The impact of injection timing and pressure on a CRDI engine's combustion characteristics

Abstract

In this study, in which diesel (B0), pure biodiesel (B100) and diesel/biodiesel mixtures in four different ratios (B20, B40, B60, B80) are used as fuel, the effects of injection pressure and injection timing on a common rail direct injection (CRDI) engine were investigated. A single-cylinder CRDI engine with a volume of 1.12 litters was used for the engine tests. Combustion characteristics of the CRDI engine such as IMEP, combustion sound, cylinder gas pressure and heat release rate (HRR) were investigated with the experiments carried out at four different engine loads and at a constant engine speed of 1500 rpm. It was found that IMEP raised as the injection pressure increased. The highest increase was observed at 75% engine load and injection pressure of +200 bar. The IMEP values of B0, B20, B40, B60, B80 and B100 fuels were measured as 11.01, 10.13, 10.88, 10.34, 10.11 and 9.86 bar, respectively. The combustion noise values of B0, B20, B40, B60, B80 and B100 fuels at 75% engine load and at the original injection time were 93.73, 92.49, 91.63, 91.01, 92.82 and 92.27 dB. All fuels' combustion noise levels rose as a result of the shorter injection timing. A similar situation was observed when the injection pressure was reduced. The combustion noise generally decreased as injection timing and pressure were increased. Ignition delay values of B0, B20, B40, B60, B80 and B100 fuels at 50% engine load and STD injection timing were found to be 7.5, 6.5, 6, 5.5, 5 and 5.5 CA, respectively. However, increasing the injection timing decreased the ignition delay value for all fuels. Decreasing the injection pressure resulted in an increase of ignition delay for all fuels.