A real-time quantification infra red method has been developed with a gas cell to determine the composition of hydrocarbon pyrolysis products. The aim is to chemically characterise the fuel decomposition in case of regenerative cooling. The method can be extended to a large variety of applications. A transient analysis of the method behaviour is conducted to estimate its capacity to be applied to unsteady conditions (one measure per second), which can be encountered in cooling activity and unsteady processes. A numerical tool called RESPIRE (French acronym for Supersonic Combustion Ramjet Cooling with Endothermic Fuel, Transient Reactor Programming) is used to help in understanding the complex phenomena involved in such a chemical reactor. The validation of transient behaviour with respect to the computations shows negligible time delay (lower than few seconds with gasification rate higher than 60 wt.%) due to residence time in the experimental setup. The quantification accuracy is confirmed to be around 2 molt The agreement obtained on gas cell measurements is found to be correct over 10-20 wt.% of gasification rate and very satisfactory over 60 wt.% but this depends on the species. An extension of the method has been developed with a dedicated online cell to be specifically applied to supercritical and multiphase flows. The quantification of the gas phase in the pyrolysis mixture in case of biphasic flow is proposed and validated with an uncertainty around 3 wt.%. The coke formation is monitored as a function of time and its quantification is even tested with 50% of uncertainty after a numerical calibration with respect to simulation. (C) 2011 Elsevier B.V. All rights reserved.

Due to large heat load encountered in high speed flight (over Mach 5), the regenerative cooling of the engine leads to the study of the endothermic pyrolysis of the onboard hydrocarbon fuel, which acts as a coolant. However the control and regulation of such a technology implies to have a correct knowledge of the endothermic pyrolysis of the onboard hydrocarbon fuel, which motivates the development of a quantitative measuring method adapted to in-flight applications. A Fourier transform infra red spectrometer is used and a specific method has been developed to identify and to quantify the major hydrocarbon products of the pyrolysis. The technique is validated and tested at the outlet of the experimental pyrolysis process which operates under steady-state conditions from 823 K to 1023 K and up to 60 bar. Two mass flow rates (0.05 g s−1 and 0.1 g s−1) are studied with titanium reactor to determine the limits of validity and to improve the method. Several synthetic and jet fuels have been tested (heptane, decane, dodecane and two kerosenes). The quantities of five light hydrocarbons (methane, ethane, ethylene, propane, propylene) are determined. The method, based on classical least square processing, is validated with respect to gas chromatograph (and mass spectrometer) analysis notably. A minimum molar fraction of 5 mol.% can be obtained and the accuracy is better than 2 mol.%.

Hypersonic flight is expected to be achieved with dual-mode-Ramjet (Ramjet under Mach 6 and Scramjet beyond) because of its high specific impulse and its capability to be reusable (especially interesting for space transportation)1, but one of the main issues at these flight conditions is the thermal management of the engine and the vehicle. Different cooling strategies have been evaluated by MBDA-France (calculations, material tests). Metallic panels have been tested as CMC composite ones (C/SiC for instance)2, which seem to be promising. But even CMC materials could not withstand such large heat loads (for example, total temperature of external air reaches 2000 K at Mach 7 and combustion add more energy as the inner part of the engine cannot be radiatively cooled). Consequently an active cooling system has to be used but not a dedicated one because it would increase the vehicle weight. Furthermore, another issue occurs under theses flight conditions. The time allocated to mix the injected fuel with inlet air, to ignite the combustion and to complete it before the chamber outlet is about 1 ms. These two points lead to the so-called "regenerative cooling" solution : using the fuel to cool down the engine's wall and then burning it in the engine. The fuel is injected in a composite channel (which surrounds the engine) near the outlet of the combustion chamber, it flows to the injection on the opposite way of the burned gases. For "moderate" hypersonic flight Mach numbers (below Mach 8), a heavy hydrocarbon fuel is often chosen here because of its high density compared to cryogenic fuels (800 kg.m-3 instead of 70/80 kg.m-3 for cryogenic hydrogen, with a specific impulse of liquid hydrocarbon halved)3. When heated and pyrolysed, it produces lighter hydrocarbons species that are considered as more energetic and easier to ignite. This point allows responding to rapid phenomenon in the combustion chamber.

One of the main issues of hypersonic flight is the thermal management of the overall vehicle. In order to simulate the behaviour of a complete actively cooled Supersonic Combustion Ramjet, a one-dimensional transient numerical model has been developed with heat and mass transfer particularly in a cooling channel for supercritical fuel under pyrolysis. It uses a detailed pyrolysis mechanism for n-dodecane (1185 reactions and 153 species). A further validation of the model, based on experimental and numerical data, is presented in this paper. The hydrodynamic behaviour is considered to be good enough for this numerical tool as the accuracy of fluid velocity computation is about few percents. The model is quantitatively validated under stationary conditions for both hydrodynamic and thermal aspects. The discrepancies between computed and experimental data remain close to 5 % or less on a thermal point of view. Furthermore, good agreement is found with transient experimental test case. Discrepancies are analysed and they remain in an acceptable range of a tenth of degree. A validation of the chemistry is provided thanks to experimental results. The pyrolysed mixture's compositions are well reproduced with only few percents of error. RESPIRE is now considered to be validated and it brings further analysis of the experimental data obtained with the new pyrolysis bench. Some interesting examples of use are given.