Once a month SZP opens the airport for visitors. Those of us with
unusual air planes open our hangar doors and people stroll by and
ask questions. Many are questions I have heard over and over again.
The rotary powered RV4 with the cowl off is prominent and draws a lot
of people,
I am scheduled to give a talk about rotaries at AusFly in Narrowmine
NSW Aus next week. To speed the process I am getting a large poster
printed with some of those questions.
Here is a preliminary version. Comments are welcome.
Paul Lamar
Paul,
You know far more about rotary engine durability than I do, but you
continue to bury your head in the sand when it comes to the fuel
efficiency of rotary engines--at least when it comes to cars. The
fact of the matter is that rotaries use 20-30 percent more fuel than
comparable, modern piston engines. That's why even Mazda has given
up on them. The proof of this is incontrovertible and as a rational
engineer, you should accept this fact. That shortcoming doesn't
disqualify the rotary as an aircraft engine, where its other
virtues--light weight, compact size, smoothness, and
durability--might be more important.
Csaba Csere
The BSFC is now within 5% of a piston engine
The car problem has more to do with the gear box chosen by Mazda
than the BSFC of the rotary.
My RX8 is doing 3000 rpm at 80 while my 250 HP Honda Odysseys is
doing 1800 RPM. This the same reason the 400 HP Corvette gets 25 MPG
on the free way. My 1994 Mercury Cougar was doing 1900 at 80 MPH.
At a steady 70 MPH the RX8 is getting 25 MPG. The same as my old RX2
and the two RX7s I have owned. All had the wrong gearing.
All you need do is look at the OBD data attached.
Another factor is when the Mazda computer leans the engine and when
it does not. Leaning improves the BSFC. Honda circumvents the NOX
emissions laws by not leaning the engine during the smog test. The
rest of the time they lean it frequently. Nox is a big problem for
diesels as nox increases when running lean. Mazda never leans the
RX8 engine no matter what.
I have developed and patented a high speed MSD ignition system that
I hope will knock a few points off of the BSFC.
The exhaust valve, in a 4 stroke, waste 20% of the of the recoverable
energy in turbo compound use. The exhaust normally waste 50% of a
gallon of gas. Harvesting in F1 speak. A turbo compound rotary would
therefore become the most efficient IC in the world maybe short of
some diesels.
The F1 hybrid scheme is not the most efficient for free way use,
http://www.rotaryeng.net/Oxford-TC-talk.mp4
If Mazda does not build a turbo compound rotary they are not
informed.
Mercedes, Renault , Ferrari and Honda will.
We now have a RB 650 HP 2 rotor that weighs less than 200 pounds in
a time to climb project air plane. It has a controlled leak in the
exhaust manifold because there is too much energy in the exhaust. In
other words it would over boost the engine. This is in addition to
the waste gate.
Mazda ought to hire me as a consultant. I would straighten them out
damn quick :-)
Paul Lamar
Paul,
The rotary has relatively short gearing because it has little low-rpm
torque and if the gearing were any taller, it would have no
acceleration in top gear--at least with a manual. Most of the other
cars you quote are non -porting and have automatics, so they kick
down when you floor the accelerator.
Also, there are other cars with similar gearing to the Mazda, such
as a BMW 335i. But that car gets better mileage--over 30 mpg at 70
mph--while delivering far more performance--in a much heavier car.
As to the Honda leaning out during off-cycle driving, I don't know
what your car does, but such a calibration would be highly illegal
and I doubt that Honda, or anyone else, uses it.
Your turbo-compound rotary idea has merit, but it says nothing about
the efficiency of real-world rotaries.
Csaba
Of course. It does need an automatic manual. (Computer controlled hyd
shiifting}.
30 MPG verses 25 MPG is 20% not 30%. My neighbour has an M3 and I
will ask about the 80 MPH RPM.
The piston engine has millions of more hours of R & D. Due to new
apex seal materials the leaning angle can be increased allowing a
higher compression ratio or a better combustion chamber shape.
I had the OBD II on the Honda and I saw a lot of situations where it
went way lean. The gov only cares about the arbitrary driving cycle
and they don't peer over the shoulders of the company EFI
programmers. From a software point of view it is easy to detect the
silly driving cycle.
The nox v BSFC situation was discussed in Bruce Briggs book War
against the Automobile.
Paul Lamar
What is not real world about turbo compound. CW made thousands of
R3350 TCs. A Super Connie could stay aloft for 24 hours. Actually
the exhaust valve was the Achilles heel. The head would come off and
take out the turbine. Rotary no problem no exhaust valves.
