Hypergolic studies of ethanol gelled propellant

Abstract

Gelled fuel with share thinning viscoelastic nature formulated, further studies were necessary for determining their hypergolic nature and ignition delay for propulsion applications. The experiments conducted for this thesis mainly examines the hypergolicity and ignition delay time of the formulated ethanol, and ethanol base, gelled fuel when comes in contact with, hydrogen peroxide, oxidizer in a bipropellant system. The hypergolicity and ignition delay investigation for bipropellant system are highly essential for propulsion application. It was observed in the presented research that the ethanol based gelled fuel systems were hypergolic with hydrogen peroxide (90% pure) in a presence of a suitable catalyst defined as copper (II) chloride and Manganese (II) acetylacetonate. The observed ignition delay was within the range of 10~50ms, which was comparable with the existing liquid hypergolic bipropellant systems. Temperature profile also indicated that the formulated gel hypergolic system attained a very high temperature profile range of 1000 to 1400$\circ C$ for a very small weight percent of catalyst. Different samples of ethanol gelled fuel with different weight percent of gelling agent were formulated, and hypergolicity was achieved through addition of catalyst with less than one weight percent, ranging from 0.2 to 0.9wt%. The detailed understanding of hypergolicity and ignition delay of gelled ethanol fuel was mainly focused on gelling agent type and concentration, along with achieved apparent viscosity through gelation. The formulated gel fuel was thixotropic in nature with low apparent viscosity and yield point. Since viscoelastic properties of formulated gel systems plays a vital role to determine its hypergolicity and ignition delay time, which is an important parameter for any propulsion system. For further understating of hypergolicity and ignition delay dependent parameters, experiments were conducted with two separate volumes of oxidizer (hydrogen peroxide), 0.014 and 0.05ml. In both cases the bipropellant system was fuel rich. During this study, the formation of cage in the gel network was observed, which could encapsulate the higher temperature gases and flame in a network system, might be a plausible reason for recorded higher ignition delay. Hypergolic and ignition delay studies for energized gelled ethanol with hydrogen peroxide was also carried out. Experimental setup was designed for drop test studies, from which results were obtained using Photron high speed camera imaging. This study represented a sufficient repeatability of ignition delay for hypergolic gel bipropellant development. Gelled ethanol base fuel (pure and energized with nanoparticle of Al/B/C substitution) mixture with metal catalysts were formulated to examine its hypergolicity with ignition delays on the order of 1 to 30 milliseconds in most of cases, which are comparable with the existing liquid hypergolic bipropellant systems. The minimum ignition delay time was recorded for boron case at 1.33ms. Activation energy for the gelled ethanol fuel with pure and energetic particle substitution system was investigated in order to understand the minimum energy required for network breakdown and this resided within the range of 7 to 13 kJ/mole along with shear thinning behavior. Temperature profile also indicated an exothermic nature of the bipropellant 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. For any energetic system, its enthalpy is one of the very essential parameter. Therefore, thermal characterization of such material is very essential and can be conducted through calorific value study. In present research, the gross calorific value (GCV) was investigated to determine the enthalpy of all the formulated gel system, followed by, comparative study of calorific value, hypergolicity and ignition delay of gel bipropellant system of ethanol and hydrogen peroxide. For this, efforts were made to design a shear thinning catalytically promoted fuel rich hypergolic bipropellant system with ethanol gel fuel by introducing two different molecular weight organic gelling agent wt% (6, 8 wt% and 2, 2.5 wt%) and transition metal salt wt% (0.1 to 0.7wt%) in the parent fuel. Doing so further studies regarding the hypergolicity and ignition delay for the formulated gel bipropellant system were studied experimentally using Photron high speed camera imaging technique. It was observed that the hypergolicity was achieved even for a small wt% of two different transition metal catalysts approximately varying from 0.1 to 0.7wt%. The calculated ignition delay for the formulated system was in the order of 1 to 200 milliseconds at a static state with an addition of 30 and 100 $\mu l$ of peroxide. For catalytically promoted fuel with MCAT mostly, shows the delay time comparable with the existing hypergolic liquid propellant system with minimum delay time calculated for pure gel fuel-MCAT case at 2.6ms. Through this study it was noticed that MCAT catalyst seems to be more promising catalyst in comparison to CCAT at static condition. Temperature profile also indicated an exothermic nature of the designed system with maximum temperature recorded was 1360$\circ C$. Calorific value analysis shows that, the organic gelling agent (Sigmacell cellulose, and Hydroxypropylcellulose ($S_1$ and $S_2$)) has calorific value of 4571.67, 4733.66, 3500cal/g, 6468.69cal/g for CCAT and 6401.13 for MCAT. Also, it can be deduced that, gelation with organic gelling agent helps and participate in the combustion process of the formulated gel fuel with respect to gel system with inorganic gelling agent.