Wei Fan

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 didnt 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.

Experimental Investigations on Detonation Initiation in a Kerosene-Oxygen Pulse Detonation Rocket Engine

A series of experiments was carried out on a pulse detonation rocket engine (PDRE) running on a liquid kerosene-oxygen mixture to investigate the indirect detonation initiation. The experiments investigating the effect of Shchelkin spiral on the deflagration-to-detonation transition (DDT) process demonstrated that all spirals were able to enhance flame acceleration to some extent, but successful DDT was achieved only when the length of spiral was increased to six times of the inner diameter of detonation tube (6D). For the model with the spiral length of 6D, the DDT run-up distance was about 0.5 m (10D) and the sum of ignition delay and DDT run-up time was around 0.6 ms, which only occupied 0.6% of the whole cycle (100 ms). It implied that ignition delay and DDT run-up time were not the key factors of limiting the increase of frequency in a kerosene/oxygen PDRE. In addition, an experiment on detonation initiation by a flame jet through an orifice plate was successfully conducted on the multi-cycle PDRE. For detonation tubes with the orifice plate mounted 10 cm and 20 cm away from the thrust wall, the DDT run-up distance obtained was approximately 0.30 m (6D) and 0.2 m (4D). Compared with the spiral configuration, the DDT run-up distance was shortened by 40% and 60% in the two cases, respectively. The results implied that a rapid initiation of detonation could be achieved in a shorter distance with the approach of the flame jet ignition.

Numerical Investigation on Multi-cycle Operation of Pulse Detonation Rocket Engine

In order to investigate the multi-cycle operation process of pulse detonation rocket engine (PDRE), estimate the propulsion performance and obtain the regulation of the control parameters for performance optimization, a one-dimensional unsteady performance analysis model of PDRE is established and a CFD code is developed. The AUSM scheme and the third-order TVD Runge-Kutta method are used for spatial and temporal discretization, respectively. Chemical kinetics is modelled by a one-progress-variable scheme. The stiffness is dealt with by using the Strang-splitting method and fully implicit method. Through the simulation of the PDRE utilizing stoichiometric hydrogen/oxygen as the detonative mixture and nitrogen as purge gas, it can be found that the flow field in the detonation tube is much more complicated in multi-cycle operation due to the coupling of each cycle, compared with in single-cycle operation. The effects of the duty cycle of the filling period on flow characteristics and propulsion performance are also investigated here. As the duty cycle of the filling period decreases, the average thrust reduces too, but all filled mixture based specific impulse and detonative mixture based specific impulse increase. However, if the duty cycle of filling is too small, the gas temperature at the exit of PDRE will significantly increase. The results suggest that appropriately reducing the valve duty cycle of filling to decrease detonative mixture filling length can improve the propulsion performance and make PDRE run in an economical way.

Experimental Study of Kerosene-Fueled Pulse Detonation Rocket Engine

Pulse detonation rocket engines (PDREs) have attracted considerable research interests in recent years as chemical propulsion systems potentially offering improved performance and reduced complexity compared to conventional steady-state liquid rocket engines. PDREs harness the high-energy release rate and thermodynamic characteristics of detonation waves to produce thrust. The PDRE test facility used in the paper utilizes kerosene as fuel, oxygen as oxidizer, and nitrogen as purge gas. Solenoid valves were employed to control intermittent supplies of kerosene, oxygen, and purge gas. The spark plug igniter used in the study had ignition energy of only round 50mJ. Two PDRE test models with different sizes were constructed: 25-mm internal diameter by 0.8-m length and 50-mm internal diameter by 1.2- m length. Both test models were used DDT enhancement device called Shchelkin spiral. The utilization and performance of liquid fuel kerosene used in PDRE were experimentally investigated, since its attraction for volume-limited aerospace propulsion system. The effects of detonation frequency on thrust of PDRE test model were experimentally studied. The obtained results have shown that the time-averaged thrust of PDRE test model is approximately proportional to the detonation frequency. At the operation frequency 20Hz, the time-averaged thrust was around 107N, for the test model with 50-mm internal diameter by 1.2-m length. The effects of nozzle on PDRE thrust were experimentally investigated. Seven conic exhaust nozzles of different area ratio were tested. The nozzle area ratio varied from 0.3 converging to 4.24 diverging. The nozzle length is negligible to total detonation tube. It is shown that all of the seven conic exhaust nozzles provide performance benefits for PDRE applications. Both converging and diverging nozzles had an optimum area ratio.

One-dimensional unsteady design method for pulsed detonation engine nozzles

A new design method for pulse detonation engines nozzle was developed theoretically. The effects of non-uniform exhaust on the performance of pulse detonation engine were analyzed by constant volume cycle model. The results showed thrust losses induced by the non-uniform exhaust could be decreased by increasing fill pressure ratio. If the fill pressure ratio was larger than 10, the performance losses with a fixed optimal nozzle could be controlled within 3%. The optimal area ratio of the nozzle was obtained when the time-averaged pressure at the nozzle exit equals the ambient pressure. This was also applicable to one-dimensional unsteady frictionless pulse detonation engine model. Thus an optimal area of the nozzle could be calculated by the time-averaged total pressure. Compared with the zero-dimensional results obtained by numerical search technique, the errors of predicted optimal area could be neglected if fill pressure ratio is too large to prevent shock from propagating back to the nozzle. And the errors of predicted optimal area are lower than 5% compared with the results of the one-dimensional unsteady pulse detonation engine model.

