Experimental investigation of the entrainment during combustion of soybean biodiesel sprays

Pure soybean biodiesel and diesel were experimentally tested inside a constant-volume combustion chamber. The effect of ambient temperature on the flame lift-off length of direct-injection (DI) sprays under quiescent conditions was investigated using OH chemiluminescence imaging. Then the impacts of the observed lift-off length variations on the entrainment (i.e. oxygen ratio) at the lift-off location were studied. The ambient temperature was varied from 800 K to 1200 K. The ambient density, oxygen concentration, injection pressure and duration were unchanged during the experiments. The results show that as the ambient temperature increases, the lift-off length will decrease for both fuel sprays, especially when the ambient temperature changes from 800 K to 900 K. Biodiesel has a longer lift-off length than diesel at all tested ambient temperatures. Similar trends happened to the oxygen ratio at the lift-off length of sprays, however, the difference in oxygen ratio of biodiesel and diesel is more significant compared with lift-off length results.