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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.

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.

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.

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 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.

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.

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.

As idle condition in gasoline direct injection (GDI) engines always has high particulate number (PN) issue, the effects of coolant temperature coupled with controlling strategies on PN emission has been experimentally studied. Two sets of experiments have been conducted to make a comprehensive understanding. The first set is aimed to analyze ignition timing and excess air ratio characteristics, and the second one mainly investigates injection strategies. The experimental results indicate that the total PN declines with increased coolant temperature. When coolant temperature exceeds 70 °C, PN dramatically decreases. 5–22 nm PN emissions increase and 22–50 nm PN emissions decrease with higher λ. Besides, richer mixture has higher 50–150 nm PN than leaner ones. Properly advanced ignition timing will decrease total PN under idle stage and the decrement is mainly from 5 to 22 nm particles. The total PN minimizes at 5 MPa injection pressure, which can fulfill fuel evaporation and restrict nucleation process simultaneously. The total PN minimizes at 80 CAD BTDC injection timing, which is only 14% of the minimum value in 140 CAD BTDC. Thus, coolant temperature has crucial effect on PN emissions and optimizing other operating parameters will further reduce PN.

Spark induced compression ignition (SICI) combined mode combustion can effectively solve the problems existing in homogeneous charge compression ignition (HCCI) combustion, and expand its operation range. The SICI combined combustion of methanol is divided into two combustion stages and has the characteristics of spark ignition (SI) and compression ignition (CI) combustion modes at the same time. This paper studies the SICI combustion mode of methanol from two aspects: simulation and experiment. The simulation results show that with the increase of the wall temperature, it indirectly affected the SICI combined mode combustion by affecting the hot atmosphere in the cylinder, which shortened the whole combustion duration, the SI and CI duration, it had little effect on the combustion ratio of SI and CI. The bench test results show that the methanol engine can obtain stable SICI combined mode combustion mode under the conditions of appropriate intake temperature and suitable ignition timing. From the comparison of three combustion modes of methanol, the results show that the cyclic variability of SICI combustion is the smallest. With the increase of inlet air temperature and the delay of ignition, the BP of SICI combustion at methanol starting point moves backward, the CI combustion rate decreases, but the SI combustion duration changes slightly, and the compression ignition ratio decreases. In the SICI combustion mode of methanol engine, with the increase of intake temperature, NOx emission increases, HC and CO emission decreases. With the advance of ignition timing, CO emission decreases, HC and NOx emission increases.

Opposed rotary piston (ORP) engines as a new type of internal combustion engines are free of connecting-rod mechanisms, have small engine size and mass. ORP engines have the abilities of delivering high power density. Hydrogen fuel applications in internal combustion engines contribute to nearly zero carbon emissions in the combustion processes. In this paper, the effect of hydrogen direct injection strategies and ignition timing on hydrogen diffusion, in-cylinder combustion, energy distributions, and nitric oxide (NOx) emissions are investigated using a numerical simulation method regarding this novel internal combustion engine. The results showed that hydrogen was the most unevenly distributed in the combustion chambers for the start of injection (SoI) of −68.2° crank angle (CA) after top dead centre (aTDC) among the three hydrogen injection strategies; meantime, it presented the lowest combustion efficiency, being smaller than 98.5%. The peak in-cylinder pressure ranged from 40 bar to 83 bar for the given scenarios. The combustion durations were in the range of 20 °CA ~ 30 °CA for the ignition timing of −20.85 °CA aTDC ~ −11.06 °CA aTDC. The indicated thermal efficiency was higher than 38% over early ignition cases; the energy losses in total fuel energy by cylinder walls were lower than 15%. NOx emissions factors were lower than 36 g/kWh, and they were reduced by the retarded hydrogen injection. The engine performance and NOx emissions under early hydrogen injection scenarios are less sensitive to late ignition; additionally, the crank angle corresponding to the optimal efficiency was almost the same under different hydrogen injection strategies.

A computational fluid dynamics model was established and validated to numerically investigate the effects of different injection positions and injection angles on the mixture formation and combustion process in a gasoline direct injection rotary engine. The results show that as the injection position approaches the top dead center and the increasing injection angle, the rich zone of fuel changes from the rear to the front of the combustion chamber. The local equivalence ratio near the two spark plugs shows an increasing trend with the injection position upward and the increasing injection angle. Compared with the lower and middle injection positions, the upper injection positions can make fuel more concentrated near the leading spark plug and the trailing spark plug at ignition timing. The injection strategies corresponding to the upper injection position are conducive to complete combustion, in which the mass fraction of fuel burned all beyond 99%. Besides, with the increasing injection angle, the oil film formation position changes from the rotor recess to the middle cylinder block, which further affects the mixture formation and combustion process. Especially, the highest peak pressure is obtained at 0° injection angle corresponding to the upper injection position and is 12.39% higher than the in-cylinder peak pressure of intake port injection.

