The effect of ethanol–diesel–biodiesel blends on combustion, performance and emissions of a direct injection diesel engine

•Ethanol–diesel–biodiesel blends were tested at the same air–fuel ratios and three ranges of speed.•The fuel oxygen mass content reflects changes in the autoignition delay more predictably than the cetane number does.•Using of composite blend E15B suggests the brake thermal efficiency the same as the normal diesel fuel.•Adding of ethanol to diesel fuel reduces the NOx emission for richer air–fuel mixtures at all engine speeds.•The ethanol effect on CO, HC emissions and smoke opacity depends on the air–fuel ratio and engine speed. The article presents the test results of a four-stroke, four-cylinder, naturally aspirated, DI 60kW diesel engine operating on diesel fuel (DF) and its 5vol% (E5), 10vol% (E10), and 15vol% (E15) blends with anhydrous (99.8%) ethanol (E). An additional ethanol–diesel–biodiesel blend E15B was prepared by adding the 15vol% of ethanol and 5vol% of biodiesel (B) to diesel fuel (80vol%). The purpose of the research was to examine the influence of the ethanol and RME addition to diesel fuel on start of injection, autoignition delay, combustion and maximum heat release rate, engine performance efficiency and emissions of the exhaust when operating over a wide range of loads and speeds. The test results were analysed and compared with a base diesel engine running at the same air–fuel ratios of λ=5.5, 3.0 and 1.5 corresponding to light, medium and high loads. The same air–fuel ratios predict that the energy content delivered per each engine cycle will be almost the same for various ethanol–diesel–biodiesel blends that eliminate some side effects and improve analyses of the test results. A new approach revealed an important role of the fuel bound oxygen, which reflects changes of the autoignition delay more predictably than the cetane number does. The influence of the fuel oxygen on maximum heat release rate, maximum combustion pressure, NOx, CO emissions and smoke opacity of the exhaust is highly dependent on the air–fuel ratio and engine speed. Fuelled with blend E15B the diesel engine develops the brake thermal efficiency of 0.362, i.e. the same as a straight diesel running on slightly richer air–fuel mixture λ=1.5 at rated 2200rpm speed. Adding of the ethanol to diesel fuel reduces the NOx and the HC emissions for richer combustible mixtures whereas the influence of a higher ethanol mass content on CO emissions and smoke opacity depends on the air–fuel ratio and engine speed.