RCCI combustion with renewable fuel mix - Tailoring operating parameters to minimize exhaust emissions

This article demonstrates a feasible approach towards minimizing negative impact of combustion, which comprises low net carbon emissions operation of internal combustion engines while achieving ultra-low engine-out exhaust emissions. Ultra-low emission operation was achieved by combining Reactivity Controlled Compression Ignition (RCCI) combustion concept and the use of an advanced fuel mix featuring low carbon life cycle emissions. This fuel mix consists of hydrotreated vegetable oil (HVO) as a representative of high reactivity renewable fuel and a methane rich (greater than 95% by volume) natural gas (MRNG) being a model fuel representing biomethane. Comprehensive mapping and identification of optimal operating regions of a small-swept volume engine was performed using an experimental setup comprising advanced real-time acquisition and control systems, developed specifically for robust RCCI engine operation. Combustion process was tailored to comply with limits of mechanical stresses of engine components, favourable thermodynamic parameters and ultra-low engine-out emissions. Combustion and thus engine operation was optimized based on a sensitivity analysis of the rate of exhaust gas recirculation (EGR) and energy share supplied by MRNG, which are the main influencing parameters to control NOx and soot emissions in RCCI combustion concept. Experimental results demonstrate that it is possible to simultaneously achieve ultra-low engine-out emissions of NOx, PM and PN with an innovative fuel mix resulting in a significant decrease in life-cycle carbon emissions compared to conventional fuels on an account of higher CO and THC emissions, what is a known disadvantage of RCCI concept.