The Potential for Reducing CO and NOx Emissions from an HCCI Engine Using H2O2 Addition

The effects of hydrogen peroxide addition on iso-octane/air Homogeneous Charge Compression Ignition (HCCI) combustion have been investigated analytically. Particular attention was focused on the predications involving homogeneous gas-phase kinetics. Use was made of Peters' iso-octane mechanism in CHEMKIN and convective heat transfer was included in the analyses. This enabled the influences that H₂O₂ addition has on species concentration and ignition promotion and hence exhaust emissions to be determined. It was found that both CO and NO_x emission levels could be ameliorated. The former effect is considered to be a result of the decomposition of H₂O₂ into OH intermediate species and hence reducing the time to ignition and the onset of combustion. With regards to the potential for reducing NO_x, it was found that addition of H₂O₂ could lead to a reduction in the inlet air temperature required for the fuel/air mixture to attain auto-ignition at/near top dead centre, thereby, depressing the average cycle temperature and increasing the cycle time spent below the normal threshold temperatures required for NO_x formation.