Title : Studies on decomposition and combustion mechanism of solid Fuel Rich

Hypersonic air breathing propulsion system has been in the minds of human being for a very long time. Ramjet propulsion provides efficient operation along with very high specific thrust and is very attractive for gun launch ramjet projectiles, hypersonic cruise vehicles and hypervelocity missiles. In the present investigation, Zr based fuel rich propellants in NC-NG matrix and HTPB matrix were evaluated for ballistic performance and mechanical properties. Although both the systems are attractive to produce higher density and high specific thrust, NC-NG based systems containing 3060% Zr produce very high burn rates, comparable with modern advanced solid rocket propellants containing powerful oxidisers and metallic fuels. They are also attractive from the point of view of structural integrity of the propellant. It is possible to obtain very high burn rates (15-20 mm/s) by using 30-60% Zr. However, it is not possible to load more than 75% Zr in HTPB matrix and more than 65% Zr in NC-NG matrix for practical propellant compositions, as propellant slurry becomes very thick and it is not possible to cast propellant in mould or rocket motor. Zr based propellants are very attractive for volume restricted propellant systems. Unlike boron, no ignition related problem is visualised even in highly Zr loaded propellant formulations. Higher propellant density (1.92.95 g/cc) along with low pressure index values are other attractive features of Zr based fuel rich propellant formulations. Their thermal decomposition and combustion behaviour has been studied using various modern techniques in the present investigation. While FRPs containing Zr in HTPB matrix decompose at higher temp., FRPs based on Zr in NC-NG matrix decompose at lower temperatures of 160-170 C. A probable mechanism on the combustion behaviour of Zr based fuel rich propellant has been suggested based on data generated and also considering earlier findings on Zr oxidation and combustion. It is believed that data generated in the present study will be very useful to develop practical powerful fuel rich propellants for ramjet and scramjet applications. It is also felt that further study on Nickel based fuel rich propellants, which appear to be very promising candidates, must be undertaken, in view of their unique characteristics of producing stable combustion at low pressures and very high density of Ni (8.9 g/cc).