The direct injection technology is easy to achieve stratified combustion and greatly improves the fuel economy and power of free piston generator (FPG), but it also exacerbates the cyclic combustion fluctuation caused by the structure. Therefore, based on the dual spark ignition strategy, the influence of the ignition position and ignition time on the combustion process for dual cylinder FPG under direct injection was studied. The research results show that compared with the changes in the ignition angle position, the combustion process of direct injection FPG is more sensitive to changes in moment of ignition. Furthermore, with the ignition timing advances from 6°CA BTDC to 18°CA BTDC, the indicated thermal efficiency rises constantly at a rate of 25.1% and reached a high value of 33.9% in the same ignition position, although the uniformity of the mixture in the cylinder and the concentration of the mixture around the spark plug decrease gradually. While, in the same time of ignition, the increase rate of the indicated thermal efficiency reaches 6.6% at the maximum along with the increase of the spark plug angle and the increasing rate drops continuously along with the advancement of the ignition timing. Furthermore, compared with single spark ignition, the dual spark ignition can increase the cylinder pressure by 30% and the indicated thermal efficiency by 2% respectively.

To investigate the influence of operation parameters on the cyclic variation of the Wankel rotary engine with hydrogen enrichment, an intelligent regression model based on the support vector machine (SVM) was implemented to predict the cyclic variation. For modeling the prediction model, the cyclic variation of speed ( CoV n ) and cyclic variation of the main combustion duration ( CoV C A 10 - 90 ) were used as an evaluator for idle and part load conditions, respectively. The operation conditions including main fuel type (gasoline and n-butanol), hydrogen volume percentage ( β H 2 ), excess air ratio ( λ ), ignition timing (IT)and speed were used as independent variables. When optimizing the prediction model, the data processing method, kernel function, loss function and optimization method on the prediction performance were discussed in detail. The results indicated that an optimized model can be obtained by using genetic algorithm combined with [0, 1] data processing method, and the coefficient of determination, mean square error and mean absolute percentage error of CoV n were 0.9904, 0.0783 and 0.3845%, corresponding to CoV C A 10 - 90 were 0.9972, 0.0197 and 1.1729%, respectively. For the CoV n , gasoline as the main fuel was lower than the n-butanol at the same operating condition. The CoV n at high speed was greater than that at low speed. When operating at part load conditions, the CoV C A 10 - 90 decreased with the increasing β H 2 , and first decreased and then increased with advancing IT.

Gasoline compression ignition (GCI) engines favor low-octane fuels (RON = 60–80). However, low-octane fuels possessing low-temperature reactions strongly interact with in-cylinder thermodynamic conditions, which in turn significantly affect GCI combustion characteristics. In this work, using a toluene primary reference fuel (TPRF) with RON = 75, the effects of intake pressure and temperature on combustion evolutions, low-temperature heat release (LTHR), high-temperature heat release (HTHR), and indicated thermal efficiency were numerically investigated in a single-cylinder GCI engine, allowing for the role of octane sensitivity. An early injection timing was considered to obtain relatively homogeneous mixtures and large variations in intake pressure were employed to simulate low to medium loads. The results show that for a given equivalence ratio, the peak of the LTHR and HTHR and the main combustion phasing positively correlates with intake pressure. However, an opposite tendency in the peak of the HTHR is observed for a fixed amount of fuel injection. When octane sensitivity is elevated, the peak of in-cylinder pressure and heat release rate is reduced and ignition timing is retarded, especially for the HTHR. Elevating intake temperature facilitates high-temperature combustion while suppresses low-temperature reactions, which results in nonlinear variations in combustion phasing at a certain range of intake temperatures. The correlations of operating conditions and combustion evolutions are evaluated by pressure-temperature trajectory and Livengood-Wu integration, which indicates the significance of intake pressure in GCI combustion. Finally, combustion evolutions show that low-temperature reactions first take place at fuel-lean regions and hot flame pockets develop in fuel-rich regions, which suggests that low-temperature ignition is more sensitive to ambient temperatures while high-temperature ignition is more dependent on equivalence ratio.

In this study, a four-cylinder, four-stroke GDI engine was used to study the effects of refined aromatic components combined with advanced ignition timing on engine combustion and emission performance at 1800 rpm, 80% load rate. It was found that the different types of aromatics in the fuel have a considerable impact on the combustion and emission performance of the engine. The aromatic components of fuel Me and fuel Tr are toluene and trimethyl-benzene, respectively. They have shorter combustion durations and ignition delays, which mean better combustion effect, compared with fuel B, whose aromatic component is mixed with toluene, xylene and trimethyl-benzene. Fuel Xy whose aromatic component is xylene has a longer combustion duration, lower indicates mean effective pressure (IMEP), and increased fuel consumption. When ignition timing is −3.75°CA ATDC, fuel Xy has the shortest ignition delay and combustion duration, which shows that fuel Xy has the best combustion effect at this ignition time. On the premise that the combustion stability does not deteriorate, when the aromatic component of the fuel is mainly toluene and the ignition timing is advanced to −5.25°CA ATDC, the IMEP of fuel Me increased by 3.16%, the brake specific fuel consumption (BSFC) decreased by 5.06%, and the THC content remained almost unchanged, but NOx emissions increased by 31.35%, compared with that of fuel B. Refining the type of aromatics in the fuel, combined with the adjustment of ignition timing, can optimize the combustion process to a certain extent, increase engine power output and reduce BSFC, but it will increase NOx emissions.

