Rotary engine fuel consumption improvement for cars through better
rotor cooling management.


The rotary engine suffers from high BSFC at low loads.
Low loads are the name of the game for automotive engines.
GM found back in 1978 that the temperature of the rotor face had a strong
effect on the low load BSFC. A 9.8% improvement in the BSFC
was possible with a hot rotor at low loads. Higher rotor temperatures  gave
lower fuel burn at low loads. However if the rotor was not
cooled at high loads the cast iron over heated.
GM got a patent in 1976 on a hot rotor face insulated from
the rest of the rotor. Here is a pdf on the 3,995,602 patent.
The SAE GM paper on the subject was 780419.

The obvious solution is to control the temperature of
the rotor as a function of the load on the engine.

The amount of oil cooling on the rotor is now controlled
by a ball and a spring that opens at a certain RPM.
See the attached jpg.

RPM is not the problem. Engine load is the problem.
A way can be found to cut off the oil cooling to the
rotor at low loads regardless of the RPM. In other
words run the rotor face as hot as possible at all RPM's.

One mechanical way of doing that is insert a stationary tube
in the center of the e-shaft that moves back and
fourth controlled by a servo that senses engine
load and cuts off the cooling oil supply to the
rotor. A peice of cake for todays computer controlled
engines. In fact it need not be controlled by a computer
or electrical servo but by a simple air servo connected to the
intake manifold pressure.


Patent applied for :)

This is for cars only.
Aircraft engines run at higher power levels so this is not
necessary. Please confine your responses to the subject heading.

Paul Lamar



It would appear from the drawings that some of the fuel is exiting the
exhaust not yet burned and completing the burn cycle inside the exhaust
system. This would account for the high exhaust temps and the high BSFC.

Is there any insight on why the fuel isnt burned inside the combustion
chamber?
Is the rotational speed too high to allow for complete burning during the
power cycle, meaning simply not enough time?
Or is the shape of the chamber to blame with too many places for the fuel
to condense and hide?


Trying to wrap my head around it, who knows something might come out.

Kevin Alderman

That burn fuel in the exhaust theory is in doubt. The air to
burn it must come from somewhere. In the early days Mazda actually
used an air pump to burn it in the exhaust.

Lots of exhaust heat goes into the valves in a piston engine. That is why
they go away so frequently in aircraft applications. In the RX8 with cooler
side exhaust some of the heat goes into the end housing cooling system.

The best BSFC occurs at 6000 RPM. The best explanation is unburned
fuel hides in the very flattest parts of the combustion chamber and is quenched
by close proximity to the cool metal walls. That is a very rich mixture and as
we all know very rich fuel mixtures refuse to burn. Drop a lighted
cigarette in your gas tank next time you get a chance :)

The only hope is to make it so hot in there the fuel vaporizes and is forced into
the general population. You want to closely control the temperature so
it is hot but not too hot to melt the metal.

Stainless steel does not conduct heat as well as cast iron so perhaps
a stainless steel rotor, rotor housing liner or end housings can be tried.
Even hydraulic pressed chrome nikel steel (4130) could be welded into a rotor.

"Thermal conductivity is the quantity of heat transmitted through a unit thickness
in a direction normal to a surface of unit area, due to a unit temperature
gradient under steady state conditions."

I don't know how to plate SS with chrome or even if it can be done.
Silicon nitride ceramic seals and synthetic oil must be used to deal with the higher
surface temperature of the liner. Mazda is already using chrome nickel
steel for the liner. A 2 piece end housing with a chrome nickel
or stainless steel wear surface might help. Perhaps Mazda has
that planned for the so called all aluminum  16X.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

1 W/(m.K) = 1 W/(m.oC) = 0.85984 kcal/(hr.m.oC) = 0.5779 Btu/(ft.hr.oF)

k - W/(m.K)
........................25C.....125C....225C
Monel ...........    26
Steel, Carbon 1%     43
Stainless Steel     16     17     19
Iron, cast ......     55
Aluminum ........    250     255     250
Chrome Nickel Steel      16.3    
Carbon Steel ....     54     51     47
Iron ............    80     68     60

It will be interesting to measure the BSFC on Jeff's upcoming
titanium rotors.

Paul Lamar