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
For cruise on the highway a tall OD ratio is OK. With the higher load
and low RPM there is less pumping loss. To maintain speed on a
level stretch of freeway a lot of torque is not required. Hills and
acceleration
are easily accomplished with downshifting one or two gears. Lamar
Ignition system should give a more complete fuel burn.
Mazda made a mistake with the 13B by going to a rotor width of more than
75mm.
The flame front does not reach more than the 75mm which leaves
2.5mm on each side not burned which is wasted fuel and higher
emissions. The power advantage of the wider rotors is minimal. If
rotors of 80mm or wider are to be implemented, then 4 to 6 spark
plugs per rotor are required set up as two or three pairs.
How much better fuel economy might be realised just with this change?
Then add a power recovery turbine as the CW R3350 had and you should
be in the 30 - 35 MPG range. The added torque from the power recovery will
maintain highway cruise without gear changes. One thing will not cure
what ails the rotary, but a combination of seemingly small items
could produce a big difference. This is where thinking outside the box
is required.
Dale Davies
The Rotary Engine News Letter. Powered by Linux. If you want off the
list PLEASE let me know and I will remove you. ACRE NL web site.
http://www.rotaryeng.net You Tube
http://tinyurl.com/beqqxas
Copyright 1998-2015 All world wide rights reserved.