Challenges in Combustion for Aerospace Propulsion

228 Pages·2016·59.35 MB·English

Issue 11
Challenges in Combustion for Aerospace Propulsion
June 2016
AL11-00 - Research Activity to Tackle the Challenges in Combustion for Aerospace Propulsion
DOI : 10.12762/2016.AL11 F. Dupoirieux
AL11-01 - ONERA Test Facilities for Combustion in Aero Gas Turbine Engines,
and Associated Optical Diagnostics
A. Cochet, V. Bodoc, C. Brossard, O. Dessornes, C. Guin, R.Lecourt, M. Orain, A. Vincent-Randonnier
AL11-02 - CORIA Aeronautical Combustion Facilities and Associated Optical Diagnostics
F. Grisch, A. Boukhalfa, G. Cabot, B. Renou, A. Vandel
AL11-03 - Numerical Simulation of Reactive Flows in Ramjet Type Combustor and
Associated Validation Experiments
T. Le Pichon, A. Laverdant
AL11-04 - Research on Supersonic Combustion and Scramjet Combustors at ONERA
D. Scherrer, O. Dessornes, M. Ferrier, A. Vincent-Randonnier, Y. Moule, V. Sabel’nikov
AL11-05 - Modeling Challenges in Computing Aeronautical Combustion Chambers
B. Fiorina, A. Vié, B. Franzelli, N. Darabiha, M. Massot, G. Dayma, P. Dagaut,
Publisher V. Moureau, L. Vervisch, A. Berlemont, V. Sabel’nikov, E. Riber, B. Cuenot
Stéphane Andrieux AL11-06 - Advanced Simulation of Aeronautical Combustors
B. Cuénot, R. Vicquelin, E. Riber, V. Moureau, G. Lartigue, A. Figuer, Y. Mery, J. Lamouroux,
Editor in Chief S. Richard, L. Gicquel, T. Schmitt, S. Candel
Alain Appriou AL11-07 - Methodology for the Numerical Prediction of Pollutant Formation in Gas Turbine
Combustors and Associated Validation Experiments
Editorial Board F. Dupoirieux, N. Bertier, C. Guin, L.-H. Dorey, K.-P. Geigle, C. Eberle, P. Gerlinger
Stéphane Andrieux AL11-08 - Measuring Non-Volatile Particle Properties in the Exhaust of an Aircraft Engine
Alain Appriou I. K. Ortega, D. Delhaye, F.-X. Ouf, D. Ferry, C. Focsa, C. Irimiea, Y. Carpentier, B. Chazallon,
Philippe Bidaud P. Parent, C. Laffon, O. Penanhoat, N. Harivel, D. Gaffié, X. Vancassel
Esteban Busso AL11-09 - Investigation and Modeling of Combustion Instabilities in Aero Engines
Laurent Jacquin P. Gajan, F. Simon, M. Orain, V. Bodoc
Pierre Touboul AL11-10 - Recent Improvements in Combustion Noise Investigation: from the Combustion
Chamber to Nozzle Flow
Production M. Huet, F. Vuillot, N. Bertier, M. Mazur, N. Kings, W. Tao, P. Scouflaire, F. Richecoeur,
ONERA Scientific S. Ducruix, C. Lapeyre, T. Poinsot
Information Department AL11-11 - Experimental Investigations of a Low Emission Combustor Designed for Mid
Power Gas Turbine
On line G. K. Vedeshkin, E. D. Sverdlov, A. N. Dubovitsky
www.aerospacelab-journal.com AL11-12 - New Combustion Concepts to Enhance the Thermodynamic Efficiency of Propul-
Webmaster ONERA sion Engines
M. Bellenoue, B. Boust, P. Vidal, R. Zitoun, T. Gaillard, D. Davidenko, M. Leyko, B. Le Naour
Contact AL11-13 - Recent Advances in Research on Solid Rocket Propulsion
E-mail: [email protected] Y. Fabignon, J. Anthoine, D. Davidenko, R. Devillers, J. Dupays, D. Gueyffier, J. Hijlkema,
N. Lupoglazoff, J. M Lamet, L. Tessé, A. Guy, C. Erades
Produced by AL11-14 - Hybrid Chemical Engines: Recent Advances from Sounding Rocket Propulsion
ONERA - BP 80100 and Vision for Spacecraft Propulsion
Chemin de la Hunière J.-Y. Lestrade, J. Messineo, J. Hijlkema, P. Prévot, G. Casalis, J. Anthoine
et des Joncherettes AL11-15 - A Rocket Engine under a Magnifying Glass
91123 PALAISEAU CEDEX L. Vingert, G. Ordonneau, N. Fdida, P. Grenard
France AL11-16 - Numerical Simulation of Cryogenic Injection in Rocket Engine Combustion
www.onera.fr Chambers
P. Gaillard, C. Le Touze, L. Matuszewski, A. Murrone
ISSN: 2107-6596
Challenges in Combustion for Aerospace Propulsion
Research Activity to Tackle the
Challenges in Combustion
for Aerospace Propulsion
Francis Dupoirieux
(ONERA)
Research Director, The use of combustion for aerospace propulsion is inescapable for the long term.
