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Fundamentals of Pulse Detonation Engine (PDE)

and Related Propulsion Technology

Aerospace Engineering Consulting

Arlington, TX

Dora E. Musielak, Ph.D.

All rights reserved. No part of this publication may be reproduced, distributed, or transmitted, unless for course participation, in any form

or by any means, or stored in a database or retrieval system, without the prior written permission of the Author. Contact D. E. Musielak,

[email protected]

mailto:[email protected]

Pure PDE Cycle

1: Fuel-Oxidizer

Injected and

Mixed

2: Detonation

Initiated by

ignition source

3: Detonation

wave moves

through gas

mixture

4: High

pressure gas

fills detonation

chamber

5: Detonation wave exits

chamber and air is drawn

in by reduced pressure

Thrust is directly proportional to detonation frequency

FILL DETONATE EXHAUST

Repeat

Pulse Detonation Engine (PDE) : type of propulsion system that utilizes detonation waves to combust fuel

and oxidizer mixture. Engine is pulsed because mixture must be renewed from combustion chamber

between each detonation wave initiated .

Why PDEs?

Advantages

• Increased Thermodynamic

Efficiency

• Higher Isp

• Reduced SFC

• Design Simplicity

• Increased Thrust-to-Weight Ratio

• Increased Thrust-to-Volume Ratio

• Lower Cost

• Mach Range 0 – 4

• Easy Vehicle Integration

Applications

• Cruise Missiles

• Supersonic Aircraft

• Hypersonic Missiles

• Hybrid Turbine-PDE

• UAV

• UCAV

• SSTO Launch Vehicles

• Precision Guided Munitions

• Drones

3

PDEs potential for easier scaling extrapolates to substantial reductions in

development time, when compared to conventional turbine engines.

Increased cycle efficiency results from quasi-constant volume process

Why PDEs?

4

Is it possible to augment gas turbine performance with PDEs

to extend supersonic flight regime?

Why PDEs?

5

Is a PDE/SCRAM/PDRE a viable

propulsion system for Spaceplanes?

03-06

PDRE = Pulse Detonation Rocket Engine

SCRAM = Scramjet supersonic combustion ramjet engine for M > 5

Preface

• Revolutionary propulsion is required to achieve high-speed cruise

capability within atmosphere, and for low cost reliable Earth-to-orbit

vehicles.

• Pulse detonation engines (PDEs) have potential performance

advantages over air breathing and rocket propulsion, bypassing

limitations of existing concepts.

• Proposed applications for detonation combustion include

– cruise missiles, UAV, ...

– supersonic aircraft, and

– SSTO launchers.

• This course highlights fundamentals of pulse detonation engines

and other related propulsion concepts, addressing performance

characteristics, enabling technologies, and current R&D initiatives to

develop new propulsion systems.

6

Air Breathing PDE Technology – D. E. Musielak

Nomenclature and Terminology

• A list of common terms and basic definitions is provided in a

separate handout to facilitate communicating the concepts

introduced in the course.

• In 2002, Kaemming, Lidstone, and Sammann proposed a

component nomenclature, station (spatial) designation, process

and event (temporal) designation and terminology for the unique

PDE scheduling characteristics. Ref. AIAA 2002-3631.

• Nomenclature proposal is based on several years of PDE analysis

and testing by Boeing and Pratt & Whitney and is based on

accepted practices, such as SAE Standard AS7551.

• To date, no standard has been formally issued for PDEs, and so

we will follow the recommendations in AIAA paper 2002-3631

7

Nomenclature and Terminology

8

See Appendix 1


Introduction to PDEs

9

• Propulsion Comparison

• A Vision for the Future

• Limits of Turbo-Engines

• Ideal Cycles

• Combustion Modes

• Pure Pulse Detonation Engine

• Detonation for Propulsion

• Modeling a Single Cycle

• PDE Thermodynamic Cycle

Propulsion Comparison

fo

spmg

FI

Need improved SFC performance

Seeking Revolutionary Propulsion Ideas

10

F

mSFC

f


Highest Supersonic Speed: M = 3.2

11

SR-71

Turbofan engines in high performance aircraft such as F-15

“Eagle” fighter can achieve Mach 2.5

F-16 “Fighting Falcon” jet fighter and F-22 “Raptor” are

limited to Mach 2.


