Showing papers on "Burn rate (chemistry) published in 2000"

Burn Rate Measurements of HMX, TATB, DHT, DAAF, and BTATz

Abstract: : In this paper we present new burn rate results for several energetic materials. The burn rates of octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), HMX and estane-based binder (PBX 9501), 1,3,5-triamino- 2,4,6-trinitrobenzene (TATB), and TATB and KelF binder (PBX 9502), are reported and compared with existing data. Burn rate data of these common explosives complement and extend existing data sets. Burn rate data of three novel high-nitrogen materials are presented in this work. Specifically, the high-nitrogen monopropellants considered are 3,6-dihydrazino-s-tetrazine (DHT), 4,4'-diamino-3,3' -azoxyfurazan (DAAF), and 3,6-bis(1H-1,2,3,4-tetrazol-5-amino)-s-tetrazine (BTATz). High-nitrogen compounds may be key to meeting the advanced performance objectives of next-generation solid propellants. High-nitrogen solids offer the possibility of high performance, reduced emissions, and lower plume signature (low temperature and no HCl) than current propellant systems. The theoretical specific impulse is comparable to HMX. In contrast to HMX, however, high-nitrogen materials tend to be insensitive to impact. Because high-nitrogen energetic materials have intrinsically large positive heats of formation and produce low-molecular-weight reaction products, they may be suitable for consideration in high-performance propellant applications. BTATz appears particularly interesting because of its rapid burn rate, relatively low-pressure exponent, and high heat of formation. The effect of a small amount of binder is investigated for all but one of these materials.

Flame Propagation in a Tube: The Legacy of Henri Guenoche

Abstract: Since the time of Mallard and Le Chatelier there has been a fascination with the problems of flame propagation in tubes. An important goal has been the development of a reliable technique to measure accurately the most basic combustion parameter, the laminar burning velocity. On the one hand a stable, steady-state, flame is necessary to do this, while on the other hand many flames are inherently unstable. These conflicting tendencies have been the source of much creative combustion thinking, not least from Guenoche. The paper attempts to indicate how his work has contributed to our present appreciation of the effects of flame stretch, thermo-diffusion, Darrieus – Landau and Taylor instabilities. Some practical consequences of the effects of these on the burn rate are briefly discussed. Laminar burning velocity and its measurement The purpose of the present paper is to show how Henri Guenoche’s painstaking descriptions and analyses of experimental findings concerning flame propagation in tubes contribute greatly to our current fundamental understanding of combustion. In 1883 Mallard and Le Chatelier [1] showed that the condition of a tube closed at one end with ignition at the other, open, end is probably the one best able to achieve a constant flame speed over a distance sufficient for the measurement of the laminar burning velocity. Thereafter, the flame oscillates, particularly with lean CH4 and H2 and rich hydrocarbon mixtures with air, and then assumes a cellular structure with an enhanced flame speed [2]. Their painstaking studies of the factors that give rise to a regime in which the flame speed is constant led Guenoche and Laffitte [3] to suppress any tendencies to acoustic oscillations by fitting an orifice to vent the burned gas at the open end of the tube, a practice adopted by subsequent workers, to make the vertical tube method a recommended one for measuring burning velocity [4]. Conversely, in the unstable regime forcing oscillations can induce a cellular structure [5]. When the flame attains a constant flame speed through the use of orifice damping its shape hardly changes and hence the effects of flame stretch rate are minimal. In the last decade the quantitative understanding of these effects stretch has advanced considerably and it is now almost mandatory to measure stretch-free values of burning velocity, λ u , together with values of Markstein numbers, Ma, to express the effects of flame stretch rate, in conjunction with the Karlovitz stretch factor, K. Flame stretch can either increase or decrease the burning velocity to a value,

Stochastic prediction of cycle-by-cycle cylinder pressure fluctuations in a spark ignition engine

Abstract: The generality of recent stochastic models for cylinder pressure development is exploited, both to recreate or simulate cyclic datasets with similar statistical properties to real engine data, and to derive many of the more traditional statistics (e.g. standard deviations of maximum pressure, mean effective pressure, burn angle, etc.) directly from the parameters of the more general model form. The same approach also provides insight into the phasing of the cyclic process, since a number of statistics (such as the standard deviation of pressure or burn rate variations) can be computed directly as a function of crank angle. It is also straightforward to evaluate the contribution to such quantities from each of the physically meaningful model parameters, and thereby obtain some insight into the mechanisms involved.

