An experimental study on the fuel conversion efficiency and NOx emissions of a spark-ignition gas engine for power generation by fuel mixture of methane and model syngas (H2/CO)

This study investigated operating characteristics of spark-ignition gas engine for power generation upon mixing of CH4, the main component of natural gas, and model syngas made of H2 and CO for more efficient use of natural gas. As a result of mixing 5% of lower heating value for overall fuel mixture, the time at which in-cylinder pressure reaches maximum is advanced in CH4 + H2 + CO mixture compared to pure CH4. This phenomenon is related to flame propagation speed inside the cylinder. Mean increase of the maximum in-cylinder pressure was 7% for CH4 + H2 mixture, 4.9% for CH4 + H2 + CO mixture, and 2.2% for CH4 + CO mixture. This shows improvement of combustion phenomenon in the cylinder. Mean increase of the fuel conversion efficiency was 4.8% for CH4 + H2 mixture, 2.9% for CH4 + H2 + CO mixture, and 1.5% for CH4 + CO mixture. NOx emission was 9.0 g/kWh for CH4 + CO mixture, 6.0 g/kWh for CH4 + H2 mixture, and 5.1 g/kWh for CH4 + H2 + CO mixture. As the fuel conversion efficiency and NOx emissions have proportional relationship, their correlation must be taken into account when mixing syngas with natural gas. When the mixing ratio of model syngas was increased to 5%, 10% and 15%, combustion phenomenon was improved according to the mixing ratio. While the fuel conversion efficiency and NOx emissions also increased according to the mixing ratio of model syngas, the rate of increase was non-linear. Therefore, when using model syngas as an additive of natural gas, it is necessary to consider optimal operating conditions in gas engine for power generation according to the mixing ratio.