One advantage so far over looked is the compression ratio
could be anything we want it to be. Merely machining the pocket
differently. The RX8 rotors are 10:1 and that is a disadvantage when
it comes to turbo charging. There is just not enough material there to make the
pockets deeper to lower the compression ratio.
On the other hand we might want to make the compression ratio 11:1 to
one to improve the BSFC when burning 100LL aviation fuel.
Paul Lamar
Paul,
Please let me remind you what you have said about the fire going out
using compression ratios over 10:1 in a rotary. Have the laws of
physics changed or just your memory:) ?
I for one would love a 11:1 compression ratio with E-90.
Doug in Japan.
OK remind me :) All I recall saying is early Mazda data that says over ten to
one does not seem productive. Who knows what the shape the combustion was at
the time. The RX8 is now 10:1 and the computer probably checks for knock.
Paul Lamar
Paul,
Good and interesting data as usual but how early is it? The first and
third graph are fairly self explanatory. The second figure 4-37 however
shows mean effective pressure dropping off with rpm. Does this chart
denote that pumping losses become less until after 4,000 rpm and then
increase (become less efficient) as the engine speeds up? Stopping the
curve at 6,000 probably indicates it is very early data. I thought with
the LeMans engine frictional losses and as well as pumping losses were
minimal around 6,000 rpms.
Doug in Japan
No mentioned is made of the type of porting involved.
There is a myriad of other factors as well.
You can read about it yourself by downloading K. Yamamoto
1981 Rotary Engine book. Page 48 and 49.
http://www.wankel.net/~krwright/cars/rx7/manuals.html
You will then know as much about it as I know.
If the truth be known there is very little knowledge on the rotary
engine out there. This is one of those things that should be investigated
with a range of porting, port timing, combustion chamber shapes, octane numbers
and rotor widths to name just a few. The shape of the RX8 combustion chamber is
very different than previous rotary engines. The Le Mans engine also used 10:1
CR but who knows what type of fuel was used.
So far the only source of rotors is Mazda. Making our own rotors will allow
experimentation with a lot of factors. Aluminum rotors may be far different than
cast iron rotors due to heat transfer. Even the face curve of the rotor in the
area of the apex seal has an effect on detonation caused by the spark plug.
Paul Lamar
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