充量分层对双燃料高预混压燃燃烧过程影响的数值模拟

Numerical Simulation of the Effect of Charge Stratification on the Combustion Process of Dual-Fuel Highly Premixed Charge Combustion

针对高预混压燃模式大负荷面临高压力升高率与碳烟排放等问题,利用CONVERGE建立汽/柴油、汽油/聚甲氧基二甲醚(PODEn)双燃料燃烧仿真模型,通过燃料特性与喷油策略优化,研究浓度、活性等分层方式对放热规律与性能的影响.结果表明,挥发性改善能促进燃油破碎与蒸发,促进燃烧过程与提高热效率;计算着火延迟能很好地预测燃烧进程,通过降低燃油活性或能量喷射速率改变活性与着火能量分层,均能使低着火延迟区域变少,引燃能力下降,推迟燃烧并降低压力升高率.相较于PRF50(primary reference fuel),柴油掺混虚拟组分组合滞燃期短,后期集中燃烧放热量低,放热规律更有利于降低压力升高率,相较于基础算例压力升高率下降0.1 MPa/°CA而热效率提升0.15%.PODE掺混汽油组合推迟燃烧过程最显著,压力升高率由基准的1.54 MPa/°CA降至1.02 MPa/°CA,允许喷射时刻最为靠前,对应碳烟排放降低78%.

Aiming at the high pressure rise rate and soot emission of highly premixed charge combustion under high load conditions,the optimization of fuel characteristics and fuel injection strategy is studied based on the gasoline/diesel and gasoline/PODEn dual fuel numerical model with CONVERGE.The results show that the improvement of volatilization can promote fuel fragmentation and evaporation,improve combustion and increase thermal efficiency.Reducing fuel reactivity or energy injection rate can reduce the size of low ignition delay zone,delay combustion and reduce max pressure rise rate(MPRR).Compared with PRF50,the combination of diesel and fictitious components has shorter ignition delay time and lower centralized heat release at the later stage,and the heat release pattern is more conducive to reducing the MPRR.Compared with the baseline,the MPRR decreased by 0.1MPa/°CA and the thermal efficiency increased by 0.15%.PODE blended gasoline has the most significant delay in combustion process,reducing the MPRR from the baseline of 1.54 MPa/°CA to 1.02 MPa/°CA and allowing the most advanced injection moment,corresponding to a 78%reduction in soot emissions.