Effects of valve motion characteristics on performance in spark ignition engine

In this study, it was aimed to examine the effects of valve motion characteristics on performance in spark ignition engines. The effects of valve timing, valve lift, and valve duration variables as valve motion characteristics on the full load characteristic performance of the engine were modeled and examined. For modeling, the use of the WAVE simulation program, one of the 1-dimensional gas dynamics simulation tools, was preferred. Taguchi's experimental design method was applied for the simulation design of variables. Analysis of variance was performed for the relationship between engine performance and valve motion characteristics. Then, regression analysis was performed and linear regression equations were obtained for the relationship between engine performance and valve motion characteristics. A total of 125 simulation solutions were made, 25 solutions for each engine speed. Brake torque, brake thermal efficiency, and volumetric efficiency were preferred as engine performance parameters. By variance analysis, the optimum valve motion characteristic in which these three engine performance parameters can be simultaneously high was determined. As a result of the variance analysis, it was determined that the most effective parameters on engine performance were valve overlap and intake valve open time. However, it has been observed that increasing the valve overlap and reducing the intake valve duration improves the engine performance when compared to the performance of the reference engine in its original configuration. Engine performance comparison was made for the optimum values and the original values of the reference engine. Better performance was achieved with the original values of the reference engine at high engine speed. However, a significant engine performance improvement was seen at low and medium engine speeds. For low and medium speeds, the improvement in brake power and brake torque was determined as 8.1%, the improvement in brake thermal efficiency as 1.5%, and the improvement in volumetric efficiency as 6.8%.