Deputy Head of the Energetics The improvement of the energetic efficiency, safety and reliability, and the com-
Department, in charge of the academic
pliance with increasingly stringent environmental rules require the enhancement
research activity
of existing technologies and/or a breakthrough in propulsion devices. A vigorous
research activity must be pursued in the field of combustion to meet these goals.
DOI : 10.12762/2016.AL11-00
This issue of AerospaceLab gives the reader an overview of this intense activity,
ranging from experimental to theoretical and numerical work.
Combustion is a process that is used to supply more than 80 % of the Concerning aircraft propulsion, this issue starts with a description of
world primary energy. Since this process still mainly relies nowadays the main features of the major combustion facilities used at ONERA
on fossil fuels, it creates about 70 % of the Green House Gases (GHG). and CORIA Rouen for experimental research on aerospace propulsion
Technological solutions are today available for industry, housing and [AL11-01 and AL11-02]. The physical phenomena involved in tur-
ground transportation, to cease using carbonated fuel combustion, bulent combustion and the corresponding models to be introduced
i. e., to progressively shift to low GHG emission processes. The into the numerical tools are then discussed, and the validation of
situation is different in aeronautics and aerospace, where combus- these tools using experimental results is exemplified [AL11-05]. The
tion remains the only process able to supply the specific power and way in which these complex numerical tools are applied to industrial
energy required to propel aircraft, rockets and missiles. This means combustors is presented in AL11-06. Various solutions are used to
that the optimization of this process is mandatory, not only to ensure improve engine efficiencies and, consequently, decrease the specific
ever better operational safety and to decrease the operation costs, fuel consumption, one of which is an increase in the combustion pres-
but also to meet environmental requirements concerning emissions sure. However, this leads to a higher combustion temperature and,
and noise. Only research work aimed at improving existing combus- consequently, to higher NOx emissions. In order to offset this effect,
tion technologies as well as introducing technological breakthroughs lean premixed combustion is preferred, but this is at the expense of
in propulsion devices can allow us to achieve these objectives. This the combustion stability. The instability issue for this type of reactive
research work must be based on an experimental activity involving flow is addressed in AL11-09. Other topics of interest regarding reac-
accurate non-intrusive measurements to give us a deep insight into tive flows are combustion noise [AL11-10] and pollutant emissions
turbulent reactive flows, and an activity in numerical simulation and [AL11-07, AL11-08, AL11-11]. Concerning the last topic, [AL11-07]
modeling making possible a comprehensive analysis of these reactive deals with strategies to simulate the formation of pollutants, such
flows. Experimental and numerical activities are complementary of as soot and NOx, and presents some experiments designed to vali-
each other: numerical tools need to be validated by experiments and, date these strategies. [AL11-08] describes experimental studies to
on the other hand, the interpretation and understanding of the experi- accurately characterize the soot emissions of turbojet engines and
mental results is greatly enhanced by numerical simulations. [AL11-11] focuses on the experimental study of a low-emission com-
bustor designed for mid-power industrial turbines. Finally, technolo-
In the short term, the use of hydrogen for transport aircraft is not a gical breakthroughs are exemplified by presenting concepts allowing
viable solution because of storage difficulty and operation safety, and increased combustion pressures, using either the detonation mode or
the best way to lower the CO emissions of air transport, aside from a constant volume chamber [AL11-12].
