Investigation On Operation Characteristics Of Kerosene/Air Rotating Detonation Engines Based On An Improved CE/SE Method

In this paper,the kerosene/air continuous rotating detonation engine is investigated based on an improved CE/SE method.The operation characteristics of gaseous and liquid kerosenefueled rotating detonation engines are systematically studied using numerical simulations and experiments.The main research contents include the development of an improved CE/SE numerical platform and detonation solvers,two-dimensional(2D)gaseous rotating detonation simulations,three-dimensional(3D)gaseous rotating detonation simulations,three-dimensional gas-liquid two-phase rotating detonation simulations,and gas-liquid two-phase rotating detonation experimental study.The details are summarized as follows:(1)The computing scheme of the 2D CE/SE method based on the unstructured triangular mesh is derived.An improved scheme called κ-CNI scheme is proposed,which improves the shock capture ability of the CE/SE method.The computing program is written,and numerical examples are conducted to verify the robustness and CFL number low-sensitivity of the new scheme.Furthermore,the computing scheme of the 3D CE/SE method based on the unstructured hexahedral mesh is derived and the κ-CNI scheme is extended to 3D.The wall reflection boundary condition is derived.The chemical reaction model of gas-phase detonation is added to the improved CE/SE method.The solution of thermodynamic parameters and the relationship between pressure and conserved quantities are deduced.The computing efficiency is improved by a hybrid MPI+Open MP paralleling method.The results show that on the cluster computer system with 24 cores per node,the combination of 4 processes × 6 threads can obtain the highest speedup,and the computing efficiency can maintain about 90% when 384 CPUs are used.The 2D and 3D high-performance detonation solvers are developed.The simulations in this paper are all completed by the self-developed detonation solvers.(2)The 2D rotating detonation model is established and the effects of injection conditions on the gaseous kerosene/air rotating detonations are numerically studied.A two-step kerosene/air chemical reaction model is adopted.The rationality of the chemical reaction mechanism and the grid independence is verified.The kerosene/air rotating detonation waves under different total temperatures and inlet area ratios are simulated.The numerical results capture the main flow field structures of rotating detonation waves.The results indicate that decreasing the inlet area ratio will lead to the existence of burned gas in the fresh mixture layer,affecting the coupling of rotating detonation waves,and reducing its intensity.With the increase of total temperature,the burned gas will affect the propagation mode of the detonation wave and aggravate the pre-combustion phenomenon in front of the detonation wave,which may lead to the extinction of the detonation or transition of the propagation modes.The kerosene/air rotating detonation waves under different total pressure and equivalence ratio are simulated.The instability phenomenon of rotating detonation waves is observed and analyzed.Under low inlet total pressure(1.0 MPa),the burned gas bump tends to appear on the interface between the fresh mixture layer and burned gas.When the rotating detonation wave passes through the burned gas bump,the overall structure of the detonation wave rotates first counterclockwise and then clockwise,resulting in the periodic existence of the instability phenomenon.The increase of the inlet total pressure can significantly improve the phenomenon.(3)The 3D rotating detonation model is established and the effects of inlet configurations on the gaseous kerosene/air rotating detonations are numerically studied.The influence of slot inlet positions on the operation characteristics of the rotating detonation engine is studied,and the typical detonation wave structures in the ideal inlet,outer slot inlet,middle slot inlet,and inner slot inlet cases are captured.A stably single-wave rotating detonation wave is obtained in the ideal inlet and the outer slot inlet cases.An unstable triple-wave rotating detonation mode is obtained in the middle slot inlet case,and the detonation wave is finally extinguished in the inner slot inlet case.It is found that the detonation wave is slightly overdriven near the outer wall due to its convergence effect,which promotes the stable propagation of rotating detonation waves.The operation characteristics of kerosene/air rotating detonation engine with a divergence inlet are studied.It is found that the detonation front is divided into two sections due to the addition of the divergence section.In the expansion section,the detonation front bends and lags behind the main detonation front.Increasing the inlet area ratio can improve the total pressure gain performance.The numerical fitting results show that the critical inlet area ratio to obtain the positive total pressure gain is 0.487.(4)The 3D two-phase rotating detonation model is established and the effects of droplet size,injection total temperature,and divergence inlet on the two-phase kerosene/air rotating detonations are numerically studied.The results show that increasing total temperature can broaden the range of droplet size for obtaining two-phase rotating detonation waves.The typical flow field structure of the two-phase rotating detonation wave is observed.The main difference with gaseous detonation is the stratification of the fuel layer in front of the detonation wave.The droplet size in front of the detonation wave tends to decrease due to the shearing effects of the interface and the evaporation effect under high temperatures.The fresh fuel layer is divided into upper and lower layers,in which the upper layer is mostly fuel vapor and the lower layer is mostly fresh droplets.The stratification of the fuel layer aggravates the instability of twophase rotating detonation waves,causing the forward inclination trend of the rotating detonation wave.The operation characteristics of kerosene/air two-phase rotating detonation engines with a divergence inlet are studied.The single wave and double wave collision rotating detonation waves are observed.The self-sustained propagation mechanism of double-wave collision mode in two-phase rotating detonation wave is revealed,which plays an important role in guiding the subsequent experimental research.(5)The experimental research on gas-liquid two-phase rotating detonation engines is conducted.The initiation and self-sustaining propagation of kerosene-fueled rotating detonation waves are realized.Using room-temperature oxygen-enriched air,the operation modes such as single-wave mode,double-wave collision mode,and single-wave/double-wave collision hybrid mode are observed.The results show that the decrease of oxygen fraction has a significant effect on the propagation modes.When the oxygen fraction is high,the rotating detonation wave can self-sustained propagate with a single wave mode.With the decrease of oxygen fraction,the detonation wave mainly propagates with double-wave collision mode.Using heated oxygen-enriched air,the three operation modes are also found.The high injection total temperature can improve propagation speeds and peak pressures of the two-phase detonation wave.The increase of total temperature is conducive to the initiation of two-phase detonation waves.Furthermore,the high total temperature can effectively reduce the lower limit of critical oxygen fraction for obtaining two-phase detonation waves.The experimental research verifies the enhancement effects of high total temperatures on two-phase detonation waves in numerical simulations.The velocity attenuation of the double-wave collision mode compared with the single wave in simulations is quantitatively consistent with experiments,which enhances the understanding of the two-phase rotating detonation waves.In this paper,the operation characteristics of kerosene/air rotating detonation engines are systematically studied.The influence mechanism of the key parameters such as total temperature,total pressure,equivalence ratio,slot inlet position,divergence inlet configuration,and droplet radius is clarified.The flow field structure and self-sustaining propagation mechanism of gaseous and gas-liquid rotating detonation waves are revealed and verified with experimental research.The present paper promotes the development of CE/SE method.The research results are of great significance for realizing the engineering application of kerosene/air rotating detonation engines.