Effect of pilot injection timing, pilot quantity and intake charge conditions on performance and emissions for an advanced low-pilot-ignited natural gas engine

Abstract Diesel engines may be converted readily to operate primarily on natural gas using the injection of a diesel pilot to achieve ignition. Advanced low-pilot-ignited natural gas (ALPING) engines show significant potential to match diesel engines in their part-load and full-load efficiencies. Experiments were performed to study the effects of pilot injection timing (- 15 to - 60° ATDC), pilot quantity, intake manifold pressure and intake charge temperature on the performance and emissions from an ALPING engine under half-load (21 kW at 1700 r/min) and full-load (42 kW at 1700 r/min) conditions. Low NOx emissions (below 0.03 g/kW h at - 60° ATDC) with satisfactory fuel conversion efficiency (31 per cent) for half-load and NOx emissions of 0.2 g/kW h at -60° ATDC with fuel conversion efficiency of 40 per cent could be obtained for full-load engine operation. High HC emissions, 96 g/kW h at - 20° ATDC for half-load and 21 g/kW h at -60° ATDC for full-load operation, were recorded. The NOx emissions showed an interesting trend for varied injection timings with maximum NOx emissions occurring at -35° ATDC and minimum at - 60° ATDC injection timing. Increased pilot quantity, intake charge temperature and lower intake manifold pressures resulted in increased NOx emissions and fuel conversion efficiency, and decreased HC emissions.