Now showing 1 - 10 of 69
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    Enhancing the Regression Rate of Hydroxyl-TerminatedPolybutadiene-Based Mixed Hybrid Rockets
    (01-01-2022)
    Marothiya, Gaurav
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    Kumar, Rajiv
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    This study has identified potential hydroxyl-terminated-polybutadiene (HTPB) based fuel compositions that provide a high-density specific impulse but do not burn like a solid propellant. Due to low solid loading in these fuel compositions, precuring the HTPB and isophorone diisocyanate mixture is necessary to get uniform density and composition across the length of the grain. Nearly 7 h of precuring gave the best results in terms of uniformity of the propellant composition. This study also discusses the effect of available burn rate modifiers for ammonium perchlorate and a type of aluminium on the enhancement of regression rate in mixed hybrid rockets. Finally, the hybrid propellants developed had an oxidizer mass flux index close to 0.5, which is desirable.
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    Emission and combustion analysis of a glow-plug engine fuelled with nitromethane–methanol blends
    (01-01-2020)
    Raviteja, Sammeta
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    A small quantity of Nitromethane is often added to the glow-plug engine’s fuel to enhance the power output of an engine. The present work is aimed at characterizing performance enhancement and analyzing the in-cylinder combustion parameters to understand the reasons for the improved performance of a small glow plug-assisted compression ignition engine. The experimental tests involved the measurement of in-cylinder pressure with respect to the crank position at various equivalence ratios for different nitromethane blends. The thermodynamic analysis was carried out to obtain the heat release rates and combustion durations. Results showed increased heat release rates with nitromethane addition. Emission measurements were carried out to quantify the effect of nitromethane addition on nitric oxide (NO), hydrocarbon (HC), and carbon monoxide (CO) emissions. It was observed that the HC and CO emissions drop with nitromethane addition; however, NO emissions increase drastically.
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    Estimation of burning characteristics of AP/HTPB composite solid propellant using a sandwich model
    (01-07-2020)
    Vijay, Chaitanya
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    The present study suggests a technique to estimate the burn rate of non-aluminized propellant compositions. A random packing algorithm is used to generate a three-dimensional propellant pack consisting of spherical Ammonium perchlorate (AP) particles and Hydroxyl-terminated poly butadiene (HTPB) binder. Intercept lengths of AP and HTPB were obtained by slicing the propellant pack and lines drawn on the sliced planes. The average intercept lengths were recorded and then used as thickness of AP and binder sandwich propellants. A discussion on the choice of parameters is made for both AP monopropellant flame and the diffusion flame. Comparison of burn rates of computational results is done with experimental studies reported in literature. A reasonable match has been obtained in these comparisons. Further, temperature sensitivity, which is an important factor, has been estimated and the values are closer to those reported from experimental studies than the values reported by earlier studies.
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    Laminar burning speeds of nitromethane-gasoline blends at elevated temperatures and pressures
    (01-04-2019)
    Raviteja, S.
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    Nitromethane is extensively used in drag races and in glow plug unmanned aerial vehicle (UAV) engines. However, it has not been analyzed in the combustion literature enough. Nitromethane has a low stoichiometric air-fuel ratio; it can be blended with gasoline and used in larger quantities to enhance the power output of the internal combustion (IC) engines. This could find potential use in burgeoning UAV industry. The present investigation aims at experimentally determining the laminar burning speeds of nitromethane-gasoline blends at different equivalence ratios. Tests were conducted at both ambient conditions and at elevated temperatures and pressures. A constant volume combustion chamber (CVCC) was constructed and instrumented to carry out the investigation. The pressure rise in the chamber due to combustion was acquired and analyzed to determine the laminar burning speeds. The results showed that with an increase in the nitromethane concentration in gasoline, the laminar burning speeds for all the initial conditions also increased. With the rise in initial temperatures, the laminar burning speeds were observed to increase. However, a drop was observed with a rise in the initial pressures for all the blends. The obtained results for pure gasoline were compared with existing literature. A good match was observed. The investigation also aims at providing vital experimental data, which can be used for computational fluid dynamics validation studies later.
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    Studies on the role of iron oxide and copper chromite in solid propellant combustion
    (01-01-2014)
    Ishitha, Kumar
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    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.
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    Effect of mechanical activation of high specific surface area aluminium with PTFE on composite solid propellant
    (01-04-2016)
    Gaurav, M.
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    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.
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    Enhancement of regression rate in hybrid rockets
    (01-12-2011)
    Marothiya, Gaurav
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    Kumar, Rajiv
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    This study has identified a potential HTPB based propellant that gives a very good density specific impulse but yet does not burn like a solid propellant. Due to low solid loading in this propellant, pre-curing of the HTPB and IPDI mixture is a necessity to get uniform density across the length of the grain. Nearly 7 hours of pre-curing gave the best results in terms of uniformity of the propellant composition. The paper also discusses the enhancement of regression rate of this propellant with known burn rate modifiers like iron oxide and copper chromite. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
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    Issues related to the measurement of regression rate of fast-burning hybrid fuels
    (01-01-2013)
    Kumar, Rajiv
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    The measurement of the regression rate of a hybrid rocket fuel is the subject matter of this paper. This is an involved problem because both the regression rate and the oxidizer mass flux Gox vary with the port diameter, which itself varies during combustion. This paper addresses the issue of how Gox should be varied to obtain the regression rate correctly. The most commonly used weight loss method has been employed here. Three methods used here to vary the Gox are artificially changing the port diameter, changing the mass flow rate of the oxidizer, and interrupted burn test. From the experiments conducted, it was evident that the interrupted burn test was the best method. These experiments were also carried out for a larger motor and the results compared quite well with established literature. The role of the recirculation zone size near the head end and the overall heat transferred back to the fuel surface in influencing the regression rate have been explained. The role of the recirculation zone diminishes as the length of the rocket motor is increased.
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    Enhancing composite solid propellant burning rates with potassium doped ammonium perchlorate-Part i
    (01-01-2014)
    Ishitha, Kumar
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    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.