Neat (100%) n-butanol was implemented in a direct injection (DI) compression ignition (CI) engine. The ignition, combustion, and emission characteristics at low engine load (below 6.5 bar IMEP), including near idling, were investigated. The engine experiments were performed using a modern common rail type single cylinder DI CI engine with a compression ratio of 18.2:1. Chemical kinetic simulations were also conducted to analyze the ignition characteristics of the experiments. The research results showed that neat n-butanol could not be auto-ignited at normal intake temperature and pressure conditions due to its low reactivity. However, the use of a high intake pressure of 0.75 bar gauge, and an injection timing of −26° ATDC at 5.0 bar IMEP, enabled auto-ignition even without the use of intake heating. One possible reason for this was attributed to the enhancement of the low temperature reaction regime. The ignition timing advancement sensitivity to intake pressure was approximately 1.0 °CA/0.1 bar at 5.0 bar IMEP, and a higher intake pressure allowed a wider injection timing range. A neat n-butanol fueled DI CI engine had a five times longer ignition delay and a 85% longer combustion duration than the same engine fueled with diesel at 2.0 bar IMEP. However, the combustion duration tended to shorten rapidly with increasing engine load, which was the opposite tendency to diesel. At low load, the nitrogen oxides (NOx) and soot emissions were very low compared to those of diesel, whereas the total hydrocarbons (THC), formaldehyde (HCHO), and carbon monoxide (CO) were higher than those of diesel. Carbon dioxide (CO2) emission was lower than that of diesel. This could be due to the reduced CO oxidation and the lower carbon content in n-butanol. Finally, by combining the previously published results with these results in this research, fuel injection strategies and intake oxygen conditions required to achieve low NOx (≤0.60 g/kWh) and soot (≤0.02 g/kWh) emissions and moderated maximum cylinder pressure rise rate (≤10 bar/°CA) were summarized over a wide load range of 2.0–11.5 bar IMEP.

To study the effects of hydrogen direct injection strategies on the characteristics of combustion and emissions of hydrogen–gasoline engines, an experimental engine platform was built with gasoline intake injection and hydrogen direct injection. The effects of hydrogen injection pressure and injection timing at a minimum advance for the best torque on the characteristics of engine combustion and emissions were studied at a constant engine speed, air–fuel ratio, and hydrogen fraction. The test results showed that when the heat that was released in the cylinder was constant, a 10% hydrogen fraction had a significant influence on the engine’s performance, combustion, and emissions. Hydrogen direct injection greatly improved the combustion stability of lean-burn mixtures of the engine, and significantly improved the mean effective pressure and thermal efficiency. Hydrogen injection at optimum ignition timing would significantly shorten the flame-development period and rapid combustion duration. The heat release was more concentrated, which increased the cylinder pressure. With an excess air ratio of 1.5, the addition of hydrogen significantly reduced CO emissions, but HC emissions increased slightly. A lean burn could contribute to the reduction of NOx emissions, whereas the addition of hydrogen would increase it.

A single cylinder diesel engine was modified to operate as a Compressed Natural Gas (CNG) fuelled lean burn Spark Ignition (SI) engine. The engine was tested at 1500 rpm under wide open throttle condition at different compression ratios over varying equivalence ratios. The optimized compression ratio for CNG operation was found to be 12.5:1 which was further investigated for hydrogen substitution at 5% and 10% on energy basis to study and compare the performance, emission and combustion behavior of CNG fuelled lean burn SI engine. The brake thermal efficiency and brake power output increases with rise in compression ratio and achieved a peak brake thermal efficiency of 30.2% with 12.5:1 compression ratio and above a critical value of 12.5:1, the improvement was small when compared to the increase in emissions. Wide flammability limits of hydrogen enable ultra-lean combustion thereby extends the lean limit of operation to an equivalence ratio of 0.42 with 10% hydrogen addition as compared to 0.50 with neat CNG operation and its anti-knock enhancement makes it advantageous compared to increasing the compression ratio under low load conditions. Hydrogen addition also enhanced the combustion rate, heat release rate and reduced cyclic variations. On the emissions front, hydrogen addition showed reduction in hydrocarbon emissions from 65 g/kWh to 6.9 g/kWh at an equivalence ratio of 0.5 alongside carbon monoxide and carbon dioxide reduction. Due to retarded ignition timing to avoid knock, the Oxides of Nitrogen (NOx) emission increase was not significant.

