Effect of injection parameters on instability of detonation waves in rotating detonation engines with an S-shaped isolator
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In this study, the effects of three injection parameters on the propagation and instabilities of rotating detonation waves (RDWs) in a kerosene/air rotating detonation engine (RDE) with an S-shaped isolator are experimentally evaluated. The dimensionless parameter momentum flux ratio is considered a pivotal factor, and the influence of the injection geometry factors is analyzed. An empirical formula concerning the characteristic factor of oxidizer-fuel blending is derived to facilitate the RDE injection configuration design. The research reveals a significant correlation among the injection parameters, kerosene-air momentum flux ratios, and instability of RDWs. High dimensionless injection parameters do not necessarily result in a stable RDW phenomenon. Stable RDWs and unstable detonations are discussed under various injection parameters and momentum flux ratios. Additionally, a statistical analysis of the detonation instability is conducted, revealing two distinct cyclic categories: ignition-extinguishment-ignition and attenuation-recovery-attenuation. Two pathways of RDW instability propagation are identified to summarize the evolutionary processes of these variations and elucidate their mechanisms. Changes in the injection parameters cause the RDW to develop in two unstable orientations, resulting in the extinguishing and re-generating phenomenon of the RDW.Keywords:
Isolator
Deflagration to Detonation Transition (DDT) phenomena of liquid fuel octane droplets in air in detonation tube are simulated here. The numerical formulation is described, on which code-CPTD is developed. Basic properties of liquid-fueled detonation structure together with the effects of partial preevaporation and droplet amount on detonation structure and development are investigated in current study. Simulations reveal that the presence of some amount of initial fuel vapor in the tube will substantially expedite transition to detonation, on the other hand, the existence of some fuel droplets may exhibit a suppression to detonation wave, and increasing amount or concentration of fuel droplets will delay deflagration to detonation transition. The calculations show that the numerical results are in good agreement with experimental ones, which implies that a feasible numerical method has been provided here to simulate pulse detonation engine operation processes including DDT phenomena.
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To verify the three current international views on the generating condition of over-detonation during gaseous deflagration-to-detonation transition(DDT),the DDT process of gaseous hydrogen-oxygen mixture was experimentally studied by using pressure sensors.The whole pressure histories of gaseous DDT from detonation to DDT and then to stable detonation were obtained.The experimental results showed that the generation of DDT requires certain physico-chemical conditions,and for certain initial pressure conditions,the transformation time(or distance) decreases firstly and then increases with increasing concentration of hydrogen.The peak pressure in over-detonation is about 1.5～2 times as much as that in the stable detonation.
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The effective producing detonation is an essential technology of pulse detonation engine.The deflagration to detonation transition progress of pulse detonation engine was researched using two-dimensional numerical simulation aimed at detonation engine tube with three different sub-chamber structures.Studies indicate that:(1)the energy of electric sparks is too weak to directly trigger a detonation;the detonation is fully established through a series of interactions and impacts of reflected shock waves.(2)Because of different sub-chamber,the deflagration to detonation transition(DDT)is also different;the simulation results of three kinds of situations are contrasted,and the best sub-chamber design is obtained whose SDT time and length is the shortest.
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According to the characteristic of pulse detonation inside the pulse detonation engine,the three-dimensional models for two-phase detonation were built.The CE/SE method was used to calculate the deflagration to detonation.The cal-culation results show that the pressure field inside the tube is three-dimensional variation during the deflagration to detonation.When it is detonation wave,three-dimensional effect degenerates to be two-dimensional.The pressure data agree well with the experimental data.
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Motivated by the current interest in the mechanism of the deflagration to detonation transition(DDT),the DDT process and detonation wave structure of aluminum-air mixture are investigated experimentally by a large scale tube with length of 32.4 m and inner diameter of 0.199 m.The overall DDT process can be divided into slow reaction compression stage,pressure wave speed-up and shock wave formation stage,transfer from shock reaction to critical shock reaction,transfer from critical shock to overdriven detonation,and detonation stage.The optimal concentrations of mixtures in this experimental tube are obtained,and the critical concentration of DDT is also studied.Eight pressure gauges are well-distributed at each periphery of four certain sections in the 1.4 m long detonation testing tube for detonation wave testing.According to the test results,the detonation wave structure of aluminum-air mixture is analyzed,which shows single head mode.
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Efficient initiation of detonation waves is the key to the pulse detonation engine(AB.PDE) operation.In the process of deflagration to detonation transition(AB.DDT),detonation waves were successfully triggered by controlling the shock wave reflection.Interaction between flame and shock is strengthened by putting obstacles in detonation chamber with reasonable arrangement,which can efficiently organize reflection of shock wave and initiate detonation timely.Thus,DDT distance was shortened comparatively.Gasoline/Air detonation waves propagate successfully in the combustor.These results are valuable to the investigation on DDT process of two-phase pulse detonation engine at high frequency.
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