at the moment of entering the combustion chamber, specifies the ignition timing. In HCCI engines, the ignition timing is the most crucial factor in determining other engine operating characteristics such as power output, pollution, and fuel consumption. To control SOC, there should be an accurate predictive model based on the entering air-fuel mixture properties. The Artificial Neural Networks (ANN) approach can be considered as a solution with less computational costs than traditional physics-based modeling. In this investigation, a multi-input single-output model was developed for predicting the SOC of the HCCI engine for a wide range of engine operation. Three popular architectures namely the Nonlinear Autoregressive Network with Exogenous Inputs (NARXNET), Multi-Layer Perceptron (MLP) and Radial Basis Function (RBF) were used, for this purpose. The networks were trained using experimental data taken from a one-cylinder Ricardo engine. The network architecture was optimized using a Genetic Algorithm (GA) method. By using GA, the proposed networks also have the optimum network structures, improved model predictive behaviors, and simulation costs of the learning process. After optimization, the regression ratio between the outputs of MLP and the corresponding experimental data was increased from 0.8965 to 0.96166. This value was improved from 0.7623 to 0.83991 for RBF. By using GA, the time needed to train the NARX was reduced from 3.12 s to 0.46 s. By comparing the model predictions with the experimental data, it was shown that the selected neural network architectures are powerful approaches for non-linear modeling the SOC of the HCCI engine.

Natural gas has been suggested as an alternative fuel for compression ignition (CI) engines because it generates significantly less pollutants and has a smaller carbon footprint, while maintaining the cycle efficiency. However, the high auto-ignition temperature of natural gas typically requires the use of a quasi-compression ignition method such as homogenous charge compression ignition (HCCI) or a dual-fuel mode. Yet, methods such as these are unable to realize the full potential of high efficiency and low emissions. This motivated us to evaluate the applicability of a high-pressure direct-injected natural gas jet for a pure CI engine under various engine load, injection timing, and injection pressure conditions using a single cylinder CI engine with a compression ratio of 15.5. The intake temperature was raised to 400 °C to achieve the auto-ignition temperature of methane after compression and a multi-hole GDI injector capable of operating at a pressure of 400 bar was used for fuel injection. As a result, CI operation was possible, but ignition occurred after the end of the injection in the form of a partially premixed flame rather than a diffusion flame for all conditions under which the engine was operated. A sufficient equivalence ratio of 0.8 was achieved at an injection pressure of 300 bar and injection duration of 1.6 ms with the multi-hole GDI injector, and the GMEP value varied from 2 bar to 5.5 bar according to the equivalence ratio. However, at an equivalence ratio of 0.7 or higher, the combustion efficiency decreased drastically because of the limit of the volume fraction of the piston bowl at TDC and the narrow nozzle distribution of the GDI injector. Measurement of the pollutants indicated that the total number of particles from methane CI operation exceeded that of diesel at an equivalence ratio of 0.74 in the same engine setup because of incomplete combustion; however, the total mass of the particulate matter (PM) was approximately 15% of the diesel because the average particle size from methane CI was approximately one third smaller than that of diesel. However, the high post-compression temperature for the auto-ignition of methane gas resulted in a high peak temperature, which resulted in the production of approximately 2000 ppm NOx under all test conditions. The results of the parametric study showed that, as the injection timing retarded, the ignition timing was almost equally retarded, thus the combustion was still observed in the form of a diffusion flame. As the injection pressure increased, the ignition delay became shorter and the emission of PM could be further reduced, but the NOx emission increased.

To control the ignition timing in a gasoline compression ignition (GCI) engine, ozone (O-3) was introduced into the intake air. The O-radicals are decomposed from the O-3 above 550 K during the compression stroke, and combine into oxygen (O-2) in a very short time. The authors adopted two-stage direct injection to mix the fuel injected into the cylinder at very early timings with the O-radicals, before a reduction of the O-radicals would take place. The ignition timing of the second fuel injection for the main combustion is controlled by the heat release from the first fuel injection. In this paper, engine experiments were performed to examine the feasibility of the ignition control with a primary reference fuel, octane number 90 (PRF90). The O-3 concentration, the quantity, and the timing of the first injection were changed as experimental parameters. The results showed that a very small quantity of O-3, tens of ppm, is sufficient to promote the heat release of the first injected fuel. The heat release increases with the O-3 concentration and the quantity of fuel in the first injection. The addition of O-3 has no other impact on the ignition when the first injection timing is retarded to around - 40 degrees CA ATDC. In this manner, it is possible to control the ignition delays and to alter the combustion state from typical diesel combustion to premixed compression ignition combustion.

