Experimental study of 2-ethylhexyl nitrate effects on engine performance and exhaust emissions of a diesel engine fueled with n-butanol or 1-pentanol diesel–sunflower oil blends

•Higher alcohols (n-butanol and 1-pentanol) were mixed with sunflower oil/diesel blend.•Effects of EHN on fuel properties and engine performance were performed.•EHN promising candidate for improving cetane number and decreasing NOx emissions.•CO emissions increased with addition of EHN to vegetable oil based microemulsions.•D70S20B10 and D70S20P10 with EHN showed opposite effects on HC emissions. Vegetable oil based microemulsion blends have received increased attention due to its free major drawback like chemicals, catalysts and process heat of transesterification compared to biodiesel. However, the lower cetane number (CN) of a vegetable oil based microemulsion blends prevents its using in diesel engines because of poorer self-ignitability. This study focused on the effect of 2-ethylhexyl nitrate (EHN) (cetane improver) addition on fuel properties, and engine performance and exhaust emission characteristics of diesel engine fueled with microemulsion blends. EHN was added at 500, 1000 and 2000ppm concentration to diesel (D) (70vol.%), sunflower oil (S) (20vol.%) and n-butanol (B) (D70S20B10) or 1-pentanol (P) (10vol.%) (D70S20P10) microemulsion blends to study its effect. Microemulsion blends with EHN were tested on a turbocharged direct injection (TDI) diesel engine at fixed engine speed (2200rpm) and five different engine loads. The addition of EHN to microemulsion blends had positive effect on CN without causing any significant negative effect on other fuel properties of microemulsion blends. Engine performance test results showed that microemulsion blends with EHN had little effect on brake power and brake mean effective pressure (BMEP). Brake specific fuel consumption (BSFC) values reduced with increase of EHN concentration in the microemulsion blends in the range of 2.49–8.17%. Addition of EHN to microemulsion blends produced lower mean oxides of nitrogen (NOx) in the range of 0.26–5.26%. D70S20B10 with 2000ppm EHN has the best effects on the reduction of NOx emissions. However, carbon monoxide (CO) emissions increased in the range of 7.16–23.46% with increased presence of EHN concentration in microemulsion blends. Different trend in hydrocarbon (HC) emissions for D70S20B10 and D70S20P10 with EHN were observed.