A Computational Study on the Effects of EGR and Boost Pressure of a HCCI Engine Fueled with Natural Gas

This study was computationally investigated the effects of EGR and boost pressure to confirm the mechanisms for extending operation range and reducing NOx emission of a HCCI engine fueled with natural gas. The CHEMKIN-PRO was used to perform the numerical analysis. To set boundary of operating range, boost pressure was varied from 0.1MPa to 0.2MPa and EGR was varied from 10% to 50%. In the result, HCCI fueled with natural gas was found single stage heat release which was composed with the thermal-ignition preparation and thermal ignition. These two stages were determined mainly by H₂O₂ loop reactions, H2-O2 system reactions respectively. Also, mole fractions of H₂O₂, CH₂O and OH were considered to effect on those stages. The H₂O₂ loop reactions begin to active when the OH formation by the H₂O₂ +M → 2OH + M become at about 950K. The H₂-O₂ system reactions were begun when the transient temperature reaches over than 1200K in this study. As the increase of amount of EGR, number of important reactions and transient temperature of the contribution matrix were degreased. When we use intake pressure, number of important reactions and transient temperatures of the contribution matrix were increased. Finally, NOx emission was lower due to in-cylinder temperature lower.