Ozone addition is a promising method to enhance and control combustion and ignition processes. It can be produced efficiently at atmospheric or elevated pressure conditions and its lifetime is sufficiently long to allow for remote production and transport to reaction zones. Over the past decades, the effect of ozone addition on ignition and combustion processes has been extensively studied from bench top fundamental burners to practical internal combustion engines. Ozone has shown the capability to accelerate ignition and control ignition timing, enhance flame propagation, improve flame stabilization, pre-process fuel to modify emission and reactivity characteristics, and reduce certain pollutant formation. Such enhancement is closely related to ozone chemistry, especially the decomposition of ozone to produce atomic oxygen and the rapid exothermic ozonolysis reactions with unsaturated hydrocarbons. The former requires elevated temperature to release atomic oxygen and initiate fuel/atomic oxygen reactions typically in the preheat zone, while the latter initiates low temperature (even room temperature) direct fuel/ozone reactions. These findings provide new opportunities in the development of strategies to enhance and control combustion/ignition processes. This article provides a comprehensive review of the basic principles of ozone enhanced reactive processes, including fundamental ozone chemistry, ozone generation and quantification, and the progress in the study of ozone addition in combustion systems.

In this paper trajectory tracking algorithms for gasoline engines are devised. Specifically, precise reference tracking in engine speed and air-to-fuel ratio is enabled while satisfying initial and final conditions on the center of combustion. Such a tracking of multiple reference trajectories requires a coordinated control action for the air path, the fuel path, and the ignition timing actuators. Combining a dedicated feedforward and feedback controller structure and multivariable model-based norm-optimal parallel iterative learning control strategies, feedforward control trajectories are generated that enable a precise tracking of desired reference trajectories. Experimental results focusing on the termination of the catalyst heating mode show the effectiveness of the proposed methodology, resulting in a control error reduction above 85%.

In the current study energy and exergy analyses of a hydrogen fueled four-stroke spark ignition engine are presented. The energy and exergy analyses are performed based on experimental results conducted on single cylinder, air cooled SI engine which is operated four different compression ratios (e = 6.6, 7.1 7.6 and 8.1) seven different spark ignition timing, 1600 rpm constant engine speed, lean mixture (ϕ = 0.6) and wide-open throttle conditions. The experimental results, energy and exergy analyses showed that the increase in compression ratio yields an increase in indicated and effective performance parameters of the engine while decrease in exergy destruction is observed. However, the move away of the ignition timing from the optimum value (over or retarded ignition timing) leads to a reduction in engine performance parameters and rise in exergy destruction. Another noteworthy result of this study is that the values of both indicated and effective thermal efficiencies obtained based on experimental studies and the values of both indicated and effective exergy efficiencies obtained by thermodynamic analyses are very close to each other.

Hydrocarbon exhaust emissions are mainly recognized as a consequent of carbon-based fuel combustion in compression ignition (CI) engines. Alternative fuels can be coupled with hydrocarbon fuels to control the pollutant emissions and improve the engine performance. In this study, different parameters that influence the engine performance and emissions are illustrated with more details. This numerical work was carried out on a dual-fuel CI engine to study its performance and emission characteristics at different hydrogen energy ratios. The simulation model was run with diesel as injected fuel and hydrogen, along with air, as inducted fuel. Three-dimensional CFD software for numerical simulations was implemented to simulate the direct-injection CI engine. A reduced-reaction mechanism for n-heptane was considered in this work instead of diesel. The Hiroyasu-Nagel model was presented to examine the rate of soot formation inside the cylinder. This work investigates the effect of hydrogen variation on output efficiency, ignition delay, and emissions. More hydrogen present inside the engine cylinder led to lower soot emissions, higher thermal efficiency, and higher NOx emissions. Ignition timing delayed as the hydrogen rate increased, due to a delay in OH radical formation. Strategies such as an exhaust gas recirculation (EGR) method and diesel injection timing were considered as well, due to their potential effects on the engine outputs. The relationship among the engine outputs and the operation conditions were also considered.

A free piston linear alternator (FPLA) can convert the fuel’s chemical energy to electrical energy efficiently via a linear alternator. Since the piston motion in the FPLA is not constrained, there are significant cyclic variabilities in the FPLA’s operation; thus, advanced control methods are essential for prolonged stable operation. In this paper, an FPLA with a high-stiffness helix spring is proposed, called a spring-assisted FPLA. The spring can work as a flywheel to stabilize the engine operation and reduce the cyclic variabilities. The steady-state thermodynamic performance of the engine is studied. Homogeneous charge compression ignition (HCCI) is used for combustion due to its high thermal efficiency and low exhaust emissions. This research is the first focusing on spring-assisted HCCI FPLA with a fully functional system-level model, with accurate predictions of combustion, gas exchange, friction, etc. with each submodel validated. A zero-dimensional system-level model is built in MATLAB/Simulink with a predictive combustion model developed by experimental data on a crank-slider engine. Since the thermodynamics and piston dynamics are highly coupled in FPLAs, a decoupling algorithm called Piston Motion Generator (PMG) is developed to remove the need for controls over the model predictions so that the current study can focus on the thermodynamic performance. A parametric sweep is performed with changing compression ratio, scavenging efficiency, and spring energy ratio β , i.e., spring stiffness. The simulation results show that the free piston motion is distorted with higher acceleration near top dead center (TDC), especially with low energy ratio springs, which can significantly reduce the heat transfer losses. Low energy ratio springs can also delay the ignition timing and enable the use of a low octane rating fuel with high compression ratio to achieve high thermal efficiency. As a result, the maximum brake efficiency (electrical conversion efficiency) and thermal efficiency are 41.1% and 46.7%, respectively, achieved with a high compression ratio, high scavenging efficiency, and low spring energy ratio β .