Paul Lamar
Paul,
Here are the relevant numbers for a 2007 Mazda RX-8 versus a 2007
BMW 335i coupe, both with 6-speed manuals (Car and Driver tests):
RX-8 335i Weight 3060 3557 lbs rpm@80 mph 4020 2974rpm claimed power
232 300 hp claimed torque 159 300 lb-ft 0-60 mph 6.5 4.9 sec 0-100
mph 18.0 12.1 sec 1/4-mile 15.0/93 13.6 sec @ 105 mph 50-70 mph top
gear 10.9 6.0 sec EPA city mpg 18 19 mpg EPA highway mpg 24 28 mpg
Observed mpg at 70 25 32 mpg
In what world is the efficiency of the RX-8 engine the same as the
BMW engine, which is moving a substantially heavier car, and
delivering much greater performance, while using less fuel?
You can say that the Mazda gearing is too short for optimal fuel
economy, but if you made it any taller, it would exacerbate the
car's already poor flexibility. Yes, an automated manual with 7 or 8
gears would help address the fuel economy/performance trade-off, but
such a gearbox would help the BMW's performance and efficiency as
well. And keep in mind that modern piston engines are more efficient
than this 8-year-old BMW.
No car manufacturer that examines the above performance/efficiency
comparison would chose a rotary for a modern car in a world where the
mandated fuel economy is increasing every year (2010-2025).
As I said earlier, this doesn't mean that a rotary has no merit for
an airplane, but it explains why rotaries are extinct in
automobiles.
Csaba Csere
Quote Csaba;
"Observed mpg at 70 25 32 mpg" How was this done?
Quote Csaba; "No car manufacturer that examines the above
performance/efficiency comparison would chose a rotary for a modern
car in a world where the mandated fuel economy is increasing every
year (2010-2025).
As I said earlier, this doesn't mean that a rotary has no merit for
an airplane, but it explains why rotaries are extinct in
automobiles."
All this is biased opinion on your part. Very clever of you to mix
opinion with facts :) I am on to you :) You get an F for this :-)
(Csaba is a former student of mine.)
http://www.zeroto60times.com/vehicle-make/mazda-0-60-mph-times/
Zero to 60 2004 RX8 5.7 seconds. Not C&D 6.5.
Perhaps Car and Driver had/has defective data taking :)
The EPA MPG numbers tell a different story.
................................RX8.....Bmw EPA city mpg ..........
................................18....... 19 mpg
5% better for the BMW which is what I stated for the rotary.
................................RX8.....Bmw EPA highway mpg ....
.................................24....... 28 mpg
16% better for the BMW a long way from "20 to 30% better" This is
where the better gear box would help the most.
You are also ignoring the turbo compound situation which makes the
rotary uniquely qualified for application of such. All F1 engines
are turbo compound and will be for the next few years. The piston
engines will have exhaust valve problems.
BTW thousands of turbo compound DD15 engines have been sold and are
selling like hot cakes to the trucking industry. If that is not real
world I don't know what is.
Paul Lamar
I talked to a small company owner with three DD15 engines. He
explained that at 500HP they were not outstanding. He had a diesel
shop reflash the ECM. It needs to be reflashed in three steps to
600HP at which point he is very happy with the engines.
As far as Mazda's rotary aspirations go, I think they are on the
right track working on larger eccentricity and radius with a narrower
rotor width. I would even think the 60mm 10A width and an
eccentricity of 20mm and radius of 140mm would be of benefit. With
three spark plugs per rotor and Lamar Ignition the torque and fuel
burn would be much improved.
Dale Davies
Here is my DD15 TC unit bolted to a stock 3 rotor. It will have six
LI ignitions systems one for each spark plug. This is a dyno test set
up. The turbine rotates at 40,000 RPM and the DD15 TC unit gear box
reduces that to 8000 RPM. Ideal for a direct connection to the 3
rotor. It would work in a boat as is.
Paul Lamar
Paul,
A basic question about that "fluid coupling" in the DD15. I assume
that helps the TC to match the required speed of the crankshaft (since
the geared output directly from the turbine would not vary directly with
crankshaft speed, some sort of clutch/etc is needed). How much energy
is normally lost in that friction/slippage there, and what is done with
the heat? Is there a special fluid required (like ATF), and thus a
special radiator, or can we use engine oil?
Thanks,
Mark Waldron
In theory the fluid coupling locks up at high RPM.
My guess is the eff. is in the high nineties.
It works with engine oil. The fluid coupling is after
a spur reduction from the turbine.
Paul Lamar
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