Reduction of emissions in an automotive direct injection diesel engine dual-fuelled with natural gas by using variable exhaust gas recirculation

An experimental study was conducted to determine the performance and exhaust emission characteristics of an automotive direct injection dual-fuelled diesel engine. Natural gas was used such that 65 per cent of engine brake power was supplied from compressed natural gas and the rest was supplied from diesel fuel. The objective of this work is to investigate the possibility of decreasing exhaust emission with the lowest performance sacrifice. At part loads, a dual-fuelled engine inevitably suffers from lower thermal efficiency and higher carbon monoxide (CO) emission. This is mainly due to leaner mixture and incomplete combustion, which is a consequence of the smaller amount of pilot fuel. To resolve these problems, the effects of cooled exhaust gas recirculation (EGR) were investigated. The experimental results show that the application of EGR, at higher loads with 10 per cent EGR and at part loads with 15 per cent EGR, can considerably reduce NOx and other exhaust emissions such as unburned hydrocarbons, CO and soot. Results show that the performance parameters almost remain at the baseline engine level.