چكيده به لاتين
This dissertation examined experimentally and numerically different diesel fuel injection strategies, natural gas replacement percentage, the effect of exhaust gas recirculation and cyclic changes on the combustion and pollution of RCCI engines with Diesel-CNG fuel. In this regard, we proceeded in three main steps: In the first stage, the RCCI combustion strategy was implemented on a diesel internal combustion engine, for this purpose, the air-natural gas mixing system was added to the cylinder inlet port. In the second stage of this research, different percentages of diesel fuel and natural gas were tested, and in this case, the characteristics of fuel injection into the combustion chamber including the crank angle of one or multi-injection, injection pressure and injection rate in the first or second stage were tested to determine the stable operating point. Also, the use of biodiesel fuel to replace diesel fuel was experimentally tested. In the third stage, computational fluid dynamics modeling was performed to further investigate the various strategies of diesel fuel injection into the combustion chamber on the performance characteristics and pollution of RCCI combustion with diesel-natural gas fuel using Converg software and the results were validated with experimental results. The results show that with increasing diesel fuel injection pressure, combustion starts earlier and the maximum incylinder pressure increases and also NOx pollutants increase and UHC and CO decrease. On the other hand, the results of two-stage injection of diesel fuel show that by delaying the start angle of the first injection, the maximum incylinder pressure, HRR and IMEP increase and NOx emission increases and UHC and CO decrease and conversely, these results are obtained by delaying the starting of second injection angle. As the amount of exhaust gas recirculation rate increases, the amount of IMEP and the thermal efficiency decrease. Also, the beginning, middle and end of combustion are delayed due to the decrease of oxygen inside the combustion chamber and CO and UHC production increases and vice versa NOx decreases. In addition, increasing the premix ratio reduces the thermal efficiency but increases the UHC emission due to over premixed rich charge.
