Numerical Study of the Thermal Behaviour of a Thermo-Structural Aeronautical Composite under Fire Stress

International audienceThe use of composite materials for aeronautical applications has been growing since several years because of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The need for fireproof certification imposes costly and time consuming experiments that might be replaced or complemented in the years to come by numerical calculations. The present work creates a CFD numerical model of a fireproof test. As an example, a composite part (plenum) located in an aircraft APU (auxiliary power unit) which provides power to the aircraft is investigated. A numerical calibration of the flame is conducted according to the fireproof standards. The results of fireproof tests demonstrate a good evaluation of the plenum temperature (discrepancies lower than 19%). The influence of an internal air jet within the studied part is also evaluated observed to evaluate how this could lower the requirements of certification rules. A thermal decrease as high as 38 % is found for a velocity of 10 m/s. Proceedings of the 2 nd IAFSS European Symposium of Fire Safety Science 1. Introduction The use of composite materials for aeronautical applications has been growing since several years because of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The growing use of these materials leads to technical and design challenges to comply with safety standards and certifications, especially when fire safety requirements are concerned. Aircraft parts dedicated to firewall applications or located in a designated fire zone, should meet a fireproof requirement. Therefore the composite parts have to pass fire tests according to ISO 2685 [1] or FAA-AC20-135 (FAR-25) [2] standards. Both standards use an oil burner to heat the part with a minimum temperature of 1100°C for 15 minutes. In this work, a 3D numerical model of a fireproof test using a CFD code is created to investigate the predictivity of a numerical fireproof test. This numerical step is expected to replace experimentation during the development phases of the composite part before the certification test to reduce development cost. This numerical tool would help designers to choose between different composite materials and designs options to avoid critical temperature increases at certain areas and perforation in this composite part during fireproof tests. The second section is dedicated to the presentation of the experimental setup and the third one will present the physical and numerical modelling approaches. In the fourth section the computed temperatures are compared to the experimental ones to validate the presented numerical approach and the results are discussed. The influence of an internal air jet within the studied part is also evaluated The feasibility of replacing a thermal protection by an internal air jet is also presented in this paper as a first design variable case. 2. Experimental setup To be labelled " fireproof " as it is requested in most of the APU (Auxiliary power unit) part specifications and according to the related standards, the concerned part (here a composite plenum) has to resist 15 minutes to a calibrated flame. Criteria to establish the test is passed include no burn through of the part structure, as well as no ignition of the emitted smokes (backside part inner surface self-ignition). This second criteria is here investigated by measuring the part material temperature increase. The Figures 1 and 2 present respectively a picture and an overview of the experimental setup. The composite part is located at 100 mm from the outlet of the cone burner above a vibrating table (sinusoidal vibration of 0.4 mm amplitude and 50 Hz frequency). The oil burner (kerosene-air) operates with a kerosene flow rate o

Experimental investigation of fuel-cooled combustor: Cooling efficiency and coke formation

Scramjet is an air-breathing engine designed to propel advanced aircrafts in the atmosphere, suitable, according to various studies, to thrust high-speed hypersonic flights (over Mach 5). The thermal protection of vehicles flying at hypersonic velocities is a critical problem; as at supersonic speeds the incoming air is at too high temperature to be used as a coolant, the fuel becomes the only adequate source of cooling for the vehicle. Regenerative cooling is a well-known cooling technique using the fuel as coolant. As the development of regeneratively cooled engines faces many difficulties, an empirical study of this cooling technology and of its complex dynamics is of high interest. In this context, a remotely controlled fuel-cooled combustor, suitable for the experimental analysis of the pyrolysis-combustion coupling characterizing a fuel-cooled combustion chamber when a hydrocarbon propellant is used, has been designed. Tests are realized under both stationary and transient conditions using ethylene as fuel and air as oxidizer. Two operating parameters, i.e. fuel mass flow rate (between 0.010 and 0.040 g.s-1) and equivalence ratio (between 1.0 and 1.5), have been investigated. It has been observed that fuel mass flow rate increases always result in the raise of the heat flux density passing from the combustion gases to the combustor walls. It has been seen that mass flow rate raises between 16 and 20 % lead to increases in the thermal energy evacuated by the fuel-coolant in the range from 30.4 to 48.5 %, depending on equivalence ratio and pressure. The dependence of the cooling system heat exchange efficiency on the two operating parameters has been demonstrated. The consequences of the coking activity of the fuel have also been investigated. For applied interest, a monitoring method for carbon deposits formation has been developed and validated

Experimental investigation on the concentration and voltage effects on the characteristics of deposited magnesium–lanthanum powder

International audiencePhone: +33 248 484 065 Highlights x We synthetize Mg-La powders by means of an electrodeposition process. x We characterize Mg-La powders using EDS, SEM, XRD and FTIR techniques

Investigation on the Emission of Volatile Organic Compounds from Heated Vegetation and Their Potential to Cause an Accelerating Forest Fire