2
improving the specific fuel consumption, is the use of biofuels recy-
cling the atmospheric CO. The question of biofuel use is wide and The use of combustion is also required for rocket and missile pro-
2
goes far beyond the sole problem of combustion. Therefore, it will not pulsion. For such vehicles, the main issues are improving operation
be addressed here. safety (by limiting the combustion instabilities, for instance) and opti-
mizing the specific impulse and the operating cost. Despite the low
The objective of this AerospaceLab issue is to give an overview of the number of flights, the emission of pollutant species, such as chlo-
vigorous research activity in the field of combustion. We focus here rinated species, can also be addressed if solid propellant is used.
on research work with a TRL (Technology Readiness Level) lower A close look at air breathing combustion in ramjets and scramjets
than or equal to 6, in other words, on research concepts that have not respectively [AL11-03, AL11-04] is taken. For ramjets, the objective
yet been tested on flying vehicles. is to improve the combustion efficiency and to prevent instabilities;
Issue 11 - June 2016 - Challenges in Combustion for Aerospace Propulsion
AL11-00 1
for scramjets, the difficulty lies in mixing fuel and air, and in anchoring is commonly used because it yields a high specific impulse. Two
the flame without thermal choking and/or an exceedingly great pres- papers describe research work in the field of cryotechnical propul-
sure drop. The physicochemical phenomena involved in solid-fuel sion, the first being dedicated to the experimental activity carried out
rocket propulsion are described in AL11-13, with special emphasis with the ONERA MASCOTTE facility [AL11-15], and the second to the
on the unsteady behavior of reactive flows inside rocket combustion numerical simulation of H2-O2 combustion with injection of cryoge-
chambers. This is followed by a paper that concentrates on hybrid nic oxygen [AL11-16].
propulsion, combining solid and gaseous propellants to obtain a more
flexible engine thrust [AL11-14]. This issue of the AerospaceLab Journal is far from being exhaus-
tive, but it is aimed at convincing the reader that top level research
The last topic developed in the issue is liquid propulsion, a complex combining experiments, physical modeling and numerical simula-
technology that requires the injection of propellants into a high-pres- tions remains mandatory to tackle the wide range of issues linked to
sure chamber, either by means of sophisticated pumping devices or combustion in propulsion systems for aeronautics and aerospace,
high-pressure tank storage. In addition, it often requires the storage which are issues that extend from operation safety to performance
of cryogenic propellants. Despite its complexity, liquid propulsion optimization and environmental impacts 
Issue 11 - June 2016 - Challenges in Combustion for Aerospace Propulsion
AL11-00 2
Challenges in Combustion for Aerospace Propulsion
A. Cochet, V. Bodoc ONERA test Facilities for Combustion
C. Brossard, O. Dessornes,
C. Guin, R. Lecourt
in Aero Gas Turbine Engines, and
M. Orain, A. Vincent-Randonnier
(ONERA) Associated Optical Diagnostics
E-mail: [email protected]
DOI : 10.12762/2016.AL11-01
The aim of this paper is to provide an overview of the ONERA test facilities devoted
to the study of combustion in gas turbine engines. The objectives of the experimen-
tal studies performed with these test rigs are very ambitious and extend from building
databases for the validation of codes and models used in numerical simulation to
applied research for evaluating the performance of advanced aero injection systems
in mono-sector, multi-sector or full annular combustion chambers. For more than ten
years, aside from standard measurements (i.e., pressure, temperature, mass flow
rates, gas analysis sampling), optical diagnostics have been widely associated with the
test campaigns carried out in these rigs. Many optical methods are now very common-
ly used to measure for instance flow velocity fields, size and velocity of droplets, and
the location of combustion zones. Other methods that are more difficult to implement,
or still under development, are being increasingly used or proposed for measuring phy-
sical or chemical parameters, such as temperature, size of soot particles or concen-
tration of combustion products. Examples of the results obtained with the ONERA test
facilities and optical diagnostics are given, in order to illustrate the studies presented in
this paper.
