Effects of Rail Pressure on the Combustion and Vibro-Acoustic Characteristics of a Diesel Engine Running on Biodiesel

This study investigated the combustion, sound and vibration characteristics of petroleum-based diesel fuel (PBDF) and waste cooking oil methyl ester (WCOME) at different rail pressures and engine loads. In the engine tests, engine vibration levels varied significantly with fuel type, rail pressure and engine load, with PBDF producing higher vibration levels at lower rail pressures and WCOME tending to produce lower vibration levels at higher rail pressures. In the 4-5 kHz frequency band defined as the premixed combustion phase, the cylinder sound pressure level was 99.4 dB for WCOME and 105.2 dB for PBDF at 950 bar. The increase in rail pressure results in an increase in engine vibration, so the lowest vibration amplitude is at 40 Nm and 750 bar, while the lowest total engine noise is 86 dBA for WCOME and 90.6 dBA for PBDF. An increase in THC and CO emissions was observed with the use of WCOME compared to PBDF, while CO2 and NOx emissions decreased. It was observed that as the rail pressure increased, CO2 and NOx emissions increased approximately twofold, but CO and THC emissions decreased approximately 25% and 45% respectively. Analysis of variation (ANOVA) and regression analysis were used to analyze the effect of engine input parameters on output parameters. The influence of the factors on the response is confirmed by larger F-values and is considered statistically significant at 95% confidence level when p < 0.05. It is statistically observed that engine load and rail pressures have a significant effect on the engine response parameters of THC, CO, CO2, NOx and noise.