正丁醇/柴油发动机燃烧排放特性及喷油、燃烧室形状影响

针对某型号直喷柴油机,建立了该柴油机中单缸完整燃烧室及气道三维模型,使用三维计算流体力学(computational fluid dynamics,CFD)分析软件CONVERGE对其进行模拟计算,研究了正丁醇掺混比例对柴油机燃烧排放的影响。结果表明:随着正丁醇掺混比例的提高,峰值缸压、滞燃期和燃烧速度均呈递增趋势,碳烟及CO排放量逐渐减少,NO_x排放量小幅增加。为了进一步改善缸内燃烧情况和降低污染物排放,对正丁醇掺混时喷油策略、燃烧室几何形状的综合影响进行了研究,结果表明:掺混时多次喷油及采用合适的燃烧室模型可以有效改善掺混后缸内油气混合情况,增加缸内湍动能强度,进一步降低碳烟排放量。与纯柴油工况对比,掺混并采用多次喷油策略后碳烟排放明显下降,且通过掺混能够有效简化喷油策略,但弱化了燃烧室形状对碳烟排放量的影响。

Combustion and Emissions Characteristics of N-Butanol/Diesel Engine and Impact of Injection Strategy and Combustion Chamber Geometry

For a certain type of direct injection diesel engine, a three-dimensional model of a single-cylinder complete combustion chamber and intake/exhaust port was established. Three-dimensional Computational Fluid Dynamics (CFD) analysis software CONVERGE was used for simulation calculation. The effect of n-butanol blending ratio on combustion and emissions of diesel engine was studied. The results show that with the increasing of the n-butanol blending ratio, the peak cylinder pressure, ignition delay period and burning rate are all increasing, soot and carbon monoxide emissions are gradually reduced, and the nitrogen oxides emissions are slightly increased. In order to further improve the combustion situation and reduce pollutant emissions, the combined effects of fuel injection strategy and combustion chamber geometry to diesel engine fueled with the butanol/diesel blend were studied. The results show that the multiple injections and a suitable combustion chamber geometry of diesel engine fueled with the butanol/diesel blend can effectively improve the mixing of oil and gas in the cylinder, increase the intensity of turbulent kinetic energy in the cylinder, and further reduce the emission of soot. Compared with pure diesel operating conditions, the use of multiple injections after blending reduce the soot emissions more significantly, and blending can effectively simplify the fuel injection strategy, but blending reduces the effect of combustion chamber geometry on soot emission.