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The combustion and exhaust emission characteristics of a DME fueled HCCI engine were investigated. Different fuel injection strategies were tested under various injection quantities and timings with exhaust gas recirculation (EGR). The combustion phase in HCCI was changed by an in-cylinder direct injection and EGR, due to changes in the in-cylinder temperature and mixture homogeneity. The gross indicated mean effective pressure (IMEPgross) increased and the hydrocarbon (HC) and carbon monoxide (CO) emissions decreased as the equivalence ratio was augmented. The IMEPgross with direct injection was greater than with the port injection due to retarded ignition timing resulting from latent heat of direct injected DME fuel. It was because that most of burn duration was completed before top dead center owing to higher ignitability for DME with high cetane number. However, HC and CO emissions were similar for both injection locations.

Dimethyl-ether combustion with pilot injection was investigated in a single cylinder direct injection diesel engine equipped with a common-rail injection system. Combustion characteristics and emissions were tested with dimethyl-ether and compared with diesel fuel. The main injection timing was fixed to have the best timings for maximum power output. The total injected fuel mass corresponded to a low heating value of 405 joules per cycle at 800 rpm. The fuel quantity and the injection timing of the pilot injection were varied from 8 to 20% of the total injected mass and from 50 to 10 crank angle degrees before the main injection timing, respectively. Ignition delay decreased with pilot injection. The effects of pilot injection were less significant with DME combustion than with diesel. Pilot injection caused the main combustion to increase in intensity resulting in decreased emissions of hydrocarbons, carbon monoxide and particulate matter.

The combustion, knock characteristics and exhaust emissions in an engine were investigated under homogeneous charge compression ignition operation fueled with liquefied petroleum gas with regard to variable valve timing and the addition of di-methyl ether. Liquefied petroleum gas was injected at an intake port as the main fuel in a liquid phase using a liquefied injection system, while a small amount of di-methyl ether was also injected directly into the cylinder during the intake stroke as an ignition promoter. Different intake valve timings and fuel injection amount were tested in order to identify their effects on exhaust emissions, combustion and knock characteristics. The optimal intake valve open timing for the maximum indicated mean effective pressure was retarded as the λTOTAL was decreased. The start of combustion was affected by the intake valve open timing and the mixture strength (λTOTAL) due to the volumetric efficiency and latent heat of vaporization.

A detailed chemical model was implemented in the KIVA-3V two dimensional CFD code to investigate the effects of the spray cone angle and injection timing on the PCCI combustion process and emissions in an optical research diesel engine. A detailed chemical model for Primary Reference Fuel (PRF) consisting of 157 species and 1552 reactions was used to simulate diesel fuel chemistry. The model validation shows good agreement between the predicted and measured pressure and emissions data in the selected cases with various spray angles and injection timings. If the injection is retarded to -50° ATDC, the spray impingement at the edge of the piston corner with 100° injection angle was shown to enhance the mixing of air and fuel. The minimum fuel loss and more widely distributed fuel vapor contribute to improving combustion efficiency and lowering uHC and CO emissions in the engine idle condition.

The effect of multiple injections in a heavy-duty diesel engine was investigated by focusing on single-pilot injection and double-pilot injection strategies with a wide injection timing range, various injection quantity ratios, and various dwell times. Combustion characteristics were studied through flame visualization and heat release analyses as well as emissions tests. Single-pilot injection resulted in a dramatic reduction in nitrogen oxide and smoke emissions when the injection timing was advanced over 40° CA before the start of injection (BSOI) due to combustion with partially premixed charge compression ignition. A brown-colored flame area, which indicates a very fuel-rich mixture region, was rarely detected when more fuel was injected during single-pilot injection. However, hydrocarbon emission increased up to intolerable levels because fuel wetting on the cylinder wall increased.

Low temperature diesel combustion with a large amount of exhaust gas recirculation in a direct injection diesel engine was investigated. Tests were carried out under various engine speeds, injection pressures, injection timings, and injection quantities. Exhaust emissions and brake specific fuel consumption were measured at different torque and engine speed conditions. High rates of exhaust gas recirculation led to the simultaneous reduction of nitrogen oxide and soot emissions due to a lower combustion temperature than conventional diesel combustion. However, hydrocarbon and carbon monoxide emissions increased as the combustion temperature decreased because of incomplete combustion and the lack of an oxidation reaction. To overcome the operating range limits of low temperature diesel combustion, increased intake pressure with a modified turbocharger was employed.

