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The effects of hydrogen ratio and exhaust gas recirculation (EGR) on combustion and emissions in a hydrogen/diesel dual-fuel premixed charge compression ignition (PCCI) engine were investigated. The control of combustion phasing could be improved using hydrogen enrichment and EGR due to the retarded combustion phasing with a higher hydrogen ratio. The indicated mean effective pressure (IMEP) was increased with a higher hydrogen ratio because the hydrogen enrichment intensified the high temperature reactions and thus decreased the combustion duration. Hydrocarbon (HC) and carbon monoxide (CO) emissions were reduced significantly in a hydrogen/diesel dual-fuel PCCI mode with a similar NOx emissions level as that of the diesel PCCI mode.

The compression ignition combustion fuelled with hydrogen and dimethyl-ether was investigated. Exhaust gas recirculation was applied to reduce noise and nitrogen oxide (NOx) emission. When dimethyl-ether was injected earlier, combustion showed two-stage ignitions known as low temperature reaction and high temperature reaction. With advanced dimethyl-ether injection, combustion temperature and in-cylinder pressure rise were lowered which resulted in high carbon monoxide and hydrocarbon emissions. However, NOx emission was decreased due to relatively low combustion temperature. The engine combustion showed only high temperature reaction when dimethyl-ether was injected near top dead center. When exhaust gas recirculation gas was added, the in-cylinder pressure and heat release rate were decreased. However, it retarded combustion phase resulting in higher indicated mean effective pressure.

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.

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.

The effects of charge dilution on low-temperature diesel combustion and emissions were investigated in a small-bore single-cylinder diesel engine over a wide range of injection timing. The fresh air was diluted with additional N2 and CO2, simulating 0 to 65% exhaust gas recirculation in an engine. Diluting the intake charge lowers the flame temperature T due to the reactant being replaced by inert gases with increased heat capacity. In addition, charge dilution is anticipated to influence the local charge equivalence ratio ϕ prior to ignition due to the lower O2 concentration and longer ignition delay periods. By influencing both ϕ and T, charge dilution impacts the path representing the progress of the combustion process in the ϕ-T plane, and offers the potential of avoiding both soot and NOx formation.

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.

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.

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%).