Investigation On Detonation Characteristics Of The Gelled Gasoline In Pulse Detonation Engine

Gelled fuels which combined the advantages of solid fuels and liquid fuels have a broad application prospect in future propulsion systems. Compared with the propellers worked with deflagration mode, the thermal efficiency of propulsion systems relied on detonation wave mode is higher. The combination of gelled fuels and pulse detonation engine (PDE) is expected to make full use of their advantages, and improves the performance of the propulsion systems. However, the mechanism how the non-Newtonian behavior of gelled fuels that differs from liquid fuels affect its detonation performance is not very clear. Therefore, to investigate the detonation characteristics and the application in PDE of gelled fuels is significant for understanding the detonation mechanism of gelled fuels and expanding the application scope of the PDE. In this thesis, with the problems involved in detonation of the gasoline gelled fuels in PDE, the model establishments and numerical simulations for flow field in PDE with gelled fuels’detonation were carried out, the preparation, atomization and detonation of gelled fuels were accomplished experimentally. These investigations revealed the detonation characteristics of gelled fuels based on gasoline. The main contents are as follows:1) A two-phase detonation model for the silica and gasoline gelled fuels and gas phase oxidation with non-Newtonian behavior considered was proposed. The codes for solving the governing equations of that model with conservation element and solution element (CE/SE) method were programmed. The two-phase detonation processes of gasoline gelled fuels with silica as gellant were studied numerically, and the influences of gellant content, initial droplet size and oxygen content on detonation parameters of gelled fuels were analyzed. The results show that the detonation process of gelled fuels is like to that of liquid fuels, but the apparent viscosity of gelled fuels’droplets is variable, and is higher than that of liquid fuels’droplets 1 to 2 orders of magnitude during the reaction. The minimum ignition strength for successful detonation formation of gelled fuels was raised with the increasing of gellant content, but there are a few differences for detonation parameters such as pressure under different gellant contents. There is a upper limit of the initial droplet size for the formation of the self-sustained propagation detonation wave in detonation tube with gelled fuels. With the increased oxygen content in detonation tube, the energy density is amplified, so the initial ignition strength for detonation formation of the gelled fuels is reduced, and the detonation parameters such as pressure and wave velocity were higher. Therefore, in practical engineering applications, it can be considered that to improve the oxygen content of induced segment of detonation appropriately to accelerate the detonation formation.2) The pre-detonation pulse detonation engine models including the pressure relief bypass were built with silica and gasoline gelled fuels. Numerical simulations of the detonation flow field under different detonation tube diameters and initial filling oxygen contents of the pre-detonation tube were conducted, and the influences of these conditions on the wave propagation time in detonation tube were analyzed. The back pressure transmissions in intake pipe of the main detonation tube were studied numerically, and a preliminary idea that to improve the pressure characteristics of the intake pipe with pressure relief bypass was proposed and verified numerically. The results indicate that the time of the detonation wave propagated in pre-detonation tube is decisive for the total time of detonation wave propagation in detonation tube. With the pressure relief bypass, the peak values of the back pressure and reflux speed in intake pipe were decreased, the new filling gas pollution caused by back flow of exhaust was cut down.3) A three phase detonation model of aluminized gasoline gelled fuels with silica as gellant and gas phase oxidation was established. The Jacob matrixes of the governing equations were deduces, and the relevant programs were written with the CE/SE method. Numerical studies on multi-phase detonation processes of the aluminized silica and gasoline gelled fuels in detonation tube were accompilshed. The reaction of the aluminized gelled fuels droplet during the detonation process and the transient characteristics of the detonation exhausts were analyzed. The effects of aluminum contents and stoichiometric ratios on detonation properties of the gelled fuels were compared. The results show that the strip of the aluminized gelled fuels droplet under the detonation wave is predominant, the aluminum particles scatter into the detonation tube accompanying with the strip of droplets, and participate in reaction, so the aluminum quantity accumulated in the final stage is small. After the sweeping of detonation wave, the platform density of exhaust was formed in detonation tube which was litter than initial density. The process of the gelled fuels’ detonation exhaust can be divided into three typical stages which are expansion stage attached to detonation, gas "choked" expansion stage and weaken expansion stage in sequence. Compared with the non-aluminized gelled fuels, energy density of the aluminized gelled fuels is greater, and the initial ignition strength for detonation formation of the gelled fuels is reduced. In the stoichiometric mixture of gelled fuels and oxygen enriched air, with the increased aluminum mass fraction, the detonation parameters such as pressure, temperature and detonation velocity is raised, the exhaust impulse and fuel volumetric specific impulse is increased, but the fuel weight specific impulse is decreased. With the increased stoichiometric ratio in range of 0.5 to 1.2,both the detonation properties such as pressure and detonation wave velocity and the detonation exhaust impulse are increased, but the fuel specific impulse is decreased.4) The gelled fuels based on gasoline with nano silica as gellant were prepared, the rheological characteristics such as thixotropy, shear thinning and yield stress of these gelled fuels were studied. The experimental platform of internal mixing air-blast atomizer of silica and gasoline gelled fuels was established, the effects of spray pressure on velocity field of the atomizing jets were investigated. The results suggest that the gasoline gelled fuels with silica as gellant are non-Newtonian fluid which own the characteristics of shear thinning and partially reversible thixotropic. With the same shear rate, the apparent viscosity of the gelled fuels increases with increasing gellant mass fraction, the apparent viscosity of the aluminized gelled fuels is greater than that of non-aluminized gelled fuels at the same gellant mass fraction. The atomizing jets of the gelled fuels with the internal mixing air-blast atomizer is a triangle shape with the atomizer as a vertex, a symmetrical rectangular core jet area was formed at the center axis of the atomizer, and there is a small high-speed jet region near the atomizer’s exit corresponding to the core jet area. When the injection pressure of the gelled fuel is lower than that of atomizing air, the high-speed jet regions are like to the inverted "Y" or "V" shapes, and the velocity distributions of the downstream jets are more uniform.5) The platform for detonation experiments of gelled fuels was set up, and the deflagration to detonation transition processes of silica and gasoline gelled fuels under multi-cycle were realizes with the platform. With the application of the tunable diode laser absorption spectroscopy, the impulse generated by detonation exhausts was measured indirectly, and analysis on relationship between impulse generation and gas exhaust was conducted. The results show that the temperature, velocity and density of the exhaust at the detonation tube were increased abruptly under the influence of the detonation wave, and then were quickly dropped to their platform values respectively under the action of expansion wave. In the later stage of the detonation exhaust, the gas temperature decreases and the gas density increases due to the mixing of the fresh filling gas and the residual exhausts. Under the condition of this paper, the impulse produced by the momentum of detonation exhausts during the expansion stage attached to detonation, gas "choked" expansion stage and weaken expansion stage are 58.1%,18.7%and 11.6% respectively of the total impulse.In this thesis, the mathematical and physical models for detonation of gelled fuels based on gasoline were proposed in consideration of the fuels’ non-Newtonian behavior, and the numerical studies and experimental investigations on detonation of gelled fuels in PDE were carried out. The results of influences of many factors such as gellant content, the initial droplet diameter and the aluminum content on detonation characteristics of gelled fuels, the suggestion of pressure relief bypass for pre-detonation PDE, the division of the three typical stages of detonation exhausts and the non-contact measurement method of impulse for detonation exhausts which have important significances to the application researches of PDE with gelled fuels.