Technical difficulties of pulse detonation engine

Although the concept of PDE has been verified in the laboratory, there are still the following technical problems to be solved:

(1) Detonation, control and maintenance

Fast and reliable initiation is one of the most important problems in the practical application of PDE, because high working frequency and repeated ignition times are the basic requirements for the normal operation of PDE. Using deflagration to detonation (DDT) process is the best scheme for PDE research in the near future. In the past, most of the studies on initiation and deflagration to detonation were carried out in static gas, and most of the studies used very long shock tubes, which was inconsistent with the fact that the actual PDE length was less than 2 meters. Because these data are the result of a single detonation in a mixture with uniform concentration and no temperature gradient, they are almost completely different from the data of multiple detonation. In addition, the actual working frequency of PDE is very high, and the speed of mixed gas is very fast, so the results at low frequency are difficult to be used as the design basis at high frequency. Therefore, in order to develop PDE, a large number of experiments must be carried out to solve the problems caused. Including initiation energy, DDT method, DDT strengthening, detonation transition from confined environment to unrestricted environment, etc.

(2) Atomization, injection and mixing of liquid fuel and oxidant

For PDE burning liquid fuel, it is quite difficult to inject, mix and ignite the fuel. The injection system with fast response, high mass flow and high controllability is very important to meet the high frequency operation of pulse detonation engine. The injection system must meet the requirements of cost, weight, volume and power. Therefore, the physical, chemical and thermal characteristics related to the injection and mixing of gas and liquid fuels should be studied.

(3) Design of 3)PDE auxiliary system

The practical application of PDE should include several detonation chambers, which are connected with the same inlet and nozzle. The practical application of PDE system also includes pressurized fuel storage and supply system, fuel/air injection system, initiation system and propellant injection system.

Detonation pressure acting on the closed wall (thrust wall) at the end of PDE detonation chamber converts chemical energy into kinetic energy. PDE needs an auxiliary power system for start-up and flow control, and may also include a special-purpose power extraction system. In addition, PDE also needs to design components such as propulsion valve, fuel valve, control system, advanced combustion control system, effective inlet and nozzle, and consider the comprehensive design scheme of special parts of the system.

(4) Design of inlet/detonation chamber interface

Because the detonation process is very sensitive to stoichiometric ratio, particle droplet size and local mixing degree, it is very difficult to design the best inlet/detonation chamber interface, so it is necessary to study the efficient integration method between PDE and mixed compression supersonic inlet.

(5) Design of high performance nozzle

(6) Dynamic coupling of multiple detonation tubes

Due to the unstable thrust, the actual PDE needs to adopt multi-tube structure with high frequency (greater than 80 Hz), and there is a dynamic coupling problem between multi-tube detonation combustion chambers.

(7) cooling problem

The hot gas velocity after detonation wave is extremely high, which leads to the increase of heat in the pipe wall, so efficient cooling measures must be taken.

(8) Accurate theoretical analysis of knocking phenomenon

Advanced numerical simulation and multi-component detonation simulation using real chemical model and molecular mixing model are very important for understanding detonation combustion mechanism. The measurement technology of PDE is different from that of traditional engines, for example, the airflow needs to be measured with a laser velocimeter.

(9) Design of hybrid PDE

Ducted air and turbomachinery can be used, and active noise suppression may be required.