Introduction Research on the injection system and combustor is being carried
out in close cooperation with engines manufacturers, mainly within
In the coming years, air transport will face societal and environmen- the framework of European projects. Reducing pollutant emissions
tal challenges requiring cleaner and more efficient aero-engines to and specific consumption, or evaluating alternative fuels for aeronau-
be designed. The development of advanced combustors is based on tics, are some issues of interest in combustion testing with ONERA
reliable numerical tools and high-class experiments involving a great facilities.
amount of physical and chemical phenomena, such as combustion
in a two-phase flow with complex chemistry, pollutant formation, For code validation, experimental databases must be obtained from
or heat transfer and radiation. Experiments must thus be performed experiments carried out in either basic configurations or very close to
under thermodynamic conditions representative of those encountered the true engine design and operation mode (i.e., multi-swirl injectors,
in true engines. Test facilities capable of reproducing these specific multipoint fuel injection, pilot + main fuel injection).
operating conditions are available at ONERA and enable subsonic air-
breathing reacting flows occurring within gas turbine based aero-en- For these experiments, various measurements are applied to charac-
gines to be studied. terize non-reacting and reacting flows inside aero-combustors. Aside
from standard measurements using, for instance, pressure transdu-
These combustion test facilities are used to perform tests aimed at cers, thermocouples, a gas sampling probe and an analyzer, optical
tuning the aero-engine injection system and combustor, building diagnostics are increasingly being used. Their continuous development
experimental databases to validate CFD codes and supporting the made it possible to achieve non-intrusive measurements of a very large
development of new diagnostics under harsh conditions. set of physical and chemical quantities, such as gas velocities, soot
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 1
particle or fuel droplet sizes, gas concentrations, or temperatures. In obtained. Optical measurements used to perform these studies will
order to apply these techniques, test models are equipped with optical be also mentioned.
accesses, the material of the windows being selected depending on the
wavelength requirement of the applied diagnostics.
Test facility general features
For a long time, many research centers and laboratories, in France
and all over the world, have developed test facilities devoted to stu- Simulation of representative test conditions on test rigs
dies on combustion in gas turbine engines. For instance, many world-
wide test facilities are listed in Reference [1] and the example of the Aero-combustor testing requires facilities that are capable of simu-
French laboratory CORIA, located in Rouen, is detailed in Reference lating aero-thermodynamic conditions at the inlet of the combustion
[2]. ONERA facilities are mostly devoted to applied research of inte- chamber; that is to say, downstream from the compressor. Chamber
rest for aero-engine manufacturers, although some of them are dedi- pressure, inlet temperature and injection system global equivalence
cated to fundamental research. ratios are the governing parameters to be respected for a repre-
sentative simulation of the combustion chemical reactions inside
This article is aimed at providing an overview of the experimental test the combustor. The air mass flow rate depends on the size of the
facilities of ONERA at its Palaiseau and Le Fauga-Mauzac centers. combustor to be tested and is directly linked to the Reynolds number
Each test facility will be briefly described and examples of fundamen- to be reproduced in the experiments. In addition, it is essential to
tal and/or applied research carried out in these various facilities will obtain a convective Damkhöler number very close to those of real
be given, through the presentation of some past and recent results aero-engines.
BOX 1 – Combustor inlet air temperature versus compressor overall pressure ratio
The compressor overall pressure ratio P/P and the temperature at the inlet of the combustion chamber are linked by Relation (1) at sea
2 1
level
: heat capacity ratio
T =T×P2η1Pγγ−1(1) TP:: ptootlaylt rteompicp eerfafitcuireen acty the compressor outlet and at the combustor inlet
2 1 P 2
1 T: total temperature at the compressor inlet (here, T = 288 K)
1 1
P: total pressure at the compressor outlet and at the combustor inlet
2
P: total pressure at the compressor inlet
1
Figure B.1 shows the air temperature at the entrance of the combustion chamber vs. the overall pressure ratio under a sea level operating
condition.
1100
1000
900
=0.85
P
800 =0.90
K) P
(mpressor outlet 700 P=0.95
T Co 600
500
400
300
0 5 10 15 20 25 30 35 40 45 50
Overall pressure ratio
Figure B.1 - Air temperature at the compressor outlet vs. overall pressure ratio under a sea level operating condition
for different values of polytropic efficiencies
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 2
In addition to the thermodynamic conditions attainable in each test Test facilities are mainly characterized by the minimum and maximum
rig, the nature of the phenomena under investigation can make the chamber pressure, inlet temperature and air mass flow rate that they
difference between the purposes of each test facility. For example, are capable of simulating. The maximum test duration depends on
the ONERA/Le Fauga-Mauzac test facilities are focused on the cha- the test conditions (air mass flow and pressure) and air supply capa-
racterization of the spray generated from advanced injection systems, bilities (continuous air flow up to 10 kg/s at 1.0-1.2 MPa and high
whereas the ONERA/Palaiseau test facilities are more devoted to pressure storage of 21 tons at 25 MPa). Table 1 summarizes the test
combustion studies with the same injection systems. Experimental facilities that are of interest in this paper with their operating condition
data obtained with the facilities of each center are complementary and ranges. They are listed according to increasing thermal power sup-
are both used for code and model validation. plied to the test line.
