Experimental study of the ignition delay of diesel/biodiesel blends using a shock tube

Ignition delays of a pure biodiesel, which is produced from palm oil, as well as its blends with petroleum diesel were experimentally quantified using a preheated shock tube. The emission of OH∗ radical signals, which was observed by a photomultiplier via a monochromator, was used to identify the time for onset of ignition. Experiments were performed behind the reflected shock waves at a pressure of 0.12 MPa, equivalence ratios of 0.5, 1.0 and 1.5, and a range of temperatures from 1174 to 1685 K. Fuel blends B0, B20, B40, B60, B80 and B100 (corresponding to 0, 20, 40, 60, 80 and 100 vol% of biodiesel with petroleum diesel, respectively) were tested. The results show that ignition delay variations of blends versus temperature were similar to those of pure diesel fuel. It was consistently found that for all fuel blends, ignition delay increases with an increase in equivalence ratio. An equivalence ratio exponent of 0.73 in Arrhenius correlation was observed. At a constant equivalence ratio, the effect of biodiesel fraction on chemical ignition delay of the fuel blends was not significant. The overall activation energy of diesel/biodiesel mixtures in this study is 161,937.5 J mol−1.