The effects of hydrogen ratios on combustion and emission characteristics of gasoline engine were studied under different exhaust gas recirculation (EGR), ignition timing and ignition pressure. The test performed in a modified gasoline direct ignition engine at different hydrogen ratios of 0%, 5%, 10% and 25%. In addition, the EGR rate set to 0%, 5%, 10% and 20% to study the combustion and emission characteristics. Addition to the different hydrogen fractions, 5% of TiO2 is added to increase the combustion characteristics with reduced emission. Regarding the results of the current study, the engine torque increases by 15% due to the addition of hydrogen in gasoline, while mechanical efficiency is improved by achieving a large throttle opening. At the same time, NOx emission decreased by 62% compared to the unmodified engine due to the influence of EGR, hydrogen ratio and high oxygen concentration TiO2. Moreover, the emission of CO and HC also reduced due to the influence of hydrogen fuel. Additionally, few more tests are taken to monitor the effect of the injection pressure for the hydrogen fuel. Higher injection reports higher effective thermal efficiency at 4 MPa and lower NOx. Reasonable injection pressure results in shorten flame development period.

This paper analyzed low emissions on a hydrogen-fueled spark ignition (SI) engine at the cold start period under rich combustion through ignition timing (IT) control. Cold start characteristics of hydrogen-fueled engine were investigated experimentally. The study was performed under different IT. The results demonstrated that when excess air ratio (λ) was 0.7 and IT varied from 25 °CA BTDC to 10 °CA ATDC, the peak cylinder pressure of the first cycle and the successful start time (SST) of hydrogen engine first increased and then decreased with the retard of IT. At 15 °CA BTDC, the hydrogen engine gained the shortest SST and the highest cylinder pressure in the first cycle. Flame development period (CA0-10) first shortened and then lengthened, and flame propagation period (CA10-90) prolonged when IT gradually retarded. The average NOx emissions efficiently reduced by 90.2%, HC and CO emissions caused by the evaporated lubricant oil reduced individually by 33.8% and 19.7% in the first 6 s during the cold start process with the retard of IT. Especially when IT delayed from 25 °CA BTDC to 15 °CA BTDC, the effect of IT on HC emissions was significant.

The favorable physicochemical properties of kerosene have contributed to its widely application in aviation. However, knocking is more prone to take place in kerosene than in gasoline under the same conditions. This paper presents a study on the knock characteristics of a ROTAX914 engine that is fueled by kerosene. The knocking combustion process was simulated under various engine operating conditions. The effect of engine ignition timing, exhaust gas recirculation (EGR), and mixture concentration on the engine knocking combustion were studied based on a three-dimensional simulation. The results showed that engine knock could be effectively suppressed by delayed ignition timing. With increased EGR rates, knocking intensity was greatly suppressed.

A Wankel engine with hydrogen direct-injection enrichment is recognized as an attractive method to enhance combustion efficiency. In this paper, on the basis of the chemical kinetic mechanisms, a three-dimensional simulation model was established and validated by the measured results. The ignition and combustion processes in a gasoline Wankel engine with hydrogen direct-injection enrichment were implemented for numerical simulation. The influence of twin-spark timing was firstly analyzed by synchronous ignition. Further investigation was then conducted to simulate how to effect the combustion by asynchronous ignition based on the favorable synchronous ignition timing. Results showed that, the average flow velocities were 18.8, 20.7, 23.6, and 25.4 m/s for the spark timings (ST) of 45, 35, 25, and 15°CA BTDC respectively. With retarded ST, the rich equivalence ratio approached to twin-spark plug continually. For synchronous ignition, at a larger advance of ST, the duration between the timing of the vortex dissipation and ST was longer, and the ignition delay was more prolonged. As the ST advanced, the combustion rate was enhanced with the increment in chamber temperature, the reactants (C8H18, C7H16, and H2) consumption and intermediates (H2O2, OH, and CH2O) generation were accelerated, the maximum H2O2 and CH2O decreased whereas the maximum OH increased, and nitrogen oxides (NOx) and carbon monoxide (CO) increased sequentially. For asynchronous ignition, the accelerated flame front was in accordance with the rotating direction of the rotor while the opposite direction was inhibited during the combustion process. An earlier ignition of leading-spark plug (L-plug) or trailing-spark plug (T-plug) provided the higher flame speed and faster H2 consumption, which contributed to the higher in-cylinder pressure, combustion temperature, and NOx and CO production. The preferable ignition and combustion characteristics was realized when the L-plug angle was 25°CA BTDC, and the T-plug angle was 35°CA BTDC. Compared with the favorable synchronous ignition timing, the flame propagation and H2 consumption were expedited, the peak pressure increased by 2.8%, the corresponding crank position advanced by 3°CA and there was no increase in NOx and CO generation. Therefore, it was recommended in engineering applications that the ST of T-plug advanced appropriately while the ST of L-plug remained constant.

