|
Hi Al,
THEORY vs EXPERIMENT
I've been studing the development of the rotary for
30+ years. I also had the dubious priviledge of working on NSU Ro80s
in the early '70s. Nothing that ever came out of the NSU Factory
ever worked (for long). MTBF of the engines was around 15,000 -
17,000 miles!!! All good German
Engineering Theory that didn't EVER work (for long) in practice.
For sure, the NSU Ro80 chassis
itself was a magnificent road car (thanks to Audi knowhow), but the
powerplant and drivetrain was a mobile (more often than not IM-mobile)
mechanical disaster from day 1. They were NEVER able to satisfactorily fix
it. Many a divorce and many a heart attack was caused by these
infernal contraptions.
It also took Mazda several years to get it
right. By 1974, with the intro of 3mm steel seals, different
alloy in the rotor housings, and proper teflon/silicone water seals,
most of the problems were fixed. But it was mainly by trial and
error, and observation, and sheer dogged perseverence. The exercise
nearly sent Mazda broke too. In the end, it was what worked in
practice that mattered. Bugger the theory!!
By 1974, Mazda had fixed most of the basic
intractable sealing problems. Looked after, the engines would go well
over 250,000 miles between overhauls. Now, with the REW powered
RX7s, the motors are so reliable that Mazda don't even have an
engine reconditioning facility in Oz any more. However, I still
get ignorant people coming up to me telling me that rotary engines are no good
because the "seals blow". (But that is another issue) .. I do digress
....
SUMP MOUNTED HEAT EXCHANGERS
Back to the matter at hand. Personally,
I can't see what oil flow rate has to do with convective flow/heat
transfer, at least in the application I'm proposing. Maybe I'm like
the bumble bee that is too ignorant of physics to know what can't work??
As it happens, the flow I've used is a
kinematic inversion of a normal oil/water heat
exchanger !!!
The coolant is INSIDE the tubes) of the heat
exchanger, and is at normal block pressure (15-22 PSI). The hot oil
is passing over the EXTERNAL fins of the heat exchanger, so it will
experience TURBULENT flow. Really good for convective heat
transfer, or so they tell me!!
The HOT oil actually enters from the top and flows
(drizzles - depending on engine RPM) down to the bottom of the pan over the fins and is continually
removed by the pick-up, which is below the heat exchanger. Bulk
oil flow rate will depend on engine RPM. As Mike Wynn said,
if the oil dwells on the fins a little, so much the
better. There's (relatively) cold water running through the
tube(s), taken from the cold side of the rad, so it is just going to
cool the oil a bit more ...
The flow of cooling water can be controlled either
by a thermostat, a manual heater tap, or an electronically
controlled EBP. (Electronic Booster Pump - shock horror Batman!) In
cold climates, you want to be able to warm the oil quickly, and keep
it at near water temp when running hard.
As I mentioned in a previous post, the best
heat exchanger unit I've found is something like a Hayden auto tranny oil
cooler. See attached pic. The one on the right is about the
G_O. Also see:
Different sizes are available, and depending
on the heat rejection capacity required, (and available space), often
it is better to run 2 or 3 small ones in parallel rather than one giant
one.
So to summarise, COLD water passes through
the tube(s), and the oil flows over the outside fins. NOT
expensive, NOT heavy, and really easy to engineer, and a lot
more compact than an oil/air heat exchanger, AND no high pressure oil
hoses to spew hot oil at 70+ PSI all over your pristine engine bay and
canopy!!
Cheers,
Leon
----- Original Message -----
Sent: Saturday, January 15, 2005 1:44
PM
Subject: [FlyRotary] Re: water cooled
matrix in oil pan
And BTW, folks. A
good balance of theory and experiment is where it’s at. Let’ not forget
that without the theory and engineering; there wouldn’t be a rotary
engine.
Al
|