Pressure Dependence Of Burning Rate Research Articles

Unsteady Combustion Modeling of Metallized Composite Solid Propellant

This paper presents a physical-mathematical model of a metallized composite solid propellant (MCSP) unsteady combustion. The approach is based on the heat-transfer equations and oxidizer decomposition equations in the solid phase, the two-phase, the dual-velocity, and the two-temperature model of a reactant flow of the decomposition and gasification products over the propellant surface. The matching conditions on the surface of the fuel are set to provide the mass and the energy conversation laws. The stationary burning rate-pressure dependence for composite solid propellant on basis of ammonium perchlorate obtained during the simulation is in a good agreement with the experimental data described in the scientific researches. The calculation results of the unsteady burning rate depending on the pressure value are presented. The obtained fuel burning rates depending on the value and the rate of pressure drop fairly consistent with the experimental data. The paper provides the values of the pressure drop which leads to the extinction of the solid charge.

Combustion of micron-aluminum and hydrogen peroxide propellants

In this paper we report the burning rate characteristics of hydrogen peroxide and micron-aluminum propellants. Theoretical calculations show that the sea level specific impulse of this simple binary mixture is comparable to standard composite propellant. In addition, the aluminum particle size, hydrogen peroxide concentration, and mixture ratio can be adjusted over a flat peak performance regime to attain specific thrust profiles and durations. We measured the burning rates in a windowed pressure vessel at pressures ranging from 7 to 14MPa. Results show that mixture burning rates span from 0.5 to 4.5cm/s at 7MPa with power law burning rate pressure exponents ranging from 0.33 to 1.07. In this study, we focus a statistical analysis on the determination of the most influential variables affecting the burning rate and apply a thermal analysis to determine the combustion regimes of these mixtures. The statistical analysis provided a multivariate regression model for the logarithm of the burning rate with a correlation coefficient of 0.93. The model suggests aluminum diameter is the most important factor affecting the overall burning rate, and H2O2 concentration as the most influential variable on the burning rate pressure dependence. The burning rate dependence on theoretical combustion temperature shows two distinct combustion regimes attributed to kinetic and diffusion controlled combustion. A simple thermal analysis confirms the experimental burning rate pressure dependence observed for these two regimes.

Assessment of kinetic modeling for lean H2/CH4/O2/diluent flames at high pressures

Experimental measurements of burning rates, analysis of key reactions and kinetic pathways, and modeling studies were performed for H2/CH4/O2/diluent flames spanning a wide range of fuel-lean conditions: equivalence ratios from 0.30 to 1.0, flame temperatures from 1400 to 1800K, pressures from 1 to 25atm, CH4 fuel fractions from 0 to 0.1. The experimental data show negative pressure dependence of burning rate at high-pressure, low-flame-temperature conditions for all equivalence ratios and with CH4 addition. Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves – up to a factor of four at high pressures. Similar to our previous work that demonstrated that none of the recent kinetic models reproduced the measured pressure dependence of the mass burning rate for all diluent concentrations and medium to high equivalence ratios, here it is demonstrated that none reproduce the measured pressure dependence for very low equivalence ratios. The effect of pressure on the kinetics of lean flames is largely driven by competition of both H+O2(+M)=HO2(+M) and HO2+O/OH/HO2 with the main branching reactions, in contrast to rich mixtures that are largely driven by competition of both H+O2(+M)=HO2(+M) and HO2+H with the main branching reactions. Methane addition is shown to influence the pressure dependence mainly through reactions of CH3 with H and HO2. Given the nature of the modeling problem for high-pressure flames, it appears that a rigorous solution to improving predictive capabilities will require both empirical adjustments of multiple rate constant parameters as well as improved characterization of the functional temperature and pressure dependence of certain highly sensitive reactions. Furthermore, many of the reactions responsible for uncertainties in the pressure dependence of H2/O2 flames at high pressures are shown to contribute significantly to uncertainties in the pressure dependence of flames of hydrocarbon fuels.

Negative pressure dependence of mass burning rates of H 2/CO/O 2/diluent flames at low flame temperatures

