喷油策略对自由活塞直线发动机燃烧过程的影响

研究不同喷油策略对自由活塞发动机燃烧排放性能的影响,探索了适合自由活塞发动机柴油燃烧系统的喷油策略。基于AVL FIRE仿真平台,搭建三维动网格计算模型,通过台架试验数据,对试验喷油策略为矩形的缸压数据进行标定,验证了模型的准确性。然后对4种不同曲线形状喷油策略(普通三角形、等腰三角形、矩形和梯形)下的发动机燃烧放热及排放性能进行了仿真计算。研究结果表明:压缩上止点前采用矩形喷油策略缸内油气混合速率最快,压缩上止点后采用等腰三角形喷油策略更有利于油气混合;等腰三角形喷油策略下发动机峰值燃烧压力最大,最接近上止点,而且指示热效率最大,达到0.371;等腰三角形喷油策略下,缸内峰值燃烧压力和温度最大,NO排放最高而碳烟排放最低。

Effect of Fuel Injection Strategy on Combustion Process of a Free-Piston Linear Engine

The effect of different fuel injection strategies on the combustion and emissions of a free-piston linear engine was researched, and diesel fuel injection patterns suitable for the engine were explored. A three dimensional moving mesh model was established based on the AVL FIRE platform, and the accuracy of the simulation model was validated by the experimental in-cylinder pressure under a rectangle-shaped injection strategy. The engine combustion and emissions under four different injection strategies(normal triangle-shaped, isosceles triangle-shaped, rectangle-shaped and trapezoid-shaped) were simulated. The results indicated that the mixing rate in cylinder was the greatest when adopting the rectangle-shaped injection strategy before the top dead center(TDC), and the mixture homogeneity was better when employing the isosceles triangle-shaped injection strategy after TDC. The peak pressure in cylinder was the greatest and nearest to TDC when adopting the isosceles triangle-shaped injection strategy, with which the indicated thermal efficiency was the highest, reaching 0.371. Besides, the NO mass fraction under the isosceles triangle-shaped injection strategy was the largest while the soot emission was the least among the four injection strategies.