Two-stage injection strategy was studied in dimethyl-ether homogeneous charge compression ignition engine combustion. An early direct injection, main injection, was applied to form a premixed charge followed by the second injection after the start of heat release. Experiments were carried out in a single-cylinder direct-injection diesel engine equipped with a common-rail injection system, and the combustion performance and exhaust emissions were tested with the various second injection timings and quantities. Engine speed was 1200 rpm, and the load was fixed at 0.2 MPa IMEP. Main injection timing for homogeneous mixture was fixed at −80 CAD, and the fuel quantity was adjusted to the fixed load. Second injection quantity was varied from 1 to 5 mg, and the timing was selected according to the heat release rate of the HCCI combustion without second injection.

The effect of the composition of propane (C₃H₈) and butane (C₄H₁₀) in liquefied petroleum gas (LPG) was investigated in a dual-fuel HCCI engine fueled with di-methyl ether (DME) and LPG. The composition of LPG affects DME-LPG dual fuel HCCI combustion due to the difference in the physical properties of propane that and butane such as octane number, auto-ignition temperature and heat of vaporization. DME was injected directly into the cylinder at various injection timing from 160 to 350 crank angle degrees (CAD). LPG was injected at the intake port with a fixed injection timing at 20 CAD. It was found that power output was increased with propane ratio. This gain in power output resulted from increased expansion work due to the better anti-knock properties of propane. However, higher propane ratio made combustion efficiency decrease because of the suppression in low temperature reaction of DME which determines heat release amount of high temperature reaction.

Diesel fuel injection system is the most important part of the direct-injection diesel engine and, in recent years, it has become one of the critical technologies for emission control with the help of electronically controlled fuel injection. Common rail injection system has great flexibility in injection timing, pressure and multi-injections. Many studies and applications have reported the advantages of using common rail system to meet the strict emission regulation and to improve engine performance for diesel engines. The main objective of this study is to investigate the effect of pilot-, post- and multiple-fuel injection strategies on engine performance and emissions. The study was carried out on a single cylinder optical direct injection diesel engine equipped with a high pressure common rail fuel injection system. Spray and combustion evolutions were visualized through a high speed charge-coupled device (CCD) camera.

This paper describes the results of a DOE (design of experiment) applied to an exhaust heat exchanger to lower the exhaust gas temperature mainly under high load conditions. The heat exchanger was installed between the exhaust manifold and the inlet of the close-coupled catalytic converter (CCC) to avoid thermal aging. The DOE evaluates the influence of the selected eight design parameters of the heat exchanger geometry on the performance of the exhaust gas cooling system, and the interaction between these parameters. To maximize the heat transfer between exhaust gas and coolant, fins were implemented at the inner surface of the heat exchanger. The design parameters consist of the fin geometry (length, thickness, arrangement, number of fin), coolant direction, exchanger wall thickness, and the length of the heat exchanger. The acceptable range of each design parameter is discussed by analyzing the DOE results.

A diesel-fueled premixed charged compression ignition (PCCI) combustion technique using a two-stage injection strategy has been investigated in a single cylinder optical engine equipped with a common-rail fuel system. Although PCCI combustion has the advantages of reducing NOx and PM emissions, difficulties in vaporization of a diesel fuel and control of the combustion phase hinder the development of the PCCI engine. A two-stage injection strategy was applied to relieve these problems. The first injection, named as main injection, was an early direct injection of diesel fuel into the cylinder to achieve premixing with air. The second injection was a diesel injection of a small quantity (1.5 mm3) as an ignition promoter and combustion phase controller near TDC. Effects of injection pressure, injected fuel quantity and compression ratio were studied with variation of an intake air temperature.

Exhaust gas recirculation (EGR) and lean burn utilize the diluents into the engine cylinder to control combustion leading to enhanced fuel economy and reduced emissions. However, the occurrence of excessive cyclic variation with high diluent rates, brings about an undesirable combustion instability within the engine cylinder resulting in the deterioration of both engine performance and emissions. Proper stratification of mixture and diluents could improve the combustion stability under high diluent environment. EGR stratification within the cylinder was made by adopting a fast-response solenoid valve in the midst of EGR line and controlling its timing and duty. With EGR in both homogeneous mode and stratified mode, in-cylinder pressure and emissions were measured. The thermodynamic heat release analysis showed that the burning duration was decreased in case of stratified EGR. It was found that the stratification of EGR hardly affected the emissions.

In order to reduce hydrocarbon emission in gasoline engine, especially during warming-up period, it is necessary to estimate the fuel and fuel product flow rate in the emission gas. The intake airflow rate should also be estimated. A strategy was proposed to estimate air fuel ratio in a spark ignition engine. The mass of air in the cylinder was determined by filling-emptying method, and the fuel in the intake manifold and cylinder was estimated by the “wall-wetting” effect calculation. The use of graphical dynamic system control software is becoming more popular as automotive engineers strive to reduce the time to develop new control systems. The rapid prototype engine controller has been developed by using MATLAB, SIMULINK, REAL TIME WORKSHOP, xPC Target, and WATCOM C++. The sensor data from the engine will be transferred to computer, and the fuel delivery will be calculated.

