Effect of the pilot quantity on the ultrafine particle emissions and the combustion characteristics of a biodiesel pilot-ignited natural-gas dual-fuel engine

Abstract

Natural gas has been widely utilized in urban transportation and power generation owing to its relatively low price and large abundance. One typical application of natural gas is as the primary fuel with dual-fuelling operation in compression ignition engines. In this study, biodiesel was used as the pilot fuel in a natural-gas dual-fuel engine, and the effect of the pilot quantity on the performance, the combustion and the emissions (especially the ultrafine particle emissions) were analysed. The test results show that, with increasing pilot quantity, the peak particle number concentration shifts from 29 nm to 100 nm while the peak particle mass concentration is stable and remains at 200 nm. Also, increasing the pilot quantity improves the brake’s thermal efficiency at low and medium loads, but this improvement is not obvious at high loads. With increasing pilot quantity, the first-stage heat release appears earlier and its peak value is also increased, accompanied by a decrease in the peak value of the second-stage heat release. The increase in the pilot quantity reduces the carbon monoxide emissions and the hydrocarbon emissions but increases the nitrogen oxide emissions. In comparison with the diesel pilot case, the size distribution of the ultrafine particle emissions from biodiesel pilot operation changes little, but both the number concentration and the mass concentration are reduced.