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Combustion visualizations were carried out in a constant volume vessel to study the partially premixed combustion of a gasoline-like fuel using high speed imaging. The test fuel (G80H20) is composed by volume 80% commercial gasoline and 20% n-heptane. The effects of ambient gas composition, ambient temperature and injection pressure on G80H20 combustion characteristics were analyzed. Meanwhile, a comparison of the EGR effect on combustion process between G80H20 and diesel was made. Four ambient gas conditions that represent the in-cylinder gas compositions of a heavy-duty diesel engine with EGR ratios of 0%, 20%, 40% and 60% were used to simulate EGR conditions. Variables also include two ambient temperature (910K and 870K) and two injection pressure (20 MPa and 50 MPa) conditions.

In order to enhance the thermal efficiency of gasoline engines, a combustion mode namely Homogeneous Charge Induced Ignition (HCII) was introduced and examined in this paper. Port-injected gasoline was used as the main fuel and formed a homogeneous charge in the cylinder. Diesel was used as the pilot fuel, directly injected into the cylinder, and self-ignited and this induced the ignition of the premixed gasoline-air charge. The images of HCII combustion process were taken on an optical engine through a high-speed CMOS camera. The multi-point induced ignition phenomena were observed and the parameters like flame luminance, ignition delay and combustion duration were analyzed by image analysis. The result shows that as the gasoline/diesel ratio increases with a fixed low pilot amount, the ignition delay increases, the initial ignition area extends from the center towards the periphery of the combustion chamber, and the combustion velocity increased.

Super knock which occurs in highly boosted spark ignition engines in low speed pre-ignition regime can lead to severe engine damage. However, super knock occurs occasionally, it is difficult to clearly identify the causes. The widely accepted assumption for the cause of this phenomenon is oil intrusion. Most of oils have been proved to have higher cetane number than n-heptane dose, indicating that the intruded oil is very liable to auto-ignition in a boosted engine. Although there have been reported the type of base oil and additive has significant effect on pre-ignition frequency, the oil induced super knock is still so far not supported by any direct evidence. This paper presents the effect of direct oil intrusion into cylinder on super knock. The experiment was carried out in a single cylinder engine. The diluted oil by gasoline with different ratio was directly injected into cylinder using a modified single-hole injector with 4MPa injection pressure.

The effect of ethanol blended diesel fuels on brake specific fuel consumption (BSFC), brake specific energy consumption (BSEC), smoke and NOx emissions has been investigated in a direct-injection diesel engine. Unregulated emissions including formaldehyde, acetaldehyde and unburned ethanol emissions are also analyzed. The results indicate that with the increase of ethanol in the blends, smoke reduces significantly, BSEC improves slightly and combustion duration decreases. However, the rate of heat release increases. Ignition delays. BSFC, NOx, acetaldehyde and unburned ethanol emissions increase. The maximum acetaldehyde emissions reached up to 100 ppm at low load. Compared to a gasoline engine using ethanol blended gasoline fuels, unburned ethanol emissions of the diesel engine are higher than those of the gasoline engine at the same ethanol concentrations and similar loads.

Gasoline Direct Injection (GDI) engines developed at nineties of the twentieth century can greatly improve the fuel economy. But the combustion chamber design and mixture control of the engines are very complex compared with Port Fuel Injection (PFI) gasoline engines. A two-stage gasoline direct injection (TSGDI) combustion system is developed and aimed to solve the problem of the complexity. Two-stage fuel injection and flexible injection timings are adopted as main means to form reasonable stratified mixture in the cylinder. A simple combustion chamber and helical intake port are designed to assist the mixture's stable combustion, which reduces the difficulties of the combustion system design. Systematical simulation and experimental studies of the effects of injection strategies such as different first,second injection timings and injection ratios, on the mixture formation processes and engine performanc are made in detail.

This paper studied the knock combustion process in gasoline HCCI engines. The complex chemical kinetics was implemented into the three-dimensional CFD code with LES (Large eddy simulation) to study the origin of the knock phenomena in HCCI combustion process. The model was validated using the experimental data from the cylinder pressure measurement. 3D-CFD with LES method gives detailed turbulence, species, temperature and pressure distribution during the gasoline HCCI combustion process. The simulation results indicate that HCCI engine knock originates from the random multipoint auto-ignition in the combustion chamber due to the slight inhomogeneity. It is induced by the significantly different heat release rate of high temperature oxidation (HTO) and low temperature oxidation (LTO) and their interactions.

Turbulent jet ignition (TJI) combustion using pre-chamber ignition can accelerate the combustion speed in the cylinder and has garnered growing interest in recent years. However, it is complicated for the optimization of the pre-chamber structure and combustion system. This study investigated the effects of the pre-chamber structure and the intake ports on the combustion characteristics of a gasoline engine through CFD simulation. Spark ignition (SI) combustion simulation was also conducted for comparison. The results showed that the design of the pre-chamber that causes the jet flame colliding with walls severely worsen the combustion, increasing the knocking intendency, and decrease the thermal efficiency. Compared with SI combustion mode, the TJI combustion mode has the higher heat transfer loss and lower unburned loss. The well-optimized pre-chamber can accelerate the flame propagation with knock suppression.

