Nicolas Gascoin

Validation of Transient Cooling Modeling for Hypersonic Application

Hypersonic flight is expected to be achieved in the coming years by use of supersonic combustion ramjet. One of the main issues is the thermal management of the overall vehicle and more specifically the cooling of the engine. To simulate the behavior of an actively cooled supersonic combustion ramjet by use of supercritical endothermic fuel, a one-dimensional transient numerical model has been developed with heat and mass transfer, fluid mechanics and detailed pyrolysis chemistry. A supplementary step by step validation of the model is presented in this paper thanks to numerical and experimental comparison test cases. Fluid temperature profiles are in good agreement for steady-state calculations despite unconsidered 2-D effects due to momentum and thermal boundary layers. Heat fluxes conservation is verified. Thermal and hydraulic transient behavior are close to those of validation data. The present numerical modeling is quantitatively validated under steady state and transient conditions

Thermal and Hydraulic Effects of Coke Deposit in Hydrocarbon Pyrolysis Process

Fuel pyrolysis can be of benefit for regenerative cooling techniques, due to its endothermic effect in ensuring the thermal resistance of hypersonic vehicles and structures. Among pyrolysis species production, there is that of coke formation. A numerical code is used in this paper to investigate the related phenomena, based on two experiments using titanium and stainless steel reactors, which present different pyrolysis rates under similar operating conditions. The absence of effect of the reactor’s physical properties on the pyrolysis is demonstrated. The thermal insulationeffectbycokedepositisprovedtohaveanegligibleimpactonthesystem.Thecloggingofthereactorfound experimentally is confirmed numerically at the same time. The carbon deposit thickness reaches the value of the reactor’s inner radius: 2.175 mm. The corresponding reduction of flow cross section modifies the Reynolds number, the residence time (decreased by a factor of 4) and the absorbed energy (reduction by a factor of 3). This last point is responsibleforthediscrepanciesobservedexperimentally.Thecokestickstothestainlesssteelreactorandnottothe titaniumreactor.Consequently,pyrolysis islowerforthe stainlesssteelcasethanforthe titaniumcaseunder similar furnace-temperature setups.

Dynamic Study of Coupled Heavy Hydrocarbon Pyrolysis and Combustion

Hypersonic flight at over Mach 5 can be achieved with supersonic combustion ramjets. The regenerative cooling presents the advantage of using the fuel as a coolant, which results in its pyrolysis. Both cooling channel and combustion chamber are studied numerically by coupling the transient phenomena with detailed pyrolysis and combustion chemistry (360 species and 2777 reactions). A Mach 6 flight configuration has been chosen to study the impact of fuel mass flow rate on the combustion for equivalence ratio varying from 0.01 to 1. The time characteristics of the phenomena have been determined. A higher flow rate provides higher hot gas temperatures and faster stabilization time and auto-ignition delay. This affects positively the flame anchoring. Several analytical laws are proposed for later development of a control strategy. A hysteresis has been found due to the heat transfer dynamics.

2-D Transient Numerical Code for Hybrid Rocket Simulations with Detailed Chemistry

Hybrid rocket technology is known since the 30s and it is covered by a large number of experimental, fundamental and applied research works. It still suffers from a lack of chemical description and of detailed numerical simulation of core phenomena. Several numerical codes have emerged to simulate hybrid rocket combustion chamber but with limited consideration for detailed chemistry. They generally use global Arrhenius law or tabulated regression rate to simulate the solid fuel pyrolysis and equilibrium calculation for the combustion. A new 2-D transient reactive numerical code is proposed in this paper with the use of detailed chemical mechanisms for both pyrolysis and combustion reactions (over 1000 species and 10000 reactions). The features of the numerical code are presented in this paper, as well as the equations used to model the physical and chemical phenomena. The simplification assumptions are presented and the code validation is proposed through analytical and numerical comparisons with bibliographic data on reference test cases. The heat transfer in solid phase has been validated with a 99,9% accuracy. The mass and heat transfer in the gas phase have shown a mass and energy conservation of around 99,7%. The gas flow has been validated also on the boundary layer with more than 99,5% accuracy. For chemistry phenomena, special treatment must be applied, leading to an error less than 2% on the ignition delay for combustion process.

