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Pilot ignited high pressure direct injection of natural gas fueling of diesel engines

University of British Columbia

Measurements of performance and emissions of a Diesel engine fueled with natural gas have been made with high-pressure direct-injection (HPDI). Natural gas is injected late in the compression cycle preceded by an injection of diesel pilot. Tests were performed on a DDC 1-71 Diesel engine with electronic controls. Influence of several physical parameters has been investigated in light of the results obtained by other researchers through 3-dimensional numerical simulation of the combustion process using a modified KTVA code. These were: natural gas injection pressure, absolute beginning of injection (BOI) and relative timing between injection of pilot diesel and natural gas (RBOI). It was found that, on the range of 100 to 160 bar, combustion rate and NO₂ emissions increase with gas injection pressure. Best thermal efficiency results were obtained for a gas pressure of 130 bar. With HPDI fueling of a diesel engine, injection timing delay has proven to be an effective way of reducing NO₂ emissions. By appropriately adjusting beginning of injection, NO₂ reduction of up to 60 % over the diesel baseline could be obtained, while preserving conventional diesel efficiency. Over the BOI and load range of study, a longer relative injection delay appears to give lower NO₂ emissions and improved thermal efficiency. KTVA 2 simulations indicate that the interlace angle (defined as the angle between the diesel and gas plumes as viewed in the direction of the cylinder axis), which changes during engine operation, has a significant effect on combustion rate and NO₂ emissions. Experimentally it was observed that with an equal number (6) of nozzle holes for both natural gas and diesel pilot there was instability in engine operation at low load and wide scatter in emission measurements. Guided by the simulation results it was found experimentally that data reproduciblity and engine operating stability could both be much improved by choosing a different number of jets for injection of natural gas. An arrangement of 7 natural gas and 6 diesel holes has proven to give better results of engine stability, thermal efficiency and exhaust emissions. KTVA 2 simulations indicate attachment of the gas jets to the fire deck for inclination angles less than about 20 degrees. The reduced contact area between the flame and oxygen lead to somewhat lower combustion rate and NO₂ emissions.

Thesis/Dissertation

application/pdf

2009-06-26

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http://hdl.handle.net/2429/9690

Mechanical Engineering

University of British Columbia

UBCV

DSpace