Flammability limits of the fuels are defined as leanest or richest fuel concentration in fuel/air mixtures which will lead to flame propagation when external energy for ignition is introduced. The flammability limits depend on a number of parameters such as temperature, pressure, impurities, and moisture. Although there is a great deal of work has been done on the flammability limits of a variety of combustible gases and liquids in air, there appears to be lack of information on the flammability limits of diesel in air at elevated temperatures and moderate pressures.
Accordingly, a study was undertaken to investigate the flammability limits of the two diesel samples (commercial Diesel from “Esso” and “Shell”) at elevated temperatures and pressures using a specially designed apparatus. The test operating parameter matrix includes: four different temperatures and three pressures. Initially, the physical and chemical properties of the two diesel samples, including heating value, molecular mass, densities and simulated distillation characteristics were established.
The results show that heating value of the Shell diesel sample was higher than the Esso one. On the other hand, the density and molecular mass of the Esso diesel sample were higher than the Shell one, which indicates the Esso diesel sample contained more heavier components and was less volatile compared to the Shell one. The simulated distillation also confirmed this conclusion. Based on the experimental results, in general, the Esso diesel sample exhibited a wider flammability range than the Shell one. However, the Shell diesel sample was easier to ignite than the Esso one. In addition, the effect of pressure on the flammability of the Esso sample was more profound compared to the Shell one. The results for the diesel samples were compared with those for a pure saturated hydrocarbon, n-Tridecane in air at the same operating conditions.