Effect of ethanol/water blends addition on diesel fuel combustion in RCM and DI diesel engine

The effect of ethanol/water blends addition on diesel fuel combustion and emissions is investigated experimentally in this study using optical diagnostics. Basic study is performed using rapid compression machine (RCM) under CI conditions. The tested ethanol energy fractions varied in the range of 10-40% of the total added fuel energy, while water volume ratios varied in the range of 10-40% of the injected ethanol. Ethanol and water were evaporated before entering the combustion chamber to eliminate their endothermic effect. Results reveal that addition of ethanol/water blends to diesel fuel results in longer ignition delay and promote the apparent heat release rate (AHRR) at the premixed combustion phase compared to absolute ethanol addition. Additionally, soot and NOx emissions are reduced with ethanol/water addition compared to absolute ethanol addition and neat diesel combustion. The basic study is then extended to investigate the effect ethanol/water blends addition on diesel fuel combustion using single cylinder diesel engine. Waste heat in exhaust manifold is utilized to vaporize ethanol/water blends before combustion. Results reveal that ethanol/water blends injection leads to increase in peak cylinder pressure, indicated mean effective pressure (IMEP), and AHRR at premixed combustion phase. Additionally, the ignition delay increased with ethanol/water addition. NOx emission is decreased up to 88% along with a reduction in soot by 50%. The lower ethanol to water volume ratios show better combustion efficiency, IMEP, NOx and soot emissions compared to the higher ethanol to water volume ratios. The addition of water to ethanol leads to longer ignition delay and lower soot concentrations compared to absolute ethanol. Additionally, water addition reduces the flame temperature, which leads to NOx reduction.