The free-piston gasoline engine linear generator (FPELG) is linear type power device, which couples a linear internal combustion engine and a linear electrical generator together. Free-piston gasoline engine is commonly modeled using simplified zero-dimensional models. In this paper, parametric analysis of a dual-piston type FPELG is presented, aiming to find the piston operation characteristics and the performances of the FPELG during the generating process. Model validation was undertaken with the test data from a running prototype, which showed good agreement. The results show that with fixed stroke, lower moving mass would lead to higher indicated power. With fixed moving mass, shorter stroke would make higher indicated power. The FPELG was observed to be operated at high load, and it was prone to operate at relative low speed. The influence of combustion parameters, i.e. the ignition timing and the combustion efficiency to the FPELG engine performance were also investigated respectively.

Based on a retrofitted optical engine, high-speed photography technology is applied to obtain combustion flame patterns within the cylinder. The flame temperature and the space-time distribution of the characterize soot concentration (KL factor) are calculated using two-color method. Effects of coal-based synthetic fuel (CTL) and its mixture with oxygenated fuels on the combustion and soot generation process of the engine are experimentally studied. Two additional fuels are used in this study; one is alcohol-based fuel, the n-butanol and the other one is dimethyl carbonate (DMC). Result shows that when oxygenated fuels are mixed into the CTL, the ignition timing is postponed, and the ignition delay is prolonged. At the same time, with a shortened ignition duration caused by the additional oxygenated fuels, the flame area and flame brightness are significantly reduced. For the CTL and DMC blends, as the percent of DMC increases, both the combustion temperature within the cylinder and the KL factor are observed reducing in gradient, those are favorable for inhibiting formation of the soot. Comparison between the two mixed fuels shows that, with a same oxygen fraction, the temperature distribution of the CLT/n-butanol blends presents a bimodal form, and the average in-cylinder temperature is lower than that of the CTL/DMC blends, these characters are conductive to low-temperature combustion. With regards to the KL factor, the CTL/n-butanol mixture has a stronger effect on reducing the KL factor compared to that of the CTL/DMC blends.

At high loads, Diesel-Methanol Dual Fuel (DMDF) engines strongly rely on high methanol substitution for diesel proportion (MSP) to achieve high efficiency combustion and reduce nitrogen oxides (NOx) and soot emissions. However, high MSP is limited by the probability of methanol auto-ignition. The experimental study was conducted to investigate into the influence factors of methanol auto-ignition under diesel engine conditions at 50% of full load. Meanwhile the testing results concerning combustion characteristics and emissions have been analyzed. Experimental results showed that if there was apparent heat release before TDC, which was earlier than diesel fuel injection, it indicated that methanol auto-ignition occurred. In order to avoid methanol auto-ignition which is very easily to cause knock or rapid pressure rise, the in-cylinder mean temperature should be less than 990 K (at this case, the intake temperature was 338 K) before diesel injection timing. As intake temperature increased, methanol heat release timing was advanced and the heat release rate (HRR) was gradually accelerated. If the injection timing of diesel was later than that of methanol auto-ignition, almost all diesel fuel would be burned in the form of diffusion combustion in the methanol flame, leading to the increase of soot emissions. Methanol auto-ignition would be inhibited by EGR gas. The EGR and MSP had a great impact on both the ignition timing and the peak HRR of methanol auto-ignition. As EGR ratio increased, so did the incomplete combustion loss of methanol. As long as methanol auto-ignition occurred, the increase of MSP would result in a decrease in NOx emissions, but soot emissions were increased instead.

To further improve the performance of diesel rotary engine, a novel natural gas-diesel rotary engine was proposed and studied in this paper. Based on a spray experimental setup, the diesel spray characteristics under diesel rotary engine working conditions were obtained and analyzed. Thereafter it was used to validate the spray model for diesel rotary engine modeling and simulation. The effect of different natural gas blending ratios on mixture formation and combustion process in the natural gas-diesel rotary engine were investigated. Simulation results showed that for fuel-air mixing process, the natural gas movement process was susceptible to the airflow motion. However, the diesel distribution range was obviously enlarged under the influence of high-speed unidirectional flow. At assisted ignition timing, the stratified distributed diesel made the combustion process mainly occured at the front and middle of the combustion chamber. Besides, the flame propagation speed was accelerated with natural gas blending ratio increasing, which effectively improved the total combustion rate. Compared to single-fuel mode, when natural gas blending ratio increased to 20%, the maximum combustion pressure increased by 24.17%. Meanwhile, soot and CO decreased obviously, but NO and CO2 also increased.

Fuel Jet Controlled Compression Ignition (JCCI) was proposed to control the combustion phasing of premixed charge. In this mode, a small quantity of jet-injection diesel fuel was used to ignite the premixed charge, which was prepared by the main pre-injection blended fuels of diesel and ethanol-gasoline. Experiments of JCCI mode combined with dual-direct injection strategy were conducted on a modified single-cylinder naturally aspirated diesel engine. Effects of jet-injection and pre-injection parameters on the combustion and emission characteristics were investigated in detail under four engine load conditions at the rated speed of 3000 r/min. Experimental results showed that the diesel fuel jet-injection could control the ignition timing and combustion phasing robustly at all the four engine load conditions. The combustion process was composed of two stages, the jet fuel spontaneous combustion stage and the pre-mixture combustion stage. Besides, sensitive analysis of the jet-injection and pre-injection parameters on the JCCI mode performance were also accomplished. Advancing the jet-injection timing could shorten the combustion duration and improve the indicated thermal efficiency (ITE), but along with an increase in the nitrogen oxides (NOx) emissions, especially at higher engine loads. As the pre-injection energy ratio was upgraded, the local equivalence ratio and the diffusion-controlled combustion could be reduced, resulting in the reduction of soot emissions. Sensitivity interval was introduced to access the effects of pre-injection timing. Beyond this interval, the pre-injection timing showed insignificant effects on the combustion characteristics and emissions. With the increase of pre-injection pressure, more pre-injection fuels penetrated into the crevice and near liner regions, and the total hydrocarbon (THC) emissions were increased. Finally, the enhanced reactivity of pre-injection fuels was demonstrated to effectively reduce THC emissions at lower engine loads.

