Abstract
HCCI operating range can be expanded by using two fuels with different ignition characteristics. In this study, the effect of oxidation characteristics of main fuel on the operating range was investigated. Toluene and methane were used as main fuel, and DME as ignition trigger fuel. Engine experiments using a single cylinder research engine showed that methane/DME HCCI operating range extended to higher equivalence ratio compared with toluene/DME HCCI. This is explained by numerical analysis based on elementary chemical reaction model that steep heat release rate can be controlled when higher ignition temperature fuel is used, because time lag between the first stage of high temperature oxidation induced by decomposition of hydrogen peroxide (H2O2) and onset of chain-branching reaction of main fuel increases. It was also found that the higher the reactivity with OH, the more the trigger fuel requirement, because low temperature oxidation of the trigger fuel was suppressed.
