suggested new scaling the jet volume Viet as (po poo) 4 taz. Figs. 5 and 6 show the tip penetration and volumetric growth for the different under-expanded jets of the current study based on those scaling parameters. Specif Fig, 5 illustrates that using the scaling expression of Ouellette and Hill 671 collapsed the penetration lines onto almost a single line for hydrogen and methane with NPR- 8.5 and hydrogen with NPR 10. The respective data of the hydrogen jets with NPR 30 70 are also plotted in Fig. 5 and will be discussed later this paper. shows that scaling expression of Vuorinen al. 151] resulted in volumetric growth lines have collapsed onto a single line the hydrogen jets NPR 8.5 and 10. However, the methane jet with NPR did not show a collapsed behav- iour onto the same line that of hydrogen.