Impact of oxygen enrichment on the engine's performance, emission and combustion behavior of a biofuel based reactivity controlled compression ignition engine

Abstract

Diesel engine with RCCI (Reactivity Controlled Compression Ignition) finds the next generation technology in engine research for combusting slow burning fuels such as vegetable oils and arriving extremely lower levels of smoke and NO (Nitric Oxide) emissions simultaneously. An attempt was made to operate a diesel engine on RCCI mode by injecting ethanol as low reactivity fuel at the intake manifold of the engine using sunflower based Waste Cooking Oil (WCO) as high reactivity fuel under oxygen enriched intake air. The influence of the combined effect of oxygen enrichment and RCCI mode on engine's behavior was studied using WCO as the high reactivity (main) fuel. Significant improvement (upto 33.5% with RCCI mode from 29.1% with neat WCO at peak power) in BTE (brake thermal efficiency) with drastic reduction in smoke (upto 48% with RCCI at the maximum efficiency point from 69% with neat WCO at peak power) and NO were achieved with injection of ethanol under RCCI mode when using WCO as base fuel mainly at high loads (power outputs). Combining oxygen enrichment with RCCI resulted in further improvement in BTE (upto 36.2%) and reduction in smoke (upto 37% at the maximum efficiency point), HC and CO emissions at all power outputs. Peak pressure and energy release rate were found to be superior with RCCI mode with EF (electronic fuel) injection of ethanol associated with oxygen enriched combustion. It is concluded that RCCI operation with injection of ethanol combined with oxygen enrichment could be preferred for very high BTE, lowest smoke and NO emissions using WCO as base fuel. The optimal level of low reactivity fuel blending with high reactivity WCO could be at the ethanol energy share of 25% for the highest thermal efficiency at peak load. The optimal oxygen concentration of 23% by volume could be preferred for best performance of the engine fueled with WCO as main fuel.