An instrumentation system exploits laser-induced incandescence (LII) to measure the concentration of soot particles in an exhaust stream from an engine, furnace, or industrial process that burns hydrocarbon fuel. In comparison with LII soot-concentration-measuring systems, this system is more complex and more capable

Bachalo, William D.

Sankar, Subramanian V.

NASA Technical Reports Server

NASA Tech Briefs, January 2005 25
Real-Time Simulation of Aeroheating of the Hyper-X Airplane
Computational simulations are expected to provide guidance for initial design choices.
Dryden Flight Research Center, Edwards, California
A capability for real-time computa-
tional simulation of aeroheating has
been developed in support of the
Hyper-X program, which is directed to-
ward demonstrating the feasibility of op-
erating an air-breathing ramjet/scram-
jet engine at mach 5, mach 7, and mach
10. The simulation software will serve as
a valuable design tool for initial trajec-
tory studies in which aerodynamic heat-
ing is expected to exert a major influ-
ence in the design of the Hyper-X
airplane; this tool will aid in the selec-
tion of materials, sizing of structural
skin thicknesses, and selection of com-
ponents of a thermal-protection system
(TPS) for structures that must be insu-
lated against aeroheating.
The Hyper-X airplane will include an
inlet/combustor/nozzle assembly at-
tached to an airframe. The forebody of
the inlet will consist of a leading edge
and a tungsten ballast. Movable wings
and vertical tail rudders will give the 
autonomous airplane controllability.
Mounted inside the airframe will be all
the active systems needed to fly and to
demonstrate the ramjet/scramjet en-
gine. The fuel-burning and flight hard-
ware will be instrumented to collect and
telemeter flight data.
Because of the short duration of
flight, critical areas on the airframe TPS
will be limited to the leading edges on
the nose, cowl, and side walls of the inlet
and the horizontal wings and vertical
tails. In addition to other aeroheating ef-
fects, gap heating is expected to occur at
horizontal wing roots, and at vertical
rudder roots by amounts that will vary
with movement of the rudders.
The present capability for real-time
computational simulation of aeroheating
makes it possible to predict temperature
as a function of time at critical heating lo-
cations on the Hyper-X airplane. Simula-
tions of this type are used extensively to se-
lect acceptable flight trajectories by
eliminating ones for which structural-de-
sign temperature limits would be ex-
ceeded (see figure). Other real-time simu-
lations can be performed, using software
modules that enable evaluation of other
aspects of operation and design, including
aerodynamics, reaction control system,
flight guidance, and airplane structures.
At speeds in excess of mach 2, aeroheating
is considered important enough to affect
design parameters, so that it becomes nec-
essary to include a software module for
simulation of aeroheating.
Thus far, a mathematical submodel of
a nose with a solid carbon/carbon lead-
ing edge has been incorporated into the
mathematical model used in the simula-
tion of aeroheating. This submodel
model includes 14 temperature nodes.
Other submodels of aeroheating of the
tail rudder and the leading edges of the
horizontal and vertical tails were under-
going development at the time of re-
porting the information for this article.
This work was done by Les Gong of Dry-
den Flight Research Center. For further
information, contact the Dryden Commercial
Technology Office at (661) 276-3143.
DRC-98-76
Candidate Trajectories
at Mach 5, 7, and 10
Selection of Materials for
Leading Edges of Nose,
Wings, and Vertical Tails
and/or
Geometry, Thermal
Properties, Lumped-Mass
Calibration
Calculate Surface
Temperatures &
Heating Rates
Exceed Peak Use
Temperature of
Materials? Yes
No
Saved for Thermal &
Stress Analysis
The Computational Simulation of Aeroheating is
one of several real-time simulations used in ini-
tial design studies. This simulation can be used
to eliminate flight trajectories that would give
rise to local temperatures in excess of structural-
design temperature limits.
bore must not be so narrow that the
consequent resistance to flow exceeds
the capability of the well pump, and the
bore must be wide enough to accom-
modate suspended particles. The tube
must not kink or fracture at low tem-
peratures. It should be sufficiently insu-
lated to prevent freezing during normal
