The performance of a turbocharged spark-ignition engine fuelled with natural gas and gasoline

This thesis presents an investigation of the influence of turbocharging on the performance and combustion behaviour of a dual fuelled, spark-ignition engine fuelled with natural gas and gasoline. The investigation was carried out using a combination of experimental and analytical methods. The experimental data was obtained from an instrumented, four cylinder, Toyota engine mounted in a test cell. An electrically driven Roots blower was used to provide compressed air to the engine, and a restriction was placed in the exhaust pipe to simulate the effects of an exhaust-driven turbine. Cylinder pressure data were recorded and analysed using a computer routine in order to provide information on mass burning rates and burning velocities. Computer routines were also developed to simulate the compression, combustion and expansion processes in the engine. It was found that the laminar burning velocity of natural gas is 50% to 60% lower than gasoline, under engine-like conditions of temperature and pressure. Mass-burning rate analyses of measured cylinder pressure data showed that the lower burning velocity of natural gas has its greatest influence during the ignition delay period (up to 1% mass burned) and that it can cause increases in ignition delay of between 50% and 100% relative to gasoline. It was observed that the low burning velocity of natural gas also affects the main combustion period, but to a much lesser extent, increasing it by up to 10% relative to gasoline. It was concluded that the main combustion period is dominated by turbulence effects and that it is relatively unaffected by variations in fuel type, air/fuel ratio or boost pressure. Results from the engine tests and simulation program indicated that it is possible to recover the power loss experienced by an engine running on natural gas by boosting the intake pressure to 3 psig (20 kPa) above that provided when the engine is running on gasoline. This increase in boost pressure does not significantly reduce the efficiency or raise the specific fuel consumption. It was found, however, that the peak cylinder pressures attained can be as much as 20% higher on natural gas than on gasoline at the same power level.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat