The effects of DTBP on the oxidation of SI primary reference fuels: A study in an HCCI engine and in a pressurized flow reactor

A promising new engine operating mode, Homogeneous Charge Compression Ignition (HCCI), does not use traditional Spark Ignition (SI) or Compression Ignition (CI) -combustion control systems. Instead it relies completely on the inherent preignition chemistry of the cylinder charge to control combustion phasing and ignition timing. The subsequent HCCI combustion process determines the rate of heat release, the reaction intermediates and the ultimate products of combustion. Therefore, understanding the ignition and oxidation chemistry of potential HCCI fuels is particularly important.; One option for ignition control of HCCI engines is to use small amounts of ignition-enhancing additives to alter the ignition properties. Di-tertiary Butyl Peroxide (DTBP) is one such additive and it has demonstrated its capacity to improve ignition of fuels in diesel engines.; In this study, the oxidation of SI primary reference fuels (PRFs) and their blends, and the effects of the additive DTBP on their ignition and oxidation behavior were investigated experimentally in both an engine operating in the HCCI mode and a Pressurized Flow Reactor (PFR). The effect of DTBP on iso-octane in the PFR shows evidence of reactivity promotion by a chemical effect rather than just a thermal effect. Experimental results in the engine show an ignition delay time reduction of at least 3 CAD for all tested fuels; COVIMEP improvement to <10% (a 37.5% reduction) for PRF92 at inlet temperature of 450 K and equivalence ratio of 0.49; and extension of stable HCCI operations for relatively high RON fuels to a broader equivalence ratio range and to lower inlet temperatures.; In parallel to these experimental studies, an initial modeling effort was undertaken to modify and reformulate a skeletal chemical kinetic model for the SI PRFs and their blends. The model was developed as an extension of our previous preignition model by modifying several reactions to incorporate recent advances in our understanding of the relevant chemistry. The model was also reformulated to be compatible with the standard CHEMKIN simulation package. In general, the updated skeletal model successfully predicted the reactivity behavior of the fuels tested over the 600--800 K experimental range of this study.