Before describing the methodology used here, it was important to ascertain certain things. First and foremost was the variation of C⋆theo with O/F which is calculated using NASASP273 [35]. The O/F ratio was varied and the correspondingvariationof C⋆theo at threedifferent pressuresisshownin Fig. 6. From Fig. 6, it is evident that C⋆theo is as trong function of O/F but is avery weak function of chamber pressure for the pressures considered here. Thus, the curve fit given in Fig. 6 is only a function of O/F.
Next was the possible variation of η as a function of L⋆.The L⋆ in the motor considered here changes with burn time from 0.17 m at the start of the experiments to 2 m at theend of 4 sburn time. The final value of L⋆ is approximately 12 times the starting value. To determine
this variation, experiments similar to ones described earlier in this paper with regard to determining the pressure variation with time were carried out. The burn time used was 0.5 s. Here, the pressure time graphs along with the information on mass loss of fuel obtained were used to determine the L⋆ and η as described below.
Knowing the mass of fuel burnt after each 0.5 s, the final averaged port diameter was calculated and it was used tocalculate L⋆ according to