Optimization of simultaneous reduction of NO and soot by using simulated-exhaust gas recirculation (CO_2 + N_2) in compression ignition engine under early combustion conditions

摘要

The objective of this study is to investigate the effect of CO_2 mole fraction by simulated-exhaust gas recirculation (EGR) on the simultaneous reduction of exhaust emission in Cl engine, and to find the optimal operating conditions. For the better expression of the actual EGR, the different CO_2 mole fractions from 0% to 20% were applied for the simulated-EGR. The CO_2 mole fraction by simulated-EGR was changed in the initial air in steps of 5% from 0% to 20% in the cylinder. The N_2 mole fraction in the initial air was also changed according to the CO_2 mole fraction, and the O_2 mole fraction was fixed by 16.2% due to the same overall equivalence ratio. When the CO_2 mole fraction by simulated-EGR increased by 5%, the peak cylinder pressure was decreased by about -1.5% and the indicated specific nitrogen oxide value was also reduced from -4.9% to -48.8% because the ignition delay was longer by the higher specific heat of CO_2 than N_2, it induced to suppress the rise of cylinder temperature. In addition, when the start of energizing timing was advanced until BTDC 23 deg, the ISSoot value was decreased because the proportion of premixed combustion was increased.