甲醇-汽油复合喷射发动机燃烧排放性能研究

Combustion and Emission Performance of Methanol-Gasoline Dual-Injection Engine

为了研究不同比例甲醇和汽油混合燃料对发动机燃烧排放性能的影响,对1台1.4 L缸内直喷发动机加装了进气道喷射系统,改造为甲醇进气道喷射(MPI)+汽油缸内直喷(GDI)发动机,运用CFD技术建立该发动机模型,对不同甲醇热值替代比下的缸内混合气形成、燃烧和排放特性进行了研究。研究结果表明:在混合气形成方面,随着甲醇替代比的提高,缸内温度逐渐下降(但在点火时刻缸内温度下降趋势减缓),未蒸发燃料质量迅速增加。在缸内燃烧方面,提高甲醇替代比能够有效地加速缸内燃烧过程,提高缸内峰值缸压和峰值放热率,缩短滞燃期和燃烧持续期,使燃烧重心提前,但较高甲醇替代比下加速燃烧过程趋势减缓。在排放物生成方面,随着甲醇替代比的提高,NO x排放逐渐增加,CO总排放量降低,但峰值CO量却呈现先增后减趋势,THC排放逐渐增加,其中大部分为未燃甲醇。

In order to study the influence of methanol and gasoline blended fuel with different mixing ratios on the combustion and emission performance of gasoline engine,a 1.4 L direct injection engine that was equipped with intake port injection system was retrofitted to an engine with methanol inlet injection(MPI)and gasoline direct injection(GDI).The engine model was established by using CFD technology and the in-cylinder mixture formation,combustion and emission performance were further studied under different methanol substitution ratios.The results show that the in-cylinder temperature gradually decreases with the increase of methanol substitution ratio,but decreases slowly at the ignition timing and the mass of non-evaporated fuel increases rapidly for the mixture formation.As for the in-cylinder combustion,the increase of methanol substitution ratio can effectively accelerate the in-cylinder combustion process,improve the peak cylinder pressure and peak heat release rate,shorten the ignition delay period and combustion duration,and advance the barycenter of combustion process,but the trend of accelerating combustion process slows down under a high methanol substitution ratio.In addition,NO x emission gradually increases and total CO emission reduces,but the peak CO emission first increases and then decreases,and THC emission that is mainly composed of unburned methanol gradually increases with the increase of methanol substitution ratio.