In the present investigation, experiments were conducted in a 4.4 kW, single cylinder, water cooled, constant speed, spark ignition (SI) engine fuelled with raw biogas. The engine was operated at four different compression ratios (10.52, 11.94, 13.96 and 15.29) and within a load range of 6 to 77%. The effect of load level on the performance and emission characteristic of the engine at different compression ratios are analysed and presented in this paper. The brake power producing capability of the engine corresponds to CR 15.29 was maximum and found to be 2.93 kW with 76.27% of brake load. With increasing CR the engine becomes more stable and operates with an appreciable deviation in speed. Irrespective of engine loading condition, the minimum HC and CO emissions were noticed at CR 15.29 and found to very between 23-144 ppm and 0.016-0.091 %, respectively. The maximum NOx emission was detected at CR 15.29 and was found to very between 27-240 ppm.
The present experimental investigations deal with the spark plug location and its effect on the performance and emission of a 100% raw biogas-fueled variable compression ratio engine. Different measurements of performance, combustion, and emission parameters are used to analyze the effect of four spark locations protruded inside the clearance volume (viz. 0, 2, 5, and 10 mm). The protrusion of the spark plug by 2 mm is observed to be optimum for compression ratios 8, 9, and 10. For this optimum spark plug location, engine efficiency and fuel economy are found to be higher. Faster combustion, in this particular case, has led to early and higher peak cylinder pressure and burnt gas temperature. Lower emissions of hydrocarbons and carbon monoxide have verified the optimality of 2 mm protrusion location of the spark plug for all the compression ratios. Thus, present investigations recommend minor protrusion of the spark plug to assist the combustion process, to enhance the performance and lowering the emission of a biogas-fueled engine.
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