[AR] Re: coaxial injectors, venturi effect
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 29 Jan 2021 11:18:05 -0500 (EST)
On Fri, 29 Jan 2021, Robert Steinke wrote:
The term you're looking for is not "venturi" but "jet pump".
Another issue is that you wouldn't want the propellants to burn until they
exit the jet pump at high pressure, but they would be mixed in the low
pressure region inside the pump so there might be flashback problems.
Yeah, even if the injector elements themselves are the jet pumps, this
would be a concern. Early in liquid rocketry, there were some experiments
with "premixing injectors" in which the mixing was done during, rather
than after, injection. They quickly got a repution for explosions, and
the idea was dropped. Maybe a determined effort could come up with a
well-behaved design, but the development process seems likely to be noisy
and expensive.
As an exercise for the reader, design a dieseling jet pump where the
propellants autoignite from the temperature rise in the pressure recovery
section of the pump.
Bonus for extra marks: discuss the effects of using (e.g.) a cryogenic
oxidizer like LOX and a room-temperature fuel like kerosene, where the
large difference in liquid ranges is nearly certain to cause gas bubbles
during mixing (sudden compression of gas bubbles being notoriously
effective at setting off liquid explosives).
Henry
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