Cycle-to-cycle variations under cylinder-pressure-based combustion analysis in spark ignition engines

Abstract: Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper was to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. To analyse the cyclic variation in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. The burn rate analysis program was used here and the burn parameters were used to determine the variations in the input parameter—i, e,, fuel, air, and residual mass. In this study, we investigated the relationship of indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, burn angles, and lowest normalized value (LNV) in a spark ignition engine in a view of cyclic variations.

Detailed Combustion Modeling as an Aid to Propellant Formulation: Two New Strategies

Abstract: : There has been considerable progress recently in the development and use of elementary chemical reaction mechanisms to describe the gas phase energy release of energetic materials Such advances present an opportunity to examine the extent to which these models might be used to provide guidance to the propellant formulator In this report, we develop two methodologies that may prove helpful to the development of propellant formulations with tailored combustion characteristics First, the dependence of the burning rate on the path of condensed phase decomposition was computed for nitroglycerine (NG) combustion It was found that some sets of decomposition products lead to nearly an order of magnitude higher burning rate than is observed experimentally This indicates that efforts to influence the path of decomposition might be a novel and powerful approach to tailoring burning rate Second, a methodology for calculating the effectiveness of different chemical additives on the burning rate was developed and demonstrated for several chemical additives added to NG Burning rates were calculated for the additives H2, CH2O, and NH3 and flame structure calculations made for HNCO as an additive NH3 accelerates the burning rate of NO, and HNCO is expected to retard it; both reduce the dark zone length and thus may reduce ignition delays in guns

Ballistic studies of wide distribution propellants

Abstract: The objective of this research is to describe the effects of oxidizer particle size distribution on the burning rate of solid propellants used in rocket motors. Current models over predict the burning rate of wide distribution (wide distribution denotes two oxidizer modes that have extreme differences in mean diameter) formulations by 40 to 200 percent indicating combustion mechanisms unique to this type of propellant. Four sets of AP/HTPB propellants were formulated to control the physical and chemical heterogeneities characteristic of the propellant surface using 400 and 20u oxidizer particles. The propellants were tested at pressure levels from 0 to 2000psig. The results indicate that the burning rate of wide distribution propellants is suppressed by the formation of a layer of liquid binder on the burning surface. High-speed motion pictures showed molten binder flowing off the burning surface during the propellant combustion. The flow increased as the oxidizer-to-fuel ratio of the pocket propellant is decreased. Examination propellant surfaces, extinguished by depressurizat ion, showed that the oxidizer surface was partially covered with a thin binder layer during the burning. This phenomenon accounts for the difference in model predictions and experimental results. Because of the fuel-rich nature of the fine particle combustion, the propellants also exhibited extreme sensitivity to changes in binder composition.

Modelling of Heat Loss in Closed Vessels during propellant Burning

Abstract: Closed vessel technique is essentially used to determine the force constant, vivacity and the burning rate of gun propellants. In fact, it is the only method to find out these three parameters experimentally. It is a well-known fact that however small the propellant burning time may be, there will be heat loss to the walls of the vessel due to conduction, convection, radiation and also due to the expansion of the vessel. This fact necessitates applying correction to the observed maximum pressure in the experiment. An analysis is presented in this paper as to how this heat loss can be modelled along with discussion about other models reported in this field.

Method for velocity precision pointing in spin-stabilized spacecraft or rockets

Abstract: A method of velocity precision pointing of spin-stabilized spacecraft or rockets is disclosed This method involves softening the ignition transient of the ramp up phase of thrust, which may be achieved by modification of the solid propellant, applying a coating of slow burning material upon the solid propellant varying the grain density of the solid propellant over an exposed surface area or as a function of propellant depth, where depth is defined in the direction of the burn surface area regression, pre-pressurizing the combustion chamber with a gas having a molecular mass smaller than that of the combustion products and which is unreactive with the propellant, installing one or more relief valves in the combustion chamber to regulate the pressure, forming a ring of an ablative material on the throat section of the nozzle, having a rubber fitting at a throat section of the nozzle to regulate the pressure of the combustion chamber, pulsing the engine, or using a pyrogen igniter to soften the ignition transient

Propellant composition having a relatively low burn rate exponent and high gas yield

Abstract: A propellant composition that results in a desirable gas output when combusted is provided. The propellant can be part of an inflator used in a vehicle for inflating an air bag. The propellant has a relatively low burn rate exponent of no greater than about 0.7. The propellant is substantially dense, with the propellant having a density that is at least 85 % of theoretical density. The process of forming the propellant includes mixing the propellant composition in a mixing vessel (30), extruding the propellant composition into a propellant having a first density in an extrusion machine (40), drying the extruded propellant in a dryer (50), and flattening the dryed propellant to a controlled thickness using a roller mill (60) to provide a propellant having a second greater density correponding to the final density. The propellant preferably includes phase-stabilized ammonium nitrate and fibrous cellulose.

