Angelo Minotti

Subtranscritical and Supercritical Properties for LO2-CH4 at 15MPa

Future launchers will use rocket propulsion systems burning CH 4 /LO 2 at high chamber pressure, and so it is useful to analyze the thermophysical properties of these species and their combustion products at these conditions. High-pressure (real-gas) effects significantly modify combustion regimes, for instance, the propellants Re injected near the critical temperature, and so to simulate mixing and combustion processes in subtranscritical regimes high-pressure effects must be described. This paper analyzes the compressibility factors of CH 4 , O 2 , CO 2 , and H 2 O at a pressure of 15 MPa and calculates the difference between ideal- and real-gas thermophysical properties for these species in the range of temperature in which experimental data are available. Finally, the paper describes thermophysical properties at typical liquid rocket engine combustion chamber conditions (100 < T < 6000 K, 15 MPa) by polynomial fits. As there are no experimental data at high temperatures, theories are necessary to predict properties at temperatures different from the experimental ones: thus, low-temperature experimental data (National Institute of Standards and Technology tables) are used in conjunction with predictions obtained with the Lee-Kesler equation of state (for density and isobaric specific heat) and with the Chung et al. method (for viscosity and thermal conductivity). This paper will try to clarify the impact of subtrans-supercritical parameters on mixing and combustion in future liquid rocket engines.

A LES Simulation of a CH4/Air Microcombustor with Detailed Chemistry

The authors compare numerical simulations and experiments carried out on a swirling methane/air cylindrical microcombustor with diameter and height 0.006 m and 0.009 m, respectively. They extend previous work, using LES and Flamelet methodology; here the EDC finite rate model and the GRIMech 1.2 (32 species and 177 reactions) mechanism are used. Gas temperature at the exhaust section, together with CH* chemiluminescence measurements and combustion efficiency analysis are provided. Results reproduce exhaust temperature and combustion efficiency measurements, generally differing by less than 10%. This work should be seen as an advance in the understanding of how to design future microcombustors, presently under rapid development in particular for propulsion (e.g., for UAVs) and microelectrical power generators.

Numerical Simulations of a Micro Combustion Chamber

The goal of this paper is to investigate the performance of microcombustors for microturbines and for propulsion. Such field is currently under rapid development because of new market requirements. In particular, main areas of interest for microcombustion are propulsion, e.g., for UAVs, and micro

LES simulation of an ultra-micro combustion chamber based on a 177 reactions mechanism

electrical power generators. This study is focused on a cylindrical microcombustor fed by methane and air, with diameter and height 0.006m and 0.009m, respectively. Following a preliminary scaling analysis, two combustion models were tested, and 3D RANS numerical simulations were performed. The two combustion models simulating micro

Design Methodology and Performance Evaluation of New Generation Sounding Rockets

combustor flames are the ed dy dissipation model with fast chemistry and the flamelet model. Both use a novel 2

LES of a CH4/air Mesocombustor at 3 atm: EDC and Laminar-rate models

step reduced kinetics mechanism: this was properly tuned for the present device. Results indicate that the two models predict similar results for what concerns the chamber maximum temperature and outlet temperature; they differ in predicting combustion efficiency: in particular the eddy dissipation model underpredicts the measured combustion efficiency while the flamelet model overpredicts it. Compared to the eddy dissipation model, the advantage of the flamelet model is its enormous computational time saving. This work should be seen as an advance in the understanding of how to design, and what to expect from future microcombustors applications.

Comparison between real and ideal sub and supercritical combustion simulations of LO2-CH4 LRE flames at 15MPa

Goal of this paper is to investigate the performance of microcombustors, a field currently under rapid development in particular for propulsion, e.g., UAVs and micro-electrical power generators. This study focuses on a cylindrical microcombustor fed by methane and air, with diameter and height 0.025m and 0.06m respectively. A 3D LES simulation with the WALE subgrid scale models, the EDC combustion-chemistry model and the reduced GRIMech1.2 mechanism has been performed. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. Reported results are at 0.05s, that is after 5 residence times. This ultra-microcombustor displays an excellent combustion efficiency which makes it a suitable for application in ultra-small energy producing devices. This work is part of a broader work that includes an experimental analysis, and it was conceived as a contribution towards a better understanding of the most convenient simulations guidelines for future microcombustor applications, and to a more accurate estimate of the performance parameters to apply to first-order design procedures.© 2010 ASME

LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models

Sounding rockets are currently deployed for the purpose of providing experimental data of the upper atmosphere, as well as for microgravity experiments. This work provides a methodology in order to design, model, and evaluate the performance of new sounding rockets. A general configuration composed of a rocket with four canards and four tail wings is sized and optimized, assuming different payload masses and microgravity durations. The aerodynamic forces are modeled with high fidelity using the interpolation of available data. Three different guidance algorithms are used for the trajectory integration: constant attitude, near radial, and sun-pointing. The sun-pointing guidance is used to obtain the best microgravity performance while maintaining a specified attitude with respect to the sun, allowing for experiments which are temperature sensitive. Near radial guidance has instead the main purpose of reaching high altitudes, thus maximizing the microgravity duration. The results prove that the methodology at hand is straightforward to implement and capable of providing satisfactory performance in term of microgravity duration.

Swirling Combustor Energy Converter: H2/Air Simulations of Separated Chambers

3 volume; diameter and height are 0.006m and 0.009m, respectively. The combustion chamber pressure assumed is 3 atm, in order to produce mechanical work when connected to an internal combustion engine, f.i., a gas turbine. Two simulations are carried out by means of the LES� WALE approach, with finite rate chemistry taken from the GRIMech 1.2 kinetic mechanism (32 species and 177 reactions). The Kolmogorov scale analysis suggested to adopt both the laminarrate and the EDC combustion models. Gas temperature at the exhaust section and combustion efficiency are also predicted. Results show that the methane duct diameter should be of appropriate size to prevent air reflux and that, its small dimensions notwithstanding, relatively high combustion efficiency is possible with such chamber, making it suitable to power devices or recharge batteries. The two combustion models predict combustion efficiency difference of just few percentage points (demonstrating the complex fluid dynamics inside the chamber) and different products maps. This work advances previous simulations at ambient pressure, where results were also compared to experimental measurements. These are taken at 3 atm, are still underway and will be reported later.

Energy Converter with Inside Two, Three, and Five Connected H 2 /Air Swirling Combustor Chambers: Solar and Combustion Mode Investigations

This work is to be considered a contribution toward a better understanding of the impact of subcritical and supercritical parameters on mixing and combustion in future Liquid Rocket Engine (LRE) using LO2/CH4 as propellants. To this purpose four simulations of a reacting coaxial LO2/CH4 LRE jet at 15MPa and 1.18 equivalence ratio are presented. Real and ideal gas properties data have been reproduced with 6 th order polynomials and introduced in the FLUENT 6.2.16 software. An E.D.M. model describes the turbulencechemical kinetics coupling. Real gas simulations are carried out predicting the real gas properties at 15MPa: one simulation assumes the O2 injection temperature supercritical, the other subcritical, while CH4 is always injected supercritical. The third and the fourth simulations reproduce the previous two but using ideal gas properties in order to analyze and quantify differences. The simulations performed predict that, due to compressibility, pressure is not uniform inside the combustion chamber. Because “Real gas” Reynolds numbers are lower than those for ideal gas, “Real potential core lengths” are predicted shorter than “Ideal ones”, and temperatures are substantially lower due to the different Cpi behaviors. These results show that Real gas properties as accurate as possible are a key issue in preliminary design parameters of LRE combustion chambers.