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<< Lancair Builders' Mail List >>
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In a message dated 9/2/2001 11:12:20 AM Pacific Daylight Time,
gwbraly@gami.com writes:
<< Using our PRISM (Pressure Reactive Intelligent Spark Management)
system we are able to do this almost effortlessly. I have been able to
operate these engines at 375 to 400 Hp with the peak cylinder pressures at
or below the values traditionally seen with the engines in the stock
configuration operating at 350 Hp. >>
George:
Nice to hear from you regarding your work. We have read a lot in the Av Press
about GAMI and other programs you're involved in.
Your comments regarding BMEP and combustion quality are well-understood. You
have probably experienced the fact that many people misunderstand BMEP and
fail to recognize that although is is derived from the conecpt of mean
cylinder pressure, it's purely a mathematical representation of net ("Brake")
torque per cubic inch of displacement. The concept derivation (mean cylinder
pressure) often masks the fact that one can increase BMEP by making changes
which have absolutely nothing to do with the combustion process, such as
installing a more efficient water pump, for example (lower power consumed to
produce the same coolant flow, resulting in higher engine output power).
I'd be very interested in learning more about the specifics of the LycoNental
technology you developed which reduces the peak cylinder pressure while
maintaining the same BMEP. It sounds as if (reading between the lines) that
you've come up with a means of speeding up the burn rate and delaying
ignition so as to reduce the negative torque which results from the large
pressure spike before TDC.
Again, reading between the lines, the PRISM acronym suggests an active,
real-time monitoring of cylider pressure and corresponding closed-loop
control of teh spark event. Do you have any published info on the system (or
unpublished info you'd be willing to share)?
At EPI, we have found some pretty significant power increases in certain
high-performance engine combinations as a result of increasing the mixture
quality (better homogeneity, smaller SMD particle size, etc.) and mixture
motion (smaller port velocity gradients, more induction and compression
swirl, "fast-burn" chamber technology, etc.) which allow us to remove as much
as 8 degrees of advance.
We have not tried any of the "fast-burn" mods on LycoNentals, mainly because
our recent engine development efforts have been focused on liquid-cooled
technology. Because the chamber layout of both the Lyc and big Continental
heads is so far superior to the compromised chambers available in lightweight
pushrod V8 cylinder heads, we have been working on the development of a new
cylinder head which attempts to capture some of the chamber and port
advantages found in the best of the LycoNentals.
I assume that, in addition to your stated improvements in BMEP, you have also
realized improvements in BSFC. If so, that could slightly reduce the net heat
rejection load on the engine. However, the fact still remains that more HP to
the prop means that more BTU's per minute must be removed from the engine,
primarily the combustion chamber areas (heads, valves, piston tops). Although
your fast-burn technology can result in better bottom-end reliability, you
must know that the heat rejection load imposed by more power output doesn't
change significantly (although we have found an interesting reduction in the
DISTRIBUTION of heat-rejection resulting from the use of a particular
coating).
Keep in touch.
Jack Kane
EPI, Inc (www.epi-eng.com)
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