Multicycle Detonation Investigation by Emission–Absorption-Based Temperature Diagnostics

In order to analyze and improve the performance of pulse detonation engines (PDEs), detailed detonation processes deserve much more attention. However, the measurements of characteristic parameters are difficult because the flow field in detonation is unsteady, with high pressure and high temperature. A new device based on the emission–absorption principle is developed specially for measuring pulsed temperature in a PDE plume. Experimental results show that the measured pulsed temperature can diagnose the PDE operation, such as multicycle detonation wave formation, operation frequency, and overfilling process. Effects of PDE configuration, operation frequency, and fuel on PDE plume temperature were investigated experimentally. The plume temperature increases with operation frequency. The PDRE average peak plume temperature is much higher than direct-connected PDEs and air-breathing PDEs. The newly developed plume temperature measurement method is simple, cheap, and easy to operate, which provides a useful tool to diagnose PDE multicycle operation and interaction of external flow field and PDE operation.

Experimental Study on DDT Characteristics in Spiral Configuration Pulse Detonation Engines

Abstract This work investigated features of the deflagration to detonation transition in a curved tube. A number of experiments were performed to acquire the transition rule of DDT, which would provide the design data and theoretical basis for the curved detonation chamber. The content of research is as follows: (1) Flow resistance experiments of nine detonation chambers have been explored. The results show that the spiral configuration can reduce the axial length of DC, and the total pressure recovery coefficient increases with the spiral pitch. (2) Single-cycle detonation experiments have been conducted using the 9 tubes in the resistance experiments. Liquid-gasoline/air is used as the detonative mixture in all the experiments. The detonation experimental results indicate that there is no detonation wave formed in the straight tube, but in all the selected spiral tubes fully-developed detonation waves have been obtained; compared to the straight tube case, the DDT time decrease with the decreasing of the radius of curvature (RC) by 6.2%∼19.8% in the spiral detonation tubes.

Experimental Study of Kerosene/air Valveless Air-breathing Pulse Detonation Engines

Detonation initiation of liquid hydrocarbon-air mixtures is critical to the development of the pulsed detonation engine (PDE). This paper focused on investigating the ignition and detonation-initiation performance of kerosene/air based on valveless air-breathing pulse detonation engines (PDEs) with inner diameters of 50mm and 120mm. Because of the poor detonability of kerosene/air mixture, a variety of devices and means were used to promote the detonation initiation. A flash vaporization system was designed and used to heat the kerosene and observed the effect of fuel temperature on ignition-detonation performance of PDE. And the centrifugal nozzle and twin-fluid air-assist atomizer were used to investigate the fuel droplet size effect on detonation-initiation performance. The results indicated that increasing ignition energy and fuel temperature was helpful for quick ignition and flame acceleration although detonation didn’t occur when the centrifugal nozzle was used. When air-assisted atomizer was used, detonation was initiated successfully no matter the fuel was heated or not. However, the ignition-detonation times of kerosene/air in air-breathing PDE at several operation frequencies were longer than that of gasoline/air respectively. As the operation frequency increased, the difference between the ignition-detonation times of kerosene/air and gasoline/air decreased. When the PDE inner diameter increased to 120mm, detonation occurred much more difficultly. Detonation was not initiated until the ignition energy increased to 4J and the mixing of kerosene and air was enhanced ulteriorly. And each of the ignition-detonation time at different operation frequency increased as the PDE inner diameter increased.

Performance Measurements of a Kerosene-Oxygen Pulse Detonation Rocket Engine at the Frequencies of 35-40Hz

With the goal of further increasing the operation frequency of PDRE, some measures were taken and a series of experimental studies were performed on a kerosene-oxygen pulse detonation rocket engine (PDRE) model. The PDRE detonation model was constructed of a steel pipe of 850mm length (LPDRE) and 30mm (DPDRE) diameter. The model was performed with liquid kerosene as fuel, compressed oxygen as oxidizer and nitrogen as purge gas, and was ignited by a spark with low energy. The supplies of fuel, oxidizer and purge gas are controlled by solenoid valves respectively. The main performance parameters, thrust and the pressure along the length of the model were measured at the frequencies of 35-40Hz. Thrust calibration test was conducted to get more accurate thrust. The measured results showed the operation frequency of the PDRE model can reach up to 40Hz, which as we know is so far the maximum operation frequency of PDRE with solenoid valves and liquid fuel. When the operation frequency is 35Hz, the peak value of detonation wave pressure is more than 3.4 MPa and the time-averaged thrust of PDRE is 43.9N. The peak value of detonation wave pressure is about 3.2 MPa and the time-averaged thrust of PDRE is 50N while the operation frequency is 40Hz. Nomenclature PDE = Pulse detonation engine PDRE = Pulse detonation rocket engine DDT = Deflagration-to-detonation transition P1 = Pressure at position 1 along the PDRE model Pi = Pressure at position i along the PDRE model det V = detonation wave speed

Experiment on Kerosene-Fueled PDRE: DDT Enhancement by Shchelkin Spirals and Exhaust Plume

*† ‡ § Pulse detonation rocket engines (PDREs) have attracted considerable research interests in recent years as chemical propulsion systems potentially offering improved performance and reduced complexity compared to conventional steady-state liquid rocket engines. An experimental investigation was carried out on a multi-cycle pulse detonation rocket engine test model, running on a liquid kerosene-oxygen mixture using a solenoid-valve injection system and a low-energy ignition source, to investigate the effectiveness of Shchelkin spiral on the Deflagration to Detonation Transition (DDT) process. Detonation frequency of test model was fixed in 10Hz. Automobile spark plug was used to ignite the detonative mixture, and the ignition energy was around 50mJ. The pressure was measured by piezoelectric pressure transducer. The results showed that Shchelkin spiral was able to achieve successful DDT in the detonation tube. In addition, a Phantom V7.2 CMOS color digital high speed video camera was used to record the exhaust plume of PDRE test model.