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 Simplified System Schematic Upper stage propellant tanks 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 Transformation (resultant lift-off mass benefit) 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
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 1 st Concept Prove-out Wankel ICE 2 nd Concept Prove-out New I6 Flathead ICE 1 st 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
ICE Design Analysis via GT-Power Flathead chamber plan view 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 1 st Experimentally measured burn rates used SITurb was approximated for the flathead geometry (spark plug is offset to bore) 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
Exhaust Valve Duration Exhaust Valve Duration DOE Optimization Example (Valve Event Schedules) Intake Valve Duration Intake Valve Duration 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
Cryogenic Propellant Heat Exchangers
Cryogenic Heat Exchangers: Overview 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: Architecture 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 body Liquid flows helically around interior of heat exchanger end caps with inlet/outlet fittings for fluids
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 Cool GH2 outlet Warm coolant inlet Cool GH2 inlet Example: Simulation module for Coolant-to- GH2 heat exchanger 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 Warm coolant outlet
Cryogenic Heat Exchangers: 1-D Simulation Coolant-to-GO2 HEX Coolant-to-GH2 HEX Temperature Gaseous Oxygen Gaseous Hydrogen Coolant Liquid Oxygen Liquid Hydrogen GO2-to-LO2 HEX GH2-to-LH2 HEX
Cryogenic Heat Exchangers: 3-D Simulation To validate the 1-D modeling approach, the Coolant-to- GO2 heat exchanger was simulated using 3-D conjugate heat transfer CFD Temperature CFD Temperature Contours: Coolant Circuit 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 Temperature CFD Temperature Contours: GO2 Circuit
Heat Exchangers: Fabrication & Experimental Setup 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 assembly ready for installation into test cell
Qdot (BTU/s) Heat Transfer Rate Qdot (BTU/s) Heat Transfer Rate Qdot (BTU/s) Heat Transfer Rate Cryogenic Heat Exchangers: Model vs. Data 6 5 4 3 2 1 0 Qdot (simulation) Qdot (lab) 2% overprediction Case 1 1 Performance of Coolant-to-GO2 Heat Exchanger 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Qdot (simulation) Qdot (lab) 48% underprediction Case 1 1 Performance of GH2-to-LH2 Heat Exchanger 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Average of 43% underprediction Case 1 1 Case 2 2 Case 3 3 Case 4 4 Qdot (simulation) Qdot (lab) 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
IVF System Level Simulation
IVF System Level Simulation The entire IVF System was modeled in GT-Suite per the projected flightready 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 Compressor O2 Compressor H2 Accumulator Engine Heat Rejection Coolant-to-GH2 HEX GO2-to-LO2 HEX Coolant-to-GO2 HEX GH2-to-LH2 HEX GH2-Regen HEX Avionics Heat Rejection
Tank Pressures Pressure IVF System Level Simulation 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 Full system coolant circuitry Model predicted performance for using only ullage gas to pressurize tanks Oxygen Tank Hydrogen Tank Time
Other ICE/IVF Elements (with unique challenges)
SITurb Predictive SI Combustion Model 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) Simulated engine flathead combustion chamber Spark location Actual engine flathead combustion chamber Vertical Distance from Deck Face
Engine Cooling System Redesign 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 Coolant Outlet Head Cooling Velocity Coolant Inlet Cylinder Wet Liner Cooling Valve Seat Cooling
P_exhaust Cryogenic Compressor Design Analysis Single Stage gas/mixed phase cryogenic compressor modeled in GT-Suite Model used to optimized design parameters, verify function prior to build Power Consumption N_compressor
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