Preliminary pyrolysis and combustion study for the hybrid propulsion.

The hybrid propulsion can be of interest for civilian applications such as space tourism or small size launchers (1000 N thrust). The PRISME institute from the University of Orleans is working since 2007 on related activities. PRISME aims at studying numerically and experimentally a hybrid rocket engine and more specifically the chemical reactions involved within the reducer and in the combustion chamber thanks existing code. A complementary approach during the development of both experimental and numerical tools will ensure their high efficiency and reliability. With a time shift, a full scale demonstrator should be designed and assembled in 2011 thanks to the knowledge acquired on reduced scale benches and on the numerical model. The present paper aims at presenting the previous PRISME activities related to solid reducer fuel pyrolysis and combustion of byproducts with oxidizer. Thermodynamic equilibrium approach and detailed kinetic studies (several hundredths of species and several thousandths of reactions) have been conducted on a wide range of reducers and oxidizers depending on the availability of detailed chemical mechanism notably. This work is implemented directly in an existing numerical code which will be extended to a 2-D approach to be suitable for hybrid technology studies. The RESPIRE code to be used as a basis already integrates highly detailed chemistry with adapted calculation of fluid properties to be applied to both fuel pyrolysis and combustion of its by-products with the oxidizer. A large range of physical phenomena aim at being considered in the future: the reducer regression and the related change of phase, the oxidizer flow with the boundary layer, the diffusion flame. By considering the chemistry, it is shown as a result of the preliminary study that the best reducer/oxidizer couple depends on several parameters. The High Density PolyEthylene (HDPE)/H 2O2 is the most promising couple (ignition delay of 4 µs, temperature of 3025 K) if liquid O 2 (LOx) is preferred not to be used. For a first step, HDPE/GOx is considered for this work.

SFGP 2007 - Pyrolysis of Supercritical Endothermic Fuel: Evaluation for Active Cooling Instrumentation

Hypersonic flight is expected to be achieved in the coming years by use of Supersonic Combustion RAMJET (SCRAMJET). One of the main issues is the thermal management of the overall vehicle and more specifically the cooling of the engine. In order to simulate the behaviour of an actively cooled SCRAMJET by use of supercritical endothermic fuel, a one-dimensional transient numerical model has been developed with heat and mass transfer, fluid mechanics and detailed pyrolysis chemistry. A dedicated experimental test bench is now available since 2006 at the LEES laboratory of Bourges to study supercritical fuel pyrolysis under steady-state and transient conditions. It aims to provide understanding of coupled phenomena, validation data for the numerical code and evaluation of onboard and real-time measurement methods for industrial use. A brief overview of the numerical code and a presentation of the experimental bench are proposed in this paper. Experimental results are discussed and a comparison is provided between numerical and experimental data. Discrepancies are shown to be lower than a few percent in terms of molar chemical compositions. This is due to uncertainties on experimental temperature measurement and to 2-D effects, which are not taken into account by the modelling. The numerical code appears to be of great importance in accessing unmeasured data and providing new understanding of coupled phenomena. Experimental and numerical tools are proved to be efficient to test future measurement methods under extreme conditions, especially at supercritical states.

Characterization of supercritical reactive flow for hypersonic real-time application

In the framework of the hypersonic propulsion, with cooled engine by endothermic hydrocarbon fuel, it is necessary to provide adapted measurement methods for the cooling regulation as for the control of the engine thrust. The sensors should be robust because of the extreme in-flight conditions, of vehicle acceleration and vibration, of the fluid temperature (1500 K) and pressure (3.5 MPa) and of the multi-component supercritical mixture. Their response time should be lower than one second. Therefore, a large range of real time and on line measurement methods has been tested and some of these methods among the most promising are presented in this paper. The aim is not to necessarily develop a new technology but to evaluate the feasibility and the adaptability of existing ones for our purpose, even if those are not especially dedicated for it. Numerical evaluation is firstly conducted then some of the techniques are experimentally tested. Two of them, the sonic throat and the Fourier Transform Infra Red spectroscopy (FTIR), appear to be particularly promising and allow uncertainties of few percents. The first one allows evaluating the mass flow rate of a supercritical reactive mixture. The second one characterizes the chemical composition before injection in the combustion chamber, for mole fraction greater than 5 %. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

