Performance and environmental impact assessment of diesel engine operating on high viscous punnai oil–diesel blends

The increasing demand for energy consumption because of the growing population and environmental concerns has motivated the researchers to ponder about alternative fuel that could replace diesel fuel. A new fuel should be cheaply available, clean, efficient, and environmentally friendly. In this paper, the engine operated with neat punnai oil blends with diesel was investigated at various engine load conditions, keeping neat punnai oil and diesel as base fuels. The performance indicators such as brake specific energy consumption (BSEC), brake thermal efficiency (BTE), and exhaust gas temperature (EGT); emission indicators such as carbon monoxide (CO), oxides of nitrogen (NOx), and smoke opacity; and combustion parameters like cylinder pressure and heat release rate were examined. The brake thermal efficiency of diesel is 29.2%, whereas it was lower for neat punnai oil and its blends at peak load conditions. Concerning the environmental aspect, oxides of nitrogen emission showed a decreasing trend with higher smoke emissions for Punnai oil blends. Detailed combustion analysis showed that on smaller concentrations of punnai oil in the fuel blend, the duration of combustion has improved significantly. However, for efficiency and emissions, the P20 (20% punnai oil and 80% diesel) blend performs similar to that of diesel compared to all other blending combinations. When compared with diesel, the P20 blend shows an improvement in BSEC by 26.37%. It also performs closer in HC emission, a marginal increase in smoke opacity of 4% with reduced NOx and CO 2 emission of 7.9% and 4.65% respectively. Power loss was noticed when neat punnai oil and higher blends were used due to the high density and low calorific value of punnai oil blends which leads to injecting more fuel for the same pump stroke. Graphical abstract