Development and verification of a supersonic nozzle with a rectangular cross section at a Mach number of 2.8 for a scramjet model combustor

Forced ignition is important for the scramjet engines in supersonic flights. When compared to other forced ignition devices, burned-gas torch igniters are considered suitable for scramjet combustors because it is easy to control the input energy of burned-gas torch igniters. In the conventional burned-gas injection methods, the injection gas total temperature is estimated by assuming a discharge coefficient in the range of 0.90-0.95. However, the assumption has not been validated and it may cause misestimations when analyzing combustion in scramjet engine in supersonic flight. Therefore, a validated temperature estimation method is needed. In this paper, a new total temperature estimation method was proposed and investigated experimentally and numerically. Additionally, a novel hydrogen/air burned-gas torch igniter, which can control the injection gas total temperature by controlling the overall equivalence ratio, was also developed. The experimental results showed that the newly-developed hydrogen/air burned-gas torch igniter can successfully control the injection gas total temperature by changing the overall equivalence ratio in the range of 1.0-10.0. Also, the chemical equilibrium assumption for estimating injection gas compositions was validated by O2 mole fraction measurement. The numerical results showed that the estimated discharge coefficient results in a maximum underestimation of 7.02% due to wall heat loss, which means that the maximum uncertainty of the estimated total temperature is 14.7%. This, in turn, indicates that the influence of wall heat loss on the discharge coefficient should be considered to estimate the injection gas total temperature more accurately.