Deflagration-to-detonation Transition Distance Research Articles

Explosions and deflagration-to-detonation transitions in epoxy propane/air mixtures

The explosion and deflagration-to-detonation transition (DDT) in epoxy propane (E.P.) vapor/air mixture clouds under weak ignition conditions has been studied in an experimental tube of diameter 199 mm and length 29.6 m. E.P. vapor clouds were formed by injecting liquid E.P. into the experimental tube and evaporating of the fine E.P. droplets. The dimension and the evaporating process of the E.P. droplet were measured and analyzed. The E.P. vapor/air mixture clouds were ignited by an electric spark with an ignition energy of 40 J. The characteristics and the stages of the DDT process in the E.P. vapor/air mixtures have been studied and analyzed. A self-sustained detonation wave formed, as was evident from the existence of a transverse wave and a cellular structure. Moreover, a retonation wave formed during the DDT process in the E.P. vapor/air mixture. The influence of the E.P. vapor concentration on the DDT process has been studied. The minimum E.P. vapor concentration for the occurrence of the DDT in the E.P. vapor/air mixture has been evaluated and the variation of DDT distance with E.P. vapor concentration has been analyzed.

E225 渦流中でのDDT特性に及ぼすシェルキンスパイラルの閉塞比の効果(OS-9:燃焼の最近の進展(6))

The effects of blockage ratios (BR) of the Shchelkin spiral on characteristics of deflagration-to-detonation transition (DDT) in a vortex flow were examined in order to control the DDT distance without losing the simplicity inherent pulse detonation engines. The DDT distance decreases with increasing the BR of the Shchelkin spiral. However, the optimum value of BR exists. The DDT distance is deteriorated if the BR exceeds the optimum value. Optimizing the BR of the Shchelkin spiral is another way to shorten DDT distance in a vortex flow.

Experimental Study of Ignition and Detonation Initiation in Two-Phase Valveless Pulse Detonation Engines

This paper addressed the ignition and detonation initiation investigation of two-phase valveless pulse detonation engines (PDEs) in different operational cases. To quantify the ignition and detonation initiation performance, the parameters detonation initiation time and deflagration-to-detonation transition (DDT) distance were examined. Detonation initiation time was defined as the time between the times when the spark plug received the ignition signal and when detonation initiated by DDT, which was the sum of the ignition time and DDT time. In order to observe the effects of ignition energy, operating frequency of the PDE, liquid fuel type, and inner diameter of the PDE on detonation initiation characteristics, proof–of-principle experiments of PDEs with inner diameters of 50 mm and 120 mm were carried out. Gasoline and kerosene were used as the liquid fuels of PDEs. A conventional Schelkin spiral is used to obtain DDT in liquid fuel/air mixtures. The results indicated that the ignition energy, operating frequency, fuel type, and PDE diameter had important effects on detonation initiation time. As the ignition energy increased, the detonation initiation time decreased, and the average thrust of PDE increased while the DDT distance didn't change notably. As the operating frequency increased, the detonation initiation time and the optimum equivalence ratio required to stabilize multi-cycle detonation decreased while the ignition energy effect on detonation initiation time degenerated. The detonation initiation time and DDT distance of kerosene/air was longer than that of gasoline/air. As the operating frequency increased, the difference between the detonation initiation time of kerosene/air and that of gasoline/air decreased. The experimental data suggested that the detonation initiation time and DDT distance increased at the increased PDE diameter.

Investigation of Detonative Combustion Characteristics

The pressure and deflagration-to-detonation transition (DDT) characteristics of acetylene and oxygen flame were studied in a detonation tube. The pressure history and the flame velocity along the tube were measured with high frequency pressure transducers and ion probes. By analyzing the data recorded in the experiment, the detonation wave pressure, post-wave pressure and DDT distance were obtained, together with the effects of the initial pressure varying from 2 104 Pa to 105 Pa, equivalence ration from 0.3 to 1.0, and mixture concentration from 60% to 100%. It was found that the detonation pressure was decreased respectively with the decrease of initial pressure, equivalence ratio and mixture concentration, but the DDT distance was enlarged. The DDT distance was found particularly sensitive to mixture concentration.

Spray combustion in the presence of a travelling wave

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.