A 1-Dimensional (1-D) model of fluid dynamic and chemistry kinetics following hot spot auto-ignition has been developed to simulate the process from auto-ignition to pressure wave propagation. The role of wall effect on the physical-chemical interaction process is numerically studied. A pressure wave is generated after hot spot auto-ignition and gradually damped as it propagates. The reflection of the wall forms a reflected pressure wave with twice the amplitude of the incident wave near the wall. The superposition of the reflected and forward pressure waves reinforces the intensity of the initial pressure wave. Wall effect is determined by the distance between the hot spot center and the cylinder wall. Hot spot auto-ignition near the wall easily initiates detonation under high-temperature and high-pressure conditions because pressure wave reflection couples with chemical reactions and propagates in the mixture with high reactivity.

In this paper, a hybrid combustion mode in four-stroke gasoline direct injection engines was studied. Switching cam profiles and injection strategies simultaneously was adopted to obtain a rapid and smooth switch between SI mode and HCCI mode. Based on the continuous pressure traces and corresponding emissions, HCCI steady operation, HCCI transient process (combustion phase adjustment, SI-HCCI, HCCI-SI, HCCI cold start) were studied. In HCCI mode, HCCI combustion phase can be adjusted rapidly by changing the split injection ratio. The HCCI control strategies had been demonstrated in a Chery GDI2.0 engine. The HCCI engine simulation results show that, oxygen and active radicals are stored due to negative valve overlap and split fuel injection under learn burn condition. This reduces the HCCI sensitivity on inlet boundary conditions, such as intake charge and intake temperature. The engine can be run from 1500rpm to 4000rpm in HCCI mode without spark ignition.

Gasoline engines suffer low thermal efficiency and diesel engines have the emission problem of the trade-off between NOx and soot emissions. Homogeneous Charge Induced Ignition (HCII) is introduced using a port injection of gasoline to form a homogeneous charge and using a direct injection of diesel fuel to ignite. HCII has the potential to achieve high thermal efficiency and low emission combustion. However, HCII combustion mode still has problems of high THC emissions at low load and high pressure rise rate at high load. In order to improve the gasoline reactivity and reduce THC emissions, double injection of diesel was applied in HCII mode. In order to reduce peak pressure rise rate (PPRR), a two-staged high-temperature heat release is achieved at suitable engine condition. The effects of HCII mode on combustion and emission characteristics are studied in a light-duty engine.

A conceptual approach to help understand and simulate droplet induced pre-ignition is presented. The complex phenomenon of oil-fuel droplet induced pre-ignition has been decomposed to its elementary processes. This approach helps identify the key fluid properties and engine parameters that affect the pre-ignition phenomenon, and could be used to control LSPI. Based on the conceptual model, a 3D CFD engine simulation has been developed which is able to realistically model all of the elementary processes involved in droplet induced pre-ignition. The simulation was successfully able to predict droplet induced pre-ignition at conditions where the phenomenon has been experimentally observed. The simulation has been able to help explain the observation of pre-ignition advancement relative to injection timing as experimentally observed in a previous study [6].

Wide Distillation Fuel (WDF) refers to the fuels with a distillation range from Initial Boiling Point (IBP) of gasoline to Final Boiling Point (FBP) of diesel. Polyoxymethylene Dimethyl Ethers (PODEn) have high oxygen content and cetane number, are promising green additive to diesel fuel. In this paper, WDF was prepared by blending diesel and gasoline at ratio of 1:1, by volume; the mass distribution of oligomers in the PODE3-4 product was 88.9% of PODE3 and 8.46% of PODE4. Diesel fuel (Diesel), WDF (G50D50) and WDF (80%)-PODE3-4 (20%) (G40D40P20) were tested in a light-duty single-cylinder diesel engine, combustion characteristic, fuel consumption and exhaust emissions were measured. The results showed that: at idling condition, G40D40P20 has better combustion stability, higher heat release rate, higher thermal efficiency compared with G50D50.

Polyoxymethylene dimethyl ethers (PODEn) are promising alternative fuel candidates for diesel engines because they present advantages in soot reduction. This study uses a PODEn mixture (contains PODE3-6) from mass production to provide oxygen component in blend fuels. The spray combustion of PODEn-diesel bend fuels in a constant volume vessel was studied using high speed imaging, PLII-LEM and OH* chemiluminescence. Fuels of several blend ratios are compared with pure diesel. Flame luminance data show a near linear decrease tendency with the blend ratio increasing. The OH* images reveal that the ignition positions of all the cases have small differences, which indicates that using a low PODEn blend ratio of no more than 30% does not need significant adjustment in engine combustion control strategies. It is found that 30% PODEn blended with diesel (P30) can effectively reduce the total soot by approximately 68% in comparison with pure diesel.

