Alexandre Mangeot

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.

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.

Firing tests of hybrid engine with varying oxidiser nature and operating conditions

Hybrid combustors are of increasing interest for space and civilian propulsion. A test facility has been settled to investigate high-density polyethylene combustion (propellant of length 0.15 m). A parametric study has been conducted on the oxidiser nature (gaseous oxygen diluted in nitrogen, from 31.4 vol.% to 69.2 vol.% of O2), on the oxidiser flow rate (from 28.6 g/s to 53.1 g/s), on the combustor pressure (from 11.4 bar to 25 bar) and on the nozzle diameter (from 6.4 mm to 12.9 mm). The regression rate has been estimated by weight loss (mean value of 0.207 mg/s) and by thermocouples (0.198 mg/s). Its values are compared to existing data through the Marxman law; this enlarges the range of validity of this law. The conduction heat flux in the solid reducer is estimated around 6000–8000 W; which is related to the low regression rate of the solid fuel. The axial thrust has been measured in addition to other parameters (pressures, temperatures and mass flow rates). Solid particles have been gathered at the combustor outlet to conduct additional chemical analyses. These particles were formed at the surface of the reducer and extracted by the oxidiser from the solid surface.

Kinetic Modelling of High Density PolyEthylene Pyrolysis: Part 1. Comparison of existing models

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Kinetic Modelling of High Density PolyEthylene Pyrolysis: Part 1. Comparison of existing models Nicolas Gascoin, Ana Navarro-Rodriguez, Philippe Gillard, Alexandre Mangeot

Micro and Full-Scale Experiments on Hybrid Rocket Fuel and Prelude to Hybrid Rocket Combustor Simulations

The high density polyethylene, as hybrid rocket fuel, has been chosen to be studied. Thermogravimetric analysis allowed to determine an Arrhenius type equation for its regression rate. A flash pyrolysis coupled to GC/MS/FID has been used to observe influence of oxidative environment on pyrolysis byproducts quantity. With a test bench, the regression rate of the solid fuel under various conditions (pressure, oxidizer mass flow rate, oxygen mass fraction) has been evaluated at an average value of 0.2 mm.s -1 . The Marxman law is completed with other studies conducted at higher oxidizer mass flow rates, between 0.6 and 20 g.s -1 .cm -2 . Finally, the first hybrid rocket combustor simulation is presented along its governing equations. Preliminary comparison gives a numerical regression rate 10% above the value found during experimental firing despite assumptions on the gas phase model.

Methodologies for Detailed Chemistry Computation, Application to Hybrid Rocket Combustion Chamber Simulations

Hybrid rocket technology is known since the 30s and a large number of experimental, fundamental and applied research works covers it. 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. A new 2-D transient reactive numerical code has been proposed in the goal of using detailed chemical mechanisms for both pyrolysis and combustion reactions (over 1000 species and 10000 reactions). The direct computation of such mechanisms is too much time consuming. In order to speed up the computation, methodologies for treating chemistry have been set up. In this paper, one of the methodologies is explained and validated trough several validation cases. With all methods combined, the results show an error less than few percents on the ignition delay of the flame and a computational time cut by a factor higher than 1.