A Vision for the Future

12

Reduced SFC

Higher Thermodynamic Efficiency

Higher Isp

Design Simplicity

Increased Thrust-to-Weight Ratio

Increased Thrust-to-Volume Ratio

Lower Cost

Mach range 0 – 10

Manufacturing Simplicity

Easy Vehicle Integration

Air Breathing Propulsion Requirements

Develop air-breathing engine capable of

propelling aircraft beyond Mach 2.5.


Turbine Engine Limits

13

)1(1

2 4

o

t

o T

T

am

F

Inlet

Efficiency

Rotational

speed Compressor exit

temperature limits

pressure ratio

Static pressure

balance

P&W F100 AB Turbofan

• At Mach > 3, compressed air reaches such extreme

temperatures that compressor stage fan blades begin to fail.

• Compressor exit temperature limits pressure ratio.

• Turbine inlet temperature limits thrust.


Turbofan with Afterburner

• Efficient with continuous afterburner at ~ Mach 3.

• Afterburner provides temporary increase in thrust,

for supersonic flight and take off

• Slower bypass airflow produces thrust more

efficiently than high-speed air from core, reducing

specific fuel consumption.

14


P&W F-100-

15

Performance Maximum thrust:

17,800 lbf (79.1 kN) military thrust

29,160 lbf (129.6 kN) with afterburner

Overall pressure ratio: 32:1

Specific fuel consumption:

Military thrust: 0.76 lb/(lbf·h) (77.5 kg/(kN·h))

Full afterburner: 1.94 lb/(lbf·h) (197.8

kg/(kN·h))

Thrust-to-weight ratio: 7.8:1 (76.0 N/kg)

F-16


Ideal Thermodynamic Cycle

Brayton cycle: heat addition

at constant pressure

16

in

outth

Q

Wnet

inQ = rate of thermal energy released

= net power out of engine outWnet

= thermal efficiency of engine th

)( 34 TTcmQ pin

)]([ 2354 TTTTcmWWWnet pctout

3

2

34

25

34

2354 1)(

)(1

)(

)()(

T

T

TT

TT

TT

TTTTB

/)1(

23 )/(

11

ppB


Burner Exit Temperature T4

17

• Increasing T4 enlarges useful work output (isobars diverge )

• However, distance between stations 3 and 4 increases also

more heat has to be added and thus more fuel is needed.

• Thermal efficiency is only dependant on compressor pressure

ratio P3/P2 and does not change with T4


Higher T4, Lower Efficiency

18

• However, isentropic exponent is not constant but

decreases when temperature increases

thermodynamic efficiency decreases with T4!


Heat Addition and Pressure

Can we improve thermodynamic cycle

efficiency with a pressure-gain process?

4

19


Ideal Thermodynamic Cycle

Humphrey cycle: heat

addition at constant volume

20

1

1

1

3

4

3

4

3

2

1

T

T

T

T

T

TH

Constant volume

heat addition

inQ

5 2

4 3

3*

Thermal efficiency improves by more

than 15% and as much as 10 to 40%

improvement in Isp (Ref. Bussing (1996);

Heiser & Pratt (2002); Povinelli (2002))


Pulse Detonation Engine (PDE)

21

Ideal PDE thermodynamic efficiency higher than turbo-

engine because a detonation wave rapidly compresses

mixture and adds heat at ~ constant volume.


Propulsion Performance

22

Combustion Modes

Deflagration Subsonic

Combustion

Detonation Supersonic

Combustion

Unsteady

Pulsed or

Intermittent

Steady or

Continuous

Combustion

Unsteady

Pulsed or

Intermittent

Steady or

Continuous

Pulse Jets Turbojets

Ramjets

Scramjets

PDEs

PDREs Scramjets ?

RDE

Detonation supersonic spread of

combustion by shock compression.