ONERA combustion test facilities
Whatever the purpose of the studies taking place, the various test rigs
for aero gas turbine engines (single or multi-sector)
6
are operated with connected pipes and in non-vitiated air, in order
to investigate combustion in a fully representative chemical environ- LACOM
5
ment. One of the challenges to perform this kind of test is to provide
the air mass flow rate at the right chamber pressure and inlet tem-
4 Take-off
perature (for instance, a pressure combustion chamber of 4.0 MPa Pa) MICADO 2
corresponds roughly to an inlet temperature of 900 K). Regarding M
e ( 3 M 1
air heating, two technical options are mainly used. The first is a heat ur
s
exchanger, in which the air mass flow rate is heated through a hot flux es MICADO 1
generated by air/hydrocarbon combustion inside a slave burner. The Pr 2
second is an electrical heater, in which the mass flow is heated using
Cruise
electric rods immersed in the air that supplies the test rig. In addition, 1
MICADO
gaseous or liquid fuel distribution lines are available, depending on the
purposes of the studies. Some specific tanks can be implemented to 0 Idle LAERTE
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
operate the combustors with alternative fuels.
Air mass flow rate (kg/s)
Microcombustion
ONERA test facilities Figure 1 - ONERA test facility operating conditions shown in a pressure-air
mass flow rate diagram
As mentioned in the introduction, the test facilities described in this
article are located at: Additionally, Figure 1 shows the position of each test facility listed in
•ONERA/Le Fauga-Mauzac center: MERCATO and LACOM test Table 1 in a Pressure - Mass flow rate diagram. In this diagram, typi-
rigs; cal pressure domains, corresponding to the operating conditions of
•ONERA/Palaiseau center: micro-combustion laboratory, EPIC- an actual aero-engine with mono-sector or multi-sector combustor,
TETE test rig at LAERTE facility, M1 and MICADO (1 and 2) test rigs are shown. It can be seen that most test facilities are well suited to
at the Aerothermodynamics Laboratories. the high-pressure operating conditions typical of new combustors,
Minimum Maximun Minimum Maximum Minimum Maximum Maximum air
Test bench air mass air mass pressure pressure air inlet air inlet supply power
flow rate (kg/s) flow rate (kg/s) (MPa) (MPa) temperature (K) temperature (K) (MW)
Microcombustion
0.0002 0.005 0.1 4 293 293 0
test bench*
MERCATO 0.01 0.1 0.05 4 233 473 0.0246
EPICTETE test
bench 0.08 0.6 0.1 3 293 600 0.194
(LAERTE facility)
LACOM 0.1 1 0.1 50 293 900 0.68
MICADO 1
0.5 3 0.1 30 250 900 2.19
(ATD laboratories)
M1
0.1 4 0.05 30 250 900 2.91
(ATD laboratories)
MICADO 2
0.5 4 0.1 40 250 900 2.91
(ATD laboratories)
* No air preheating
Table 1 – Main Characteristics of ONERA test facilities
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 3
for either large engines in single sector studies or smaller engines in niques in both research institutes and industry [4]. Its major asset is
multi-sector studies. The LACOM test rig is more dedicated to studies its capacity to deliver a quantitative and instantaneous measurement
in which the influence of very high pressure and temperature on phy- of the velocity, not only at one point like Laser Doppler Velocimetry
sical phenomena is of interest, such as those of spray characteristics (LDV) does, but over a whole plane simultaneously: both visualization
in two-phase flows. and quantification of the 2D flow structure become available. Two or
three components of the velocity can be obtained by using one or two
cameras (stereoscopic PIV), respectively. Compared to non-reacting
Optical diagnostics applied to combustion studies flows, the implementation of PIV in reacting flows requires additional
technical constraints to be taken into account. The seeding of the flow
Full experimental investigation of the flow inside combustors requires must be performed with small (in the micron range) solid particles
visualizations and measurements of key physical quantities, such as (usually metal oxides, such as MgO or TiO). For instance, disper-
2
gas velocity, gas temperature, and concentration of major and minor sing systems used to generate such particles are prone to unsteady
species, as well as droplet size, velocity and temperature in two-phase behavior, and precautions in the operating procedure must be taken in
flows [3]. Due to the fact that they provide access to such quantities, order to limit particle deposits on the windows. Another critical issue
optical diagnostics have become an indispensable tool. They allow a is window access: in combustion chambers, it is usually dictated by
deeper understanding of the inner physical and chemical processes mechanical and thermal constraints. In particular, in stereoscopic PIV
at play, which is required to validate and improve computer-based each camera has to view the laser sheet with an angle of approxima-
simulations and to assist applied research in practical combustors. tely 45°: this results in limitations in the measurement plane locations
that can be investigated using this technique.