This chapter starts by providing an overview of fuel-metering techniques developed for spark ignition (SI) engines, following by a case study on liquid versus gaseous phase liquified petroleum gas (LPG) port injection in a single-cylinder SI engine. Fuel-metering approaches, from the least to the most modern, include carburettor, throttle body injection (TBI), manifold port injection (MPI or sometime called PFI, port fuel injection), and gasoline direct injection (GDI). Based on the mixture formation process, GDI engines can be categorised into air-guided, wall-guided, and spray-guided methods while based on the ignition modes they can be homogeneous spark ignition - (HCI), stratified spark ignition (SPI) and homogeneous charge compression ignition (HCCI) engines. The comparative study shows significant variations in cylinder to cylinder mixture distribution for both liquid and gaseous LPG phases. The experimental data confirms the power and efficiency advantages of liquid phase injection over gaseous phase injection. Analysis shows the charge state at the end of compression is the major contributor to the performance difference. Secondary differences such as the mixture homogeneity also have an important impact. The lower temperature combustion with liquid phase LPG also delivers substantial NOx emission reduction. Suggestions are made for overcoming the deficiency of gaseous phase injection which may be preferred as its application avoids the high cost of the high pressure in-tank LPG pump needed for liquid phase injection.

A single cylinder CI engine was modified to operate as a LPG fuelled lean burn SI engine. The engine was tested at 1500 rpm and 20% throttle opening at compression ratios 9:1, 10:1, 10.5:1 and 11:1 by varying equivalence ratios. The influence of compression ratio and 15% hydrogen substitution on energy basis at the optimal compression ratio of 10.5:1 on performance, emission and combustion behavior were studied and compared. The brake thermal efficiency and brake power output increases with rise in compression ratio, and above a critical value of 10.5:1 the improvement was small when compared to the increase in emissions. The advantage of brake thermal efficiency from higher compression ratio is narrow under low load conditions. The ever increasing load due to the auxiliaries which are likely to grow more require better low load performance and emissions. Wide flammable limits of hydrogen enable ultra-lean combustion and its anti-knock enhancement makes it advantageous compared to increasing the compression ratio at part throttle condition. Hydrogen addition enhanced the combustion rate and heat release rate, reduced cyclic variations, and extended the lean limit of operation. There was perceptible improvement in brake thermal efficiency, brake power and considerable reductions in hydrocarbon, carbon monoxide and carbon dioxide levels. Due to retarded ignition timing the NOx emission increase was not significant.

The effects of overall equivalence ratio, injection timing, and ignition timing on formaldehyde and unburned methanol emissions, cylinder temperature histories, and formaldehyde emission histories of a spark ignition direct injection stratified charge methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics coupling the methanol chemical kinetics reaction mechanism. The model results show that the overall equivalence ratio is less than 0.43, and unburned methanol significantly higher for cold start mode. For steady state mode, when the overall equivalence ratio is less than 0.4, formaldehyde and unburned methanol emissions increase rapidly. When the overall equivalence ratio is larger than 0.4, formaldehyde and unburned methanol emissions are very low. Formaldehyde and unburned methanol emissions for steady state mode are significantly lower than for cold start mode. For steady state mode at engine speed 1600 rpm and brake mean effective pressure 0.67 MPa formaldehyde and unburned methanol emissions are reduced 90% and 98%, respectively, compared to cold start mode at the same overall equivalence ratio (0.5). Cylinder temperature is the main factor that affects formaldehyde generation and consumption. There is a rapid decrease due to oxidation at the corresponding position of the maximum cylinder temperature, after which formaldehyde is quickly generated for any operating conditions.

Legacy integral compressor engines are crucial to the operation of the North American natural gas pipeline network. Many of these engines are uncontrolled utilizing mechanical scavenging or light turbocharging. The engines typically operate between ∼10 and 20 g/bhp-hr of NOx with a minimal knock margin. While suitable for typical pipeline gases, high ethane shale gas can erode the knock margin with the added risk of performance degradation and engine damage. Phase one of the project investigated the impact of variable fuel quality and determined which engine parameters (ignition timing, air manifold temperature, and trapped equivalence ratio) were most effective in preventing and controlling knock. Phase two of the project evaluated the ability of an accelerometer and a NOx emissions sensor to detect engine knock as well as the development of knock prediction models. Testing confirmed elevated fuel ethane could induce continuous engine knock but ignition timing was the most effective method to mitigate engine knock, followed by trapped equivalence ratio. Air manifold temperature did not significantly affect knock onset. When properly tuned, a typical off the shelf accelerometer knock detection system could detect and protect against the onset of knock. Persistent knock lead to a steady increase in NOx production, but NOx values alone were inadequate to detect and protect against knock. The knock prediction models accurately predicted the onset of knock based on ignition timing, trapped equivalence ratio, and fuel composition, suggesting a fundamental relationship between operating parameters and engine knock.

