Effect of Exhaust Gas Recirculation on a Spark Ignition Engine Fueled with Biogas-Hydrogen Blends

Efforts have been made to apply biogas to an IC engine for power generation as a way to cope with the energy crisis as well as to reduce greenhouse gas. However, due to its gas component variations by origin and low energy density, using biogas in the engine applications and achieving a steady power generation is not an easy task. One way to overcome these deficiencies is to add hydrogen in biogas. Because of the excellent combustion characteristics of hydrogen, use of hydrogen-biogas blend fuel can allow not only accomplishing stable in-cylinder combustion, but also reducing the harmful emissions such as THC and CO. Despite several advantages of this approach, there exists a major drawback~a significant increase in NO_x emission caused by high adiabatic combustion temperature of hydrogen. Therefore, in this study, use of exhaust gas recirculation (EGR) gas was employed to resolve this issue and performance and emission characteristics of an 8-liter spark ignition engine with both simulated EGR and biogas with varying hydrogen content were examined. From the results, optimum and practical operating conditions, EGR rates, and hydrogen blending ratio to realize maximum efficiency and minimum emission were suggested, and an effect of EGR introduction on NO_x emissions reduction was assessed.