Effects of intake valve angle on combustion characteristic in an SI engine

In this study, 2 different valve-angle engines, one is wide and the other is narrow, were prepared for investigating the effects of the angle on the combustion. For this purpose, the part load performances were evaluated and the pressures were measured for combustion analysis at an engine bench under 5 different operating conditions, varying the compression ratio. The results show that the combustion proceeds so faster in the small IVA engine that its MBT timings are retarded considerably compared with that of large one and result in lower NOx emission level; however, unburned HC is higher because of its geometrical feature. In addition, there is no substantial difference between 2 IVA engines in the timings of combustion initiation and completion as a crank-angle-position-base in spite of the considerable difference of spark timing, on the other hands, the ignition delay of the small IVA is shorter than that of large one. Also the phenomena that the flame propagation is faster and the instant heat release rate is more concentrated and higher in the small were observed. Also, the burn duration of small one is shorter and the combustion process is more accelerated up to the mid-combustion stage; however, the process of large one is faster as the combustion approaches the last stage and the differences of combustion duration reduce as the compression ratio increases. Finally, the engine runs more stable when the IVA is small without any exception because of its rapid burn at the initial combustion stage.