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Detonation and Preignition with BMWIIIa Engines

 
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hfriedman



Joined: 21 Jun 2004
Posts: 26

PostPosted: Mon Nov 21, 2005 18:41    Post subject: Detonation and Preignition with BMWIIIa Engines Reply with quote

We are looking at a series of accidents involving Junker F-134/LJ-6 airplanes with BMW IIIa engines.* The power is given at 185 hp so these may have been derated from their WW I form. At least some models of the engine had very high compression for that time and even with benzol fortified fuel could not operate safely at full power below say 8,000 ft. Observers reported that as the airplane passed over at low altitude the engine was either backfiring or cutting out. The forward part of the airplane then became enveloped in flame and the machine crashed.

We have read Kevin Cameronís superb treatment of detonation and preignition in the current TM but most discussions of those subjects end at detailing the possible internal damage leaving the ultimate results to the imagination.

Would detonation, possibly followed by preignition, cause backfiring? Would it result in fire?

*While some of these airplanes were powered by Mercedes D IIIa engines it seems a reasonably safe bet that the machines in question had the BMW.
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wallan



Joined: 13 Jul 2003
Posts: 229
Location: UK

PostPosted: Tue Nov 22, 2005 06:48    Post subject: Reply with quote

Have you read the NACA report on this engine?

http://naca.central.cranfield.ac.uk/reports/1923/naca-report-135.pdf

http://naca.larc.nasa.gov/reports/1923/naca-report-135/
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hfriedman



Joined: 21 Jun 2004
Posts: 26

PostPosted: Tue Nov 22, 2005 18:28    Post subject: Reply with quote

Thanks Wallan. We had not seen it before. It must have been an extremely efficient engine. It held the world endurance record for awhile and the LJ-6 was touted for its range.
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