From: egruf_usenet@cox.net
On 20 Nov 2004 01:20:44 GMT, in sci.space.tech Jim Davis
wrote:
>peter wrote:
>
>> In looking at a ramjet/scramjet diagram, it seems that the burnt
>> gas would want to go in both direction: towards both the inlet
>> and the outlet. Since there is no valve to prevent a back flow,
>> why wouldn't this push the air out of the inlet and stall the
>> engine?
>
>The inlet raises the static pressure of the incoming air by slowing
>it down. In a scramjet the inlet is a carefully designed converging
>duct. A supersonic flow in a converging duct will slow down although
>in a scramjet the flow never goes subsonic. In a ramjet the inlet is
>a (also carefully designed) converging-diverging duct which slows the
>flow to subsonic speeds.
In the above ramjet inlet of either converging-diverging or
convergining-dump constant area geometry, the geometric configuration
allows the pressure increase to move slightly upstream in the diverging or
dump area and remain stable.
In the classical high speed scramjet the flow remains totally supersonic.
Hence pressure information, which travels at the speed of sound, can not
travel upstream, as the flow is moving faster than the speed of sound.
In the mid-speed scramjet, also known as the dual-mode scramjet, the
pressure rise due to fuel addition and combustion is great enough to
separate the boundary layers and allow this pressure rise due to combustion
to move upstream of the point at which the fuel is injected. In this regime
a constant area section, called an isolator is used to buffer the inlet
from this pressure rise. This isolator is just a constant area supersonic
diffuser.
________________________________________________________
Ed Ruf Lifetime AMA# 344007 (Usenet@EdwardG.Ruf.com)
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