Re: Wankels ???


_Bob Nixon_ wrote:
On 16 Feb 2006 13:30:10 -0800, "Trochoidophobic"
<flying_booger@xxxxxxxxx> wrote:

Cheezus H. Kee-ryst! Is "trochoidophilia" contagious, or what? Does it
reduce the number of function brain cells in Wankel engine lovers? In
the balance of things, "smooth" has more value than "clean running"?

In some cases; "like the Hinkley triples":)

Bob is emotionally connected to his personal choices...

A modern conventional engine operating at 15000 RPM has only 1/5th as
much time
to "get 'er done", i.e., burn the fuel/air mixture that a Wankel engine
turning it's rotor at 3000 RPM has. Why can't the Wankel engine manage
to burn all of its charge in 5 times the amount of time taken by the
piston engine. Don't just say "because the rotor never stops turning",
give us numbers for degrees of rotation per second.

Look at the conventional engine that turns 15000 RPM. That's 15000 / 60
= 250 revs/second.
Time to complete 1 revolution = 1/ 250 = 0.004 seconds. How much time
is allowed to complete combustion if it has to take place in 90
degrees, which is 1/4 of a turn?

Time = 0.004 * 0.25 = 0.001 seconds. The conventional engine has to get
the charge lit and burn it in 0.001 seconds and it actually manages to
accomplish this miracle in appreciably *less* time than that if it
employs lean burn technology with its swirling, tumbling action that
mixes the fuel and air so well.

But the Wankel engine's never-stopping rotor turns 3000 RPM, completing
50 turns per second. It has to complete burning in 90 degrees of
revolution. 1/50 = 0.02 seconds.

T = 0.02 * 0.25 = 0.005 seconds. The Wankel has five times as much time
to light the fire and burn the charge as the conventional engine has,
but it can't "get 'er done"?

Maybe the answer to the problem is direct fuel injection and figuring
out a way to increase turbulence in the intake chamber?

I'm naive. I lack the intuition and insight (according to Bob) to
understand the innate workings of the Wankel contraption, and yet I
calculated the probable BMEP of a 1986
RX-7 engine as being around 111 PSI. If I use the FIA's formula for
determining the 1308cc Wankel's actual displacement, it works out to be
about 150 cubic inches and the BMEP would be a pathetic 120 PSI. That's
about equivalent to a touring 2-stroke engine's BMEP.

But, I am *so* lacking in intuition and insight! Cheez. I wonder how I
did this at all, even with the help of the brain cells of K. Cameron?
It must have been a miracle or something. I must be channeling
Einstein.

Why is the torque output of a Wankel so low? Is it because the BMEP of
a Wankel is so low? Why is the BMEP of a Wankel so low? Is it because
the Wankel cannot make use of
exhaust port and intake port overlap without blowing unburned HC's, and
CO into the atmosphere?

Did Mazda ever make use of a tuned exhaust system on any of their
peripheral port-engined race cars, or did they just blast a lot of
noise and pollution out the exhaust pipe? I dunno, I either sold my
coffee table book at a yard sale or I threw it away.

Howstuffworks also boasts of this apparently longer power stroke due to
the output shaft being overdriven:

"This means that a single-rotor engine delivers power for
three-quarters of each revolution of the output shaft. Compare this to
a single-cylinder piston engine, in which combustion occurs during 180
degrees out of every two revolutions, or only a quarter of each
revolution of the crankshaft."

Yup.

Oh, so you agree with the disinformation about how long the combustion
process takes in a conventional engine. Like I said above, it has to
happen in 1/1000th of a second, taking 90 degrees (or less of
crankshaft rotation). As I previously mentioned, some engine designs
have managed to light the fire and "get 'er done" in only 46 degrees of
crankshaft rotation and yet the Wankel cannot do that in five times as
much time?

And. combustion does NOT take 180 degrees in a conventional engine. The
piston is done extracting most of the useful energy from the mostly
burned gasses by 120 degrees ATDC and the camshaft is already starting
to lift the exhaust valve off the seat to use the remaining
gas pressure to rapidly blow down the cylinder pressure and suck out as
much remaining spent charge as possible so the crankshaft doesn't waste
energy pumping out the spent gasses.

For the purposes of racing at Le Mans, the FIA came up with a formula
that said the actual displacement of a Wankel engine was 1.89 times the
claimed displacement. But the Mazda racers still won the race. Racers
using Mazda engines were despised by their competitors using
conventional engines.

So you are willing to admit the Wankel is a simple/elegant design. I'd
even call it beautiful and given the time and right fuel it could turn
out a real winner. Though electric motors will soon take over, I still
love odd IC engine designs, providing they are elegant. IOW, the HD V45
& SB Cheby's ARE NOT elegant engines;)

It was interesting enough to make me buy a coffee table book about the
history of Wankel engine development and Mazda's history and I
considered buying a turbo RX-7 before I decided to get a sportscar with
a proven conventional engine.

I have only seen two engines whose torque and horsepower curves
intersected anywhere other than 5252 RPM. They were both 1997 or 1998
Hinkley Triumphs, Daytonas as I recall. Their torque curves and
horsepower curves did not cross at 5252 RPM for some reason, apparently
due to port diameters and cam timing. I don't have that literature
anymore.

I think this last point is a non sequitur in a discussion about how
engines work. Thus no comment.

No, it's not a non-sequitur. You claimed that I was saying that a sonic
wave develops in an intake tract at a constant 5750 RPM, and I
explained what I meant. And other users helpfully responded that the
reason torque and horsepower curves don't cross on dyno charts using SI
units is because they are different units.

BTW. I own a Hinkley triple. One of the 10 best piston engines of all time:)

If all you could afford was a split-single Jawa, you'd brag about it,
because you're Bob Nixon.
You're emotionally connected with your choices. It's the nature of Bob
Nixon to boast about his material surroundings.

OTOH, I'm looking for rational debate of the merits and faults of
various designs so I can get the most bang for my riding buck. It sure
looks like Hinkley Triumphs are cheap enough alternatives to Japan
Inc.'s offerings.

If I buy a Hinkley 675 Triple, will I rise in your esteem?

.

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