An attempt was made in this paper to determine the regression rate of a hybrid fuel by using combustion chamber pressure. In this method, the choked flow condition at the nozzle throat of the hybrid rocket was used to obtain the mass of fuel burnt and in turn the regression rate. The algorithm used here is better than those reported in the literature as the results obtained were compared with the results obtained using the weight loss method and was demonstrated to be in good agreement with the results obtained using the weight loss method using the same motor and the same fuel and oxidizer combination. In addition, the O/F ratio obtained was in good agreement with those obtained using the weight loss method. The combustion efficiencies obtained were in good agreement with the average values. © 2014 IAA. Published by Elsevier Ltd. All rights reserved.

Periyapatna A. Ramakrishna

Department of Aerospace Engineering

Combustion chambers

Fuels

Paraffin waxes

Rockets

Average values

Chamber pressure

CHOKED-FLOW CONDITION

Combustion efficiencies

HYBRID ROCKETS

Nozzle throat

REGRESSION RATE

WEIGHT LOSS METHOD

Regression analysis

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

Acta Astronautica

Polytetrafluoroethylene is known to enhance the reactivity of aluminum. The enhancement in the reactivity is produced by mechanically activating the aluminum using polytetrafluoroethylene. In this study, mechanically activated aluminum powder is used along with paraffin wax as the fuel grain for a hybrid propellant. Here, gaseous oxygen is used as oxidizer. To achieve an optimum composition for the best specific impulse, the aluminum fraction in the composition is restricted to 50% of the base fuel composition along with 50% wax/ethylene vinyl acetate (combination of wax and ethylene vinyl acetate, in a ratio of 4∶1). The polytetrafluoroethylene in mechanically activated aluminum powder is added at the expense of wax/ethylene vinyl acetate in the fuel composition. When compared with the composition having pyral aluminum powder (which has flake like particles of very high specific surface area), mechanically activated powder increases the fuel regression rate by ∼40% at an oxidizer mass flux of 35 g∕cm2-s. It is also observed that the combustion efficiency of the hybrid motor is 59% with the use of mechanically activated aluminum powder in comparison to 39% obtained with micron-sized aluminum powder. Copyright © 2018 by Indian Institute of Technology, Madras, India.

Journal of Propulsion and Power

Utilization of mechanically activated aluminum in hybrid rockets

A fuel for the hybrid rocket system was developed. The attempts made to improve the mechanical properties of wax by adding EVA (ethylene vinyl acetate) are illustrated. It was observed that the mechanical properties obtained by adding EVA to wax were dependent on the process of curing the fuel specimen. A proprietary method of curing the fuel specimen was established. The percentage elongation obtained with 20 % EVA and 80 % of wax was around 17 %, which was much higher than the values obtained with pure wax (4 %). It was observed from the study that the higher the percentage of EVA content in wax was, the better the mechanical properties were. Regression rate studies with EVA and wax combination were carried out. It was observed that the regression rate decreased upon addition of EVA in wax. This reduction was compensated by using a bluff body at the head end. The regression rate obtained with 20 % EVA and 80 % wax even with the use of bluff body is lower than that obtained with pure wax, but is around 3.5 times the regression rate obtained with polymeric fuels. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Propellants, Explosives, Pyrotechnics

Studies on EVA-Based Wax Fuel for Launch Vehicle Applications

In this work, the effect of solid oxidizer (AP) mixed fuel grain (HTPB) on regression rate and performance in GOX hybrid rocket motors is numerically studied. Here the pyrolysis products of AP and the fuel forms a premixed flame very close to the grain surface in addition to the fueloxygen diffusion flame located further away from the grain surface. The presence of premixed flame increases heat feedback to the grain and consequently increases the local regression rate throughout the grain length. This is contrary to the locally limited influence observed while using other regression rate enhancement techniques like swirling oxidizer, or transverse diaphragms/protrusions. Scaling of motors with AP mixed grain of a given composition follows that of a pure fuel grain where the grain geometry and the inlet oxidizer mass flux need to be maintained. © 2015 Elsevier Masson SAS. All rights reserved.

Aerospace Science and Technology

A numerical investigation of oxidizer mixed hybrid rocket motors

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.

Issues related to the measurement of regression rate of fast-burning hybrid fuels

The results of a systematic experimental investigation on the methods of enhancing the regression rate in hydroxyl-terminated polybutadiene (HTPB) fuel used in an HTPB/gaseous oxygen hybrid motor are presented. The effects of the addition of ammonium perchlorate (AP) or aluminum in the fuel, the variation of oxidizer-fuel ratio, and the variation of characteristic dimensions of fuel grain are presented. For the extents of the parametric variations considered, while the addition of AP and/or Al and the reduction of grain port diameter enhance the regression rate, the effect due to the latter is the most significant one. Furthermore, the regression rate increases along the axis, and it becomes essentially constant in the port region corresponding to a fuel-rich composition. The possible physical processes for all of these behaviors are discussed. The experimentally obtained exponents of the variables for regression rate (oxidizer mass flux and port diameter) are found to be significantly different from those of the conventional theory. The similarity between the fuel regression rate equation used in solid-fuel ramjet and that obtained in hybrid motor is discussed.

Fuel regression rate in hydroxyl-terminated-polybutadiene/gaseous-oxygen hybrid rocket motors

International Journal of Aerospace Engineering

Approaches to Low Fuel Regression Rate in Hybrid Rocket Engines

47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &amp; Exhibit

Effect of Protrusion in the Enhancement of Regression Rate in Hybrid Rocket

Measurement of regression rate in hybrid rocket using combustion chamber pressure

Journal	Data powered by TypesetActa Astronautica
Publisher	Data powered by TypesetElsevier Ltd
ISSN	00945765
Open Access	No