Ignition timing is an important parameter that impacts flame formation, early combustion process, and emissions of spark-ignition (SI) engines. Hydrogen as an auxiliary fuel may improve combustion and emission characteristics of SI engines. In this study, we experimentally investigated the effects of ignition timing on combustion and emissions of an SI methanol engine with added hydrogen at different engine speeds. At low engine speeds with various ignition timings, increasing hydrogen decreases indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and combustion duration. While at high engine speeds with different ignition timings, more hydrogen increases the indicated mean effective pressure, maximum cylinder pressure, maximum heat release rate, and decreases the ignition delay, combustion duration, and COVimep. By comparison with cases without hydrogen, the COVimep can be respectively reduced by 21.5% and 36.8% with hydrogen ratios of 3% and 6% at engine speed of 2400 rpm and ignition timing of 28 °CABTDC. In addition, hydrogen additive decreases the carbon monoxide (CO) and hydrocarbon (HC) emissions at low engine speeds, but increases the nitrogen oxides and soot emissions at high engine speeds under various ignition timings.

To achieve wider reactivity control, single-fuel reactivity controlled compression ignition (RCCI) through low temperature reforming (LTR) was proposed and experimentally explored. An LTR system was established on an optical compression ignition engine to investigate the impact of LTR on engine performance, where LTR products of the same fuel (n-heptane) as in-cylinder direct injection was routed into the intake port. The quantitative online gas chromatograph (GC) measurements indicate that LTR of n-heptane can produce numerous species with different chemical structures. The higher reforming temperature can lead to the higher fuel conversion rate. Optical engine experiments show that the ignition timing is retarded significantly via LTR. A two-stage low temperature heat release (LTHR) arises at the reforming temperature of 423 K (LTR-423 without LTR). CH2O-PLIF images suggest that the HCCI combustion of unreformed n-heptane cause the first LTHR because of its earlier occurrence time than in-cylinder direct injection and the homogeneous distribution of CH2O fluorescence. Meanwhile, the chemical calculation of CH2O formation manifests that the contributions of each reaction pathway to CH2O formation are different in each stage of LTHR. At the reforming temperature of 523 K (LTR-523 with LTR), prior to LTHR, weak PLIF signals were also captured, emitted by aldehydes and ketones LTR produced in the reformer. In the subsequent LTHR stage, formaldehyde develops at a relatively low speed due to LTR. In the HTHR stage, high-speed images show that LTR leads to a smooth combustion and reduces soot formation. The effect of LTR products on mixture reactivity was analyzed by the constant volume ignition delay model. The calculation results manifest that the reactivity of each LTR product is different, influenced by both thermal dilution effect and chemical effect. The combined impact of LTR products on mixture reactivity depends on both the chemical structure and the concentration in the mixture. The thermal dilution effect of LTR products contributes more for the final decline of mixture reactivity LTR caused. Finally, although the reactivity just decreased under current LTR conditions, it is believed that LTR has the potential to achieve further reactivity control of RCCI combustion to accommodate changes in the operating conditions of engines by changing LTR conditions (temperature, equivalence ratio, residence time, fuel type, feeding water, etc.).

The understanding of particulate matter emissions from Dimethyl ether (DME)/gasoline combined injection engine is crucial for the application of DME in engines. In this study, the particulate number (PN) and the size distribution of particles from a combined injection spark ignition DME/gasoline engine are studied experimentally. The results show that the addition of DME can effectively reduce both the accumulation and nucleation mode particle numbers for the DME/gasoline engines compared with pure gasoline engines. The distribution of the particle sizes follows a single peak distribution pattern, and the size of the most of particles from DME/gasoline engine are in the nucleation mode, peaking at around 17.8 nm for different ignition timing and DME ratios. Both the nucleation particle numbers (NPN) and accumulation particle numbers (APN) are dependent on the operating conditions investigated in this study and the affecting degree depends on the DME ratios. The accumulation particle numbers (APN) fractions are almost the same for pure gasoline, but the APN fraction increased with the increase of engine load after DME additions.