To meet stringent emission standards, a considerable amount of development work is necessary to ensure suitable efficiency and durability of catalyst systems. The main challenge is to reduce the engine cold-start emissions. Close-coupled catalyst (CCC) provides fast light-off time by utilizing the energy in the exhaust gas. However, if some malfunction occurred during engine operation and the catalyst temperature exceeds 1050°C, the catalytic converter becomes deactivated and shows poor conversion efficiency. Close-coupled catalyst temperature was investigated under various engine operating conditions. All of the experiments were conducted with a 1.0L SI engine at 1500-4000 rpm. The engine was operated at no load to full load conditions. Exhaust gas temperature and catalyst temperature were measured as a function of lambda value (0.8-1.2), ignition timing (BTDC 30°-ATDC 30°) and misfire rates (0-28%).

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean burn operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean burn performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using a UV intensified high-speed CCD camera. Concepts of flame area speed, in addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics.

To investigate the mixture distributions in an LPG engine with Liquid phase port injection for heavy duty vehicles, an optical single cylinder engine, which is optically accessible both in side and bottom view, and laser diagnostic system were incorporated to apply PLIF (planar laser induced fluorescence) technique. Acetone was used as a dopant in LPG fuel, which was excited by KrF excimer laser (248nm), and its fluorescence images were acquired with ICCD camera. The effects of fuel injection timing, swirl intensity and excess air ratio were investigated. For the case of open valve injection, favorable stratification of fuel, both in axial and radial direction, was clearly observed compared to the closed valve injection, where reverse stratification in axial direction was observed. At the Ricardo swirl ratio of 3.4, it was apparent that excessive axial stratification of fuel got dominant, which would lead to poor engine performances.

Submodels are developed for injection, evaporation and wall impingement of a liquid LPG spray. The injection model determines the quality of fuel as two-phase choke flow at the nozzle exit. Wind tunnel experiments show the spray penetration more sensitive to ambient flow velocity than to injection pressure. Most evaporation occurs during choking, while heat transfer from surrounding air has a negligible effect on downstream droplet sizes. Three dimensional simulation shows that the bathtub cavity is better than the dog-dish cavity for stable flame propagation in lean-burn conditions. The injection timing during the IVC period has a negligible effect, while injection during an intake stroke enhances fuel/air mixing to result in more homogeneous cylinder charge.

The spray and combustion of diesel fuel were investigated to provide a better understanding of the evaporation and combustion process under the simulated cold-start condition of a diesel engine. The experiment was conducted in a constant volume combustion chamber and the engine cranking period was selected as the target ambient condition. Mie scattering and shadowgraph techniques were used to visualize the liquid- and vapor-phase of the fuel under evaporating non-combustion conditions (oxygen concentration=0%). In-chamber pressure and direct flame visualization were acquired for spray combustion conditions (oxygen concentration=21%). The fuel was injected at an injection pressure of 30 MPa, which is the typical pressure during the cranking period.

Premixed compression ignition (PCI) combustion was implemented using advanced injection strategy and exhaust gas recirculation in a direct-injection single-cylinder diesel engine. The injection timing swept experiment using a baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained three types of combustion regime: conventional diesel combustion for an injection timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for an injection timing of 40° CA BTDC and homogeneous charge compression ignition (HCCI) combustion for an injection timing of 80° CA BTDC. PCI combustion can be verified by burn duration analysis. The burn duration, which was defined as the period from 10% to 90% of the accumulated heat release, was very short in PCI combustion but not in the others. PCI combustion with an injection timing of 40° CA BTDC was achieved in a range of an exhaust gas recirculation (EGR) rate from 0% to around 40%.

The effect of pilot injection and exhaust gas recirculation (EGR) on premixed charge compression ignition (PCCI) combustion was investigated in a single-cylinder direct-injection diesel engine with low engine speed and low load. The injection timing of PCCI combustion was fixed at 25 ~ 30 crank angle degree before top dead center (°CA BTDC) based on the ignition delay and power output. The level of oxides of nitrogen (NOx) emissions of PCCI combustion was 68% lower than that of conventional diesel combustion owing to the reduction of near-stoichiometric region which is well known as the main source of NOx formation. However, the indicated mean effective pressure (IMEP), hydrocarbon (HC), particulate matter (PM) and carbon monoxide (CO) emissions deteriorated compared with conventional diesel combustion because of early injection, advanced combustion phase and lowered combustion temperature. EGR has been applied to PCCI combustion.