X-Mozilla-Keys:
Fred wrote:
Going through my text books on IC engines, I conclude that all else being
held equal, the biggest effect on SFC for a piston engine is compression
ratio. The limitation is, of course, detonation. Lower combustion chamber,
piston, and cylinder wall temperatures permit higher compression radio prior
to onset of detonation.
Hence it seems to my simplistic mind that liquid cooling (with good high
velocity liquid flow around the aforementioned surfaces) should allow much
lower surface temperatures and thus higher compression ratios and lower SFC.
I would think that with modern knock detectors and good combustion chamber
design, a piston engine with 180F coolant temperature should be able to run
11 to one compression or better with 100 octane gasoline, particularly if
enrichened for high manifold pressure (take off). This compares to about 8
to one for current air cooled aircraft engines, or 7.5 to one for the
turbocharged Continental 550.
A side effect of higher compression ratio: lower exhaust temperatures (due to
higher efficiency or higher expansion ratio, depending on your preferred
viewpoint) and thus longer lifetime of exhaust components.
Shouldn't this same analysis hold true for the Wankel engines?
Constantly curious,
Fred Moreno
Things get really complicated when you throw emmisions into
the equation. Mazda is heavily driven by emmisions so we more or
less have to live with what they offer in compression ratios.
Nox and Hc increase with compression ratio.
This is discussed somewhat in K. Yamamoto's book "ROTARY ENGINE"
According to Ken Yamamoto about 10.5 to one is max
for 97 research octane number.
I guess one could bolt in a plate to reduce the volume of
the bath tub depression in the rotor flank.
Turbo's are a entirely different matter of course.
Paul Lamar
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