To improve the combustion efficiency of the rotary engine fueled with natural gas/hydrogen blends, the effect of the injection strategy of the blended fuel on the combustion process in cylinder was studied. In addition, considering that apex seal leakage (ASL) is difficult to avoid in the actual working process of rotary engines, the action of ASL was considered in the study. Therefore, a 3D dynamic calculation model of a peripheral ported rotary engine considering the ASL was established. Based on the calculation model, the impact of the blended fuel injection position (BFIP) and the blended fuel injection timing (BFIT) on the combustion process was numerically researched. The results showed that when the fuel injection strategy was Case: B-150, whose BFIP was located at the intersection of the cylinder profile and the long axis with the BFIT of 150°CA (BTDC), the blended fuel was more distributed in the front of cylinder (FOC) and the middle of the cylinder (MOC) at the ignition timing, which effectively avoided the problem of the incomplete combustion in the back of the cylinder (BOC). Therefore, to optimize effectively the combustion performance of the rotary engine, the injection strategy of Case: B-150 was recommended in engineering applications.

To use methanol as a mono-fuel in large bore marine engines, a distributed jets ignition combustion mode was applied on a 320 mm-bored engine, in which pre-chamber initiated jets were employed to ignite the in-cylinder lean mixtures and to enhance the flame propagation. A preliminary numerical study was carried out to investigate the effects of in-cylinder excess air ratio and ignition timing on combustion characteristics and performances of the engine. Conditions with excess air ratios ranged from 2.0 to 2.8 and ignition timings ranged from −8°CA ATDC to the top dead center were calculated. The numerical results show that, under the distributed jets ignition combustion mode, the in-cylinder lean methanol-air mixtures could be reliably ignited and the heat release rates showed a firstly slow and then rapid trend, resulting in high thermal efficiencies and low NOx emissions, which could meet for the IMO Tier III emission regulations without aftertreatment. Moreover, with the increase of the in-cylinder excess air ratio and the delaying of the ignition timing, the in-cylinder pressure, the peak pressure rising rate, the ringing intensity and the NOx emissions were continuously decreased. As the in-cylinder mixture becoming leaner, the combustion efficiency firstly kept constant and then rapidly dropped when the excess air ratio increased to 2.4, resulting in a peak value of the indicated thermal efficiency (49.2%) at this excess air ratio. According to the numerical results, a combustion control strategy was proposed: when the brake mean effective pressure was below 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.4 and coupled with an earlier ignition timing to obtain high thermal efficiency, and when the brake mean effective pressure was higher than 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.1 and coupled with a later ignition timing, thereby to achieve high power density.

In light of the recent high temperature flame experiment conducted in a shock tube, the main objective of the present study is to understand flame initiation regimes and propagation features with various ignition energy and various extents of unburnt mixture reaction progress. Flame initiation and propagation are numerically investigated for a partially reactive, near stoichiometric n-heptane/air/He mixtures under elevated temperature 700 K in a one-dimensional planar domain under nearly isobaric condition. Emphasis on flame initiation is placed on the effects of ignition energy and initial reaction progress. For ignition timing at tig = 0 s, while regular hot flames are directly initiated with higher ignition energy as expected, a class of autoignition-assisted cool flames can be directly triggered with relatively low ignition energy. By postponing ignition at later times, more pronounced chemical reaction progress is associated with the unburnt mixture such that autoignition-assisted hot flame can be achieved. For such flames, a notable flame speed increment is observed after the first-stage ignition occurs in the upstream unburnt mixture. It is found that both autoignition-assisted cool and hot flames prior to the first-stage ignition strongly depend on the ignition energy and ignition timing, and hence are case-sensitive. Extra caution needs to be taken to evaluate and compare these data. Hot flames in the post first-stage ignition mixture nevertheless exhibit much less variation to the ignition energy and initial reaction progress. For steady-state simulation, it is emphasized that a sufficiently short upstream and sufficiently long downstream domain are needed to obtain desired flame solution in the classical diffusion-reaction limit. A good agreement between the steady and unsteady simulations demonstrates the unsteady flame propagates in a quasi-steady manner with the classical flame structure, as long as τchem/τflame>>1. Sensitivity analysis and reaction network analysis have further suggested the similar key reactions on flame speed compared with regular conditions and demonstrated indirect effects from the low temperature ignition chemistry. This work provides useful insights into flame initiation regimes and propagation features under elevated temperature.

Miller Cycle technology, High Compression Ratio technology and Variable Valve Timing (VVT) technology are the advanced technologies of the SI engine in hybrid vehicle at home and abroad. The best technical parameters under different operating conditions cannot be obtained easily through bench test due to the interaction among engine technologies. Therefore, this study picked up the above technologies on PSA 1.2THP engine simulation model, and the multi-objective optimization of the engine technologies scheme based on fuel economy was addressed. The optimization results which were selected based on fuel economy showed that with the increase of the geometric compression ratio, the knocking phenomenon was generated. However, the generation of knocking can be suppressed by adding the Miller Cycle technology, adjusting VVT and adjusting ignition timing. It was found that under the simultaneous action of Miller Cycle technology, High Compression Ratio technology and VVT, fuel economy and power can be balanced to achieve engine performance optimization.

