Abstract
The effects of ethanol on combustion and emission were investigated on a single-cylinder unmodified diesel engine. The ethanol content of 10–50 vol % was chosen to blend with diesel and biodiesel fuels. Selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the passive mode was also studied under real engine conditions. Silver/alumina (Ag/Al2O3) was selected as the active catalyst, and H2 (3000–10000 ppm) was added to assist the ethanol-SCR. The low cetane number of ethanol resulted in longer ignition delay. The diesel–biodiesel–ethanol fuel blends caused an increase in fuel consumption due to their low calorific value. The brake thermal efficiency of the engine fuelled with relatively low ethanol fraction blends was higher than that of diesel fuel. Unburned hydrocarbons (HC) and carbon monoxide (CO) increased, while NOx decreased with ethanol quantity. The higher ethanol quantity led to increases in the HC/NOx ratio which directly affected the performance of NOx-SCR. Addition of H2 considerably improved the activity of Ag/Al2O3 for NOx reduction. The proper amount of H2 added to promote the ethanol-SCR depended strongly on the temperature of the exhaust where a high fraction of H2 was required at a low exhaust temperature. The maximum NOx conversion of 74% was obtained at a low engine load (25% of maximum load), an ethanol content of 50 vol %, and H2 addition of 10000 ppm.
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