Combined effect of oxygenated additives, injection timing and EGR on combustion, performance and emission characteristics of a CRDi diesel engine powered by sapota biodiesel/diesel blends

Biofuels from renewable sources deem itself as a sustainable option for a diesel engine as fuel. In the present study, biodiesel extracted from seeds of sapota through the transesterification method was used along with diesel in one single cylinder, common rail direct injection (CRDi) diesel engine. Also, this research attempt to study the influence of oxygenated additives, injection timing (IT) and exhaust gas recirculation (EGR) on different engine characteristics fueled with diesel/biodiesel blends. For this purpose, oxygenates viz., n-butanol (n-B) and dimethyl carbonate (DMC) were used as an additive to B40% blend (60% vol. diesel + 40% volume biodiesel). Two test fuels (blends) were prepared by adding 10% by volume of n-butanol and DMC to B40% blend separately. Experimentation was operated at three different injection timings like (21 degrees CA, 23 degrees CA and 25 degrees CA bTDC) and EGR rates (5%, 10%, and 15%) at the engine rated power output. Results reveal that the peak in-cylinder pressures and heat release rate (HRR) let fall slowly as the injection timing was late from 25 degrees CA bTDC to 21 degrees CA bTDC at all the EGR rates. When related to diesel, the combustion incident happened nearer to the top dead center (TDC) when advanced injection timing from 21 degrees CA to 25 degrees CA bTDC. Both oxygenated blends exhibit similar brake thermal efficiency (BTE) among them and a 4.7% decrease in performance was noted against diesel operation. Oxygenated additive to B40% blend elevated the oxides of nitrogen (NOx) emission. Nearly 7% and 60% of reduction in NOx emission were achieved when fuel with an n-butanol blend when related to DMC blend and diesel. About 14%, 10% and 8% lesser smoke opacity than diesel, B40%, and n-butanol blends were achieved with DMC blend injected at 25 degrees CA bTDC and 5% EGR rate. In summary, n-butanol and dimethyl carbonate can be recommended as oxygenated additives when fueled with diesel/biodiesel blend at advanced injection timing and low EGR rates.