Dave H

Why are two strokes not used in automobiles? There have been some, but the majority are four strokes.<br><br>Is is because they operate at lower rpms? This is what I have gathered from looking over the specs of production two strokes, most of which are huge engines. <br><br><br>Thanks,<br>Dave<br><br><br><br><br><br >

phox_mulder

Main reason I think would be emissions.

All the talk of banning snowmobiles in Yellowstone and
personal watercraft on Lake Powell is due to the majority of the craft out there being 2-stroke.

Once the powers that be were convinced that 2-strokes are on their way out and 4-strokes are becoming the norm, the talk of bans died down, with the 4-stroke stipulation.

phox

AlpineRAM

Hehe- teacher mode on ;D<br><br>The 2 stroke concept has the great disadvantage that the flow of fresh air and exhaust gas can not be controlled as precisely as in a 4 stroke. The 2 stroke does work very well at a certain rpm and a certain load- in all other situations it is quite challenged. A ships engine or a powerplant will work on fixed parameters all of the time. <br>A standard 2 stroke gasser is very inefficient, because you will blow lots of the fresh gas through and combust only some of it. The more modern two strokes use direct injection because it's not that bad if you just blow through air without fuel in it. Another point against the 2 stroke is that if you use the standard crank case flow version you will need to blow oil through it to keep things lubricated. In a small engine scenario you can not process exhaust gas to recover the oil. Big 2 stroke diesels use a compressor or turbo to scavenge the old gas out and the fresh gas in, and are controlled by valves. Since this scavenging takes time the capability for high engine speeds is quite limited. <br>Since the amount of scavenging, and therefore the mixture of gas constituting the load is very difficult to guess ( how much old exhaust and how much fresh air) it is also quite difficult to find the right amount of fuel to inject for the charge. Hence it is very difficult to build a 2 stroke engine that offers good driveability, fuel economy and low emissions over a wide rpm band. <br><br>Teacher mode off ;D<br><br>AlpineRAM

Dieseldude4x4

The big 20 cylinder back up diesels we have here at work are two stroke, 3800 HP at 900 rpm. They have a turbo but it is gear driven from start up to the point where the engine is loaded enough and the exhaust is hot enough to overide the overunning clutch and provide boost directly from the exhaust drive. Can't say as they are very efficient but they work very well for something that was designed in the 50's. Looks funny to pick the covers up see four valves per cylinder and they are all exhaust valves.<br>We also have some 8V-71 Detroits at the river that are two stroke. We are running them at the wrong RPM though and burn valves all the time. They are running maxed out at 1800 rpm which is not good for a two stroke. They are just a miniature version of the big 20's. Sound sweet loaded up though.

shortround

Hey dd, I had forgotten all about that problem with the Detroits. Our 8V92's have a rpm band where it is not reccommended to run for any length of time. It's like 2050-2200 rpm on the 92's. The 53's are down around 1500. Something about the <br>airflow/heat removal/resonance/scavaging effect/engine speed/etc factor. I didn't worry about that too much, that was for the enginemen.<br>The backup engines. Are they 20 cyl or 10 cyl opposed piston? EMD or Fairbanks? <br>

Dave H

Thanks guys, <br><br>

Mexstan

AlpineRAM, good 'teach'.<br>The last 2 stroke car I remember was the DKW. Seem to remember it was a 3 cylinder. It did not use the compression of the engine to slow it down as the tranni had some sort of free wheeling device. Don't remember if this could be locked out. Do remember that many drivers used the wrong oil/fuel mixture as many of these cars trailed smoke. It did not have a good repution for fuel consumption. The letters DKW had an acronym that I can't use here.

Dieseldude4x4

[quote author=shortround link=board=8;threadid=16663;start=0#156433 date=1057318026]<br>The backup engines. Are they 20 cyl or 10 cyl opposed piston? EMD or Fairbanks? <br> <br>[/quote]<br><br>Ours are 20 cyl EMD's. We got a V12 Cat that is putting out 4800 hp too. SWEEEEEET.<br><br>Our sister station has those goofy opposed Fairbanks. Better them than me.

Mexstan

No Gary, that was not it. More like Deutsche, bad word, Wagen

AlpineRAM

Well even though the DKW was not the last 2stroke, it has some nice history to it. The abbreviation means Dampf Kraft Wagen (Usually one word) meaning steam powered car. <br>Gary is right, &quot;Das Kleine Wunder&quot; was a nickname for a 2stroke bycicle helper engine.<br>The gerbox Mexstan is talking about was called SaxoMat, an automatic clutch system. This was available in the F94 from 1957 on. These cars were called 3=6, because the 3 cyl 2stroke should run as smooth as a 4 stroke I6 engine. (Regarding to engine harmonics and work strokes this is true). These cars smoked a lot, and were difficult to handle. If you used engine braking the engine got no fuel, and in consequence, no oil. :'( <br>The last 2 stroke engines I remember off hand in cars were built by Trabant or Wartburg somewhen in the 80s. They smoked a bit less due to the fresh oil lubrication. The Trabant was a nice car, extremely small, made of plastic and a real dog with its 27hp engine. Lots of tuners in the GDR were tunint trabants for racing, and some of them had more than 100 hp in the 1100 pounds racing trabant. <br>The need for a catalytic converter and some emissions regulations ended the 2 stroke history in European cars. <br><br>Just some trivia<br><br>AlpineRAM

hellotbone

The two stroke technology no adays blows the doors off of everything else. The Direct injection engines use pracically no fuel and run with less emissions then any four strokes out there. The new Sea Doo watercraft using these engines perform so well its amazing.

AlpineRAM

Jamie: in Sea Doos you usually use WOT and a certain fixed RPM, so it's relatively easy to get good emissions and economy. The downside is that it gets very complicated to build a 2 stroke with a wide economic powerband. Sometimes the 2 stroke will be more expensive and heavier than the 4 stroke of the same power. You are right that modern 2 strokes are getting better. Main reason is that now there is direct injection and layered charge technology available. Big constant speed engines where fuel economy is an issue have been 2 stroke for a long time. Now the downscaling begins. I am curious whether the car market will accept the 2 stroke with it's a little different sound and characteristics. I think that it does offer amazing possibilities, especially as a diesel. Think of good scavenging control instead of EGR, double the power strokes per revolution etc. <br><br>AlpineRAM

Mexstan

Thanks AlpineRAM for joging my memory. You right, they were called 3=6. I had forgotten about that. Now you mention it I remember the Wartburg. It was not very successful in my part of the world at that time. Never had any experience with the Trabant but know about them. Were they not produced mainly in eastern Germany?

hellotbone

Actully the sea doo 2 stroke technology is very simple and light weight and is being transfered to the snowmobile industry which we all know is obsessed with weight. The entire DFI injection system only adds 2 lbs to the entire craft. The technology also works all the time meaning its not for a set rpm like it was in the past its efficient at all rpm settings.