In this paper a Particle Image Velocimetry (PIV) was used to measure flow velocity fields in different inlet cones under different mass flux conditions on a steady state flow rig. Meanwhile, a mathematical model of the flow in catalytic converters was established and simulated using CFD code. Validation of the model shows that simulation results have a good agreement with experiments, which means that the established model is feasible and can be applied to predict the flow characteristics in catalytic converters with different inlet cone configurations. Experimental and computational results indicate that the inlet cone configuration significantly affects flow distribution. For a conventional inlet cone, the cone angle is one of the key factors to affect flow characteristics and should be kept as small as possible in a design. An enhanced inlet cone can greatly improve flow uniformity in catalytic converters.

A computational fluid dynamics (CFD) guided design optimization was conducted for the piston bowl geometry for a heavy-duty diesel engine. The optimization goal was to minimize engine-out NOx emissions without sacrificing engine peak power and thermal efficiency. The CFD model was validated with experiments and the combustion system optimization was conducted under three selected operating conditions representing low speed, maximum torque, and rated power. A hundred piston bowl shapes were generated, of which 32 shapes with 3 spray angles for each shape were numerically analyzed and one optimized design of piston bowl geometry with spray angle was selected. On average, the optimized combustion system decreased nitrogen oxide (NOx) emissions by 17% and soot emissions by 41% without compromising maximum engine power and fuel economy.

Ammonia shows promise as an alternative fuel for internal combustion engines (ICEs) in reducing CO2 emissions due to its carbon-free nature and well-established infrastructure. However, certain drawbacks, such as the high ignition energy, the narrow flammability range, and the extremely low laminar flame speed, limit its widespread application. The dual fuel (DF) mode is an appealing approach to enhance ammonia combustion. The combustion characteristics of ammonia-diesel dual fuel mode and ammonia-PODE3 dual fuel mode were experimentally studied using a full-view optical engine and the high-speed photography method. The ammonia energy ratio (ERa) was varied from 40% to 60%, and the main injection energy ratio (ERInj1) and the main injection time (SOI1) were also varied in ammonia-PODE3 mode.

Homogeneous Charge Induced Ignition (HCII) combustion is believed to be a promising approach to achieve clean and high efficiency combustion. HCII can be realized by using port-injection of the high-volatile fuel (gasoline) to prepare in-cylinder homogeneous charge and direct injection of the high-ignitable fuel (diesel) near the top dead center to control the start of combustion. In the current study, a numerical study was carried out to understand the mixing and auto-ignition process in HCII combustion. A multicomponent chemical kinetic mechanism for gasoline and diesel, consisting of n-heptane, iso-octane, ethanol, toluene, diisobutylene and n-decane, has been developed for predicting their ignition and oxidation. The final mechanism consists of 104 species and 398 reactions. This mechanism was validated with the experimental data of ignition delay times and laminar flame speeds for each component and real transportation fuels.

Homogeneous Charge Compression Ignition (HCCI) combustion concept has advantages of high thermal efficiency and low emissions. However, how to control HCCI ignition timing is still a challenge in the application. This paper tries to control HCCI ignition timing using gasoline direct injection (DI) into cylinder to form a desired mixture of fuel and air. A homogeneous charge can be realized by advancing injection timing in intake stroke and a stratified charge can be obtained by retarding injection timing in compression stroke. Multi-stage injection strategy is used to control the mixture concentration distribution in the cylinder for HCCI combustion. A three-dimensional Computational Fluid Dynamics (CFD) code FIRE™ is employed to simulate the effects of single injection timing and multi-stage injection on mixture formation and combustion. Effects of mixture concentration and inlet temperature on HCCI ignition timing are also investigated in this paper.

In this paper, the detailed chemical kinetics was implemented into the three-dimensional CFD code to study the combustion process in HCCI engines. An extended hydrocarbon oxidation reaction mechanism (89 species, 413 reactions) used for high octane fuel was constructed and then used to simulate the chemical process of the ignition, combustion and pollutant formation in HCCI conditions. The three-dimensional CFD / chemistry model (FIRE/CHEMKIN) was validated using the experimental data from a Rapid Compression Machine. The simulation results show good agreements with experiments. Finally, the improved multi-dimensional CFD code has been employed to simulate the intake, spray, combustion and pollution formation process of the gasoline direct injection HCCI engine with multi-stage injection strategy. The models account for intake flow structure, spray atomization, spray/wall interaction, droplet evaporation and gas phase chemistry in complex multi-dimensional geometries.

Ammonia (NH3), a zero-carbon fuel, has great potential for internal combustion engine development. However, its high ignition energy, low laminar burning velocity, narrow range of flammability limits, and high latent heat of vaporization are not conducive for engine application. This paper numerically investigates the feasibility of utilizing ammonia in a heavy-duty diesel engine, specifically through low-pressure direct injection (LP-DI) of hydrogen to ignite ammonia combustion. Due to the lack of a well-corresponding mechanism for the operating conditions of ammonia-hydrogen engines, this study serves only as a trend-oriented prediction. The paper compares the engine's combustion and emission performance by optimizing four critical parameters: excess air ratio, hydrogen energy ratio, ignition timing, and hydrogen injection timing. The results reveal that excessively high hydrogen energy ratios lead to an advanced combustion phase, reducing indicated thermal efficiency.