Atkinson vs. Otto Cycle

[David Beale]

Originally Posted by FL_Prius_Driver

All we need to do is find someone who has done an analysis of the residue and we would know. Any clues where to look?

I'll bet it's mostly fuel, with some oil dissolved in it. Easy to test. Take a "Q" tip and sample some. Smell it. If it smells like gasoline there is some in it. Let it evaporate. Is there oil left? If so, it's as I think.

This is called "fuel standoff". All engines do it, but some do it more than others. Two stroke engines have enormous fuel standoff - I've seen it projected 2 feet above an open carb., which is why the intake plenum/filter is mandatory for safety when they're running. Otherwise it's quite a fire hazard! Rotary engines also have high fuel standoff. Low compression Otto cycle engines have very little fuel standoff, but high compression engines have more, not so much as the first two I mentioned though.

In all cases there is some oil mixed into the fuel. The first two mix the oil in themselves, but the rest get it from the previously mentioned paths.

[Nonhypermiler]

Originally Posted by David Beale

I do have to disagree with the statement that the Atkinson cycle is "much different" from the Otto cycle. It's only slightly different. All you do is construct the engine with a long stroke. To avoid the high compression this would normally give you (and which is undesirable if you want to burn low octane rated fuel), you hold the intake valves open during the start of the compression stroke.

The result is a long power stroke, allowing more energy to be extracted from the expanding gases, without the high compression complications seen in high power engines and diesels. I'm told efficiency gains are an extra 5-10%, which is quite a bit when you are starting from about 25-30%. The downside is a loss of about 30% of the power output.

BTW, this was done many years ago (probably unintentionally) in the old GM 6 cylinder engine, though most of the low compression was gained there with an inefficient intake path and largish combustion chamber (and therefore high pollution generation).

Look here, it is different. WOW!

[Nonhypermiler]

ww.keveney.com/Atkinson.html