Role of different antioxidants additions to renewable fuels on NOx emissions reduction and smoke number in direct injection diesel engine

The changes in the emission characteristics of a diesel engine were experimentally verified when using diesel fuel, neat sun-flower biodiesel (B), and a biodiesel-diesel blend (B20). Four types of antioxidants, including phenols (BHT, BHA) and aromatic amines (DPPD, PPD), were mixed with neat biodiesel and B20. The effects of these antioxidant additions to the neat biodiesel and B20 on the engine performance, NOx emissions, and smoke number (SN) of the diesel engine were experimentally studied under variable engine loads. The brake specific fuel consumption (BSFC) slightly increased with the combustion of B20, while there was a clear improvement in the brake thermal efficiency compared to the diesel fuel. The results showed that the PPD provided a clear benefit in terms of the NOx emissions, with a decrease of 52% with respect to the other types of antioxidants with variable engine loads for all the fuels studied. An effective reduction of the NOx emissions could also be achieved with the addition of 1000 ppm of the different antioxidants to B20 compared to their addition to the neat biodiesel. Additionally, the NOx emissions were reduced by 5.7%, 7.3%, 7.2% and 11.3% during the combustion of the phenol-biodiesel blend, phenol-B20 blend, aromatic amine-biodiesel blend and amine-B20 blend, respectively, compared to the neat biodiesel. The carbonaceous emissions of CO and HC were slightly reduced by the addition of the antioxidants to the neat biodiesel compared to B20. The SN increased with increasing the antioxidant concentrations and engine load for the neat biodiesel and B20.