Solid propellant bulk temperature directly influences rocket thrust and specific impulse
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Peer-reviewed literature establishes that propellant temperature affects burning characteristics and that performance metrics like thrust and specific impulse are directly influenced by propellant conditions such as thermal conditioning and aging.
Abstract Composite solid propellants (CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides (MOs), complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.
Burning rate of a solid rocket propellant depends on pressure and temperature. Conventional strand burner and Crawford bomb test on propellant strands was conducted to assess these dependent parameters. However, behaviour of propellant in rocket motor is different from its behaviour in strand form. To overcome this anomaly, data from static evaluation of rocket motor was directly used for assessment of these burningrate controlling parameters. The conventional empirical power law (r=aoexp[p{T-To}]Pn) was considered and a method was evolved for determination of pressure index (n) and temperature sensitivity coefficient (p) of burning rate for solid rocket propellants from static evaluation data. Effect of pressure index and temperature sensitivity coefficient on firing curve is also depicted. Propellant grain was fired in progressive mode to cover a very wide pressure range of 50 kg/cm2 to 250 kg/cm2 and propellant burning rate index was calculated to be 0.32 in the given pressure range. Propellant grain was fired at +35 °C and 20 °C temperatures and temperature sensitivity coefficient of burning rate was calculated to be 0.27 % per °C. Since both the values were evaluated from realised static evaluation curves, these are more realistic and accurate compared to data generated by conventional methods. Defence Science Journal, 2009, 59(6), pp.666-669 , DOI:http://dx.doi.org/10.14429/dsj.59.1573
Burn rate is a vital parameter of a propellant that highly influences the internal ballistics of a rocket motor. In the case of military applications of solid rocket motors, they are stored for a long duration, during which their performance deteriorates considerably due to aging. Conventionally, the accelerated isothermal technique is used for studying the effects of aging. However, in actual storage conditions, the temperature experienced by the propellant varies over time. In the present work, experimental investigations were carried out using accelerated cyclic and isothermal aging schemes. Here, the burn rates and temperature sensitivity of the propellant were recorded after the accelerated aging. A reduction in burn rates was observed in all aging techniques. There was a strong influence of the frequency of the aging cycle on burn rates. Theoretical analysis of motor performance indicates a reduction in chamber pressure to the tune of 18%, leading to deterioration of thrust by 20% and specific impulse by 2.5%. Remedies to recover the performance of the motor with aged propellant were explored, and throat inserts and thermal conditioning of aged motors were suggested as possible ways to overcome the aging effects.
<div class="section abstract"> <div class="htmlview paragraph">This specification established the requirements for a 5 second duration, 4500 pound thrust (when determined at 60°F) solid propellant rocket engine hereinafter specified as 5 S-4500.</div></div>
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