Numerical investigation of detonation initiation for low-volatility liquid fuel/air mixtures

Numerical simulation has been performed to characterize the detonation initiation and propagation for low-volatility liquid fuel /air mixtures in an obstructed tube. The effects of the shock waves formation and the vaporization of the droplets on the flame acceleration were researched based on comparison with the corresponding gaseous detonation behavior. The computational results indicate that the time delay of liquid-fueled detonation initiation mainly derives from the slow deflagration stage where the atomization and evaporation of liquid fuel introduced by the hot products dominates the time scale. Longer run-up distance in two phase system is mainly attributed to the incomplete combustion. Besides, the hotspots are generated at different position and controlled by different regimes in gaseous and liquid fuel cases. Then, the detonation initiation characteristics under different small droplet sizes (10 μm, 20 μm, 30 μm) were discussed in detail. As the droplet diameter increases from 10 μm into 30 μm, the deflagration to detonation transition (DDT) time increases by 126%, while the DDT distance increases by 33.8%, which indicates that the run-up time is more sensitive to the changes of droplet size. Furthermore, the factors such as weakening effects of droplets on leading shock, fuel vapor content and incomplete combustion are found to have great impact on the velocity deficit in liquid-fueled case. The achievements in current work aid understanding of natural detonation behavior and serve as a possible design suggestion of future PDE based on liquid fuel.