UBC Theses and Dissertations
Performance and emission characteristics of a gas-diesel engine Tao, Yinchu
The performance and emission characteristics of high pressure injection of natural gas with liquid pilot-diesel fuel (ie. gas-diesel operation) was investigated in a single-cylinder, two-stroke compression-ignition engine with a poppet-valve gas-diesel injector. The investigated injector geometries and engine operating parameters included: fuel injection angle, fuel jet interruption ratio, engine speed, load, beginning of injection timing, natural gas injection pressure, pilot-diesel to total-fuel energy ratio and pilot-diesel cetane number. These parameters were found to have very strong effects on thermal efficiency and exhaust emissions (ie. NOx, THC, CH₄, CO, CO₂ and BOSCH smoke index). The thermal efficiency and exhaust emissions were determined as a function of load (ie. BMEP). The thermal efficiency of the optimum gas-diesel operation was shown to exceed that of the conventional diesel operation at full load, but was lower at low load. With this gas-diesel injector configuration, it was found that the pilot-diesel fuel was not mixed well enough to burn completely. A new gas-diesel injector designed to overcome this drawback is in process. A three-zone combustion and exhaust emission analysis model was established to deduce ignition delay from cylinder pressure data with crank angle. At low loads, it was found that the ignition delay of natural gas was excessive with very late burning and consequently low thermal efficiency. At high loads, the ignition delay of natural gas was considerably longer than that of diesel fuelling, but not so long as to affect the thermal efficiency. The three-zone model was also used to deduce maximum burned-gas temperature. It was found that equilibrium NO concentration calculated from this temperature and cylinder pressure can be used to correlate the exhaust NO measured from engine exhaust pipe.
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