Combustion and Flame 176 (2017) 318–325 Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustfame Hypergolicity and ignition delay study of pure and energized ethanol gel fuel with hydrogen peroxide B.V.S. Jyoti, Muhammad Shoaib Naseem, Seung Wook Baek ∗ Aerospace Engineering Department, Mechanical Engineering Building, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, South Korea a r t i c l e i n f o Article history: Received 9 September 2016 Revised 17 November 2016 Accepted 17 November 2016 Keywords: Ethanol Gel Propellant Hypergolic Ignition delay Viscosity a b s t r a c t An experimental study of hypergolicity and ignition delay of pure and energized gelled ethanol with hy- drogen peroxide was carried out. Experimental drop test results were obtained and discussed by using Photron high speed camera imaging. This study represented a sufficient repeatability of ignition delay for hypergolic gel bipropellant development. Gelled ethanol fuel (pure and energized with nano-Al/B/C parti- cle substitution) mixture with metal catalysts were formulated to examine its hypergolicity with ignition delays on the order of 1–30 ms in most of cases, which are comparable with the existing liquid hyper- golic bipropellant systems. The minimum ignition delay time was recorded for boron case at 1.33 ms. And the calculated activation energy for the gelled ethanol fuel with pure and energetic particle substitution system resided within the range of 7–13 kJ/mole along with shear thinning behavior. Temperature profile also indicated an exothermic nature of the propellant system with 1000 to 1600 K recorded. Parameters such as apparent viscosity of the fuel, drop height and drop volume also played an important role for the hypergolicity of the system in a drop experimentation. It was also observed that the formation of a cage encapsulating the high temperature gases in a network formed by the gelling agent could result in a longer ignition delay. © 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction The term hypergolicity is the spontaneous ignition of a fuel and an oxidizer in contact. Hypergolic propellants are preferred for sev- eral rocket propulsion missions, mostly when multiple and reliable ignitions are required for mission success [1]. Ethanol and hydrogen peroxide based hypergolic bipropellant system can impart several properties that can contribute sys- tem advantages when compared to the traditional hypergolic sys- tem such as unsymmetrical dimethylhydrazine-Red fuming ni- tric acid (UDMH-RFNA), monomethylhydrazine-nitrogen tetroxide (MMH–NTO) etc. [2]. It has high density, low vapor pressure, less toxic, corrosive and ecofriendly nature. Additionally, the hydrogen peroxide decomposition and combustion products with ethanol are non-toxic and environmentally more friendly than traditional hy- pergolic systems which are in current use. However, the hydrogen peroxide provides some challenges too along with a number of ad- vantages such as thermal stability, storage, handling and material compatibility. The interest in using an alternative and more ecofriendly fuel and oxidizer system (such as ethanol and hydrogen peroxide) in ∗ Corresponding author. Fax: +82423503710. E-mail address: swbaek@kaist.ac.kr (S.W. Baek). rocket propulsion application has been renewed over the past decades [2–7]. Ethanol was selected based on its application in past as a rocket fuel such as German V-2 missile, Jupiter C, Amer- ican Redstone Rocket, etc. In addition, the ethanol is a biofuel, which is least negative to the environment, easy to handle and transport, cheap and economical. Moreover, the hypergolic bipro- pellant system based on catalytically promoted gelled ethanol fuel and hydrogen peroxide requires very less quantity of catalyst for its hypergolicity and produces non-toxic the combustion products from the reaction which are mostly water vapor and CO 2 gas with less than 1 mole% of metal catalyst oxide in solid form. On the contrary, a higher concentration of transition metal catalyst can re- duce the exhaust velocity and specific impulse, since the exhaust velocity is inversely proportional to the square root of the average molecular weight of the exhaust product. In order to maximize the specific impulse, a reduction of the transition metal concentration of the fuel is required without affecting the ignition delay time of the hypergolic system. The use of catalysts for promoting decom- position and combustion of hydrogen peroxide (80% concentrated) with methanol fuel dates back to German use of calcium perman- ganate as a hypergolic combination in the Me163 [8]. Also, recently a study has been done in which fuel additives were introduced for the purpose of ignition delay control specially for ethanol and peroxide systems [9]. For keeping a prospective for rocket system, a critical concentration of catalyst was considered for the study. http://dx.doi.org/10.1016/j.combustflame.2016.11.018 0010-2180/© 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.