A DNS study of CH2O and H2O2 effect on the ignition of lean PRF/air mixtures under HCCI conditions

Abstract

The impacts of dual additives including formaldehyde (CH2O) and hydrogen peroxide (H2O2) for the control of ignition of primary reference fuel (PRF)/air mixture in homogeneous charge compression ignition (HCCI) engine conditions have been investigated numerically. It is found that CH2O addition causes ignition retardation, which may result in a misfire. The chemical effect of CH2O is to eliminate OH radicals and hence increases the main ignition delay. On the other hand, the addition of H2O2 decomposes H2O2 into two OH radicals, which promotes the main ignition. It is also found that the overall combustion mode is determined by two different additives with different ignition delay characteristics. For CH2O and dual additive cases, a mixed combustion mode of both spontaneous ignition and deflagration occurs. However, the spontaneous ignition occurs dominantly in H2O2 and no additive cases with short combustion duration. These results suggest that addition of CH2O provides smooth operation of HCCI engines and besides, dual additive injection can precisely control the ignition timing for HCCI combustion.