Experimental Investigations on Performance and Emission Characteristics of CNG in a Spark Ignition Engine

In this study, systematical experiments were carried out to analyze the performance and emission characteristics of CNG using a single cylinder, variable compression ratio, spark ignition engine. Studies were also carried out to evaluate optimum spark timing at different equivalence ratios for the maximum brake torque. Effects of compression ratio on fuel consumption and exhaust emissions were also studied.

Compressed natural gas showed 3-5% higher thermal efficiency and 15% lower fuel consumption as compared to gasoline. Also CO emissions were lower by 30-80% in rich zone and NOx emissions were lower by 12% at equivalence ratio of 1.0. At 50% throttle opening, MBT timings for natural gas were 4 to 6 degree more advanced depending on equivalence ratios as compared to gasoline. Increasing the compression ratio from 8 to 10 and 12 improved the thermal efficiency by 3 and 8 percent respectively. However, NOx emissions were increased by 15% and 40% respectively.