Aluminum is used in solid propellants to increase the specific impulse (Isp). It is desirable to have high propellant loading in any stage as it reduces the structural coefficient and an end burning grain is known to be the one with the highest propellant loading. As aluminum combustion is a slow process, the time available for aluminum combustion in an end burning configuration will be very small at the start of the combustion process. This demands an increase in the reactivity of the aluminum. This study is built on the fact that mechanical activation of aluminum powder with PTFE (poly-tetra-flouro-ethylene) enhances the reactivity of aluminum powder. This study also deals with the use of this activated aluminum powder in conjunction with various other methods to enhance the burn rates of the solid propellant. The temperature sensitivity was also measured. Based on these results, new designs with end burning grains for the third stage of Polar Satellite Launch Vehicle (PSLV) and for the second and third stage of Pegasus launch vehicle have been proposed to increase the payload capacity. With this new design, it is seen that the payload can be increased by 12.7 % and 17.6 % for PSLV and Pegasus, respectively. The novelty of this design is that with no changes to any other hardware of the above two systems the increase in payload can be achieved. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Periyapatna A. Ramakrishna

Department of Aerospace Engineering

Gaurav Marothiya

combustion

Composite propellants

Ethylene

Launch vehicles

Polytetrafluoroethylenes

Propellants

Rocket engines

Solid propellants

ALUMINUM COMBUSTION

Burn rates

Composite solid propellant

MECHANICAL ACTIVATION

POLAR SATELLITE LAUNCH VEHICLES

PYRAL

STRUCTURAL COEFFICIENT

temperature sensitivity

Aluminum

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Propellants, Explosives, Pyrotechnics

The combustion characteristics of Ammonium Perchlorate (AP) monopropellant have been revisited. The use of silica grease to prevent heat loss from the sides of the pellet and the ignition methodology opened up new area; one of them being the low pressure deflagration limit (LPDL) of AP itself and the other being the burn rate of AP at different pressures. The new burn rate law for pure AP was obtained for conditions close to adiabatic. Using slow depressurization method, wherein the LPDL was independent of ignition transients, the LPDL of pure AP was found to be 14 bar The burn rate of pure AP at 70 bar was found to be 10.66 mm/s, which was much higher than the ones reported in literature. The pressure index for this case was found to be 0.71. This new result completely changes the understanding of AP combustion and called for a new set of parameters to be developed to predict the results obtained with silica grease on the sides. Using the same set of parameters, along with a heat loss model the predictions for the case when there was no silica grease applied was made. These results were in reasonable agreement with the experimental data reported in literature without the silica grease on the sides of the AP pellet. This brings out the critical role of heat loss in AP combustion. © 2019 The Combustion Institute

Combustion and Flame

Combustion of Ammonium Perchlorate monopropellant: Role of heat loss

This study deals with the mechanical activation of pyral with PTFE. Pyral is a flake-like aluminium particle with a large specific surface area (~22.5m2/g). This paper, through a variety of tests like the TGA, DSC, particle size analysis, SEM analysis and other tests tries to establish that this mechanically activated aluminium is a good replacement for conventional aluminium used in a solid propellant. Burn rates were also measured at pressures ranging from 10 to 70bar using a modified Crawford bomb. The burn rates of solid propellants prepared with this mechanically activated pyral powder were found to be higher than that of non-activated pyral powder and much higher than that of those reported in literature with similar mechanically activated aluminium. This has been explained to be due the large specific surface area of aluminium used in these experiments which undergo exothermic fluorination reactions with PTFE. Two phase losses and slag accumulation are the two problems encountered when aluminium is used in composite solid propellants. Slag accumulation has shown a significant reduction with the use of this activated powder over non-activated pyral. © 2016 The Combustion Institute.

Effect of mechanical activation of high specific surface area aluminium with PTFE on composite solid propellant

The objective of this paper is to understand the observed changes in behavior of ammonium perchlorate deflagration characteristics reported in literature, when it is doped with potassium. Successive recrystallization is employed to dope potassium into ammonium perchlorate. This paper, through various recrystallization techniques, conclusively puts an end to doubts regarding the actual process of acquisition of potassium by ammonium perchlorate. It is concluded that the increase in the potassium content in ammonium perchlorate is due to the filter used during recrystallization process. From the experiments conducted to obtain the deflagration rates of ammonium perchlorate, it is observed that potassium doped ammonium perchlorate has higher burning rates and also a higher low-pressure deflagration limit. As potassium doped is within the ammonium perchlorate crystal, thermal conductivity and specific heat values for ammoniumperchlorate with various percentages of potassium are obtained. These values are incorporated into the computational studies on ammonium perchlorate. The computational studies performed in this paper are not intended to reproduce the experimental results but to illustrate the various features of the potassium doped ammonium perchlorate deflagration. With these computational studies, the observed burning rate increase and low-pressure deflagration limit increase of ammonium perchlorate with doped potassium are explained. Copyright © 2013 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.

