Mach disk width with NPR 8.5 was -12% wider for methane than for hydrogen (see Table 3). The angle of the reflected shock at the triple point was found to be B 28.5 for both methane and hydrogen jets with NPR 8.5, the same to that reported by Vuorinen et al. IS1] Increasing the NPR from 8.5 to 10 reduced the reflected shock angle slightly to B-28 It was noticed that further increase in NPR did not have any noticeable effect on the reflected shock angle and for NPR 30 this was also 28 For NPR 70, the value of could not be measured with sufficient accuracy because the reflected shock was located outside ofthe refined area of the computational grid; however, based on observa- tions of the present work and previous studies IS1] it is believed that for NPR 70 the reflected shock angle would also be about 28, ie. beyond NPR 10 the value of B remains almost constant. From Fig. 9 itis evident that the shear layer thickness swas wider for methane than for hydrogen. Specifically, for NPR 8.5, the methane jet had 0.47D in comparison to 0.22D for hydrogen, ie. the shear layer was wider by about 115% for methane. The value of for hydrogen is in satisfac- tory agreement with the value of 0.25D for the under- expanded nitrogen jet with NPR 8.5 of IS1]. It was also noticed that by increasing the NPR from 8.5 to 10 and then to 30 the shear layer thickness reduced by about 3% and 19%,