International audienceAn experimental study is conducted on the emission of volatile organic compounds (VOCs) emitted by Rosmarinus officinalis plants when exposed to an external radiant flux. The thermal radiation heats the plant and causes the emission of VOCs. The thermal radiation simulates the radiant flux received by vegetation in a forest fire. The results of the experiments are used in a simplified analysis to determine if the emissions of VOCs in an actual forest fire situation could produce a flammable gas mixture and potentially lead to the onset of an accelerating forest fire. The experiments consist of placing a plant in a hermetic enclosure and heating it with a radiant panel. The VOCs produced are collected and analyzed with an automatic thermal desorber coupled with a gas chromatograph/mass spectrometer (ATD-GC/MS). The effects of the fire intensity (radiant panel heat flux) and the fire retardant on the VOCs emission are then investigated. Two thresholds of the VOCs emission are observed. The first is for plant temperatures of around 120C and appears to be caused by the evaporation of the water in the plant, which carries with it a certain amount of VOCs. The second one is around 175C, which is due to the vaporization of the major parts of VOCs. The application of a fire retardant increases the emission of VOCs due to the presence of the water (80%) in the fire retardant. However, the use of the retardant results in a lower production of VOCs than using water alone. The measurements are used to estimate the concentration of VOCs potentially produced during the propagation of a specific fire and compared to the flammability limits of a-pinene. It is concluded that the quantities of VOCs emitted by Rosmarinus officinalis shrubs under certain fire conditions are capable of creating an accelerating forest fir

Experimental study on Combustion modes and thrust performance of a staged-combustor of the scramjet with dual-strut

International audienceTo enable the scramjet operate in a wider flight Mach number, a staged-combustor with dual-strut is introduced to holdmoreheat release at low flight Mach conditions. The behavior of mode transition was examined using a direct-connect model scramjet experiment along with pressure measurements. The typical operating modes of the staged-combustor are analyzed. Fuel injection scheme has a significant effect on the combustor operating modes, particularly for the supersonic combustion mode. Thrust performances of the combustor with different combustion modes and fuel distributions are reported in this paper. The first-staged strut injection has a better engine performance in the operation of subsonic combustion mode. On the contrast, the second-staged strut injection has a better engine performance in the operation of supersonic combustion mode

Numerical investigation of the heat transfer in an Aeronautical Composite Material under Fire Stress

International audienceabstractThe use of composite materials for aeronautical applications has been growing since several years be- cause of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The need for fireproof certification imposes costly and time consuming experiments that might be replaced or complemented in the years to come by numerical calculations. The present work creates a CFD nu- merical model of a fireproof test. As an example, a composite part located in an aircraft APU (auxiliary power unit) which provides electric power to the aircraft is investigated. A numerical calibration of the flame is conducted according to the fireproof standards. After that, a comparison between three different turbulence models shows that the k–ε realisable turbulence model is the more suitable for fireproof numerical tests with discrepancies lower than 16% between computed values and measured ones. The influence of an internal air jet is observed for velocities from 1 to 10 m/s. The results demonstrate a good evaluation on how this could reduce the wall temperatures and ensure the requirements of the certi- fication rules compare to the actual external thermal protection used to ensure the certification re- quirements. Indeed, final temperature reductions up to 45% are found at reference point on the structure with the highest value of air jet velocity

Ceramic panel heating under impinging methane-air premixed flame jets

International audienceDue to the ever wider use of composite materials within aerospace applications, fireproof tests get recently an increased attention. Numerical simulation is expected in the coming years to accompany engineers in their design work to increase the chance of success in the fireproof certification tests. The current research focuses on the numerical investigation of a premixed methane-air flame impinging normal to a flat composite panel. The effects of the exit burner geometry, of the Reynolds number (jet speed) and of the distance between the nozzle and the plate have been investigated. The accuracy and suitability of different turbulence models are discussed. The numerical results are validated with available experimental data. CFD calculations reproduce within 5 % the so-called heat transfer efficiency where the realizable k-ε turbulence model demonstrates to be the best. The agreement to the experimental data is maximum (in the following order of importance): i) near the centre of the jet impingement, ii) for higher Reynolds number, iii) for higher distance between the panel and the flame. The Reynolds number increase conducts to an increase of the total heat transfer between the flame and the panel. This is related to the Nusselt number which presents higher value (over 20) in the regions for which the predictiveness of the calculation is found to be better. Efficient modelling parameters are found to reproduce an experimental flame that will serve later in fireproof test simulations

Numerical investigation of the heat transfer in an Aeronautical Composite Material under Fire Stress

International audienceabstractThe use of composite materials for aeronautical applications has been growing since several years be- cause of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The need for fireproof certification imposes costly and time consuming experiments that might be replaced or complemented in the years to come by numerical calculations. The present work creates a CFD nu- merical model of a fireproof test. As an example, a composite part located in an aircraft APU (auxiliary power unit) which provides electric power to the aircraft is investigated. A numerical calibration of the flame is conducted according to the fireproof standards. After that, a comparison between three different turbulence models shows that the k–ε realisable turbulence model is the more suitable for fireproof numerical tests with discrepancies lower than 16% between computed values and measured ones. The influence of an internal air jet is observed for velocities from 1 to 10 m/s. The results demonstrate a good evaluation on how this could reduce the wall temperatures and ensure the requirements of the certi- fication rules compare to the actual external thermal protection used to ensure the certification re- quirements. Indeed, final temperature reductions up to 45% are found at reference point on the structure with the highest value of air jet velocity