A computational study of the effect of fuel type on ignition time in homogeneous charge compression ignition engines

The homogeneous charge, compression ignition (HCCI) engine has advantages in terms of efficiency and reduced emissions in comparison to conventional internal combustion engines. One of the distinguishing characteristics of;in HCCI engine is that the ignition is controlled by the chemical kinetics, unlike the diesel or spark ignition engines, for which ignition time can be controlled externally by the fuel injection or spark time. As a consequence of being controlled by chemical kinetics, the HCCI ignition time call van significantly with changes in the operating conditions, and this variation can limit the practical range of operation of the engine Using a single-zone combustion model and established reaction rate mechanisms, the influences of the compression ratio, intake temperature. equivalence ratio, engine speed, and exhaust gas recirculation oil the ignition time of two Fuels, normal heptane and iso-octane, were studied. The model simulated the environment ill the engine combustion chamber by assuming adiabatic compression and expansion. The sensitivity of the ignition time to changes ill operating conditions was found to he dependent on the type of fuel. The results indicate that the use of fuels with a characteristic two-stage ignition (e.g., n-heptane) exacerbates the problem of ignition control compared with the use of fuels with a single-stage ignition(e.g., iso-octane).