Development and Experimental Evaluation of Endothermic Fuel for Better Combustion and Life of Combustor: In Realistic Test Setup

Abstract

The concept of endothermic fuels is not a strange thing to the aeronautical community. Research is going on, globally, to achieve these kinds of fuels experimentally; but restricted to laboratory scale test setup. This is because of the stringent and controlled method of cracking the fuel thermally as well as catalytically. In this research work we have followed a systematic approach, i.e, developed a laboratory scale reactor for the preliminary feasibility studies and a realistic experimental set up, for the development and analysis of the cracked fuel by simulating the conditions of combustor walls. Developing this technology indigenously involves many steps, namely identification of the suitable catalysts, developing the technology of preparation of catalytically active coatings and then the design and fabrication of the catalytic cracking core. Finally the catalytic cracking core has to be integrated to the test combustor with the experimental setup. To carry out the catalytic cracking reaction, a high pressure and high temperature catalytic reactor was designed and developed. The reactor can heat kerosene up to 725 K and maintain pressures up to 10 bar. The catalytic coatings were prepared with ZSM-5 and molecular sieves (20:80); coated on aluminum cylinders. A temperature drop of 114 K was obtained when kerosene fuel was passed through the catalytic system. This clearly shows the cooling effect by the endothermic fuel. A mixed bed catalytic system (Molecular sieves, Reformax-100 and ZSM-5) was also developed for the in-situ generation of Hydrogen gas along with the catalytic cracking process. The presence of Hydrogen gas in the cracked fuel is confirmed by gas chromatographic (GC) Retention time Vs Voltage investigation. The experimentation in test rig was carried out in two modes, one is for thermal cracking (absence of catalyst) of kerosene fuel and the other one is catalytic cracking. In both the cases, the combustor duct is heated by hot air to 1200 K. Skin temperatures were measured to study the cooling effect of the endothermic fuel and the results are reported in this paper. It is noticed that the chemical composition of the kerosene fuel has been changed and fragmented into lighter chains. It is evident in the Gas Chromatography results that the catalytically cracked kerosene samples (gaseous and liquid samples) are having 30% higher of lighter chains (Ethane, Propane and Butane) of chemical compounds than thermally cracked kerosene samples. As expected, the fuel has got cracked thermally and catalytically while cooling the wall of the duct (simulating the actual flight conditions to realize the practical feasibility of generating endothermic fuels rather than restricting it to laboratory scale experiments).