Breakdown of Heat Transfer for S.I. petrol (gas) engine

[diverblue]

Hello,

I would like a little assistance trying to generate a rough heat transfer breakdown out of a spark ignition 4 cylinder petrol engine. Specifically this breakdown deals with

% heat transfer through the block
% heat transfer to the cooling water
% heat transfer to the exhaust
% heat transfer to the lubrication oil

This is with respect to the initial energy input in Watts (in this case roughly 216W)

I have generated a rough estimate of;

5% heat trasfer through the block
5% heat transfer through lubrication oil
30% heat transfer through cooling water
30% heat transfer through exchaust

This leaves an overall engine efficiency of 30%

I have tried to find some references online but they are hard to trace given the rough nature of this breakdown in a very general case. If anyone on the boards believes this is a fair or inaccurate represenation of a rough engine thermal efficiency please let me know.

Regards
Ryan

 

[ivymike]

that's about right.
look at Heywood's internal combustion engine text for more info (available on google books, I think)

 

[gruntguru]

216 Watts is a very small SI engine and 30% efficiency is high for this size engine. For example a 2,000 watt Honda GXV160 lawn-mower engine (one of the most efficient engines in its class) has a peak efficiency of about 20%.