In-cylinder air flow structures are known to play a major role in mixture preparation and engine operating limits for spark-ignition engines. In this paper PIV measurements were undertaken in an optical spark-ignition at 1500 RPM, part-load with 0.5 bar intake plenum pressure. One of the PIV planes was vertical, cutting through the centrally located spark plug (tumble plane). The other plane was horizontal 1 mm below the spark plug ground electrode (swirl plane). The effect of engine head temperature was also examined by using engine-head coolant temperatures of 20 °C and 80 °C. The flow field was examined late in the compression stroke at typical ignition timing. The study was conducted under air-only motoring engine conditions but also under fuelled conditions in the early intake stroke using direct injection of gasoline, iso -octane, ethanol and butanol fuels. The flow field under air-only motored conditions showed velocities between 3 and 5 m/s predominantly from intake to exhaust. Little differences were observed between hot and cold engine-head temperature; typically ∼10% larger mean velocity and turbulent kinetic energy was seen on the intake side. Integral length scales were on the tumble plane between 2 and 4.5 mm in the vertical and 4–7 mm in the horizontal direction. The swirl view showed scales between 4 and 10 mm, larger at cold than at hot engine-head conditions. The vertical length scales appeared to be limited by the clearance height, scaling typically by about 10–15%. The horizontal components scaled to the cylinder bore diameter by about 5–12%. The fuel injection process in the early intake stroke led to little differences in the general mean flow structure at ignition timing, except for a small increase in the maximum velocities, ∼10%. The turbulent kinetic on the tumble plane was highest towards the exhaust side of the engine under non-fuelled engine conditions but fuel injection resulted in highest values on the intake side. The integral length scales with fuel injection were of the same order of magnitude to those of air only measurements on the tumble plane, but showed distinctly larger areas with length scales up to 9 mm on the swirl plane. Differences between fuels for their fuel specific injection duration were small, with average length scales between 4 and 6 mm. Ethanol exhibited typically largest scales and butanol smallest.

Pre-chamber jet ignition (PJI) is effective in accelerating combustion, expanding lean combustion limit and improving combustion stability on gas fuel and volatile liquid fuels. However, the effects of PJI on kerosene, which is less volatile and is more prone to knock than gasoline, are rarely discussed. In this work, PJI was applied to ignite kerosene in a direct injection dual spark plugs ignition (DSPI) engine and its effects on knock intensity, knock randomness, heat release rate, combustion phase and combustion stability were studied. Experiments were conducted with compression ratios (CR) of 6 and 7 respectively. Results show that PJI cannot improve the available CR of kerosene. At the early stage of PJI combustion process, a sudden increase and a fluctuation of heat release rate can be observed, which is coincident with the multi point ignition and highly turbulent flame caused by the rapid jet flow. PJI can improve the heat release rate, advance the combustion phase and improve the combustion stability of kerosene, but can also deteriorate the knock intensity without ignition timing adjustment. Due to the improved combustion stability, the randomness of knock is reduced. As a result, advanced combustion phase and reduced knock randomness lead to a better output and fuel consumption performance of PJI under critical knock condition than that of DSPI. The result shows that PJI.

In this paper, a test platform for ethanol port injection plus gasoline direct injection was built to explore the effects of different ethanol-gasoline ratios (Re), direct injection timing (DIT) and ignition timing (IT) on the combustion and emissions of a SI engine. Results clearly show that when the total fuel contains more ethanol, the ignition timing corresponding to the maximum torque is smaller than the ignition timing when the total fuel contains more gasoline. Compared with the sole ethanol port injection (EPI) mode and gasoline direct injection (GDI) mode, G25 with EPI + GDI is the best mode for high-efficiency combustion and G25 with IT = 20°CA BTDC and DIT = 120°CA BTDC can be regarded as the optimal operating condition for highest torque output, braking thermal efficiency and lowest BSFC. As for exhaust emissions, CO and HC reach the lowest at G25 while NOx has an opposite trend. Delayed ignition within the range of 10-30°CA BTDC reduces HC and NOx emissions. As for particle number emissions, the size of peak particle number gradually decreases from G100 to G0, the accumulation particle number (APN) is further oxidized and shows a significant downward trend with the increase of ethanol. The lowest TPN was obtained at G25 in which the TPN has dropped by 9% and 85% respectively compared with sole EPI and GDI mode. When Re ≥ 50%, the nucleation mode particle number (NPN) in the total particle distribution is higher than the accumulation mode particle number, while there is an opposite result when Re＜50%. Overall, the findings of this paper make contributions to the development of high-efficiency and low-pollution combined engines and further promote the application of clean alternative fuels.

It is important to improve the combustion performance of the diesel Wankel engine for its further engineering applications. Therefore, the main objective of this study was to study the dual-fuel mixture formation and stratified combustion process in the novel natural gas blended diesel Wankel engine. Meanwhile, the effects of assisted-ignition timing and assisted-ignition position on engine combustion characteristics were investigated. The results indicated that when the assisted-ignition timings and positions were changed, natural gas distribution near assisted-spark plugs changed slightly, while the variation of diesel distribution was conspicuous. Moreover, adopting dual assisted-ignition spark plugs could accelerate the fuel burning rate and improve engine combustion performance. Besides, it was found that more mixture concentrated near the assisted-spark plugs was beneficial to increase the pressure in-cylinder and combustion rate. The symmetrical arranged dual assisted-ignition spark plugs that were respected to the X-axis (Case 4) and assisted-ignition timing of 35°CA BTDC (Case 6) were the preferred practical application schemes. Compared to the schemes of single spark plug ignition (Case 1) and 20°CA BTDC ignition timing (Case 9), the peak pressure in-cylinder of the preferred application schemes increased by 42.96% and 10.91%, respectively.

