Combustion chamber pressure - calcs

[Johann]

Does anybody have more information on how to calculate the pressure inside the combustion chamber during the cumbustion cycle ? I have access to FEA software, and it would be very interesting to look at the stresses within the cranc and conrod. Thanks

 

[lohring]

Engine simulation programs do this. I use EngineMod2T for two strokes. They use empirical combustion models that should be close enough for engineering calculations. The other choice is to look at actual recorded data. That's been around a very long time and thete should be lots of examples on the web.

Lohring Miller

 

[mu38&Bg#]

Lohring do you find the program to be accurate in model scale engines?

 

[Johann]

Thanks Lohring, this might become very interesting..

 

[lohring]

We use an inertial dyno to test engines. The simulations are reasonably close but tend to overstate high rpm power. i believe this is due to the relatively simple friction model. We have mostly tested 26 cc ignition engines. The programmer has just added a glow ignition combustion model. I just built a new, smaller dyno and am looking forward to testing some 2 cc glow engines. The greatest value of the program is pipe development. A side effect is discovering details of two stroke design by running hundreds of simulated dyno runs in the time it takes to test a real engine and tuned pipe. Below is a comparison of a simulated and actual power curve on a modified 26 cc Zenoah. Unfortunately, the simulated pipe isn't the same as the pipe used in the real dyno run. Pipes are everything in two stroke power. More on pipe design can be found in Tuned Pipe Design Factors.

Lohring Miller