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  Mercury - Gemini - Apollo
  Saturn V F-1 engine combustion instability

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Author Topic:   Saturn V F-1 engine combustion instability
Obviousman
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Posts: 427
From: NSW, Australia
Registered: May 2005

posted 03-13-2010 02:43 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
I've been reading about the development of the Saturn V S-1C stage F-1 engine and the combustion instability problems it faced.

My reading of several books on it suggested that although they 'solved' the problem, they didn't really understand why it occurred.

Is this still the case today? That we don't really understand combustion instability in general, and specifically for the F-1 engine?

moorouge
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Posts: 1490
From: U.K.
Registered: Jul 2009

posted 03-13-2010 08:51 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
I think it wasn't that they didn't understand the problem, it was more that they arrived at the solution by a trial and error process.

The instability was solved by altering the angle at which the fuels - liquid oxygen and kerosene - merged (impinged) in the combustion chamber and by altering the size of the injector plate holes. They simply redesigned these two paramenters until the problem disappeared.

The solution reduced the efficiency of the F-1, but such was the margin of over design that it had little impact on the overall efficiency of the engine.

Blackarrow
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Posts: 2024
From: Belfast, United Kingdom
Registered: Feb 2002

posted 03-13-2010 06:19 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by moorouge:
The solution reduced the efficiency of the F-1, but such was the margin of over design that it had little impact on the overall efficiency of the engine.

By how much was the efficiency reduced? The thust of the F1 was eventually increased so that the S1C thrust rose from above 7.5 million pounds to about 7.7 million pounds. Do we know how much it could have been if the solution to combustion instability had not reduced the engines' efficiency?

Obviousman
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Posts: 427
From: NSW, Australia
Registered: May 2005

posted 03-13-2010 10:24 PM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by moorouge:
I think it wasn't that they didn't understand the problem, it was more that they arrived at the solution by a trial and error process.

That's what I mean - they fixed the problem but they didn't really have an in-depth understanding of why the fix worked, and how that could be applied to other engine designs.

moorouge
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Posts: 1490
From: U.K.
Registered: Jul 2009

posted 03-14-2010 03:25 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
First the instability - the problems with the F-1 were not unique as every engine built had these difficulties to varying degrees. It was just that with the F-1 they were on a much larger scale. The biggest problem to solve was that of acoustic shock at the moment of ignition. This, as I said, was achieved by altering the impingment angle and modifying the injector plate. I'll agree that they didn't know why the particular combination of these factors worked, but they did know that the solution rested within these components.

As to the thrust - a test of a prototype F-1 on 6 April 1961 produced 1,640,000 lbs before destroying itself. On 16 April 1965 a test of five of the finished article produced 7.5 million lbs for 6.5 seconds. Yes, there was an improvement during the course of Apollo to meet increased payload demands. For example, the F-1 produced 1,522,000 lbs on Apollo 9 and 1,553,000 lbs on Apollo 15.

Incidentally, the 'pogo' effect had nothing to do with the instability problems of the F-1. It was caused because the natural vibration of the thrust chambers, at 5.5 hertz, was too close to the natural vibration of the Saturn 5 as a whole at 5.25 hertz. It was cured by installing a system of shock absorbers which, in effect, detuned the engine frequencies.

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