Over the past decades, optical diagnostics have been intensively used
or developed at ONERA and applied to combustion test facilities. The Planar Laser-Induced Fluorescence (PLIF) imaging is species- and
techniques used and their proven applicability range at ONERA are quantum state-specific, and is therefore sensitive to species compo-
summarized in Table 2. sition, temperature, number density and velocity [5]. The OH radical is
the most commonly used flame front indicator. Applied to this radical
Observation is often the first step: high-speed digital imaging of spon- species, PLIF, like PIV, is able to provide instantaneous information
taneous radiation can be easily implemented on the test rigs and pro- over the whole plane of the flowfield, without the line-of-sight ave-
vides some insight into the flame structure and dynamics. In particu- raging inherent to OH* chemiluminescence imaging. Simultaneous
lar, by using an interference filter, OH* or CH* chemiluminescence information on fuel and flame spatial distributions can be obtained
emission signals can be isolated in order to trace reacting regions of with two PLIF laser systems probing OH and kerosene vapor simul-
the flow. taneously [6]. Additionally, by seeding the flow with adequate fluo-
rescing tracers or probing tracers naturally present in the flow, the
A whole range of laser-based techniques can then be used, depen- mixture fraction distribution can also be obtained. Recently, PLIF
ding on the quantities of interest and on optical access. Particle Image applied to CO molecule has been developed and successfully applied
Velocimetry (PIV) has become one of the most widely used laser tech- to air-breathing engine flow investigation at ONERA [7].
Optical technique High pressure applicability limit (as proven at ONERA)(MPa)
Chemiluminescence (OH*, CH*) 6.5
Backlight imaging 6.5
Shadowgraphy 6.5
Laser Doppler Velocimetry 1.0
Phase Doppler Anemometry 1.0
Particle Image Velocimetry 0.4 (0.2 under reacting flow conditions)
Mie Scattering planar imaging 0.2
Planar Laser-Induced Fluorescence 2.3 (OH, kerosene), 0.95 (CO) at a repetition rate of 10 Hz, 0.1 (OH) at a repetition rate of 10 kHz
Rayleigh scattering 0.5
Raman scattering 0.5
Coherent Anti-Stokes Raman Scattering 6.5 (N, H) at a repetition rate of 15 Hz, 0.1 (N) a repetition rate of 1 kHz
2 2 2
Tunable Diode Laser Absorption Spectroscopy 0.2
Table 2 – Optical techniques applied at ONERA on large-scale combustion rigs
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 4
Laser spectroscopy based on nonlinear processes is widely used, ficant light reabsorption or beam steering effects will exist. For PIV,
from the near IR to the near UV, in order to probe reactive media. for instance, so far tests under reacting flow conditions have been
Among others, Coherent Anti-Stokes Raman Scattering (CARS) was conducted at ONERA in studies with chamber pressure levels limited
developed at ONERA and extensively used for temperature measu- to 0.2 MPa [13-15]. One of the main challenges will be to adapt the
rements in harsh reactive environments of interest in the aerospace PIV technique so that it can be used at chamber pressure levels as
field [8]. The basic principle of temperature measurements by CARS high as possible. In particular, beam steering is one of the issues that
is to probe the relative population of the molecular levels, from which must be addressed. The beam steering effects, generated by optical
the thermodynamic temperature of the molecular system is drawn. index gradients in the combustion chamber, result in image blurring
Consequently, the concentration of the probed species can also be and could be very significant in highly turbulent flows at high chamber
deduced [9]. pressures.
