Experimental study on the performance of and emissions from a low-speed light-duty diesel engine fueled with n- butanol–diesel and isobutanol–diesel blends

The effects of isobutanol- and n-butanol-enriched diesel fuel on the diesel engine performance and emissions are investigated. Neat diesel, 15% isobutanol–85% diesel, 30% isobutanol–70% diesel, 15% n-butanol–85% diesel, and 30% n-butanol–70% diesel blends are investigated in this study. The tests were carried out at light and medium loads and a fixed low engine speed, and by using various combinations of the exhaust gas recirculation rate and the injection timing to investigate the effect of the molecular structure difference on soot formation. The results show that n-butanol–diesel blends give a longer ignition delay than isobutanol–diesel blends do. Hence isobutanol has a higher peak cylinder pressure and a higher premixed heat release rate than n-butanol does. Adding butanol (isobutanol and/or n-butanol) to diesel fuel is able to decrease the soot emissions substantially, while the change in the nitrogen oxide emissions varies slightly. Soot emissions from n-butanol–diesel blends are lower than those from isobutanol–diesel blends. Introducing exhaust gas recirculation and retarding the injection timing are effective approaches to decrease the nitrogen oxide emissions. However, a high exhaust gas recirculation rate leads to a loss in the fuel efficiency. The combination of a low exhaust gas recirculation rate, later injection and butanol blends can achieve low-temperature combustion and simultaneously decrease the nitrogen oxide and soot emissions.