Study On The Combustion And Particulate Matter Formation Of Biodiesel Engine Affected By EGR

Air pollution is harmful to human health. NO_x and Particulate matter?PM? emitted from diesel engine is one of the main causes of air pollution. Biodiesel has oxygen content and no sulfur, which can reduce PM emission but leads to higher NO_x emission possibly. Exhaust gas recirculation?EGR? is an effective technology to reduce NO_x, and has been widely applied to light vehicle. Howerer, EGR has an influence on PM emission. The formation mechanism of particle precursor, combustion process in cylinder, particle size, morphology, graphite structure and oxidation reactivity were investigated in present research when diesel engine used EGR was fuelled with biodiesel. The effects of EGR on formation path and production of biodiesel particle precursor, particle size, morphology, graphite structure and oxidation reactivity were ascertained. The main research work and conclusions are demostrated as follows:Numerical simulation method was used to investigate the formation path and production of biodiesel particle precursor. CHEMKIN software was used to establish and verify biodiesel mechanism including formation of polycyclic aromatic hydrocarbons. Closed homogeneous model was used to investigate the effect of EGR on formation path of biodiesel particle precursor. The productions of benzene, naphthalene, phenanthrene, pyrene, C₂H₂ and C₃H₃ were analysed. The results show that bezene forms through C₃H₃+C₃H₃=>C6H6. With the rate of EGR increasing, the maximum rates of reactions to generate or consume benzene, naphthalene, phenanthrene, pyrene increase. The times at maximum reactions rates delay. The maximum productions of enzene, naphthalene, phenanthrene and pyrene increase. The times at maximum production rate of these matters delay. The maximum productions of C₃H₃ increase by 6.1% and 15.5% respectively.Cylinder pressure sensor and combustion analyzer were used to measure cylinder pressure curves at different rates of EGR on an 186 F diesel engine fuelled with biodiesel and diesel. Cylinder pressure, ignition delay and rate of heat release were analysed. CO, HC, NO_x and smoke intensity were measured at different rates of EGR. The effects of EGR on emissions were investigated. The results show that the maximum cylinder pressure of biodiesel is higher compared with diesel under low load. The maximum cylinder pressures are basically the same for biodiesel and diesel under high load. With the increase of EGR rate, the maximum cylinder pressures for biodiesel and diesel decrease and the times at maximum cylinder pressures delay. In addition, ignition delays for biodiesel and diesel increase. When the rate of EGR increases, the maximum heat release rates decrease under low load. For instance, the maximum heat release rates of biodiesel decrease by 3.5% and 8.1% respectively for 15% and 30% EGR. The maximum heat release rates increase at the beginning and then decrease under high load. With the increase of EGR rate, he times at maximum heat release rates delay.A micro-orifice uniform deposition impactor was used to measure biodiesel and diesel particle sizes at diffenent EGR rate. Particle sizes and modes were analysed. High resolution transmission electron microscopy was used to take picture of particle morphology at different EGR rates. A laser Raman spectrometer was used to measure Raman spectras for biodiesel and diesel particles at different rates of EGR. Five-band fitting curves were adopted to fit Rama spectras. The effects of EGR on the graphite structure parameters were invesitigated. Thermogravimetric analyzer was used to TG/DTG curves for biodiesel and diesel particles at different rates of EGR. The effects of EGR on particle composition, ignition temperature, the maximum weight loss rate, burnout temperature and activation energy were investigated. It can be observed that when the rate of EGR increases, the particle sizes are in the direction of larger size. The proporation of accumulation modal particles decreases. The proporation of coarse modal particles increases. Particles agglomeration degree increases. In addition, Particles chemical heterogeneity strengthens. Particles graphitization degree increases. Soluable organic fraction in particles increases. Ignition temperature, the maximum weight loss tempeture, burnout temperature and activation energy decrease, which indicates higher oxidation reactivity.