As a promising power system, hydrogen-fueled Wankel rotary engine with excellent power and emission characteristic have received attention increasingly, which makes it of great interest to investigate it. To make up for blanks, this work was conducted to experimentally investigate the effect of spark plug position on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine under 1500 r/min, 66 kPa manifold absolute pressure and 1.5 excess air ratio. The results indicate that compared to the trailing spark plug, the leading spark plug is more suitable to hydrogen-fueled Wankel rotary engines, which can realize a wider ignition range, higher maximum brake torque, lower cyclic variation and better nitric oxide emission. The maximum brake torque of adopting trailing spark plug is 31.2 N·m, which is only 87% of the maximum brake torque of 36.0 N·m with adopting leading spark plug. At the maximum brake torque ignition timing, adopting leading trailing spark plug achieves lower cyclic variation and slightly higher thermal load than adopting trailing spark plug. Besides, the optimum central heat-release point of both spark plug positions locate between 35 and 40°CA after the top dead center, and that of leading spark plug is later 2°CA than that of trailing spark plug. Moreover, both spark plug positions obtained 0 nitric oxide emission at maximum brake torque ignition timing, which means that emission will not be a problem to limit the selection of spark plug position under tested conditions.

The present study includes an experimental investigation of the performance, combustion, and emission parameters of a hydrogen port fueled SI engine under wide-open throttle. The compression ratio (CR) is varied from 10 to 15, equivalence ratio (φ) from 0.4 to 1.0, and speed from 1400RPM to 1800RPM. The ignition timing is maintained at 20° before the top dead center. The brake thermal efficiency increases by nearly 10% from CR10 to CR15, and it also increased by 13.7% by changing φ from 0.4 to 0.9. Similarly, BP increases in the same fashion. The combustion enhances with an increase in peak pressure by increasing CR from 10 to 15 and φ from 0.4 to 0.9; however, φ 1.0 exhibits a negative trend. However, the NOX emission increases continuously with CR and φ, and so as the exhaust gas temperature. The carbon-based emissions are negligible, and volumetric efficiency decreases with φ and increases with CR.

In this study, the combustion and soot formation processes of mid-low level ethanol-gasoline blends (E0, E20 and E50) sprays injected by a hole-type nozzle were examined in a quiescently high-temperature and high-pressure constant volume vessel by various ignition strategies (e.g. ignition position, ignition timing and spark energy). High-speed imaging of OH* chemiluminescence and two-color pyrometry were employed to clarify the flame propagation and soot formation. The results show that a relatively favorable flame area is potential to achieve for both E20 and E50 at the EOI or slightly after EOI timing. Higher ethanol content blends show more sensitivity to the ignition energy due to the physical properties. The soot level tends to decrease with increasing ethanol content at EOI middle ignition, possibly attributed to the dilution effect of ethanol and the increase of oxygen content. At EOI downstream ignition, however, the soot formation increases in both E20 and E50, possibly as a consequence of the downstream fuel heterogeneity consisting of the inhomogeneous mixture and liquid droplets of highly sooting hydrocarbons. Retarding ignition timing can help to decrease the soot formation. Moreover, E20 shows not only comparably intense combustion to E0 but also less soot formation at EOI middle ignition.

This study aimed at further improving the combustion efficiency of the diesel rotary engine (DRE), and in this regard a novel natural gas-diesel rotary engine (NG-DRE) was numerically studied. Based on the experimental validated computational fluid dynamics (CFD) model, a 3D-dynamic numerical study of the NG-DRE was carried out by adopting NG port injection plus diesel direct injection mode. The influence of natural gas injection timing (NGIT) and diesel injection timing (DIT) on air-fuel mixing, combustion and emission characteristics were explored. Simulation results showed that NG-DRE performance was better than DRE. During the entire air-fuel mixing process, NG movement was easily affected by the vorticity density due to its good diffusion characteristics, however its influence on diesel movement was relatively minimal. At assisted ignition timing, NG concentrated at the rear of the combustion chamber, and diesel concentrated at the front and middle of the combustion chamber. Delaying NGIT and DIT, the mixture became more concentrated due to a shorter mixing time. Moreover, the delayed NGIT and DIT resulted in improvement of the pressure and combustion rate, while for a further delayed DIT the pressure was decreased due to the pressure negative work. Considering the engine power and emission performance, for dual-fuel injection schemes, 340°CA BTDC and 70°CA BTDC were the preferred application schemes for NG and diesel respectively. Their peak combustion pressure (Pmax) increased by 16.34% and 27.38% respectively, but due to the richer mixture, soot value increased by 0.023% and 0.054% and CO (carbon monoxide) value also increased by 0.026% and 0.039% respectively.