Experimental measurements of burning rates, analysis of the key reactions and kinetic pathways, and modeling studies were performed for H 2/CO/O 2/diluent flames spanning a wide range of conditions: equivalence ratios from 0.85 to 2.5, flame temperatures from 1500 to 1800 K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, and dilution concentrations of He up to 0.8, Ar up to 0.6, and CO 2 up to 0.4. The experimental data show negative pressure dependence of burning rate at high pressure, low flame temperature conditions for all equivalence ratios and CO fractions as high as 0.5. Dilution with CO 2 was observed to strengthen the pressure and temperature dependence compared to Ar-diluted flames of the same flame temperature. Simulations were performed to extend the experimentally studied conditions to conditions typical of gas turbine combustion in Integrated Gasification Combined Cycle processes, including preheated mixtures and other diluents such as N 2 and H 2O. Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves – up to a factor of three at high pressures. The present findings suggest the need for several rate constant modifications of reactions in the current hydrogen models and raise questions about the sufficiency of the set of hydrogen reactions in most recent hydrogen models to predict high pressure flame conditions relevant to controlling NO x emissions in gas turbine combustion. For example, the reaction O + OH + M = HO 2 + M is not included in most hydrogen models but is demonstrated here to significantly impact predictions of lean high pressure flames using rates within its uncertainty limits. Further studies are required to reduce uncertainties in third body collision efficiencies for and fall-off behavior of H + O 2(+M) = HO 2(+M) in both pure and mixed bath gases, in rate constants for HO 2 reactions with other radical species at higher temperatures, and in rate constants for reactions such as O + OH + M that become important under the present conditions in order to properly characterize the kinetics and predict global behavior of high-pressure H 2 or H 2/CO flames.

Combustion of ammonium dinitramide/polycaprolactone propellants

This paper is devoted to the investigation of characteristics and mechanisms of combustion of a compositesolid rocket pseudo-propellant of stoichiometric composition based on ammonium dinitramide (ADN) and polycaprolactone (PCL). Experimental data on the dependence of burning rate on pressure in the pressure range of 4–8 MPa for the ADN/PCL propellant and the influence of molecular weight of PCL on this dependence are presented. The temperature of the final combustion products and the temperature profile in the combustion wave of the propellant have been measured by a microthermocouple method at 4 MPa. Also, the influence of a CuO catalyst on pressure dependence of burning rate and temperature profile has been investigated. The flame structure of the propellant ADN/PCL at 0.1 MPa has been studied. Data obtained elucidating combustion mechanisms and place of action of catalyst are discussed.

Burning Behavior of Composite Propellants with Fast-Burning Inclusions

The combustion characteristics of ammonium perchlorate-based composite propellants containing granulated fastburning energetic materials (FBEM) of different particle sizes have been studied in a constant-pressure bomb and combustion mechanism has been proposed. The use of FBEM of large particle size has been shown to allow not only a considerable increase in the burning rate, but also modification of the burning rate-pressure dependence.

Mechanism of Modifying Ballistic Properties of Propellant Formulations by Fast-Burning Inclusions

The combustion characteristics of binary compositions of fast-burning energetic materials (FBEM) with main composite propellant components like ammonium perchlorate (AP) and polymeric binders have been studied in a constant pressure bomb, and combustion mechanism has been proposed. Combustion behaviour of composite propellants containing granulated FBEM of different particle sizes has been investigated. FBEM additives as high as 40 per cent of fine particle size to a composite propellant have not been shown to influence markedly the burning rate, whereas incorporation of FBEM grains of 500 micrometer particle size allows not only a considerable increase in the burning rate but also modifies the burning rate-pressure dependence. A mechanism of combustion of propellant compositions containing FBEM grains has been evolved that allows criteria for FBEM performance and combustion stability.

In search of an idealized model of homogeneous solid propellant combustion

A simple idealization of the steady-state deflagration of uncatalyzed, homogeneous solid propellants is examined to determine its adequacy in describing gross combustion features such as burn rate as a function of pressure and initial temperature. The idealization consists of a single condensed phase process (pyrolysis and evaporation are considered) and a single gas phase chemical reaction. Several analytic approximations (including one developed during the course of this work) are derived and discussed in relation to the work of other investigators. All of these approximations are shown to lead explicitly to approximate analytic expressions of the same functional form as empirical formulas for the burning rate pressure dependence. The approximation developed in this paper is shown to lead to a common empirical form for the temperature sensitivity. A means of testing the suitability of these approximations to a given propellant is also developed using temperature profiles obtained by the embedded thermocouple technique.

A phalanx flame model for the combustion of composite solid propellants

A new model for the combustion of composite solid propellants is developed. The flame is represented as burning at the interfacial region between streams of fuel and oxidant which are generated by vaporization of each solid component. The interface between the two solid phases receives the greatest heat flux from the reaction zone and vaporization occurs most rapidly near the interface. The reaction zone is a ‘phalanx’ which spearheads the attack of hot reaction gases on the solid. The model provides a rational physical explanation for many qualitative observations of solid propellant combustion and successfully correlates the pressure dependence of burning rates.

Burning Rates of Solid Propellants

The burning mechanism of a solid propellant is described in terms of a pyrolysis law, a premixed laminar flame, and nothing more. A quantitatively accurate burning rate formula is derived from the theory. The predicted burning rate pressure dependence agrees with the experimental results for ammonium perchlorate propellants.