
254 Oxygen-Enhanced Combustion
of the nozzle as shown in Figure 11.17. The critical
pressure of a gas jet typically occurs at a pressure of
12–15 psig (0.8–1 barg), depending on the gas composi-
tion and temperature. These shock cells consist of com-
pression and expansion waves that repeatedly compress
and expand the gas as it moves downstream. Using
Schlieren photography, several investigators have seen
as many as seven shock cells downstream of a nozzle.
These shock cells are responsible for creating two addi-
tional components of gas jet noise: screech tones and
broadband shock-associated noise.
Screech tones are distinct narrowband frequency ...