The primary effect of the intercooler on the power output is from the
increased mass flow of air through the engine. Power is approximately
proportional to mass flow, and at constant pressure the mass of a fixed
volume of air is inversely proportional to its absolute temperature. The
engine displacement, or volume of air entering the cylinders each cycle, is
constant. So, for a given inlet pressure and RPM, lowering the inlet air
temperature from 160 to 110 Fahrenheit (620 to 570 absolute) could give a
theoretical increase of some 8.8% in power from the improvement in
"volumetric efficiency". This should not be confused with the thermal
efficiency, which is a measure of the amount of useful work extracted from a
given quantity of fuel.
An intercooler can have a number of beneficial effects, and need not cause
an increase in cooling drag.
Mike
-----Original Message-----
From: Fred Fillinger
Subject: Re: Re:914 intercooler
In rereading the archives too, the only concern was questioning 220
MPH top speed, impliedly due to only an intercooler. No question re
some fuel efficiency, engine wear, and climb, but not cruise. There
are intercooler "tech" papers all over the web. Claims vary (mostly
auto enthusiasts but with access to dynamometers), but best I found
was (for 100HP engine) 1.5HP per 10F degrees reduction in induction
air temp. Assuming 50F drop, the math works out to about 4 MPH at
100% throttle cruise, minus effect of add'l cooling drag. Suspect
you get a bit more above the magic 16,000 ft., with controllable-
pitch prop, but altitudes much above that are not practical
unpressurized, except now and then for the fun of it!
I just read a cool (no pun!) way to look at it. Engine efficiency
goes up with the spread between induction air temp and EGT: If you
ingest 1600F air, same as EGT, the engine would produce no power. So
reduce induction air from from 160F to 110F, and do the math, that's
only a 3% increase in power and fuel efficiency, not 7.5% per above.
Regards,
Fred F., A063
KarkelB@aol.com wrote:
>
> Hi Folks,
> read an article in the forum archive about intercoolers
where
> someone expressed concern about installing one.I spoke to someone at
the
> rotax factory who actually said that rotax do recommended the fitting
of an
> intercooler to the 914 as it enhances its efficiency/performance and
reduces
> the wear and tear on the cylinder heads. In addition to that one can
have the
> maximum 115bhp for more than the stated five minutes at full throttle.
> However he went on to say that should an intercooler be fitted it must
have
> the flow rate as recomended in the 914 installation manual. And to cap
it
> all, your warranty should not be affected by the installation. Thought
i
> should share this with all those with 914's craving better
performance. If
> you are in england demon tweeks on 01978664468 have all sizes of
intercoolers
> and can custom build some if you want infact they have one that is
similar to
> Denis Vories,just seen it in their catalogue. Denis Vories
installation is a
> real clean one folks!
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