This study attempts to modify a 4-cylinder gasoline engine to run with a purified compressed biogas as substitute for fossil fuels. Water scrubbing method was used as the easiest purification technique to remove CO_2 and iron filing for H_2S. The pressurized raw biogas was fed in a low cost made portable floating type gas holder with volume capacity of 0.74 m3. The purified biogas was compressed using a reciprocating compressor through a two stage series of enrichment and moisture removal process using activated alumina into the steel cylinder to improve the quality of the methane content. The enriched biogas was filled in the LPG tank for 20 minutes at 10 bars at an average of 73.67% CH_4 with no traces of H_2S as storage for engine utilization. The modification involved the installation and mounting of LPG conversion kit. A comparative analysis of the performance and combustion characteristics of the engine was evaluated separately with gasoline and purified compressed biogas using electro-dynamometer as variable loads. The findings show that power output deterioration in compressed biogas was mainly due to high percentage of CO_2 and other gases impurities. It also shows that because of the calorific value of biogas, the thermal efficiency is lesser than that of gasoline. It implies that the overall engine performance can be improved by removing undesirable gases in the mixture.
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