An Experimental and Numerical Investigation of Spark Ignition Engine Operation on $H2$⁠, CO, $CH4$⁠, and Their Mixtures

The knock and combustion characteristics of CO, $H2$⁠, $CH4$⁠, and their mixtures were determined experimentally in a variable compression ratio spark ignition (SI) cooperative fuel research (CFR) engine. The significant effects of gaseous fuel mixtures containing $H2$ in enhancing the combustion and oxidation process of $CH4$ were examined. The unique combustion characteristics of CO in dry air and its distinct performance in mixtures with H-containing fuels were investigated. The addition of a simulated synthesis gas $(2H2+CO)$ to $CH4$ was found to enhance the combustion process of the resulting mixture and lowers its knock resistance. The effectiveness of such an addition is slightly weaker than that of a comparable $H2$ addition but much stronger than that with CO addition only. A predictive model with detailed kinetic chemistry was used successfully to simulate SI engine operation fuelled with $CH4$⁠, $H2$⁠, CO, and their mixtures. The predicted engine performance and knock limits of $CH4$⁠, $H2$⁠, CO, and their mixtures agree well with experimental data with the exception around pure CO operation in dry air with the presence of small amounts of $CH4$ or $H2$⁠. A remedial approach to improve the prediction of the knock limits of fuel mixtures containing mainly CO with a small amount of H-containing fuels such as $H2$ and $CH4$ was proposed and discussed.