Mixing exhaust and intake can't be good regardless of what the
German's found. Unless the injectors are setting right on the port,
fuel will lost into the exhaust regardless of injector timing. With
remote injectors (anything more than a few inches from the port) the
intake tubes will always contain fuel I think. Of course, what do I
know? Dummies have opinions about everything. Jerry
It all depends on the instantaneous pressures and gas velocities
Jerry. Sometimes the pressure is higher on the exhaust side
and sometimes the pressure is higher on the intake side
due to organ pipe effects. At high RPM the gas velocities
are so high (up to Mach .4) the mixing, if any, is insignificant.
Think of a jet engine. There is no physical barrier between
the compressor and the combustor yet the exhaust gas usually
does NOT flow forward to the compressor. (Yes I know about
compressor stalls.)
The p-port rotary is akin to a jet engine despite being
an intermittent combustion engine. It is the most
continuous intermittent combustion engine I can think of.
Actually I can think of a better one. A pulse jet used
in German buzz bombs in WW II.
If one injects the fuel directly into the rotary compression
chamber after the intake port closes no fuel goes directly
out the exhaust with out first getting a chance to burn in
the combustion chamber.
Ironically the BSFC is no better (so far) than a p-port with
the injectors on the open end of the pipes.
A lot of this stuff has been tried by CW, Mercedes, John Deere,
Rotary Power International and Mazda and the results have been
published in dozens of technical papers. After 40 years
of experimenting the best they came up with is .47 BSFC.
Exactly the same as the P-port Lemans engine.
One of the problems is the low compression ratio of the buzz bomb
engine, the rotary and the jet engine. If a way can be found
to increase the compression ratio with out sucking a lot of
power out of the power section than the BSFC will get better.
Organ pipe tuning helps. P-ports help because they are aerodynamically
efficient. As does a turbo charger. The more efficient
the better. The compressor section, internal or external, stores
some of the energy used to compress the air in the form of heat.
If this heat energy can be retained (no inter cooler) than
the BSFC will be better. The diesel engine is a good example.
So Doug, as I said, if you must burn alcohol, try a turbo charger
sans inter cooler and inject the alcohol directly into the
compression chamber to cool the charge and prevent detonation.
Detonation is more or less the modus operandi of the diesel
engine :)
Now to recover some of the other half of the energy in a pound of
fuel going out the exhaust we need to develop the turbo compound
rotary. If I can finish this silly house project I am going to get
back on it.
Paul Lamar ...No rotor no motor.
Jerry,
You are not wrong - mixing exhaust with intake is not desirable HOWEVER it
is tolerated by most engines to a degree - as most reciprocating engines
from factory, have overlap. All performance reciprocating engines most
definitely do have overlap. Hence my surprise when Mazda decided to
eliminate it completely. We can eliminate it completely with the P-Port if
and when we can direct inject, with high pressure. Until then we have to
accept some overlap and gas mixing, using whatever strategies we can to
minimize the effects at idle.
The effects at high RPM are negligible as the exhaust escapes at supersonic
speed and actually sucks some intake with it - hence the need to restrict
fuel intake until the exhaust port closes i.e too much fuel going out the
exhaust. Of course at lower RPM the oxygen going into the exhaust from the
inlet will help burn the unburnt fuel, slung out from the last compression
cycle. The unburnt fuel is a result of the less than desirable combustion
cylinder shape - as Paul has mentioned many times.
George (down under)
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