Study of flame quenching in SI engine

Abstract

One of the promising methods for improving both fuel economy newlineand to reducing pollution is lean mixture operation with Exhaust Gas newlineRecirculation (EGR)for SI engine. A practical problem in fully exploiting newlineEGR is that, at very high levels, EGR suppresses the flame speed sufficiently newlinethat combustion becomes incomplete and unacceptable levels of particulate newlinematter (PM) and hydrocarbons (HC) are released in the exhaust. This newlinetransition to incomplete combustion is characteristically very abrupt due to newlinethe high nonlinear effect of EGR on flame speed. Erratic combustion is the newlineproblem associated with EGR operated engine. A new method, catalytically newlineactivated lean burn combustion with EGR, has been investigated in the newlinepresent work. This method requires minimum modifications to the base newlineengine and it can be easily adopted even to the existing engines fitted in vehicles. As the aim of the present work is to develop a lean burn combustion newlinesystem, with cost effective, noble metal catalysts such as platinum, palladium newlineetc., are not used. Some non-noble metals which perform equally as noble newlinemetal catalysts for hydrocarbon oxidation are used. The results show that the newlinenon-noble metal catalysts such as copper, nickel, and chromium showed newlinereasonable catalytic activity. Many works on catalytically activated combustion in SI engine newlinereport the improvement in fuel economy and reduction in exhaust emissions. newlineThere have been some contradictions regarding the effect of catalytic coating newlineon HC emissions. Some researchers have proposed that the catalytic coated newlinesurface activates pre-flame reactions inside the boundary layer which reduces newlinethe fuel concentration in the boundary layer. When the flame arrives at the newlineboundary layer, it extinguishes before reaching the wall due to the availability newlineof less fuel near the wall. The partially burned fuel and its products contribute newlineto increased HC emissions. However, other researchers argue that the newlinepre-flame reactions helps in reducing exhaust HC emission.