Combustion, performance and emission analysis of diesel engine fuelled by higher alcohols (butanol, octanol and heptanol)/diesel blends

•The effect of heptanol/diesel blends on diesel engine combustion is tested.•The BTE were increased when higher alcohol/diesel blends were used.•Higher alcohols have long ignition delay and the longest was for But10 and But20.•The highest combustion efficiency was achieved for Hept20.•The NOx and soot were reduced but CO and HC were increased for higher alcohol blends. As there were limited efforts towards the substitution of diesel fuel with higher alcohols to operate diesel engine, the current work aims to evaluate diesel engine performance at wide operating conditions fuelled by blends of higher alcohols; including heptanol and octanol. To increase the trust of the received results, blends of lower alcohols (butanol) was studied where the attained results showed good agreement with those cited in the literature. Single-cylinder diesel engine setup equipped with the necessary sensors for measuring cylinder pressure, engine speed, output power, air flow rate, fuel flow rate and temperature at various locations in engine was used to realize the current objective. The study limits the blending ratios to be 10% and 20% v/v to keep the fuel system without any modifications. These blends showed stable and homogenous features for period of four months without phase separation. The steady state experiments were carried out at various engine loads (0%, 25%, 50% and 75% of the full load) and engine speeds (900 rpm and 1500 rpm). Results revealed that bsfc and BTE increased almost for all tested higher alcohol/diesel blends. The ignition delay increased with higher alcohols/diesel blends and the longest value was achieved by But10 and But20. The premixed combustion was enhanced for all tested higher alcohol/diesel blends. The highest cumulative net heat released was achieved for Hept20. The emissions of NOx and opacity were reduced while those of CO and HC emissions were increased for all tested higher alcohol/diesel blends compared to the corresponding values for D100.