Deflagration subsonic spread of

combustion by thermal conductivity

F

23

Combustion Modes: Detonation and Deflagration

• Deflagrations are subsonic

combustion waves: M1< 1

• Typical deflagrations

propagate at speeds on the

order of 1-100 m/s

• Across a deflagration, the

pressure decreases while the

volume increases, P2 < P1 and

V2 > V1

• Detonations are supersonic

waves: M1 >1

• Typical detonation waves propagate

at a velocity on the order of 2000 m/s

(4 < M1 < 8)

• Pressure increase across a

detonation, while the volume

decreases: P2 > P1, V2 < V1

• Detonations in HC fuel: P2/P1 ~ 20

24

u1 u2

P1 P2


Deflagration and Detonation

Flame propagates from right

25

• Combustion or burning is sequence of exothermic chemical

reactions between fuel and an oxidant accompanied by

production of heat and conversion of chemical species.

Products

u2

P2, T2, 2, M2 P1, T1, 1, M1

Reactants u1

Detonation vs Deflagration: Qualitative Differences

• Qualitative differences between upstream and

downstream properties across detonation wave are

similar to property differences across normal shock

• Main differences:

– Normal shock wave: downstream velocity always

subsonic

– Detonation wave: downstream velocity always local

speed of sound

• Note that detonation waves can fall into strong and weak

classes

• Strong detonation: subsonic burned gas velocity

• Weak detonation: supersonic burned gas velocity

26

Wave Properties

• Normal shock property ratios are qualitatively similar to those of

detonations and of same magnitude

– Except that for detonation downstream velocity is sonic

• Mach number increases across flame for deflagrations

– Mach number is very small and thus is not a very useful parameter to

characterize a deflagration

• Velocity increases substantially and density drops substantially

across a deflagration

– Effects are opposite in direction as compared with detonations or shock

waves

• Pressure is essentially constant across a deflagration (actually

it decreases slightly), while detonation has high pressure

downstream of propagating wave

• Characteristic shared by shock, detonation, and deflagration is large

temperature increase across wave

27

Detonation for Propulsion D

eto

nati

on

w

ave (

DW

)

pro

pag

ati

on

to

cre

ate

th

rust

28

Oblique Detonation Wave Engine (ODWE) • Combustible gas mixture velocity equals or exceeds detonation Chapman-

Jouguet (CJ) velocity.

• Detonation waves (DWs) or oblique detonation waves (ODWs) are positioned to

combust injected combustible mixture.

Pulse Detonation Engine (PDE) • Cyclically detonates fuel and atmospheric air mixtures to generate thrust.

• A shock wave compresses gas and this is followed by rapid release of heat and

a sudden rise in pressure.

• PDE generates thrust intermittently, and it produces a significant pressure rise

in combustor.

• Detonation-generated pressure rise represents primary benefits of a PDE in that

it may reduce engine compression requirements.

Continuous Detonation Engine (CDE) • Combustible gas mixture is injected along axial direction, and DWs propagate in

azimuthal direction.

• Two directions are independent, DWs can continuously propagate with range of

combustible gas injection velocities and do not require multi-time ignition.

Pure PDE Cycle

1: Fuel-Oxidizer

Injected and

Mixed

2: High

pressure

detonation

Initiated

3: Detonation

wave moves

through gas

mixture at

supersonic speed

4: High

pressure gas

fills detonation

chamber

5: Detonation wave exits

chamber and air is drawn

in by reduced pressure

Thrust is directly proportional to detonation frequency

FILL DETONATE EXHAUST

Repeat

Detonation Initiation

• A detonation may form via direct initiation or via deflagration-to-

detonation transition (DDT).

• Direct initiation is dependent upon an ignition source driving a blast

wave of sufficient strength such that igniter is directly responsible for

initiating detonation. It requires extremely large energy.

• DDT begins with a deflagration initiated by relatively weak energy

source which accelerates through interactions with its surroundings

into a coupled shock wave-reaction zone structure characteristic of a

detonation.

• After spark creates a deflagration, transition process can take

several meters or longer and a large amount of time.

30

Key to detonation initiation schemes for PDEs is to shorten distance

and time required for deflagration-to-detonation transition (DDT).

PDE Requirements

Ignition and mixing must occur quickly to minimize cycle

time and maximize thrust.

DDT must occur quickly and in a short distance. Shortening

DDT time decreases the detonate part of the cycle, allowing

a frequency increase that is accompanied by a thrust

increase.

