Investigation on differences in engine efficiency with regard to fuel volatility and engine load

An HSDI Diesel engine was fuelled with standard Swedish environmental class 1 Diesel fuel (MK1), Soy methyl ester (B100) and n-heptane (PRF0) to study the effects of both operating conditions and fuel properties on engine performance, resulting emissions and spray characteristics. All experiments were based on single injection diesel combustion. A load sweep was carried out between 2 and 10 bar IMEP_g. For B100, a loss in combustion efficiency as well as ITE was observed at low load conditions. Observed differences in exhaust emissions were related to differences in mixing properties and spray characteristics. For B100, the emission results differed strongest at low load conditions but converged to MK1-like results with increasing load and increasing intake pressures. For these cases, spray geometry calculations indicated a longer spray tip penetration length. For low-density fuels (PRF0) the spray spreading angle was higher. It was concluded that both, the spray geometry and the slightly longer injection event influence fuel air mixture generation disadvantageous at low load conditions. An intake pressure variation showed that ignition delay (ID) shortened considerably for all fuel types. For B100, HC emissions as well as ITE improved with higher intake pressures. This behaviour was explained by improved spray characteristics and ambient gas conditions during the injection event.