Combustion Mechanisms of Heterogeneous Solid Propellants

Abstract: : The bulk of the research on this contract was concerned with the mechanisms that cause plateau burning of ammonium perchlorate/hydrocarbon (AP/HC) propellants. The long range goal is to identify the steps in the combustion process that dominate overall burning, and in particular to understand which of these steps in the combustion process lead to plateau burning. Burning alone, matrixes (mixture of binder, fine AP, and catalysts) almost always burn slower than the bimodal propellant at all pressures. The improved burning with a catalyst is probably due to both increased surface layer heat release and to catalytic break down of the large fuel vapor molecules which cause the flame to stand closer to the surface. Deflagration rate of the large AP particles is always lower than the propellant rate, and contributes little to overall rate, except in close proximity to the matrix where a hot stoichiometric diffusion flame occurs and (apparently) supports the marginal matrix burning, accounting for the higher propellant rate. Observations of local intermittency of burning seem to contribute to the low burning rate associated with plateaus and spontaneous quenches.

Energy Management in Rocket Propulsion

Abstract: The optimal management of the available energy in an ideal single-stage rocket produces a velocity increment that is larger than the value provided by Tsiolkovsky’ s equation. This result is immediately applicable when a limited amount of energy is available from a source that is external to the propellant. A storage device is instead necessary to delay partially the use of the energy that is produced by the combustion of a reactive working e uid. The penalty of the energy-source mass and the presence of an upper limit on the propellant temperature are also discussed; in the latter case, the addition of a low-molecular-weight, inert propellant to the reactive propellant is benee cial during the e nal phase of the rocket acceleration.

Lead salt of 2, 4, n-trinitroanilinoacetic acid - an energetic ballistic modifier for double base propellants

Abstract: Lead Salt of 2,4,N-trinitroanilinoacetic acid has been evaluated as ballistic modifier in composite modified double base matrix. Burn rate measurements showed a plateau effect between 3.43 — 8.82 MPa. The salt-containing propellant composition showed a synergistic effect on decomposition of propellants as evidenced by a reduction in differential thermal analysis exotherm peak temperature. Effect of magnesium oxide-lead salt combination on burn rate of propellant formulation was also evaluated. The combination increased the burn rate at 6.86 — 8.82 MPa and decreased at 10.78 MPa. The salt has been prepared by double decomposition of lead nitrate with sodium salt of 2,4,N-trinitroanilinoacetic acid, which in turn is prepared from glycine and 2,4 - dinitrochlorobenzene. The lead salt decomposes at 187°C as shown by differential thermal analysis exotherm. Calorimetric value (+3.14 MJ/kg) of the salt has been calculated. The salt exhibits an impact sensitivity height (h50) of 97.5 cm and friction sens...

Transverse thrust flight control arrangement

Abstract: A flight control arrangement for four-quadrant final-phase guidance control of a missile using transverse thrust jets 10 mounted so flow from a dry-fuelled gas generator 13 through the jets 10 can be adjusted by a common final control element 12, 30 rotated to an angular position by actuator 16 and moved linearly to an axial position by actuator 17. In a first embodiment, the common final control element 12 obstructs the flow to three jets 10 while in a second embodiment, three valve elements 38 may be actuated to restrict the flow through three jets 10, in both embodiments this then causes transverse thrust through the forth jet and a higher burn rate in the gas generator 13 due to increased pressure. When no direction change is required, the final control element 12, 30 is moved linearly to allow flow through all thrust jets 10, the lower pressure in the gas generator 13 thus induced causing a low burn rate of fuel.

Combustion property of aluminum-magnesium fuel-rich propellant at low pressure

Abstract: The aluminum-magnesium fuel-rich propellant for unchoked ducted rocket was developed. The combustion characteristics of the fuel-rich propellant at low pressure '(0.2 2.0 MPa) was investigated by means of strand burner and direct connected-pipe testing facility.