To extend the load range of premixed combustion, the jet controlled compression ignition (JCCI) mode with dual-direct injectors was adopted in a high-speed light-duty diesel engine. The pre-mixture was flexibly prepared by the direct pre-injection of blended fuels, and the ignition timing could be controlled robustly by the diesel jet-injection. Engine experiments were conducted at 75% engine load with an engine speed of 3000 rpm. The results indicate that an obvious two-stage high-temperature heat release process is achieved by modulating the injection parameters of dual-direct injectors independently. The late combustion phasing resulted from the retarded diesel jet-injection effectively depress the reaction rate. When the pre-injection is delayed within the sensitivity interval, the local richer premixed charge accelerates the pre-mixture combustion stage. The indicated thermal efficiency is increased by 7.4%, and nitrogen oxide emission is reduced by 16.9% compared to the conventional diesel combustion mode. The increased pre-injection pressure can suppress the reaction rate but causes wall-wetting issues. The stratification of the equivalence ratio prepared by the double direct pre-injection strategy diminishes the maximum pressure rise rate by over 64% compared to that with single direct pre-injection. It is also revealed that the start of the second pre-injection plays a dominant role in modulating the combustion process, which illustrates the potential to extend the engine load of premixed combustion mode.

Ultra-lean burn combustion can effectively improve fuel economy of gasoline engines. But its application to real gasoline engines is impeded by unstable and slow combustion. Micro-flame ignited (MFI) hybrid combustion mode can be one solution. To understand the relation between heat release processes and flame features of ultra-lean gasoline-air mixture with dimethyl ether (DME) auto-ignition in MFI combustion mode, experiments were conducted in an optical engine at the lambdas from 1.8 to 2.2. The results show that the misfire limit in MFI mode can be extended to lambda 2.2. However, lambda 2.0 is a proper lean-burn limit for MFI combustion. The combustion process includes the oxidation of DME and the hybrid combustion of DME and gasoline at different lambdas while it still experiences the gasoline auto-ignition at lambda 1.8. With the increase of lambda, the ignition timing delays and combustion duration prolongs, leading to decreased indicated mean effective pressure and increased cyclic variation. The decreased stretch-rate and increased speed decay rate of blue and yellow flame can improve combustion stability. Lower stretch-rate and higher speed decay rate derived from yellow flame relative to that from blue flame contributes to the extension of lean-burn limit in MFI combustion mode.

The effects of low temperature reforming (LTR) of n-heptane/n-butanol blends on the flame development progress and combustion characteristic were investigated in an optical engine. The reforming temperatures were set as 423 K, 523 K and 623 K. Three n-heptane/n-butanol blending mixtures with volume fractions of n-butanol of 30% (B30), 50% (B50) and 70% (B70) were utilized. The detection, experiment and simulation methods included the gas chromatograph (GC) detection, high-speed imaging and chemical kinetics calculation. The main results are the following. Firstly, the LTR products were initially detected by the GC system. With the reforming temperature increasing, the mole fractions of aldehydes decrease. With the volume fraction of n-butanol increasing, the mole fractions of carbon monoxide, methanol and aldehydes increase while other species decrease. Secondly, the LTR products combined with the direct-injected fuel were introduced into the optical engine. For B30 and B50, the combustion phasing delays with the reforming temperature increasing. For B70, the combustion phasing initially advances and then delays with the reforming temperature increasing. Thirdly, the chemical kinetics simulation shows that most of the LTR products can decrease the mixture reactivity and delay the ignition timing, while small parts of the LTR products have the opposite effects.

Numerical simulations are performed to investigate the effects of ambient density ( ρ am ) and nozzle diameter ( D noz ) on the ignition characteristic of diesel spray combustion under engine-like conditions. A total of nine cases which consist of different ρ am of 14.8, 30.0, and 58.5 kg/m3 and different D noz of 100, 180, and 363 μ m are considered. The results show that the predicted ignition delay times are in good agreement with measurements. The current results show that the mixture at the spray central region becomes more fuel-rich as D noz increases. This leads to a shift in the high-temperature ignition location from the spray tip towards the spray periphery as D noz increases at ρ am of 14.8 kg/m3. At higher ρ am of 30.0 and 58.5 kg/m3, the ignition locations for all D noz cases occur at the spray periphery due to shorter ignition timing and the overly fuel-rich spray central region. The numerical results show that the first ignition location during the high-temperature ignition occurs at the fuel-rich region at ρ am ⩽ 30.0 kg/m3 across different D noz . At ρ am = 58.5 kg/m3, the ignition occurs at the fuel-lean region for the 100 and 180 μ m cases, but at the fuel-rich region for the 363 μ m nozzle case. This distinctive difference in the result at 58.5 kg/m3 is likely due to the relatively longer ignition delay time in the 363 μ m nozzle case. Furthermore, the longer ignition delay time as D noz increases can be related to the higher local scalar dissipation rate in the large nozzle case.

