High efficiency ethanol–diesel dual-fuel combustion: Analyses of performance, emissions and thermal efficiency over the engine load range

Abstract

The performance of ethanol–diesel dual-fuel combustion is evaluated against that of the conventional diesel high-temperature combustion (HTC) from 4 bar (low engine load) to 19 bar net indicated mean effective pressure (IMEP) at 1500 rpm on a single cylinder high-compression ratio diesel engine. Ethanol is injected into the intake port, along with direct injection of diesel fuel. For both combustion strategies, engine operation is optimized by modulating the intake pressure, exhaust gas recirculation (EGR) rate, ethanol energy fraction and diesel injection pressure to achieve the desired combustion performance, along with detailed feed-gas analysis to evaluate the trade-offs between combustion efficiency, NOx and PM. From 6 to 19 bar IMEP, the dual-fuel combustion results in 84 ∼ 88% lower NOx and 20 ∼ 96% lower soot emissions compared to diesel HTC, and at loads > 10 bar IMEP, attains higher net indicated efficiency than diesel HTC, with a maximum value of 46% at 19 bar IMEP. To ascertain the impact of NOx selective catalytic reduction system (SCR) on the net indicated thermal efficiency, SCR urea dosing penalties are evaluated using actual feed-gas NOx data with a simple SCR correlation for estimating the tail-pipe NOx emissions and urea consumption. To achieve 0.2 g/kWh for tail-pipe NOx, the diesel HTC requires ∼ 90% SCR conversion efficiency below 6 bar IMEP but at higher loads, the dual-fuel combustion requires a SCR efficiency of 20 to 50% only, with reduced urea consumption, and net efficiency higher than the diesel HTC. Using renewable bio-fuels such as ethanol, dual-fuel combustion can be an effective strategy to reduce the dependence on fossil fuels, reduce GHG emissions and improve the viability of diesel engines as a preferred choice for heavy-duty transport applications.