Paul,
I have been following your forum for several months now with great
interest and have learned much from it. I am sold on the rotary. But I
would like to see some discussion of detonation in the rotary engine
in
aircraft. I have not seen detonation mentioned. Does it occur or not?
Is
the Mazda engine running under conditions far from detonation? Are
precautions needed to avoid it? How vulnerable is the Mazda to
detonation damage? Thanks for any information.
Al Rees
Detonation in a normally aspirated Mazda Wankel engine is rare to
non-existent.
It is common in 3rd gen RX7 engines where people have merely turned up
the boost to generate 400 HP or more without making sure the engine
is getting the proper fuel air mixture and the compressed air is
properly
cooled with a large enough inter cooler. If you monitor the intake
charge air temperature and hold it below 140 degrees F one can almost
guarantee you will not have detonation. In case you do get it the 3rd
gen
RX7 engine's cast iron 3 piece apex seals fracture and score the
expensive rotor housings. There are some 3 mm steel seals on the
market that are way less prone to fracture however they cause more
wear on the rotor housings.
Paul Lamar
Thanks, Paul. I take it this holds for 87 octane auto gas.
Al Rees
Perhaps. I know my RX8 10:1 compression ratio engine runs on 87 auto gas
fine but it does have a detonation sensor. I might check
the OBD II real time output and see if I can record the
ignition advance. I think Mazda got such bad PR on the 3rd
gen they put in a knock sensor just in case.
Paul Lamar
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Paul,
I'm not quite sure, whether the attached pictures of the detonation
damage are meant to be circulated as they are from early MWE development
in Gloucester. Everything else can go in the news letter, if you like.
Just another comment from my past experience: When MWE developed the EFI
system for the internally R2 called twin Rotary in the late 1990es we
initially fitted knock sensors to each rotor housing. Their positions
were adjacent to the spark plugs, right in the area where we found
severe damage caused by detonation on the endplates when run on
Kerosene, see attached pictures.
But when run on AvGas or even MoGas (Super unleaded 95 RON), we hardly
ever detected any knock whatsoever, so eventually we dropped the option
and the only memories were the now obsolete bosses on every rotor
housing machined ever since because we did not bother to re-certify the
previous spec machining.
This however applied only to the 8.6:1 compression rotors machined with
the additional cut-outs on the rotor flanks as depicted in two variants
to the right of the original Norton cut-out, resulting in 9.0:1. UAV
Engines still insist on it being necessary when run at continuous high
speed, whereas Diamond delivered more than just a few Single rotor
engines without the additional cut-out towards the trailing edge without
any problems - except for a slight power increase due to the higher
compression ratio...
On the other hand a close friend of mine from Britain detected some
"pinking" (detonation) when he rode his Norton Rotary (without the
additional cut-outs) on Standard fuel (88RON) in Germany some years ago.
Regards,
Martin.
Yes I have heard that kerosene is a real problem. Gordon mentioned they
had detonation problems when running on heavy fuel.
Paul Lamar
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