Parametric optimization with Biodiesel-water emulsion under premixed lean combustion to achieve high efficiency and clean combustion

Abstract

Advanced low temperature combustion (LTC) aids in simultaneously controlling exhaust emissions of oxides of nitrogen (NOx) and particulate matter (PM). However, LTC strategies are constrained by achievable load range restriction and higher levels of unburned hydrocarbon (HC) and carbon monoxide (CO). The present investigation envisages combining renewable biodiesel-water emulsions and an advanced premixed lean combustion strategy to curtail the higher HC and CO emissions without sacrificing engine performance. Non-edible Karanja oil was the source of biodiesel and the emulsion stabilizer. A production light-duty diesel engine is modified to run under premixed lean combustion conditions based on late injection using a fully-flexible electronic fuel injection system. The engine operating parameters were optimized, including fuel injection timing, EGR flow rate, and emulsion water concentration. Emulsions of neat biodiesel were prepared to contain 6, 12, and 18% water on a mass basis using 1 and 2% surfactant by mass. The fuel injection timing was varied from 2 to 4 degrees after the top dead centre, and up to 15% EGR flow rate was utilized. Design of experiments aided in minimizing the number of engine tests. The performance and emission parameters were the output responses. Taguchi Grey Relational Analysis established the optimal combination of input factors to improve engine performance and reduce exhaust emissions. Engine experiments at optimized operating conditions revealed that compared to conventional diesel combustion, the brake thermal efficiency and brake specific fuel consumption improved by 33 and 16%, respectively, at 5.08 bar BMEP. The NOx, smoke and HC emissions were reduced by 68, 73 and 46%, while CO emissions increased nearly two-fold.