UWE Bristol Engineering showcase 2015

Tristan Maddick
MEng Aerospace Engineering
Project Supervisor
Dr Rohitha Weerasinghe
Analysis of Design and Applications of Pulsed Detonation Engines
Introduction
Pulsed Detonation Engines are engines which utilize pulsed detonations to
provide thrust. They have a similar basic operation to pulse jets with the
major difference being that pulse jets use the deflagration process.
Deflagration is a relatively low pressure process with the flame travelling at
subsonic speeds, causing the fuel to ignite through heat transfer. Detonation,
on the other hand, is a high pressure process where the flame travels at
supersonic speeds; ignition of the fuel is caused by the high pressure present
as the shockwave moves down the combustion chamber. Due to the fact that
Orifice Plate Investigation
The aim of the following experiments was to obtain a better understanding
of the use of orifice plates as a DDT device and to investigate the effects of
changing the blockage ratio of the DDT device. The experiments tested a
range of blockage ratios that is varied by changing the diameter of the holes
on the plate. By completing experiments across a range of blockage ratios
results were produced that provided further information on how the
blockage ratio affects the detonation process and what the optimum
blockage ratio could be.
Results
The graph shows that from the experiments completed that the best
blockage ratio was 77.68 (single hole). The graph also clearly shows the
difference in power between the single hole and multi-hole configurations.
Furthermore, by plotting a line of best fit on the graph the initial hypothesis
stating that an optimum blockage ratio could be found is confirmed and is
approximately 80. As an additional observation it would be expected that if
multi-hole experiments were completed for each of the same blockage ratios
as the single hole values similar power differences would be registered
resulting in a line of best fit parallel to the single hole one.
Applications
Pulsed Detonation Engines have large number of potential applications
because of their versatility as an engine. PDEs are well suited to speeds of up
to about Mach 4. At these speeds they have many advantages over solid
rocket motors such as increased range or payload. Whilst turbojet and
turbofan engines provide a long range and heavy payload they are
considerably more expensive when exceeding Mach numbers of around 2-3
and ramjets and other ducted rockets require solid rocket engines to achieve
detonation is an almost constant volume, high pressure process PDEs provide a
high thermodynamic efficiency, reducing fuel costs . The engine is described as
pulsed as the oxidizer-fuel mixture has to be replenished in the detonation
chamber between each detonation wave. The engines are capable at operating
at a range of frequencies but when operating at frequencies over 100Hz the
engine can provide almost constant thrust. The first year successfully produced
a detonation reaction using Computational Fluid Dynamics and found that
orifice plates provided the optimum engine output for the devices tested to
initiate detonation.
Power (W)
The following experiments were completed with the orifice plates:
1. Multi-hole, 77.68 blockage ratio
2. Single hole, 77.68 blockage ratio
3. Single hole, 85 blockage ratio
4. Single hole, 90 blockage ratio
5. Single hole, 95 blockage ratio
1000
900
800
700
600
500
400
300
200
100
Average Power
0
65 70 75 80 85 90 95 100
Blockage Ratio
Single Hole
Multi-hole
the speed at which the ramjet can take over, increasing the complexity.
Furthermore, due to the fact detonation is an almost constant volume, high
pressure process PDEs provide a higher thermodynamic efficiency which
reduces fuel costs. PDEs can also be designed as air breathing engines which
require a more simplistic design. Additionally, there is a reduction in weight, as
the oxidiser doesn't have to be stored onboard, which increases fuel efficiency
or allows extra weight to be used to enable greater speeds, increased ranged or
a heavier payload.
Project summary
The project researched the major problems
associated with Pulsed Detonation Engines and
looked into practical solutions. The experiments
completed were aimed at producing the optimum
detonation reaction and power output achievable by
Pulsed Detonation Engines. Finally, the project
focussed on the potential applications of the Pulsed
Detonation Engine.
Project Objectives
1. Further investigation into the use of orifice plates
as a Deflagration-to-Detonation device.
2. Improve the transient setup of the computational
experiments.
3. Use computational methods to analyse the
stresses and noise levels produced by the
detonation reaction.
4. Research the potential applications of the Pulsed
Detonation Engine.
Project Conclusion
The main conclusion from the orifice plate
experiments completed were completed using two
different configurations of the orifice plate, single
hole and multi-hole, with the same blockage ratio
value. It was expected that they would produce
similar, if not the same results, but multi-hole
configuration produced approximately 150 Watts less
power over 0.01 seconds. Despite both configurations
having the same blockage ratio; it was concluded that
as the multi-hole configuration contains a series of
smaller holes the flow experiences a greater area
reduction compared to the single hole configuration.
The remainder of the completed experiments
involved testing a range of blockage ratios for orifice
plates, investigating the hypothesis that an optimum
blockage ratio existed. It was clear from the final
graph produced that for orifice plates the optimum
blockage ratio value is approximately 80.