Why does a lean engine run hot?

[infamous]

Originally Posted by brianthepoet

the oldies will remember the days of charcoal gas producers, but my late father-in-law used to take the fan belt off and run on power kerosene. he said it made the engine run extremely hot, but did little or no damage other than creating a need for de-coking the head more often. Funny the things you remember isn't it - he told me that about 1975!













Organic gardening is a lot of rot (brianthepoet)

Thats a new one on me brianthepoet, most of the automobiles from the 1940's until the early 1960's had only 8 or 9:1 compression. Kerosene which is very similar to diesel fuel would require at least a 15 or 16:1 compression ratio. Maybe he overcame this by blending his kerosene with gasolene. This would, as you state, require regular de-carboning of the cylinder heads and valves, not to mention the possibility of burning a hole in one of the pistons because of the extra heat. In any case, thats an interesting story.

[DFINITLYDISTRUBD]

Originally Posted by dr249

So you think normal engines are running richer than stoich in order to protect the parts from over-temperature? If that is the case it would be interesting to substitute something cheap like water instead of the extra fuel (water also has an extremely high latent heat of vaporization so less water would be needed than the extra fuel). Either that or somehow provide the necessary cooling without hurting efficiency. I've heard of water injection before, maybe that's what they were doing but I thought it was knock prevention so they could run higher compression ratios and get more efficiency and power that way.

Mercedes is supposedly working on a six cycle diesel which uses water alone as fuel on the fifth cycle.

I'd just like to figure out how to rig an exhaust heated water injection system which would fire a metered amount into the jugs with the fuel air mix...betcha I could gain a 20-30% increase in fuel economy easy. (The only real question is can that lil six handle it.)

[chilehed]

Originally Posted by dr249

So you think normal engines are running richer than stoich in order to protect the parts from over-temperature?...

Yep, we do that, but only under high load because of the fuel economy hit. There are a number of engineering and manufacturing issues with water that make it unattractive on a mass-production car. Fuel doesn't freeze, the injection systems are already in place, most folks wouldn't like having another tank to fill every time they stop for gas, there'd be a significant cost hit...

One thing to remember is that the mixture isn't homogeneous, so even at stoich there are lean and rich zones in the burning charge - which means that in order to get every BTU out of the fuel you have to run leaner than stoich. But if you do that then you get more NOx, and have no way to get rid of it in the exhaust stream because the converters need to have alternating rich/lean excursions in order to function.

Of course, if you manage to get the aluminum to burn it gets REALLY hot.

[alexander]

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?

Actually much for the same reason that most drifters run their engines extra rich, especially if they are running a big turbo. Their reason for doing it is so that gas purposely does not all burn up and is ejected out of the engine, for the obvious reason that liquid fuel carries with it a lot of heat, it then burns up in the exhaust pipe, but bottom line is that it is out of the engine, by that cooling the engine down; heat is a big problem on cars that run 600+hp and run almost fully open all the time...

Just like chilehed said, most modern cars are actually ran richer at high loads to cool it down, hence if you run the engine lean, it runs hotter :P

Mercedes is supposedly working on a six cycle diesel which uses water alone as fuel on the fifth cycle.

they were supposed to present the engine at the Paris auto show last year, and i thought they did...?

[DFINITLYDISTRUBD]

they were supposed to present the engine at the Paris auto show last year, and i thought they did...?

They might have...The last I heard (which was quite a while ago I must admit)
they were still ironing out bugs. (excessive detonation issues mostly)

[alexander]

absolutely, last i heard they were still working out the bugs, but the engine was presented nonetheless... perhaps as a non-running concept at the time...

It's going to be powering their new super car too, the one with auto cambering wheels and stuff.... it's going to blow slr mclaren out of the water, lighter, faster, waay better handling, cant wait to see it

On the note of cars, drifting, heat and stuff, anyone here play Live for Speed?