When studying two-phase flows, preliminary visualization of the fuel
spray structure is usually performed. Instantaneous spatially resolved Description of the test facilities
Mie scattering planar imaging can be obtained by illuminating the
spray with a pulsed laser sheet. When using high-speed lasers and Micro-combustion test rig
cameras, this technique also provides valuable insight into the spray
dynamics. It also enables the identification of regions of interest This facility has been developed by ONERA in order to study an ultra-
where further measurements should be conducted. Phase Doppler micro gas turbine engine that can deal with power between a few tens
Anemometry (PDA) is a well-known technique that enables a local of watts up to some kilowatts with high specific energy and specific
simultaneous measurement of the droplet size and velocity distribu- power. The latest portable devices or small drones use Lithium-ion
tion. ONERA, in cooperation with CNRS, has developed new optical (Li-ion) secondary batteries as power sources. These batteries can
diagnostics in order to characterize the dispersed liquid phase in have relatively large power densities, but their energy densities hardly
sprays in terms of droplet temperature, size and velocity. In particu- reach 200-250 Wh/kg, which limits the endurance. Charging time and
lar, important work has been done on measuring the mean and local very cold external temperatures may also be critical issues. Common
droplet temperature, by coupling Standard Rainbow Refractometry hydrocarbon fuels have energy densities around 12 kWh/kg. A sys-
(SRR) and Laser Induced Fluorescence (LIF) for a monodisperse dro- tem able to convert only a small percentage of this energy density
plet stream [10]. Local characterizations of the discrete phase inside could reach higher energy densities than existing batteries. There-
a polydisperse spray have also been carried out by the simultaneous fore, over the past decade, and due to the increase in micro-power
use of the Global Rainbow Refractometry (GRR) method and the PDA requirements, many efforts have been dedicated to building a micro
technique. heat engine capable of producing electricity. Micro power generators
based on reciprocating engines, thermoelectric devices or thermo-
Optical diagnostics have continued to evolve very fast thanks to per- photovoltaic devices, Wankel engines, Rankine cycle based engines,
manent progress in laser technologies, electronic imaging systems Stirling engines, fuel cells and micro-turbines are being or were inves-
and processing algorithms. In particular, the development of high tigated. In particular, a 400 W electric micro-turbine complete system
frequency lasers and cameras have enabled the repetition rates of was demonstrated by IHI. This system can be refueled with simple
planar laser imaging techniques, such as PIV or PLIF, to be taken gas cartridges. The heat management and control of the exhaust gas
from the hertz to the kilohertz range in the last few years. Some de- temperature were also demonstrated by Isomura et al. [16]. Among
velopments are currently in progress at ONERA to increase the per- those systems, fuel cells should have the best efficiency, whereas the
formance of laser diagnostics. A new femtosecond CARS system is micro gas turbine should achieve the highest power density.
being developed at the Physics and Instrumentation Department, in
order to also increase the repetition rate of this technique from the This is the reason why ONERA decided to focus on ultra-micro gas
hertz to the kilohertz range [11]. Through a tight cooperation between turbines [17] and, in this context, designed and built a micro-turbine
the Modeling and Information Processing Department and the Fun- test rig on which a micro-combustor was firstly tested (Figure 2).
damental and Experimental Aerodynamics Department, considerable
progress has been made in the development of fast and efficient algo-
rithms for tomographic PIV, thus enabling velocity vectors to be mea-
sured simultaneously in an entire volume rather than only in a plane
[12]. Even though reliable use of this technique in reacting flows re-
mains challenging, these developments open up new capabilities and
perspectives of spatial-temporal experimental measurements never
reached so far. The combination of several optical diagnostics on the
same test facility should also be examined in the future, in order not
only to obtain different physical quantities simultaneously, but also to
reduce the number and cost of experiments.
Finally, one of the main challenges will be to adapt or develop optical
diagnostics capable of operating under higher temperature and pres- Figure 2 - Photographs of the micro-combustor
sure conditions more representative of real industrial combustors.
The new MICADO test facility at ONERA will serve that purpose (see This test rig has the capacity of dealing with fuel flow rates of a
the MICADO section in this article). The maximum targeted chamber few mg/s and air flow rates of up to 5 g/s. Fuels such as hydrogen,
pressure is 4.0 MPa. At such pressure levels in reacting flows, signi- methane or propane can be used.
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 5
For the micro-combustor tests, a special vessel was designed to
Wavenumbers
pressurize the flow at the nominal pressure corresponding to the
pressure turbine inflow (Figure 3).