An experimental study of temporally and spatially resolved spark-induced breakdown spectroscopy (SIBS) of methane and hydrogen-enriched methane mixtures is reported for premixed combustion in internal combustion engines. Experiments were conducted at quiescent conditions in a small constant volume chamber, varying pressure, stoichiometry and hydrogen admixture rates. Spectral emissions of hydroxyl (OH) at 306 nm, NH at 336 nm, the cyanogen (CN) band at 388 nm and the nitrogen second positive system (N2) were spatially resolved on a time-integrated setup. OH emissions were found to be strongest between the electrodes, whereas CN emissions were more pronounced at the center and ground electrode. Metal emission lines were observed, partially interfering with the radicals of interest. Energy dispersive X-ray spectroscopy showed nickel, copper and iron shares in the noble metal electrodes, confirming the origin of these metal emissions. Simultaneously to time-integrated spectra, temporally-resolved spectra at a frame rate of 100 kHz were recorded during the glow phase of the electrical discharge. Comparison of both spectra revealed a good agreement in terms of spectral characteristics and resolved species. Temporally-resolved spectra highlighted the strong dependence on the electric discharge characteristics of the inductive coil ignition system in the early phase of ignition. Ratios of CN/OH and CN/NH were found to correlate with the fuel-air equivalence ratio, but shot to shot repeatability was up to a factor 3 larger than the dependence on the mixture composition. Moreover, these ratios changed with increasing pressure at ignition timing, and with the higher pressure metal emission lines became more pronounced. Additionally, at pressures higher than 2 bar, the equilibrium position shifted to the disadvantage of the second positive system of nitrogen, suppressing this emission. Hydrogen admixture to methane of up to 50 vol% were found to not significantly alter the spectral signature between 300 and 400 nm, only marginally affecting the signal ratios of CN/OH and CN/NH.

In order to achieve high-efficiency and clean combustion in compression ignition engines, combustion must be controlled reasonably. A great variety of species with various reactivity could be produced through low temperature oxidation of fuels, which offered possible solutions for controlling the total fuel reactivity flexibly in engines. In experiments, a set of LTR system was established on an optical compression ignition engine to investigate the impact of LTR products on combustion characteristics, and the planar laser-induced fluorescence of hydroxyl (OH-PLIF) measurements were conducted to illustrate the flame development. N-heptane was chosen as the feedstock fuel. In kinetic calculations, a FLOW REACTOR model was used to predict the components of LTR products, and an HCCI model was used to evaluate the reactivity of each LTR product. The reactor model analysis and GC–MS measurements indicate that n-heptane does not take oxidation reaction at low reformer temperature of 473 K. When the reformer temperature rises up to 523 K, LTR products mainly include hydrogen, carbon monoxide, olefins, aldehydes, alkanes, alkynes, alcohols and C7 cyclic ethers through the prediction of the kinetic model. According to the experimental engine analysis, the ignition timing is retarded significantly and the heat release rate is slowed down due to the reactivity variety of in-cylinder mixture via LTR. The OH-PLIF images show that in addition to delaying the ignition timing and reducing the combustion rate, LTR also contributes to the improvement of in-cylinder combustion uniformity. The natural flame luminosity result indicates that less soot emission is formed in the combustion process by LTR. The reactivity evaluation using the kinetic modeling approach suggests that the ability of acetylene in improving reactivity is extremely strong, but the ability drops with the increasing mole fraction of acetylene. Though hydrogen, carbon monoxide, ethylene, propene and methane are present in large concentrations, they act to have little effect on mixture reactivity. However, most of the LTR products exhibit decreased mixture reactivity, which should cause a delay of the ignition in the experiment. The impacts of LTR products on ignition are influenced not only by the chemical structure, but also by the concentration in the mixture. It is inferred that the LTR products can control the ignition flexibly in compression ignition engines by changing reforming conditions.

In today's era, the computational capabilities of artificial neural network has endorsed to be a bedrock and inferences in many fields, including internal-combustion engines. The presented research in ANN has been germinated to anticipate the performance and emission characteristics of a turbocharged SI engine fueled with various HCNG mixtures. The experiments were accomplished at various excess air ratios (λ), ignition timings (θi) at MAP of 105 kPa and 140 kPa, while engine speed was kept constant at 1600 rpm to obtain data for testing and training ANN model. The test results show that with the increase in values of λ, MAP, and hydrogen addition, the torque output effectively decreases while BSFC first decreases and after attaining minimum value it further increases. The NOx, CO, THC, and CH4 emissions all declined with the hike of ignition advance angle, and inclined with increase of the load. ANN’s popular backpropagation algorithm is adopted in multilayered feedforward networks. In order to predict the performance and emission characteristics of HCNG engine, the four-input and one-output network structure are used. HCNG0, HCNG20 and HCNG40 blends has been studied in the presented ANN model in which the excess air ratio (λ), engine load, ignition timing, and HCNG blends has been taken as four-input parameters. The bestowed model has been trained using hyperbolic tangent transfer activation function (tansig) and Levenberg-Marquardt learning algorithm (LM) along with numerous neurons. The lowest and highest value of correlation coefficient (R) and mean square errors (MSE) for validation were dig-out for various parameters, which were BSFC, torque, NOx, CO, THC, CH4. The values of R (min–max) and MSE (min–max) were BSFC; 09519–0.9963 and 5.72–64.29, torque; 0.9948–0.9997 and 8.3935–95.8350, NOx; 0.9938–0.9992 and 0.5271–3.4340, CO; 0.8595–0.9960 and 0.0188–1.0154, and THC; 0.9644–0.9972 and 0.0714–1.1695, CH4; 0.7965–0.9973, 0.0351–1.1789 respectively for various number of neurons. This research work provides the gist of ANN as an attractive choice to researchers for classical modelling techniques. In this regard, the ANN modeling can be utilized to minutely predict the performance and emission characteristics of hydrogen added CNG engines.