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UBC Theses and Dissertations

Performance, emissions and combustion characteristics of natural gas fueling of diesel engines Douville, Brad


The performance, emissions and combustion characteristics of natural gas fueling of diesel engines have been investigated. The natural gas fueling system employs electronically-controlled late-cycle direct injection of high pressure natural gas with a small amount of diesel fuel (diesel pilot). Since the temperature in the combustion chamber at the end of compression is below the autoignition temperature of natural gas, the diesel pilot is required for ignition. Diesel engine performance and emissions have been measured using both natural-gas and conventional diesel fueling, over a wide range of operating conditions. The combustion process in diesel engines has been modeled based on measured cylinder pressure to learn about the formation rates of oxides of nitrogen and fuel burning rates. This combustion model has been developed to deal specifically with the non-uniformities and pollutant formation associated with stratified-charge combustion in diesel engines. The test results demonstrate that the thermal efficiencies for both natural gas and conventional diesel fueling at low and medium engine loads, are almost identical. The thermal efficiencies at high loads for natural gas fueling are greater than for conventional diesel fueling. Upon optimization of the natural gas and diesel pilot injection, lower pollutant exhaust emissions will be produced over the entire engine load range, while obtaining higher peak engine load capabilities than with conventional diesel fueling.

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