The research work presented in this thesis is concerned with an investigation of fuel management of diesel engines for the purposes of developing control schemes to improve fuel consumption, exhaust emissions and engine controllability.

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The present work is based on the need for understanding the in-cylinder flow and its subsequent effects on combustion in a valved-two-stroke spark ignition engine with fuel injection using Computational Fluid Dynamics (CFD) and experimental techniques. In this context, the CFD code KIVA-II has been modified to model the two-stroke engine gas exchange and combustion processes. A 3-D Cartesian grid generation program for complex engine geometry has been added to the KIVA code which has been modified to include intake and exhaust flow processes with valves. New and improved sub models for wall jet interaction, mixing controlled combustion and one dimensional wave action have also been incorporated. The modified version of the program has been used to simulate a fuel injected two-stroke spark ignition engine and parametric studies have been undertaken. The simulated flow, combustion and exhaust emission characteristics over a wide range of operating conditions show the expected trends in behaviour observed in actual engines. In the second phase of this study, the air-assisted-fuel-injection (AAFI) process into a cylinder has been simulated with a high resolution computational grid. The simulation results are presented and compared with experimental data obtained using the Schlieren optical technique. An approximate method based on the conservation of mass, momentum and energy of the spray jet and using a comparatively coarse grid has been suggested for simulating the AAFI process. The simulation study predicts a high degree of atomisation of fuel spray with Sauter mean diameter around 10 μm even with moderate air and fuel pressures. The penetration and width of spray are simulated within 15% of the experimental values. In the last phase of this study, the flow and combustion processes have been studied for a four-stroke spark ignition engine with the AAFI process. The simulation results obtained using this approximate method have been validated with experimental data generated for the same engine configuration.

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Societal concerns on combustion-based fuel consumption are ever-increasing. With respect to internal combustion engines, this translates to a need to increase brake fuel conversion efficiency (BFCE). Diesel engines are a relatively efficient internal combustion engine to consider for numerous applications, but associated actions to mitigate certain exhaust emissions have generally deteriorated engine efficiency. Conventionally, diesel engine emission control has centered on in-cylinder techniques. Although these continue to hold promise, the industry trend is presently favoring the use of after-treatment devices which create new opportunities to improve the diesel engine's brake fuel conversion efficiency. This study focuses on injection timing effects on the combustion processes, engine efficiency, and the engine system's responses. The engine in the study is a medium duty diesel engine (capable of meeting US EPA Tier III off road emission standards) equipped with common rail direct fuel injection, variable geometry turbo charging, and interfaced with a custom built engine controller. The study found that injection timing greatly affected BFCE by changing the combustion phasing. BFCE would increase up to a maximum then begin to decrease as phasing became less favorable. Combustion phasing would change from being mostly mixing controlled combustion to premixed combustion as injection timing would advance allowing more time for fuel to mix during the ignition delay. Combustion phasing, in turn, would influence many other engine parameters. As injection timing is advanced, in-cylinder temperatures and pressures amplify, and intake and exhaust manifold pressures deteriorate. Rate of heat release and rate of heat transfer increase when injection timing is advanced. Turbocharger speed falls with the advancing injection timing. Torque, however, rose to a maximum then fell off again even though engine speed and fueling rate were held constant between different injection timings. Interestingly, the coefficient of heat transfer changes from a two peak curve to a smooth one peak curve as the injection timing is advanced further. The major conclusion of the study is that injection advance both positively and negatively influences the diesel engine's response which contributes to the brake fuel conversion efficiency.

Hydrogen, as an alternative to conventional aviation fuels, has the potential to increase the efficiency of a gas turbine as well as reduce emissions of greenhouse gases. In addition to significantly reducing the number of pollutants due to the absence of carbon, burning hydrogen at low equivalence ratios can significantly reduce emissions of oxides of nitrogen (NOx). Because hydrogen has a wide range of flammability limits, fuel lean combustion can take place at lower equivalence ratios than those with typical hydrocarbon fuels. Numerous efforts have been made to develop gas turbine fuel injectors that premix methane/natural gas and air in fuel lean proportions prior to the reaction zone. Application of this technique to hydrogen combustion has been limited due to hydrogen's high flame rate and the concern of the reaction zone propagating into the premixing injector, commonly referred to as flashback. In this investigation, a lean-premixing hydrogen injector has been developed for application in small gas turbines. The performance of this injector was characterized and predictions about the injector's performance operating under combustor inlet conditions of a PT6-20 Turboprop have been made. / Master of Science

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