Abstract
The control of ignition timing and combustion period over a wide range of engine speeds and loads in HCCI engine is one of the barriers to the realization of the engine. Application of exhaust gas recirculation, EGR, is thought to be a promising option to control ignition timing, to extend combustion period and to suppress knock like combustion. In this study, the effects of N_2/CO_2, major components of exhaust gas, addition on the heat release of cool flame and the emission characteristics of CO were investigated from experiments and computations. The heat release of cool flame was reduced with N_2 addition, however, it increased with CO_2 addition. From the systematic experiments and chemical kinetic computations, it was confirmed that the amount of heat release at cool flame depends strongly on the concentration of O_2 at cool flame onset. The dominant path for CO oxidation is the reaction of CO + OH = CO_2 + H. The produced H atoms react with O_2 molecules and produce OH + O or HO_2. The CO oxidation becomes active as increasing the blanching rate to OH + O. However, with the addition of CO_2 to the mixture, the branching rate to HO_2 was increased, resulting in a higher CO emission. Though the addition of CO_2 is effective in suppressing a knocking from its large heat capacity, it has an inferior effect on CO emission.
