Synthetic and jet fuels pyrolysis for cooling and combustion applications

Abstract

Large heat load are encountered in hypersonic 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 regenerative cooling is probably the most efficient one to enable the structures withstanding (notably for reusable structures). The present study is a part of COMPARER project (COntrol and Measure of PArameters in a REacting stReam) which aims at investigating the highly coupled phenomenon (heat and mass transfers, pyrolysis, combustion) in a cooling channel surrounding a SCRamjet combustion chamber and at proposing some parameters to enable the control of such a complex technology. In this paper, we present the comparative numerical pyrolysis study of some selected synthetic and jet fuels (heptane, decane, dodecane, kerosene surrogate). The fluid pyrolysis has been studied experimentally and the results of RESPIRE numerical simulation under lab and in-flight conditions are given with validation to provide a deep understanding of phenomenon. The impact of the density, of the critical parameters, of the viscosity and of the chemistry is investigated to analyze their effect on the cooling efficiency of the engine. That also enables to estimate which properties the best cooling fuel should have. Furthermore, a combustion study is conducted because the cooling fuel is the one that ensure the thrust. The RESPIRE code enables to conduct both coupled pyrolysis and combustion studies. A first approach of the dynamic regeneratively cooled SCRamjet is provided to get a large vision of the fuel nature impact on the system.

Real-time method for the identification and quantification of hydrocarbon pyrolysis products: Part II. Application to transient pyrolysis and validation by numerical simulation

“…The heat transfers, the hydraulic and the chemistry have been studied with steady-state and transient cases for different fluid natures (mainly air, nitrogen and dodecane). Recently, computations with heptane, decane and kerosene have been conducted [7]. Actually, RESPIRE has been developed to represent the complete hypersonic vehicle with the combustion chamber, to compute the thrust and flight speed, and to enable the study of pyrolysis-combustion coupling [7], [9].…”

“…Due to the large heat load applied on the structure (elevated total temperature in case of high speed [5], [6] and combustion heat release [7]), the regenerative cooling technique could be implemented to use the fuel as a coolant but also to voluntarily decompose it. Some of the resulting pyrolysis products (among hydrogen, ethylene, methane,… [8]) can 3/38 present sufficiently low auto-ignition delays for supersonic combustion conditions (autoignition delays should be 10 % of the residence time, that is to say 0.1 ms [9]).…”

“…Due to its nature, the GC/MS apparatus is not suitable for transient analysis and the only way to validate the FTIR data is to use numerical simulation. For this purpose, the numerical code called RESPIRE (French acronym for SCRamjet Cooling with Endothermic Fuel, Transient Reactor Programming) uses experimental pressure, furnace temperatures and mass flow rate measurements as boundary conditions for an exact simulation of the pyrolysis process [7], [12]. This tool has been extensively validated since 2004 under various operating conditions, for several types of fluids, stationary and transient regimes [7].…”

Novel viscosity determination method: Validation and application to fuel flow

“…The complex and coupled phenomena need to be studied together to ensure the correct understanding of their relationship [4] even if specific studies dedicated to single phenomena are also required [5]. These latest can be investigated by numerical and experimental work while their entire coupling is preferably studied with numerical simulation [4].…”

“…For both approaches, the kinematic viscosity is of importance. It is used indirectly to determine other material properties such as porous media permeability [5] or directly in Computational Fluid Dynamics simulations [4], [6]. This fluid 3/28…”