Component and System Level Modeling of
a Two-Phase Cryogenic Propulsion System
for Aerospace Applications
J. LoRusso, B. Kalina, M. Van Benschoten,
Roush Industries
GT Users Conference November 9, 2015
Agenda
Introduction to Integrated Vehicle Fluids (IVF) System
H2-O2 Fueled IC Engine
Cryogenic Propellant Heat Exchangers
IVF System Level Simulation
Other ICE/IVF Elements
Integrated Vehicle Fluids (IVF)
System Overview
• IVF High Level Concept Description – IC engine generates mechanical power to drive starter-generator and propellant compressors
– Waste heat from IC Engine transferred to cold propellants extracted from the propulsion tanks
– Enthalpy added to the cold propellants is then transferred back to the tanks for tank pressurization
– The starter-generator transfers power to high density Lithium Ion batteries extending mission length
– Gimbaled thrusters fire directly from tank ullage gases, replacing the prior hydrazine fired thrusters
IVF Simplified System Schematic
Upper
stage
propellant
tanks
IVF Transformation
• IVF Transformation in the Launch Vehicle Upper Stage – The result is a reduced complexity upper stage with elimination of helium bottles used for tank
pressurization, hydrazine to fire the thrusters, and a portion of the batteries for electrical power
– The end result, reduced system mass, with extended mission length capability and increased
payload opportunities
(resultant lift-off mass benefit)
H2-O2 Fueled IC Engine
IC Engine (ICE) Combustion with H2/O2 Fuel • Limited published data existed on H2/O2 fueled IC engines
• Traditionally H2/Air IC engines operate at fuel-lean equivalence ratio
• In contrast, the IVF H2/O2 ICE operates fuel-rich
• Greater availability of waste H2 than O2 in the vehicle due to faster boil-off of H2
• Flame temperature and burn rate controlled to equivalent levels as gasoline-air
• Simulation results and experimental data confirmed this hypothesis
Definitions:
Mixture Ratio (MR ) =
O2/H2 mass flow rate
Fuel Air Equivalence Ratio =
Stoich MR / Actual MR
ICE Concept Prove-out & Design for Flight
Single
Cylinder ICE
1st Concept
Prove-out
Wankel ICE
2nd Concept
Prove-out
New I6 Flathead ICE
1st Pre-flight design for
cryogenic fluid system
IVF proof-of-concept
testing
Flathead architecture
simplified challenges with
lubrication at zero G
High S/V ratio increased
% of fuel energy lost to
the coolant, which was
important for IVF
To support the new I6 ICE design, numerous performance
and DOE studies were conducted using GT-Power:
• Engine displacement
• Intake & Exhaust Valve timing
• Injection timing relative to IVO
• Valve Size
• Intake manifold geometry
• H2 throttle & O2 injector geometry
• Cooling System design
GT-Power was converted to run on H2-O2
• 1st Experimentally measured burn rates used
• SITurb was approximated for the flathead geometry
(spark plug is offset to bore)
ICE Design Analysis via GT-Power
Unique Environment
• Intake H2 working gas from upper stage
ullage tank, pressurized, ambient temps due
to heat exchange of coolant w/propellants.
