Experimental Investigation into the Influence of Compression Ratio on Operating Characteristics of Single Cylinder CNG Engine with Port Injection

This paper indicates the early experimental results of a Ricardo model CNG engine R&D activity in Vietnam, the experiments were mainly focused on the effects of compression ratio on operating parameters of the tested single cylinder CNG engine particularly designed and fabricated for varying compression ratio purpose. The compression ratio was set in the range of ε = 10 to 15 with the change step of Δε = 1. For each compression ratio, the engine speed were varried from 1000rpm to 2200rpm with the change step of Δn = 200. The early spark angle was also changed to find out the maximum break torque. The limitation of compression ratio and engine speed at each operating point was determined by vibration signal and abnormal sound. The experimental results indicated the early spark angle must be adjusted premature in case of compression ratio and/or engine speed enhenced. Especially, the portion of indispensable power to perform the compression stroke is smaller in comparison with the portion to execute the both strokes of intake and exhaust. In addition, the shape of combustion chamber affected strongly the operating characteristics also found in this study.