The objective of the present research is to investigate the effects on diesel engine combustion and NOx and PM emission characteristics in case of blending the ordinary diesel fuel with biodiesel in passenger car diesel engines. Firstly, we conducted experiments to identify the combustion and emissions characteristics in a modern diesel engine complying with the EURO 4 emission standard. Then, we developed a numerical simulation model to explain and generalize biodiesel combustion phenomena in detail and generalize emission characteristics. The experimental and simulation results are useful to reduce biodiesel emissions by controlling engine operating and design parameters in the diesel engine.
Engine tests were conducted and a mathematical model created to investigate the effects of 40% and 100% methyl oleate modeled fuel representing Jatropha-derived biodiesel on diesel combustion and emission characteristics, over a wide range of passenger car DI diesel engine operating conditions.
The thermal efficiency and emissions of these fuels were compared to real Jatropha-derived biodiesel. The engine used in this study complies with the EURO4 emission regulation, having a displacement of 2.2 L for passenger car applications.
In the engine tests, seven steady-state engine operating conditions typically encountered in the NEDC and US06 modes were chosen. Emissions measurements and heat release analyses showed that biodiesel can significantly reduce PM (particulate matter) without influencing heat release rate, NOx emission and brake thermal efficiency under the tested conditions. Detailed analyses were made of particle size distributions and chemical components including the soluble organic fraction. For comparison with experimental results, we developed a zero-dimensional reaction model with detailed chemical kinetics to identify the effects on engine combustion, performance and emissions. The results show that 100% methyl oleate tends to emit soot at a higher temperature region while the blended fuel emits soot at lower temperatures much closer to those at the region where the ordinary diesel fuel emits soot. However, NOx emission did not vary significantly between diesel fuel and biodiesel. The ignition delay of methyl oleate is shorter than that of diesel and tends to be shorter as the injection pressure increases.
Based on the experimental and simulation results, the engine operating and design parameters of the diesel engine fueled with biofuel can be optimized to ensure thermal efficiency along with sufficiently reducing emissions.