• Exhaust environment, 0 psia vacuum
Metrics
• Traditional performance and fuel
consumption metrics
• Trapped vs. overall O2/H2 Mixture ratio
• Brake specific O2 consumption
Flathead chamber
plan view
• Since supply of waste H2 was more available than O2 in the vehicle, it was
important to minimize O2 consumption for a given power level
• Brake Specific Oxygen Consumption (BSOC) defined as follows:
BSOC (lbm/hp-hr) = O2 mass flow rate (lbm/hr) / PW (hp)
• Optimized valve event schedule “X” employed a balanced weighting between
power output and BSOC
DOE Optimization Example (Valve Event Schedules) E
xhaust
Valv
e D
ura
tion
Exhaust
Valv
e D
ura
tion
Intake Valve Duration Intake Valve Duration
Cryogenic Propellant
Heat Exchangers
• Three classes of heat exchangers designed utilizing GT-Suite analysis
tools:
1) Coolant-to-Gaseous H2/O2 propellant heat exchangers
• Heat from engine coolant transferred to cool propellants (ullage gases) for tank
pressurization
2) Liquid-to-Gaseous H2/O2 propellant heat exchangers
• High enthalpy propellants heated by engine coolant used to vaporize liquid
propellants for additional capacity in tank pressurization
3) Coolant-to-Gaseous H2 propellant heat exchanger
• Heat from engine coolant transferred to cool H2 propellants to IC engine
consumption
Cryogenic Heat Exchangers: Overview
end caps with
inlet/outlet fittings for
fluids
body
Liquid flows helically
around interior of heat
exchanger
• On Earth gravity is relied upon for
enhancing heat exchanger
performance, especially that of
evaporators
• Since IVF heat exchangers need to
operate in a zero gravity environment,
fluids are run through helically wound
channels which impart centripetal force
and mimic the effect of gravity
• 1-D flow analysis in GT-Suite used to model
conjugate heat transfer from the coolant to
the cool ullage gases, or from the high
enthalpy ullage gases to the liquid
propellants
• Analysis results were used to guide heat
exchanger sizing and coolant selection
Cryogenic Heat Exchangers: Architecture
Cryogenic Heat Exchangers: 1-D Simulation • GT-Suite was used to create simulation modules for each heat exchanger to
model conjugate heat transfer and size each heat exchanger
• All propellant properties were pulled from NIST REFPROP
Example:
Simulation
module for
Coolant-to-
GH2 heat
exchanger
Warm coolant inlet Cool GH2 outlet
Warm coolant outlet
Cool GH2 inlet
Adiabatic
coolant circuit
wall sections
Heat subtraction from
coolant: determined by
calculating result of
[(mdot_GH2)*(h_GH2_in
– h_GH2_out)]
GH2 circuit wall sections;
for these, wall temperature
was predicted by using
Wall Temperature Solver
Object; RLT outputs for
coolant circuit bulk fluid
convection temperature
and convection coefficient
used as inputs
Coolant-to-GO2 HEX Coolant-to-GH2 HEX
GH2-to-LH2 HEX GO2-to-LO2 HEX
Temperature
Coolant
Gaseous
Oxygen
Gaseous
Hydrogen
Liquid
Oxygen Liquid
Hydrogen
Cryogenic Heat Exchangers: 1-D Simulation
CFD Temperature
Contours:
Coolant Circuit
• To validate the 1-D modeling
approach, the Coolant-to-
GO2 heat exchanger was
simulated using 3-D
conjugate heat transfer CFD
• Delta temperatures for each
fluid across the heat
exchanger as predicted by
CFD was to be found to be
sufficiently close to 1-D
results
CFD Temperature
Contours:
GO2 Circuit
Cryogenic Heat Exchangers: 3-D Simulation
Temperature
Temperature
• All five heat exchangers
proceeded to be designed
in CAD, parts were
machined, and finished
parts were assembled; all
of this was done in-house
at Roush
• Each heat exchanger was
then incorporated into a
test assembly which
eventually included the
engine, heat exchangers,
and compressors
Heat Exchangers: Fabrication & Experimental Setup
Heat exchangers assembly ready for installation into test cell
0
1
2
3
4
5
6
1
Qd
ot
(BT
U/s
)
Qdot (simulation)Qdot (lab)
Performance of Coolant-to-GO2 Heat Exchanger
2% over-
prediction
Case 1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1
Qd
ot
(BT
U/s
)
Qdot (simulation)
Qdot (lab)
48% under-
prediction
Case 1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 3 4
