Engine friction comparison

[murpia]

How can I compare engine friction for a range of engine types, sizes and maximum revs? I don't need an exact friction calculation but some rules such as 2x cubic capacity = 2x the friction would be very helpful, also how does friction scale with revs. Also I would like to factor in in compression ratio.
I want to use published data of different engine configurations and power / torque curves to assess which designs have the lowest friction.
E.g. compare a V6 and a V8 of similar capacity and max power but produced at different revs and compression ratio.
Regards, Ian

 

[EngJW]

There is a generic equation that can be found in Heywood or Taylor. Friction increases exponentially with rpm. Only dynamometer testing can give accurate results. The equation does not distinguish between different ring and piston designs, valve trains, and how much power is used by generators, oil pumps, and coolant pumps.

 

[EngJW]

Also it is better to compare different engines according to bmep. This term eliminates the effect of increasing displacement or raising the rpm, but it includes all aspects of the engine design that affect friction, volumetric efficiency, and combustion.

 

[murpia]

I agree BMEP is the best comparison to make between engines when assessing their performance in output terms. But, I would like to calculate the FMEP and hence IMEP for various engines based on published output figures (torque / power curves). That way I can gain some insight into combustion efficiency / heat release rate / thermal efficiency etc.

 

[ivymike]

If you want to spend a few tens of thousands of dollars, I believe that Ricardo, Inc. have an empirical friction estimation tool based on thousands of dyno runs over a few decades. It is reported to take into account quite a variety of engine parameters in its model.

 

[murpia]

I found this:

http://www.engr.colostate.edu/~allan/thermo/friction/friction.html

which has proved very useful.
Regards, Ian

 

[EngJW]

Interesting program. I wonder if anyone out there can compare it to some real engines. The example given has about 20 psi fmep. Assuming the bmep is around 100 psi, the friction and pumping losses would be about 17%. Sounds reasonable.