进气道和燃烧室形状对大缸径天然气发动机缸内流动和燃烧的影响

为了提升采用当量燃烧的大缸径天然气发动机的指示热效率,提出了组织弱涡流、强滚流、高湍流强度的缸内气流运动的理念,据此设计了不同形状的进气道和燃烧室,并采用三维数值模拟的方法研究了进气道和燃烧室形状对缸内流动和燃烧的影响.研究发现:与原机相比,当将原螺旋进气道改为直进气道并配合原缩口型、新的直口型、敞口型和半球型燃烧室时...

Influence of Intake Port and Combustion Chamber Shapes on In-Cylinder Flow and Combustion of Large-Bore Natural Gas Engines

In order to improve the indicated thermal efficiency of a large bore natural gas engine with stoichiometric operation, a concept of organizing an in-cylinder air motion with weaker swirl, stronger tumble and higher turbulence intensity was proposed. According to this concept, different shapes of intake ports and combustion chambers were designed. Then, the effects of the shape of the intake port and combustion chamber on the in-cylinder flow and combustion were studied using three-dimensional numerical simulation. In comparison with the original engine, when changing the original helical intake port to a straight intake port and adopting the original reentrant combustion chamber and a new vertical-cave, open-cave, and hemispherical-cave combustion chamber in turn, the in-cylinder swirl flow was significantly weakened, and the tumble flow was obviously enhanced. Especially, the maximum tumble flow ratio during the compression stroke could reach 0.76, 0.83, 1.03 and 1.71, respectively, and the in-cylinder average turbulent kinetic energy at the ignition timing was increased by 35.27%, 36.26%, 50.33%, and 135.99%, respectively, further accelerating the combustion rate and increasing the indicated thermal efficiency. Therefore, the match of the hemispherical-cave combustion chamber with the straight intake port was more beneficial to the formation of a stronger in-cylinder tumble flow and the improvement of turbulence intensity at the ignition timing. Finally, the indicated thermal efficiency was increased from 39.51% of the original engine to 42.14%.