Qd
ot
(BT
U/s
)
Qdot (simulation) Qdot (lab)
Average of
43% under-
prediction
Case 1 Case 2 Case 3 Case 4
Cryogenic Heat Exchangers: Model vs. Data
Performance of GH2-to-LH2 Heat Exchanger
Performance of Coolant-to-GH2 Heat Exchanger
• Thermal performance of the Coolant-to-
GO2 heat exchanger as predicted by GT-
Suite showed excellent agreement with
test cell data
• Thermal performance of the Coolant-to-
GH2 and GH2-to-LH2 heat exchangers as
predicted by GT-Suite showed not as
good of agreement with test cell data
• Predicted thermal performance of the
Coolant-to-GH2 heat exchanger showed
good trend-wise agreement as compared
to test cell data
Hea
t T
ran
sfe
r R
ate
Hea
t T
ran
sfe
r R
ate
Hea
t T
ran
sfe
r R
ate
IVF System Level Simulation
IVF System Level Simulation
• The entire IVF System was modeled in GT-Suite per the projected flight-
ready configuration; key features of the model included:
– Detailed heat exchanger models, half of which were calibrated to lab data for
heat transfer and pressure loss
– O2 and H2 compressors
– Vehicle tank models which account for both ullage and liquid volumes
– Properly sized valves and plumbing
– PID controllers for regulating: • coolant flow to heat exchangers as a means of system thermal balance control
• pressure downstream of heat exchanger liquid propellant circuit as means of targeting fluid outlet
vapor quality
IVF System Level Simulation O2 Tank
H2 Tank
H2 Accumulator
Engine Heat Rejection
Avionics Heat Rejection
H2 Compressor
O2 Compressor
Coolant-to-GO2 HEX GO2-to-LO2 HEX
Coolant-to-GH2 HEX
GH2-to-LH2 HEX
GH2-Regen HEX
IVF System Level Simulation
Model predicted performance for using
only ullage gas to pressurize tanks
• Tasks accomplished with IVF System model:
– Validated compressors and heat exchangers add enthalpy to the ullage gases to
successfully pressurize O2 and H2 tanks at an acceptable rate for vehicle mission states
– Model was used to understand function of system prior to the experimental program
– Cooling system total pressure drop has become better understood
Ta
nk P
ressu
res
Oxygen Tank
Hydrogen Tank
Time
Full system coolant circuitry
Pre
ssu
re
Other ICE/IVF Elements (with unique challenges)
Spark location Vertical Distance from
Deck Face
• A key challenge to integrating a
predictive SI combustion model
was that GT-Power’s SITurb
model assumes that the
combustion chamber resides
directly above piston, which is
not the case for the engine’s
flathead chamber
• Rotating the overhanging part of
the chamber by 90-degrees
positioned the chamber above
the cylinder and served as a
workaround
• At the present, good agreement
with lab data has been achieved
at low speed conditions
• This modeling exercise could
have benefited from a
combustion model which allows
for an overhanging combustion
chamber; one such combustion
model was described in SAE
910056 (U. of Wisconsin)
Actual engine flathead
combustion chamber
Simulated engine
flathead combustion
chamber
SITurb Predictive SI Combustion Model
• A model of the engine cooling system was constructed in GT-Suite to guide CAD designs
• This cooling system model was run simultaneously with the engine model whereby the cooling
system model provided coolant temperatures and convection coefficients to GT-Power’s
predictive combustion chamber wall temperature model
• This enabled insight into required modifications to manage cylinder block and cylinder head
temperatures, and to provide boundary conditions for CFD analysis
Velocity
Cylinder Wet Liner Cooling Valve Seat Cooling
Head
Cooling
Coolant Inlet
Coolant Outlet
Engine Cooling System Redesign
Cryogenic Compressor – Design Analysis • Single Stage gas/mixed phase cryogenic compressor modeled in GT-Suite
N_compressor
P_exhaust
Power Consumption
• Model used to optimized design parameters, verify function prior to build
Thank You
• Acknowledgements – United Launch Alliance (program
sponsor)
– NASA /Marshal Space Flight Center
(program co-sponsor)
• Publications
– AIAA references
– YouTube Video https://www.youtube.com/watch?v=rwczm9ScBzE