(a)
n
o
ati
g
a
p
o
pr
er
s
a
L
Rayleigh O N HO H
2 2 2 2
1 0.12
0.98 (b)
0.10
0.96
0.08
0.94
O
Figure 3 - ONERA micro-combustor in its vessel 0.92 N2 0.06
2
HO
0.90 2
Measurements such as outlet wall temperature, exhaust gas tempe- H 0.04
0.88 2
rature and chamber pressure can be made. Special diagnostics such
0.86 0.02
as infra-red thermography (Figure 4) can also be used, as well as
spontaneous Raman and Rayleigh scattering (Figure 5), to obtain 0.84 0
composition and temperature profiles at the exhaust, respectively. --22 --11..55 --11 --00..55 00 00..55 11 11..55 22
XX((mmmm))
1100
1000
(c)
900
800
700
600
500
400
300
200
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
X(mm)
Figure 5 – Example of spontaneous Raman and Rayleigh scattering results:
raw signal (a), molar fraction (b) and temperature (c)
Figure 4 – Infrared thermography image example
A complete micro-turbine designed for around 50 W electric power
was machined and tested (see Figure 6, the scale is given by the
coin near the micro-turbine test rig) up to 170,000 rpm (2.8 kHz). At
this time, its operability was demonstrated for a few watts of electric
power output. In this case, in addition to the pressure and temperature
measurements mentioned before, the rotation speed is also measured

using Philtec optic-fiber devices connected to a high sampling rate
Figure 6 – Complete 50 W micro-turbine tested
oscilloscope. Rotation speeds up to 850,000 rpm can be measured.
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 6
MERCATO MPa and an air temperature of 233 K (-40°C), which corresponds to
a cold start at about 4000 m altitude.
The MERCATO (Experimental Means for Research in Air-breathing
Combustion by Optical Techniques) test facility, located at ONERA/ The results are summarized in the graph in Figure 8, which shows the
Le Fauga-Mauzac and shown in Figure 7, is a small air-breathing pro- global equivalence ratio needed for ignition vs. the fuel blend, desi-
pulsion research facility. Air and fuel are supplied at low flow rates, up gnated by its acronym on the horizontal axis. This graph shows how
to 100 and 10 g/s respectively, but in a wide range of temperatures the ignition performance, i.e., the boundary limit (red dash), evolves
from 233 K to 473 K for air and from 233 K to ambient for fuel. Air according to the fuel composition.
is cooled through an Air/LN2 (liquid nitrogen) cooling tower and fuel
is cooled through a cooling bath. The pressure in the test chamber
FUEL AROMATICS (%) ACRONYM
can be varied from 0.05 MPa to around 0.4 MPa. This facility has
been developed and extensively used to investigate the ignition phe- Jet A-1 20.6 JETA
nomenon, especially under altitude conditions [18-20], and to build
SPK 2.5 SPK
an experimental database of a two-phase flow under non-reacting and
reacting conditions [21, 22]. Jet A-1 + SPK 8 SPK08A
SPK + Aromatic cut 20.6 SPK20AC
air/LN2
interface cooling tower SPK + Aromatic cut 8 SPK08AC
part
Aromatic cut 100 AC
solenoid
valve fuel cooler Table 3 – Fuel compositions investigated in the ignition performance tests
plenum
chamber 2.75
ignition
misfire
combustion ignition boundary
2.50
chamber
o 2.25
ati
air e r
c
flowmeter en
al 2.00
air fuel regulation uiv
ejector valve Eq
1.75
Figure 7 – MERCATO test rig
Concerning the ignition phenomenon in turbojet engines, a recent in- 1.50
vveasritoiguast iaolnte [rn2a0t]i vhea fsu belese anc pceorrfdoirnmge tdo othne tihr ea riogmnitaioticn cpoenrftoernmt,a gnicveesn oinf JET A S P K 08 A S P K S P K 08 A C S P K 20 A C A C
Table 3. The tests were performed inside the mono-sector combus- Fuel
tion chamber shown in the photograph in Figure 7. The experiments
were carried out under altitude conditions, at an air pressure of 0.06 Figure 8 – Ignition performance test results
t=0ms t=10ms t=20ms t=30ms t=40ms
t=50ms t=60ms t=70ms t=80ms t=90ms
Figure 9 – Ignition sequence recorded with a high speed camera; 1 kHz frame rate, 130x130mm2 image size
Issue 11 - June 2016 - ONERA test facilities for Combustion in Aero Gas Turbine Engines
AL11-01 7