Saturday, March 29, 2008

Smoking Four Strokes

We often see a plume of smoke from the back of a Formula 1 car when an engine blows up. Four stroke engines are not meant to let out smoke. Then where does that smoke come from and what is it? That's what we're going to see in this article.

It's the pressurized engine oil that's getting sprayed out of the exhaust as smoke, which might resemble the exhaust smoke coming out of two stroke scooters or bikes. Remember, in four stroke racing engines, engine oil that is stored in separate tanks, lubricate the crankshaft, cylinder walls, piston pins and other moving parts. The only area where it doesn't find its way into is the combustion chamber space. Piston rings do the job of keeping out the engine oil from the combustion chamber.

As the engine nears its failure point, the piston ring is one of the first parts in becoming vulnerable to temperature and pressure damage. When the rings eventually break, oil that is under huge pressure in the crankcase, forces its way past the piston into the combustion chamber. The pressure along with the heat of the combustion chamber makes oil to 'spray' out of the chamber into the atmosphere, which is what we see as blue smoke.

What we don't often see is 'liquid' oil pouring out from the bottom of the engine. This happens when the crankcase itself breaks apart allowing the oil within to gush out of it.

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2 comments:

Sriram said...

Oh,Then what about the Fumes or smoke that appeares at the star of warm-up lap during race?Is it from engine or tyre?

S R I R A M said...

That smoke is also engine oil smoke but that's the result of over-filling of the oil tank beyond the max. limit. In that case, the crankcase oil pressure will be so high (due to excess amount of oil) that when the piston nears the end of the exhaust stroke, the excess oil gets into the combustion chamber (since near vacuum conditions exist at the start of the suction stroke). Once the oil level reaches the correct limit, this stops.