|
|
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
<< Lancair Builders' Mail List >>
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
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 Do you have any published info on the system (or unpublished info you'd be willing to share)?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)
LML website: http://www.olsusa.com/mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
|
|