Optimisation of palm oil biodiesel combustion in common rail for smalll car engine

Operating a diesel engine with biodiesel increases fuel consumption and NOx emission while producing significantly low black smoke. This is due to the inherent chemical and physical properties of biodiesel which results in un-optimised engine operating parameters. This study presents the investigation on the effects of palm oil biodiesel on the performance and emissions of a common rail passenger car engine and proposes a simplified control strategy for fuel economy optimisation for biodiesel operation. Firstly, the effects of the biodiesel on the emissions and fuel economy of a Euro2 1.5 litre engine was mapped by conducting extensive engine dynamometer and emissions testing across all operating regions. The region with significant difference between conventional and biodiesel fuels was identified for optimisation. Secondly, the effects of the fuel injection parameters to the performance and emission was studied by conducting fuel rail pressure and injection timing sweep at each speed and load region. Finally, the optimised injection parameters were determined by Multiple Response Weighted Signal to Noise Ratio techniques. It was found that the low to medium engine speed and load region, from 2000 rpm to 3000 rpm and 25% to 50% load, is where the difference between conventional and biodiesel is most significant with increased NOx and fuel consumption while the smoke emission is reduced by as much as 56%. The adopted fuel injection control strategy involved the adjustment of the end of injection timing and the fuel rail pressure. It was demonstrated that the optimised injection parameters were at the nominal end of injection settings while the rail pressure at 3% to 9% lower than nominal. Fuel economy improvement of as high as 5% was demonstrated while the NOx and smoke emissions were kept within the diesel values. At medium speed and load for 20% biodiesel, brake specific fuel consumption of 2% lower than diesel was achieved. In conclusion, a new, simplified fuel injection parameters optimisation strategy for palm oil based biodiesel was successfully developed and demonstrated, which could be applied via piggyback system for immediate application