Science Forums 2

[dr249]

This is more of a practical question than the typical discussions I've seen here but interesting nontheless. Any mechanic knows an engine which is running lean (less fuel than stoiciometric) runs hotter than one which is properly tuned. 2 stroke motorcycles can actually seize from overheating if run too lean. Normal logic would suggest that with less fuel there would be less heat generated, but it is not the case. My Internal Combustion Engines course professor did not even know about the phenomena (he was the type who knows theory but has someone else change his car's oil).

Any ideas why this happens?

One idea I had is a properly tuned engine could actually be tuned slightly richer than stoiciometric and the excess fuel provides cooling as it evaporates. This doesn't sound like it would maximize efficiency though. My nitro fuel powered RC car uses this technique for cooling but efficiency isn't important in that application.