<< Quirk, Kevin KA" wrote:
 >
 > Jeff,
 >
 > Any chance of getting a copy of your spreadsheet?
 > I am setting up a basic spreadsheet myself to attempt to determine chamber
 > pressure for some FEA on the eccentric shaft.
 > I am trying to model the combustion but have found that the fuel burn rate
 > (currently guessing curves) has a major affect on the pressure and
 > temperatures inside the chamber.  Do you have any ideas
 > on how to get a basic burn rate?
 > Any help would be greatly appreciated.
 >
 > Regards,
 >
 > Kevin Q >>

Modeling combustion is very difficult.  Usually it is not even done by engine
designers and left for the scientists.  The standard method for determining
combustion pressures is to use similarity relations to previous engines.
Also, the pressure is mostly a function of charge mass and much less affected
by mixture and other factors.  Your goal should be to find some data for
rotary engines listing typical peak to mean ratios.  Basically the higher the
BMEP the higher the peak pressure.  So, once you decide how much BMEP then
you'll have a pretty good idea of peak pressure.  Certianly the accuracy of
this method will be within the accuracy of the FEA and needed factors of
safety.

The spreadsheet is attached.  All green values are variables for the user to
define.  The current values are pretty nominal.  If you go way off the map on
the turbo, for instance, the efficiency will vary greatly.  Use the excel
solver to make the spreadsheet converge as noted within.  If it fails to
converge then you have to guess the exhaust pressure (blue cell) closer.  A
little thinking may be required to know what to guess.  Usually a ballpark
guess will lead to convergence if convergence is possible.

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