In order to satisfy the heightened emissions regulation and further enhance the performance of the engine, efforts on amelioration of the engine management system are of great significance besides using intelligent regression algorithms. Based on a hydrogen-enriched Wankel rotary engine, multiple engine operations with variable excess air ratios, variable ignition timing, and variable hydrogen enrichment have been carried out a series of engine calibration tests in detail. After recording the required experimental data, three different methods, including quadratic polynomial, artificial neural networks (ANN), and support vector machine (SVM) are applied to construct a multi-objective regression model which gives a unique insight into the mathematical relationship between the engine performance and the operation and control parameters. For the ANN, the effect of the number of nodes in the hidden layer on the regression performance was discussed, and the weight values of the ANN was optimized using a genetic algorithm. For the SVM, the effects of the kernel function and three optimization methods on regression performance were discussed. The results indicated that the SVM exhibited the best fitting results among the three methods. The optimal R2 for brake thermal efficiency, fuel energy flow rate, nitrogen oxide, carbon monoxide, and unburned hydrocarbon is 0.9877, 0.9840, 0.9949, 0.9937, and 0.9992, respectively. It is highly recommended that the SVM method as a generic methodology may be a new direction for nonlinear control system modeling of the Wankel engine.

For n-butanol/diesel dual-fuel combustion, there are two different implementations, i.e., dual direct injection (DI2) strategy and reactivity controlled compression ignition (RCCI) strategy. The DI2 strategy is a novel combustion concept, which is expected to address the inefficient combustion and high pressure rise rate dilemmas raised by RCCI. In this work, the full-parameter optimizations of DI2 and RCCI were first performed at mid load, and the optimal cases were comprehensively compared. The potential benefits of DI2 over RCCI and its optimal operating parameters were determined. The results indicate that DI2 can achieve low nitrogen oxides (NOx) emissions below 0.00094 g/kWh and near-zero soot emissions while keeping high fuel economy near 167 g/kWh comparable to that of RCCI, but it usually yields higher NOx, soot, and carbon dioxide (CO2) emissions than RCCI. In the optimal DI2 cases, very advanced n-butanol injection timing (before −120°CA ATDC), high n-butanol energy fraction (around 0.94), and early diesel injection timing (near −50 °CA ATDC) are adopted. Meanwhile, the combination of a narrow n-butanol spray angle (30° 65°) is preferred for DI2. Compared with RCCI, DI2 exhibits lower combustion losses, however, it suffers from higher exhaust and heat transfer losses. The higher intake temperature, exhaust gas recirculation (EGR) rate, and lower intake pressure are more beneficial for DI2. Moreover, it is suggested that DI2 is easier to achieve lower ringing intensity (RI), and the ignition timing and RI of DI2 are more sensitive to the n-butanol fraction than RCCI.

Opposed rotary piston (ORP) engines have advantages of high power density, few moving parts, and smooth operations, which makes ORP engines as potential power sources for hybrid vehicles and range extended electric vehicles. Ignition timing significantly affects the performance of spark ignition engines including fuel economy and emission factors. In this paper, the effect of ignition timing on the engine performance was investigated using a three-dimensional numerical simulation method. The results indicated that crank angle corresponding to the peak in-cylinder pressure over the ignition timing of −8.2° crank angle (CA) was advanced compared with other cases having earlier ignition timing; however, the crank angle of peak heat release rates were retarded. Start of combustion was delayed by retarding the ignition timing and increasing engine speed; combustion duration over the ignition timing of −18.9° CA ~ −11.1° CA changed slightly for individual engine speed. Indicated specific fuel consumption (ISFC), being hardly dependent on the ignition timing, was less than 74 g/(kW·h) over the ignition timing of −17.3° CA ~ −11.1° CA, where indicated thermal efficiency was approximately 41%, 39% and 35% for 1000 RPM, 3000 RPM and 5000 RPM respectively. When ignition timing was later than −11.1° CA, ISFC and indicated thermal efficiency were deteriorated seriously. Nitrogen oxides (NOx) emission factors increased with engine speed over early ignition timing; however, they were inverse for late ignition cases. Higher engine speed and retarded ignition timing led to higher percentage of exhaust energy in fuel chemical energy.

