An experimental study into the effect of the pilot injection timing on the performance and emissions of a high-speed common-rail dual-fuel engine

Dual fuel technology has the potential to offer significant improvements in emissions of carbon dioxide from light-duty compression ignition engines. In these smaller capacity high speed engines, where the combustion event can be temporally shorter, the injection timing can have an important effect on the performance and emissions characteristics of the engine. This paper discusses the use of a 0.51-litre single-cylinder high speed direct injection diesel engine modified to achieve port directed gas injection. The effect of pilot diesel injection timing on dual fuel engine performance and emissions was investigated at engine speeds of 1500 and 2500 rpm and loads equivalent to 0.15, 0.3, 0.45 and 0.6 MPa gross indicated mean effective pressure, for a fixed gas substitution ratio (on an energy basis) of 50%. Furthermore, the effect of pilot injection quantity was investigated at a constant engine speed of 1500 rpm by completing a gaseous substitution sweep at the optimised injection timing for each load condition. The results identify the limits of single injection timing during dual fuel combustion and the gains in engine performance and stability that can be achieved through optimisation of the pilot injection timing. Furthermore, pilot injection timing and quantity were shown to have fundamental effects on the formation and emission of carbon monoxide, nitrogen oxide and total hydrocarbons. The potential for dual fuel combustion to achieve significant reductions in specific CO2 was also highlighted, with reductions of up to 30% being achieved at full load compared to the baseline diesel case.