operation and it should tolerate inad-
vertent freezing.
This work was done by Michael Hecht and
Frank Carsey of Caltech for NASA’s Jet
Propulsion Laboratory. Further informa-
tion is contained in a TSP (see page 1).
NPO-40031
An instrumentation system exploits
laser-induced incandescence (LII) to
measure the concentration of soot parti-
cles in an exhaust stream from an en-
gine, furnace, or industrial process that
burns hydrocarbon fuel. In comparison
with LII soot-concentration-measuring
systems that have been described in
prior NASA Tech Briefs articles, this sys-
tem is more complex and more capable. 
Like the other systems, this system in-
cludes a pulsed laser and associated op-
Using Laser-Induced Incandescence To Measure Soot in
Exhaust 
This system incorporates several improvements over prior LII soot-measuring systems. 
John H. Glenn Research Center, Cleveland, Ohio
https://ntrs.nasa.gov/search.jsp?R=20110014709 2019-08-30T16:42:44+00:00Z
26 NASA Tech Briefs, January 2005
tics that shape and aim a laser beam
through an exhaust stream. The laser
beam heats entrained soot particles to
incandescence. Light from the glowing
soot particles is collected by two band-
pass-filter-and-photodetector assem-
blies for measurement of the intensity
of the incandescence as a function of
time in two wavelength bands. On the
basis of the established principle of two-
color pyrometry, the instantaneous
temperature of the glowing soot parti-
cles is determined from the ratio be-
tween the instantaneous intensities in
the two wavelength bands. 
The heating of the soot particles by
absorption of laser light and the subse-
quent cooling of the particles through
incandescence (and, when applicable,
through evaporation of volatile materi-
als from their surfaces) are complex
nanoscale processes that can be repre-
sented by a computational model in
which, during the decay of incandes-
cence following the laser pulse, the
time-dependent absolute intensities and
the time-dependent temperature de-
pend, further, on the volume concen-
tration and surface area of the soot par-
ticles. In this system, the model is inverted
to obtain the number density and size
of the primary soot particles. The mass
density of soot averaged over the probe
volume can then be calculated from the
volume concentration. 
Calibration of the photodetectors and
the optical components that precede
them is necessary for determining ab-
solute intensities. In this system, calibra-
tion is performed by use of a strip-fila-
ment lamp or other extended light
source that has a known radiance trace-
able to that of a standard source main-
tained by the National Institute of Stan-
dards and Technology. 
Uniform heating of all soot particles
in the probe volume and in a sheath
volume surrounding the probe volume
is necessary to ensure accuracy. To sat-
isfy this requirement, (1) the laser
beam is expanded into a sheet of finite
thickness that is perpendicular to the
viewing axis of the detecting optics, and
(2) the detecting optics include an iris
that defines the probe volume as a
cylindrical central, mid-thickness re-
gion within the beam. 
In prior LII systems, the laser fluence
is so great that soot particles are heated
to temperatures above the sublimation
temperature of carbon (about 4,000 K).
This was done to produce an LII signal
that was somewhat independent of laser
fluence, making it unnecessary to mea-
sure the temperatures of soot particles.
Unfortunately, the loss of mass through
sublimation alters the very quantity
(mass density of soot) that one seeks to
measure. Also for prior LII systems, the
laser fluence required to reach subli-
mation temperatures is dependent
upon the initial particle temperature,
and is affected by condensed species
such as volatile organic compounds and
water. In this self-calibrating system,
the intensity measurements are used to
adjust the laser fluence to keep the
laser-heated soot particles below the
sublimation temperature. 
This work was done by William D. Bachalo
and Subramanian V. Sankar of Artium Tech-
nologies, Inc. for Glenn Research Center.  
Inquiries concerning rights for the commer-
cial use of this invention should be addressed
to NASA Glenn Research Center, Commercial
Technology Office, Attn: Steve Fedor, Mail
Stop 4–8, 21000 Brookpark Road, Cleve-
land, Ohio 44135. Refer to LEW-17479-1.


Using Laser-Induced Incandescence To Measure Soot in Exhaust

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