Shortening DDT distance decreases necessary thrust tube

length, resulting in weight savings, a great advantage for

propulsion.

31 1 2 3


PDE Cycle (Basic Cycle Process)

32

1. Initially, chamber at ambient

conditions

2. Propellant injected from

closed end

* Sidewall injection also works

and may improve mixing

3. Ignition from closed end

4. Wave propagation and

transition in chamber

5. Wave exits chamber

6. Exhaust and purge


Rankine-Hugoniot Combustion Map

Conservation equations for mass, momentum,

and energy for combustion waves in steady,

inviscid, and constant-area flow.

Hugoniot is locus of possible solutions for state 2

from a given state 1 and a given energy release

Rayleigh line relates states 1 and 2.

Solution state is at intersection of Hugoniot and

Rayleigh line.

2211 vv 2

222

2

111 vPvP

2

221

2

2

121

1 vhvh

M1 M2

111 ,, vP 222 ,, vP

Combustion

wave

33


Chapman-Jouguet C-J Condition

• Solution to conservation equations is determined considering:

– For deflagrations, wave structure, and turbulent and diffusive processes

determine propagation speed.

– For detonations, gas dynamic considerations are sufficient to determine

solution.

– Chapman (1899) and Jouguet (1905) proposed that detonations travel

at one particular velocity, which is minimum velocity for all solutions on

detonation branch.

• At solution point (Chapman-Jouguet detonation point), Hugoniot,

Rayleigh line, and isentrope are tangent. Flow behind a C-J

detonation is sonic relative to wave: M2=1.

• C-J points divide Hugoniot into 4 regions:

– Weak deflagrations (subsonic to subsonic)

– Strong deflagrations (subsonic to supersonic)

– Weak detonations (supersonic to supersonic)

– Strong detonations (supersonic to subsonic)

34

C-J Velocity

• Chapman-Jouguet (C-J) condition: for an infinitesimal thin detonation,

detonation wave proceeds at a velocity at which reacting gases just

reach sonic velocity (in frame of lead shock) as reaction ceases.

• Assumes chemical reaction takes place at moment when shock

compresses material

• Chapman-Jouguet velocity: velocity of an ideal detonation as

determined by C-J condition: burned gas at end of reaction zone

travels at sound speed relative to detonation wave front.

• C-J velocities can be computed numerically by solving for

thermodynamic equilibrium and satisfying mass, momentum, and energy

conservation for a steadily-propagating wave terminating in a sonic

point.

• C-J velocities in typical fuel-air mixtures between 1400 and 1800 m/s.

35 Speed of sound: 331 m/s in air.


PDE Thermodynamic Cycle (Heiser & Pratt, 2002

36

• Process 3 4 models normal

detonation wave in a PDE (ZND

wave model)

• Entropy generated in detonation

wave heat addition process

is sum of that generated in

process from 3 to 3a (adiabatic

normal shock wave) and that

generated in process from 3a to 4

(constant-area heat addition

process) that follows.

Thermal efficiency of ideal Humphrey cycle is close to, but always

somewhat less than, that of ideal PDE cycle – H&P

Summary of Chapter 1

• Revolutionary propulsion is required to achieve high-speed cruise

capability within atmosphere, and for low cost reliable earth-to-orbit

vehicles.

• Pulse detonation engines (PDEs) have potential performance

advantages over air breathing and rocket propulsion, bypassing

limitations of existing concepts.

• Propulsion architectures that use pulsed and continuous detonation

combustion offer more efficient thermodynamic properties, and thus

are expected to exhibit a higher level of performance than more

conventional propulsion that rely simply on deflagration combustion

process.

• Chapter 2 will provide an overview of detonation-based propulsion,

including hybrid turbine-PDE and Continuous Detonation Wave

Engine (CDWE) concepts.

37


J58

R-R/Snecma Olympus 593

P&W F100

GE F110

P&W F119

GE F414

P&W F100-232

Next Generation Supersonic Air Breathing Engine

38

Detonation

• Detonation is a shock wave sustained by energy released by

combustion

• Combustion process, in turn, is initiated by shock wave compression

and resulting high temperatures

• Detonations involve interaction between fluid mechanic processes

(shock waves) and thermochemical processes (combustion)

39