The cold-start mixture preparation, combustion and emissions behaviors of a medium compression ratio direct-injection twin-spark plug synchronous ignition engine fueled with methanol were numerically simulated. Simulation results display that the methanol injection timing, ignition timing and the global equivalence ratio had an important influence on the concentration distribution of methanol-air mixture, the flow velocity, and the density of the flame surface during cold start. Ignition delay period reached the shortest at injection timing 70°CA BTDC. Ignition delay period for injection timing 130°CA BTDC and 50°CA BTDC increased 209% and 45.5% compared to injection timing 70°CA BTDC, respectively. Ignition delay period reached the shortest at ignition timing 21°CA BTDC. Ignition delay period of twin-spark plug was shorter than that of single-spark plug at the same equivalence ratio. There existed the maximum in-cylinder pressure, maximum heat release rate, maximum in-cylinder temperature, lowest unburned methanol and soot emissions, and highest NOX emissions at injection timing 70°CA BTDC. The maximum in-cylinder pressure, maximum heat release rate, and maximum in-cylinder temperature gradually increased with the advance of ignition timing. Injection timing 70°CA BTDC, ignition timing 21°CA BTDC, and equivalence ratio 0.9 could obtain the best cold start performance compromise using twin-spark plug ignition mode. At equivalence ratio 1.0, twin-spark plug ignition had better combustion performances, lower unburned methanol and soot emissions, and higher NOX emissions compared with single-spark plug ignition. Twin-spark plug synchronous ignition had more advantageous to cold starting ignition compared with single-spark plug ignition for a medium compression ratio direct-injection spark-ignition methanol engine.

Generally, the homogeneous charge compression ignition (HCCI) engine presents superior fuel economy and ultra-low NOx and particle matter emissions compared with the traditional combustion engine. However, the HCCI engine is essentially decoupled from the spark plug and fuel injection. That means the HCCI engine has no direct control mechanism for the auto-ignition timing and subsequent combustion phase. Without effective strategies to control the auto-ignition timing on time according to the operating conditions, the HCCI engine will be limited in a small operation range due to the cold start problem, high pressure rate and combustion noise, and even knocking combustion at the high-load. Generally, the properties of physical–chemical kinetics of fuels, as well as the mixture temperature spatial and temporal changing histories in the cylinder, strongly determine the ignition timing and affect the combustion phase in HCCI engine. Some effective techniques and controlling strategies, such as fuel management, homogeneous charge preparation, exhaust gas recirculation, etc. are widely used in the HCCI engine. These techniques and controlling strategies are used solely or conjunctively with each other to control the compressed gas temperature, pressure and mixture distribution in the cylinder at the end of the compression stroke so that the charge mixture could be auto-ignited at the desired crank angle, and thereby obtaining optimal combustion phase and heat release rate on a wide operation range for the HCCI engine. Thus, this paper comprehensively reviews different effective techniques and controlling strategies used in the HCCI engine, and also summarizes in the tables.

The application of the Livengood-Wu (LW) integral method as a tool to estimate knock onset in spark ignited (SI) engines and combustion phasing in advanced compression ignition (ACI) engines has been demonstrated through simulations several times. In this study, the effect of uncertainties associated with parameters required for the LW integral method, when used as a tool for model based control of ignition timing in an ACI engine, were experimentally studied using five full boiling range gasoline fuels. As a first step, the method was applied to experimental data from a rapid compression machine and it was found that the ability of the LW integral method to predict ignition timing was very sensitive to the performance of the chemical kinetic model of each fuel. The method was subsequently applied to experimental data from a single-cylinder gasoline engine with simple approximations for the LW integral input parameters, and it was found that the predicted time of ignition was significantly different from the actual start of combustion. Systematic evaluation of various parametric uncertainties conducted thereafter showed that the uncertainty in cylinder charge temperature has the greatest influence. Improved methods of estimating cylinder charge temperature are proposed to account for the previously determined corrections, to enable the use of the LW integral method for model based control of ignition timing.

Experiments and simulations were used to explore the cyclic variability of an ethanol/diesel dual-fuel engine. The experiments were conducted on a light-duty diesel engine fueled with port injection of ethanol and direct injection of diesel. The influences of engine load, ethanol proportion and diesel injection timing on the cyclic variability were investigated. In-cylinder pressure traces of 150 consecutive cycles were acquired at each test condition. Consequently, cyclic variations of ignition timing (CA5), combustion phasing (CA50), accumulated heat release (Qf) and indicated mean effective pressure (IMEP) were used to quantify the cyclic variability. The experimental results showed that the fluctuations of CA5 and CA50 were very small throughout the premixed ratio sweep for both the light and high loads. However, the cyclic variation of IMEP was increased with the increasing ethanol ratio at both load conditions. And the cyclic variation of IMEP was reduced at the high load. The variations of IMEP and Qf showed similar magnitudes and trends at the test conditions, indicating that the cyclic variation of IMEP was mainly caused by the variation of Qf. Simulations confirmed that the combustion of premixed ethanol showed larger variations to initial in-cylinder temperature fluctuations at the light load, and consequently resulted in higher cyclic variation of Qf. At the high load, the increased combustion temperature enhanced the oxidation of ethanol, which contributed to stabilizing the combustion and reducing the cyclic variations. The cyclic variations increased with retarded diesel injection timing, which was mainly due to the reduced combustion temperature.