Investigations on a Spark Ignition Engine, Part II: Impact of Hydrogen Addition and Compression Ratio on a Biogas-Fuelled Engine

Abstract

Performance, emissions and combustion were studied using a spark ignition engine modified from a single-cylinder diesel engine with varying compression ratios and hydrogen addition. When the compression ratio increases, there is a slight increase in brake power and thermal efficiency. There is a small increase in brake power and brake thermal efficiency when the compression ratio is above 13:1. Increased emissions of nitric oxide, hydrocarbon, and carbon monoxide were observed at compression ratios above 13:1. Leaner mixtures, brake power and brake thermal efficiency are lowered. Spark timing is retarded as the compression ratio rises which results in high peak pressure and rate of heat release. At a compression ratio of 13:1, a small amount of hydrogen (15% on an energy basis) was added along with biogas. The lean limit of biogas combustion and the combustion rate are greatly increased by the addition of hydrogen. In addition, there was a rise in brake power and thermal efficiency. The levels of hydrocarbons were significantly reduced. Nitric oxide emissions did not rise as a result of the use of the retarded ignition timing. The effect of two throttle conditions on spark ignition engines using biogas as fuel is presented as Part I of this study.