2 stroke vs 4 stroke

[PandaBear]

If we can put a turbo in a two stroke engine, wouldn't it be much more compact and efficient for the same amount of power produced? With a turbo setup the correct valve timing can get the right amount of air/fuel into the cylinder, right?

I have heard that 2 stroke is used on locomotives and container ships, generate more pollution and require to burn some oil in the process. Why is that?

I am sure that I have missed something important along the way.

 

[Gurkha]

Pollution in 2 strokes can be easily controlled today and no other engine is more efficient in any terms than 2 stroke, Orbital in Australia was working on an advanced 2 stroke which was supposed to be used by GM in their vehicles, wonder what happened to it.

 

[tom slick]

one of the reasons a 2 stroke puts out more emmisions is that it uses the fresh air/fuel charge to "push" out the spent exhaust. there is always a bit of exhaust left in the cylendar so it doesn't burn quite as cleanly.

 

[Tosh]

From Howstuffworks.com:

From this description, you can see the big difference between a diesel two-stroke engine and a gasoline two-stroke engine: In the diesel version, only air fills the cylinder, rather than gas and air mixed together. This means that a diesel two-stroke engine suffers from none of the environmental problems that plague a gasoline two-stroke engine. On the other hand, a diesel two-stroke engine must have a turbocharger or a supercharger, and this means that you will never find a diesel two-stroke on a chain saw -- it would simply be too expensive.

 

[tom slick]

I didn't think about the fact that diesels only "inject" air. it still doesn't explain why a detroit diesel (most well known 2 stroke diesel) is known for being one of the smokiest engines on the road. and if 2 stroke diesels were the best design then why aren't all diesels 2 stroke? I'll have to do some research.

gas two strokes, such as motorcycle and chainsaw engines, have a built in "supercharger" by design.

 

[Gurkha]

I have ridden and owned various two stroke road bikes, among them the legendary RD-350B, RZ-350LC, RZ-500 and also TZ-250 for a brief moment, don't remember any of them having superchargers, maybe dirt bikes of today.

I now own a four stroke suberbike which is a 750cc race winner from Honda namely the RC-45, any day I would trade it for a RZ-500 or RD-350B of 2 strokes go legal again, nothing comes close to the bang for buck in 2 strokes, they less complex design coupled with far light weight for the displacement makes them indispensable.

 

[Steve S]

quote:

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Originally posted by Gurkha:
Pollution in 2 strokes can be easily controlled today and no other engine is more efficient in any terms than 2 stroke, Orbital in Australia was working on an advanced 2 stroke which was supposed to be used by GM in their vehicles, wonder what happened to it.

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Gurkha, Mercury marine uses the orbital setup in their 2 stroke outboard engines .Visit their web site it is interesting.

 

[unDummy]

The enviro-weenies are killing the 2-stroke and the diesel, for hybrids which will only lead to future problems(battery manufacturing and recycling wastes....). Nearsighted fools

A supercharger or quick spool(VNT and ballbearing)turbocharger can push out the exhaust, and seriouly high PSI correctly timed direct fuel injection, should take care of those intake/exhaust 'mixing' problems in a 2-stroke.
http://www.orbeng.com.au/orbital/aboutOrbital/history.htm
http://www.mercurymarine.com/optimax2

 

[tom slick]

quote:

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don't remember any of them having superchargers, maybe dirt bikes of today.

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the supercharger I was refering to is the action of the piston moving up and down and the way it pumps air. the piston moving up pulls in the a/f mix into the crank area under the piston. then as the piston moves down it forces the a/f mix up though the ports and into the cylinder.

 

[mechtech]

I worked for Electromoive [who builds locomotive engines].
The Detroit diesel is dated, and is fuel inefficient. There were naturally aspirated, supercharged, and turbo charged engines, on the same platform. They are reliable, though.

 

[Gary Allan]

quote:

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I didn't think about the fact that diesels only "inject" air. it still doesn't explain why a detroit diesel (most well known 2 stroke diesel) is known for being one of the smokiest engines on the road. and if 2 stroke diesels were the best design then why aren't all diesels 2 stroke? I'll have to do some research.

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All the Detroits that I've seen have had blowers ..I believe roots type. They appear to be just like the industrial blowers that we used in everything from compressed air to atomized induction. They appear to use an (almost) open lube system that's used like a coolant. That is, the workings of the blower were bathed in oil and it appeared that gravity and drains kept it out of the intake charge. Apparently it's not a perfect science.

One of my wrench's customers just put a Detroit V6 (I didn't think it was an 8) in a F250 chassis. He had my buddy bend the exhaust for him. He couldn't do stacks due to the oil that accumulated in the exhaust..or so he said. The thing hadn't been driven yet. I wondered how the guy was going to make it streetable with a stick shift. The narrow power band of the Detroit, and the limited range of a 5 speed, would tend to make one end or the other (parking lot, low speed ..or highway) extremely awkward, I would think

 

[Steve S]

The oil consumption in the 2 cycle is from the oil being scraped off the cyl wall and into the intake ports ,there was a kit or option that would route the oil back to the pan intstead of outside the engines or burned when blown back into the cylinder ,also the earlier engines leaked like a sieve the last of the engines in over the road trucks were blown and turboed had lots of power and some engines had very wide power bands. A turboed 8v92 with about 350 h.p.would totally out pull an equal loaded truck with a 350 Cummins. The oil system is a normal automotive setup . The total loss is from all the leaks and the dribble from the intake ports. From my memory 350 to 500 miles per Gallon of oil was common. In between jobs or when I had extra energy on the weekends, I would drive truck out of the Teamsters line drivers union hall "from 1976 through 1982"