On 10/05/2012 02:15 PM, Remi Guerner wrote:
> I am just curious about the Laminova Oil-water exchanger. I
> understand that in your installation, the oil is cooled by the
> coolant exclusively. So I suppose the oil temp is higher than the
> coolant temp all the time. Am I right?
That's right. Well, almost. With just the Laminova I get a delta-T of
10C. So, you can get your coolant up to 110C and the oil will stabilize
at 120C. Note that this is rock steady, if the oil would climb to 130C
the delta-T would double, hence the cooling capacity would double. So it
is self stabilizing; you will not see much oil temp variation if you use
a Laminova. However, I wanted a smaller delta-T, so at the exit of the
Laminova I have a very small auxillary oil cooler to drop the oil temp
with 5C. Note that this is not really required, but I don't want to cool
the coolant more than necessary. I prefer to maintain an oil temp of
115C so this way I can allow the coolant to get to 110C. Otherwise I
would have to keep the coolant at 105C, but this requires more cooling
air flow and thus increases drag. Also, I like to run the engine at a
higher temperature as this ensures a cleaner combustion and higher
efficiency.
> What oil temp do you get when
> in a sustained climb at max continuous power?
Full power or cruise power don't matter. With the cowl flap I can get
any temperature I want. I usually pin the coolant to 110C, so the oil is
then 115C. This is also true when climbing from sea level to FL95 with
100% power all the way up. I always maintain 110C coolant and 115C oil.
During startup I open the cowl flap 1cm. I also open the intercooler
valve. The intercooler extis inside the cowling so this provides more
cowling air flow while still standing or taxiing. Flow through the
coolant radiator is then minimized (the intercooler air flow increases
the pressure behind the coolant radiator) and warm-up is fast. The oil
is warmed up by the rapidly heating coolant. Within a few minutes I have
everything heated up sufficiently to take off.
During the run-up I open up the cowl flap halfway (this is usually
sufficient, unless it is extremely hot) and keep the intercooler valve
fully open.
When I level off for cruise I close the intercooler (since it is now
useless and it uses the same cowl flap exit as the coolant radiator) and
I close the cowl flap to about 1cm. Closing the intercooler increases
the flow through the coolant radiator, but by closing the cowl flap I
reduce the flow to what is necessary to maintain a coolant temp of 110C.
This setting also provides minimal aerodynamic drag. During flight I can
fine tune the temperatures with the cowl flap setting.
When descending for landing I open up the intercooler valve. This
reduces the flow through the coolant radiator, so the temperature
doesn't drop too fast. At the same time it increases the flow through
the cowling, to draw as much as possible the accumulated heat away, to
prepare it for the anticipated full stop. Also, opening the intercooler
valve ensures that I have full boost power available in case of a go around.
After touch down but before shutting down the engine I open the cowl
flap fully and allow the coolant and oil temp to drop. That's right, on
the ground I have sufficient cooling to get the temperatures out of the
green arc... on the underside of it.
The Laminova offers many advantages:
1) Eliminating the oil radiator and its associated air duct workings. It
also means more freedom in positioning of the cooler and hose routings.
2) Eliminating the oil thermostat as the oil is now warmed up by the
coolant (which is even faster than the oil thermostat can achieve).
3) Faster warm up times. Oil is actively heated up by the coolant.
4) Tight coupling of coolant and oil temperatures. This reduces stress
on the engine and makes temperature management easier.
5) Self stabilizing effect. Suppose the coolant is 110C and the oil is
120C. If the oil temp would increase 1C this is an increase of 10% of
the cooling capacity. With air cooling instead (20C ambient temperature)
this would only increase the delta-T and thus cooling capacity with 1%.
With the Laminova the throttle setting has no significant effect on oil
temperature.
There are two disadvantages as well:
1) Loss of coolant means also loss of oil cooling capacity. Loss of
coolant means you are going to land asap anyway, so this is hardly a
disadvantage.
2) You can't use Evans coolant. The passages in the Laminova are just
too thin.
Frans
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