Longxi Zheng

Experimental Investigation of Ignition-Detonation Time in Two-Phase Valveless Pulse Detonation Engines

This paper focused on investigating the ignition and detonation-initiation performance of avgas-air two-phase valveless pulse detonation engines (PDEs) with inner diameters of 50mm and 120mm in different operation cases. To quantify the ignition and detonationinitiation performance, parameter ignition-detonation time was examined, which was defined as the sum of the ignition time and deflagration-to-detonation transition (DDT) time. In order to observe the effects of ignition energy, operation frequency of PDE and inner diameter of PDE on ignition-detonation time and PDE performance the proof–of-principle experiments of PDEs were carried out. The results indicated that the ignition energy, operation frequency and PDE diameter had important effects on ignition-detonation time. As the ignition energy increased, the ignition-detonation time decreased and the average thrust of PDE increased. As the operation frequency increased, the ignition and detonationinitiation time decreased and the ignition energy effect on ignition-detonation time degenerated. And the ignition-detonation time increased with the PDE diameter increasing. Each of the ignition-detonation times of avgas-air based on pulse detonation rocket engine (PDRE) was lower than that of air-breathing PDE at the same operation frequency slightly.

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.

Direct-connected experimental investigation on a pulse detonation engine

A pulse detonation engine with the inner diameter of 50 mm and total length of 1500 mm was designed. Gasoline was used as the fuel and air as the oxidizer. The Shchelkin spiral was used as the deflagration to detonation transition accelerator. The direct-connected test of the pulse detonation engine was conducted to find out the detonation initiation and propulsion performance at several different operating frequencies. The experimental results indicated that detonation waves were fully initiated in the pulse detonation engine at the operating frequency range of 1–35 Hz. As the operating frequency increased, the pulse detonation engine average thrust increased nearly linearly, while the optimum equivalence ratio decreased gradually. The volume-specific impulse and mixture-specific impulse had the similar increasing trend at the increased operating frequency. As the operating frequency increased from 0 to 25 Hz, the fuel-specific impulse increased dramatically while the specific fuel consumption decreased quickly. The fuel-specific impulse and specific fuel consumption changed slightly when the operating frequency exceeded 25 Hz. In addition, two groups of computational value of mixture-specific impulse and fuel-specific impulse were obtained by Winternberger model and Yan model considering the two-phase effect. Compared with the experimental results, similar variation trends relative to the operating frequency were achieved by the two computational models. However, the computational values of mixture-specific impulse and fuel-specific impulse by Winternberger model were much higher than that of experimental values. When two-phase effect was considered, the computational values of mixture-specific impulse and fuel-specific impulse were close to that of experimental values.

Investigation of Hot Jet Effect on Detonation Initiation Characteristics

ABSTRACT This article addresses the effect of hot jet condition on detonation initiation characteristics. Hot jets with different conditions were generated by changing the length of the pre-detonator. The change relationship between the detonation initiation characteristics and the jet condition was investigated by numerical simulation and experiment. The simulation results showed that a detonation wave could not be initiated by the low velocity jet (subsonic), but could be initiated by the high velocity jet (the supersonic jet and detonation jet) under the current simulation conditions. Meanwhile, the ignition and detonation initiation time, hot jet detonation initiation time, and detonation initiation distance in the main-detonation tube decreased as the velocity of the hot jet increased due to the increased pre-detonator length. The multi-cycle detonation experiments of pulse detonation engines (PDEs) were conducted to validate the simulation results by using a pre-detonator with two different lengths. The experimental results indicated that the ignition and detonation initiation time and hot jet detonation initiation time both decreased with increased jet velocity resulting from the increased length of the pre-detonator, which was basically consistent with the simulation results.

Experimental Research on Induction Systems of an Air-breathing Valveless Pulse Detonation Engine

Abstract An air-breathing valveless PDE model was designed and manufactured, which was made up of subsonic inlet, mixing chamber, ignition chamber, detonation chamber. The total pressure recovery coefficient, flux coefficient and intake resistance with six different induction systems were measured by a semi free subsonic flow field. The proof-of-principle experiments of PDE model with different induction systems were all successfully carried out, by using liquid gasoline-air mixture with low-energy system (total stored energy less than 50 mJ). The measured detonation wave pressure ratio was very close to that of C-J detonation. The air-breathing PDE model was easy to initiate and worked in good condition. The deflagration to detonation transition (DDT) and operation frequency effect on pressure traces were also investigated by experiments. The results indicated the oscillation of pressure peak at P6 enhanced with the operation frequency increased. DDT accomplished before P6 and the DDT distance was about 0.9 m (from the ignitor).