Rajesh Kumar Pandey, Shankar Kumar, Y. C. Sharma, Rajiv Varshney, Ashok Yadav
Retrofitting existing internal combustion engine vehicles to operate on cleaner fuels offers a practical pathway toward reducing urban emissions during the transition to sustainable mobility. This study experimentally investigates the feasibility of converting a 796 cc Maruti Alto multi-point fuel injection (MPFI) spark-ignition engine to operate exclusively on compressed natural gas (CNG) without petrol as a pilot fuel. The influence of iridium spark plug electrode gaps (0.5, 0.6, and 0.8 mm) on ignition stability, engine performance, and exhaust emissions was evaluated using a computerized test bench equipped with an eddy current dynamometer. Experimental results indicate that the 0.6 mm electrode gap provides the most stable combustion and minimum misfire tendency under lean CNG operation. Compared with conventional petrol operation, carbon monoxide (CO) and hydrocarbon (HC) emissions decreased by approximately 42% and 38%, respectively, while brake power declined by about 4-5% due to the lower energy density of gaseous fuel. ANOVA analysis confirmed the statistical significance of these variations (p < 0.05). The results demonstrate that optimized ignition parameters enable stable CNG-only operation in compact MPFI engines, supporting engine retrofitting as a cost-effective strategy for cleaner urban transportation.