Journal of Propulsion and Power

Enhancing composite solid propellant burning rates with potassium doped ammonium perchlorate-Part i

This paper examines the effect of mixer size on the density of the propellant and it also explores the role of the propellant density with regards to burning rate and burn rate pressure index. Propellant samples were prepared in the four different size (15, 70, 200 and 1000 g) mixers with identical input of ingredients to examine the effect of mixer size on density and burning rate of the composite solid propellant. It was noticed that density and burning rate of the propellant changes significantly with change in the mixer size from 15 g to 1000 g. This is because for the smaller mixers the surface area to volume ratio is large and the actual percentage of aluminum and ammonium perchlorate (especially coarse) that goes into the propellant reduces. High burning rate with decrease in mixer size is also accompanied with increase in burn rate pressure index. The composition analysis was also carried out and it is noticed that the actual percentage of the ingredients is different from the intended percentage of the ingredients and percentage change is more when the mixer size decreases. © 2013 IAA.

Acta Astronautica

Dependence of density and burning rate of composite solid propellant on mixer size

Iron oxide and copper chromite are the known burn rate enhancers used in a composite solid propellant. Lot of research has been carried out to understand the mechanism or location of action of the burn rate modifiers so as to better tailor the burning rate of a composite propellant. The literature is still very confusing in affirming the mechanism. Here, a systematic study has been carried out, by undertaking experiments at varying levels of combinations of the individual components (ammonium perchlorate, which is oxidizer and hydroxyl terminated poly butadiene, which is both fuel and binder) of composite solid propellant. Firstly, thermal gravimetric analysis, differential scanning calorimetry and burning rate measurements on the individual components are carried out to study the effect of iron oxide and copper chromite on the components themselves. It has been noticed that though both iron oxide and copper chromite are effective on ammonium perchlorate, iron oxide is slightly more effective than copper chromite. Also, copper chromite enhanced the binder melt flow, while iron oxide reduced it. These are followed-up by experiments on sandwich propellants, which give greater insight and enables better understanding of the behavior of iron oxide and copper chromite in composite propellants, as these are simple two-dimensional analogue of the composite solid propellants. Finally, experiments are carried out on the composite solid propellants to obtain a holistic understanding of the behavior/location of action of iron oxide and copper chromite in them. These studies are used to explain certain unexplained but observed phenomena, at the same time elucidating the location of action of these burn rate modifiers in composite solid propellant combustion. Based on these observations, it has been proposed that both iron oxide and copper chromite are primarily acting on the condensed phase. These studies are further complimented with experiments to analyze the thermal conductivity measurements of various propellant samples. This is pursued to understand the reason for the differences in burn rate pressure index for the composite propellants with iron oxide and with copper chromite. It has been understood from these studies that the thermal conductivity of a composite propellant is a key parameter, which affects the burn rate pressure index. Literature has never addressed it from this perspective. © 2014 The Combustion Institute.

Studies on the role of iron oxide and copper chromite in solid propellant combustion

This paper proposes the use of micron-sized aluminum (pyral, average particle size 3.66 μm) with a higher specific surface area as a good candidate to enhance the burn rate of the composite propellant. Experiments were performed in the pressure range of 10 to 70 bar in a window bomb for measuring the burn rate. Comparison of these burn rate results with those obtained using micron- and nanosized aluminum found that the performance of pyral was in between that of micron- and nanosized aluminum. The reason for the high burn rates observed with pyral is due to the flake like appearance of pyral with a large specific surface area. It is argued that, if the specific surface area is large, then the thickness becomes the characteristic length scale. This ensures the heat release from the aluminum combustion to occur closer to the propellant surface as the thickness of pyral is in nanometers. Both the x-ray diffraction and heat of formation analyses indicated that pyral had higher purity than nanoaluminum, which has an implication to the specific impulse of the propellant. In addition to this, it shows that the micron-sized catalyst is effective with pyral, whereas it is ineffective with nanoaluminum. This study also reports the mechanical properties of the propellant containing pyral.

Effect of specific surface area of aluminum on composite solid propellant burning

Enhancement of Aluminum Reactivity to Achieve High Burn Rate for an End Burning Rocket Motor

Journal	Data powered by TypesetPropellants, Explosives, Pyrotechnics
Publisher	Data powered by TypesetWiley-VCH Verlag
ISSN	07213115
Open Access	No