The Effects of Fuel Injection Pressure and Fuel Type on the Combustion Characteristics of a Diesel Engine

In an effort to understand the effects of injection system pressure on alternative fuel performance, a single cylinder diesel engine was outfit with a modern common rail fuel injection system and piezoelectric injector. As future new fuels will likely be used in both older mechanical injected engines as well as newer high pressure common rail engines, the question as to the sensitivity of a new fuel type across a range of engines is of concern. In this study conventional diesel fuel (Navy NATO F76) was compared with the new Navy HRD (Hydro-processed Renewable Diesel) fuel from algal sources, as well as the high cetane reference fuel nC16 (n-hexadecane CN=100). It was seen that in general, IGD (Ignition Delay) was shortened for all fuels with increasing fuel injection pressure, and was shortened with higher CN fuels. The combustion duration for all fuels was also significantly reduced with increasing fuel injection pressure, however, longer durations were seen for higher CN fuels at the same fuel pressure due to less pre-mixing before the start of combustion. Companion modeling using the LLNL (Lawrence Livermore National Lab) heavy hydro-carbon and diesel PRF chemical kinetic mechanisms for HRD and nC16 was applied to understand the relative importance of the physical and chemical delay periods of the IGD. It was seen that at low fuel injection pressures, the physical and chemical delay times are of comparable duration. However, as injection pressure increases the importance of the chemical delay times increases significantly (longer), especially with the lower CN fuel.