Permeation of inert and supercritical reactive fluids through metallic and composite media

Large heat load are encountered in hypersonic and space flight applications due to the high vehicle speed (over Mach 5, i.e. 5000 km.h -1 ) and to the combustion heat release. If passive and ablative protections are a way to ensure the thermal management, the active cooling is probably the most efficient way to enable the structures withstanding of such large heat load. In some conditions, transpiration cooling will be used. In this paper, the permeation of fuels and other fluids through porous media is studied up to 1150 K and 60 bars. A dedicated experimental bench has been established to ensure the monitoring of temperature, pressure, mass flow rate and chemical composition (Gas Chromatograph, Mass Spectrometer, Infra-Red spectrometer) in stationary and transient conditions. The tests on metallic and composite samples have been conducted with N2, CH4, H2+CH4 mixtures and synthetic fuels (n-C12H26). The pressure losses comparison with the mass flow rate has enabled the determination depending on the temperature of the Darcian

Flash Pyrolysis of High Density PolyEthylene

The inert and oxidative flash pyrolysis of High Density Poly-Ethylene (HDPE) is studied up to 20 000 K.s-1, under pressure up to 3.0 MPa and at temperature ranging from 1000 K to 1500 K. These conditions are considered to represent those waited onboard a hybrid rocket engine using HDPE as solid fuel. Recycling applications may also find some interest. The pyrolysis products are analysed by Gas Chromatograph, Flame Ionisation Detector and Mass Spectrometer to quantify the effects of each physical parameter on the HDPE decomposition. The classical products distribution diene-alkene-alkane for each carbon atoms number is shown to be modified at such high temperature because of the pyrolysis of primary products. The pressure effect, which is generally neglected in HDPE pyrolysis studies found in open literature, is proved to be a major factor (up to one order of magnitude on the ethylene mass fraction). The heating rate presents noticeable consequences on the pyrolysis products distribution with a larger formation of light species while heavier ones are favoured under oxidative pyrolysis conditions. The experimental data should serve in the future to improve the accuracy of kinetic mechanisms for later use in numerical computing.

Characterisation of oxidised aluminium powder: validation of a new anodic oxidation bench.

Aluminium powder is of major interest in many applications but it presents a risk due to its high explosibility, particularly when dispersed in air. The safety is directly linked to the particles oxidation because the Minimum Ignition Energy (MIE), which is required to initiate an Al dust explosion, increases with the oxide layer thickness. This study provides a controlled method to furnish reproducible homogeneous set of powder for such safety studies. Thanks to a new experimental bench, the influence on the oxidation rate of seven treatment parameters is investigated (current density, time of treatment, acid concentration, mass of powder, particles size, stirring, neutralisation by ammonia solution). The oxide content is plotted versus the current density, the time and the acid concentration to provide reference curves for further elaboration of oxidised powder. The particles size of sieved powder is measured before and after treatment by different methods (optical and Scanning Electron Microscopes, laser measurement). A high refinement of the powder in terms of size distribution is achieved thanks to the employed sieving. The present bench and the elaborated procedure are of great interest to provide well-calibrated oxidised powder directly available for safety studies. The time must be adjusted, depending on the wanted oxide content--from 2 to 18 wt.% - and the other treatment parameters must be kept constant: acid concentration (5 wt.%), current density (1 Adm(-2)), treated powder (20 g). In these conditions, the ratio of the oxide layer thickness on the particles diameter is found to be constant for a given oxide content whatever the particles size.