How many Engine 'cycles' are there?
Discussion
I know there's the Otto cycle that just about every piston engine uses but I believe Mazda did a 'Miller' Cycle Engine? I think there's also an 'Atkinson' Cycle? I know these are usually different to the conventional layout that we see in modern 4 cylinder 16 valve engines but are there any others and why have they not become more common if they have better efficiency that the Otto cycle?
Some stuff -- including rotary Atkinson and supercharged Atkinson described in Wikipaedia. http://en.wikipedia.org/wiki/Atkinson_cycle
There was some work done on a more emissions friendly 2 stroke engine (in the UK, too) but it seems to have sunk without a trace.
There was some work done on a more emissions friendly 2 stroke engine (in the UK, too) but it seems to have sunk without a trace.
The Miller cycle was a bit complex for the retail car market. Mazda had a go with a four cylinder Xedos (if memory serves), but the major disadvantage was the engine had to be supercharged.
We are all aware of the four stroke principle of operation, whereas Miller engines run in a five (!) stroke variant. After the initial induction stroke there's another one, the piston moves halfway up with the intake valve held open. Whilst this occurs the supercharger continues to load the combustion chamber with air and fuel. Then the inlet closes, the piston continues to the top and it's all followed by conventional power and exhaust strokes.
As well as the need for a supercharger, as in a proper Rootes type blower as intake pressure is required at all times, the Miller engine requires various charge coolers. Additionally cam phasing is going to be more complicated. It's a great idea - but perhaps too specialised for road use? I guess, also, that the primary intention was to generate more power - as opposed to saving fuel - which isn't the way makers are going at present.
The Atkinson cycle appears to work the other way round, in that it generates less power but is more efficient. So kind of captures the zeitgeist right now.
Basically imagine the Miller engine, detailed above, but with no supercharger. This allows the Atkinson engine to effectively push out some of the air (it would be air/fuel but these days fuel is added very late) through the open inlet during the first segment of the compression stroke. Therefore the Atkinson engine completes its compression stroke, when the valve has closed, with less air in the combustion chamber. This lowers the compression ratio and reduces the need for fuel, less is needed to maintain the stoichiometric ratio thingy, in terms of engine size.
In practice I guess you could couple an Atkinson engine to a variable valve timing/lift system to alter the phasing of the fifth 'push out' stroke. If you wanted full power then you could eliminate the air spit out effect entirely and run it as an Otto engine. Conversely when cruising you could maximise it to reduce fuel consumption.
We are all aware of the four stroke principle of operation, whereas Miller engines run in a five (!) stroke variant. After the initial induction stroke there's another one, the piston moves halfway up with the intake valve held open. Whilst this occurs the supercharger continues to load the combustion chamber with air and fuel. Then the inlet closes, the piston continues to the top and it's all followed by conventional power and exhaust strokes.
As well as the need for a supercharger, as in a proper Rootes type blower as intake pressure is required at all times, the Miller engine requires various charge coolers. Additionally cam phasing is going to be more complicated. It's a great idea - but perhaps too specialised for road use? I guess, also, that the primary intention was to generate more power - as opposed to saving fuel - which isn't the way makers are going at present.
The Atkinson cycle appears to work the other way round, in that it generates less power but is more efficient. So kind of captures the zeitgeist right now.
Basically imagine the Miller engine, detailed above, but with no supercharger. This allows the Atkinson engine to effectively push out some of the air (it would be air/fuel but these days fuel is added very late) through the open inlet during the first segment of the compression stroke. Therefore the Atkinson engine completes its compression stroke, when the valve has closed, with less air in the combustion chamber. This lowers the compression ratio and reduces the need for fuel, less is needed to maintain the stoichiometric ratio thingy, in terms of engine size.
In practice I guess you could couple an Atkinson engine to a variable valve timing/lift system to alter the phasing of the fifth 'push out' stroke. If you wanted full power then you could eliminate the air spit out effect entirely and run it as an Otto engine. Conversely when cruising you could maximise it to reduce fuel consumption.
Diesel cycle.
There are a couple of different designs described as 6 stroke: one which uses what is basically a 2 stroke piston arrangement instead of valves (4 stroke + 2 stroke = 6 stroke); the other is a normal 4 stroke arrangement with water injection on stroke 5 that provides engine cooling and an extra power stroke (water->steam which then expands) - the downside to this being that a consumable water supply needs to be carried.
sideways man said:
Interesting information on the atkinson cycle.
Has anyone used this in a successful production engine?
There's a list of them on the wiki page.Has anyone used this in a successful production engine?
There are a couple of different designs described as 6 stroke: one which uses what is basically a 2 stroke piston arrangement instead of valves (4 stroke + 2 stroke = 6 stroke); the other is a normal 4 stroke arrangement with water injection on stroke 5 that provides engine cooling and an extra power stroke (water->steam which then expands) - the downside to this being that a consumable water supply needs to be carried.
Edited by xRIEx on Saturday 15th November 10:25
Puddenchucker said:
Wasn't there an "Orbital" engine (or some such name) from the early eighties?
The one of that name that I remember was a direct injection 2 stroke engine - it got around the emissions issues of wasted fuel and burnt oil so in theory was a lot more efficient and cleaner. I think some scooter engines may have used it successfully but that was about it. Bimota tried it (I think it was their own attempt at DI) on the V Due but it ran like s
t.
Along with all the Toyota/Lexus hybrids.glazbagun said:
2 stroke? Or have you already named the invetor. Killed by emissions. 
In the days of carbs and constant loss lube I can see why 2 strokes suffered. If you could have some sort of sealed for life big/little end, lube the mains from gearbox oil and use direct injection why shouldn't the efficiency be bought into line? Would make a very simple engine to mass produce.
Have a look Here http://www.douglas-self.com/MUSEUM/POWER/unusualIC... 11 different types, the "pursuing Piston or Cat and Mouse engines" intrigue me.
If you go to the main museum section of the site there is lots of other stuff for anyone that likes engineering stuff, the "powered by boiling Petrol" sounds particularly dodgy
Edit: beaten to it, very much worth a look
If you go to the main museum section of the site there is lots of other stuff for anyone that likes engineering stuff, the "powered by boiling Petrol" sounds particularly dodgy
Edit: beaten to it, very much worth a look
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