Two stroke diesel? Neato! Why not for smaller engines?

[BLINGMW]

Reading about diesels, came across this:

http://auto.howstuffworks.com/diesel-two-stroke.htm

Didn't know there was such a thing as two stroke diesel. Makes a lot of sense, but the one thing the article didn't explain, and I can't seem to find, is why can't it be (or why isn't it) done on smaller engines? If the system takes out the emissions problems that occur with two stroke gasoline engines... well hell, that was most of the problem right? Seems like they'd be great!

Currently, this is the kind of application two-stroke diesel technology is reserved for:

[Sijray21]

holy jebus.... hock:

how bad do you think designing that thing to be balanced was?

[Evan]

strap a snail on dat bish!

[Mike]

what are current diesel motors? like in the tdi?

[BLINGMW]

it DOES have a snail! Well, at least it must have some form of forced induction since the two stroke diesel cycle requires it.

And current automotive diesel engines are 4-stroke, very similar to gas. There are smaller two stroke engines than this of course (train and boat engines), and it'd never be "small" and cheap enough for say, a lawnmower engine (since it requires FI), but I wonder why it can't work in a 2 liter (instead of 10000 liter+) or other such automotive size. My only guess is that it has to rev slow to work?

[G.Irish]

Holy crap! I didn't know there is such a thing as engine elves too! Damn maybe if I leave a glass of milk and some cookies in my engine they'll fix it for me...*Goes to Food Lion to buy cookie dough*

[CaptainHenreh]

I talked with my father about this, and consulted my "Diesel and High Compression Gas Engine Fundamentals" book.

What we concluded, is that for a smaller engine, the power-band is far, far, far too narrow for the average Joe to tolerate. Dad used to work on 2 stroke deisels, and he liked the concept alot. But for a smaller application, a CVT would be absolutely nessecary, and frankly, I doubt any car company wants to fool with designing a brand new engine and drivetrain to make a car powered by an unpopular fuel.

The reason they work so well in stationary applications is those sort of engines run at pretty much the same RPM all the time, and a 2 stroke deisel is simply one of the most efficient internal combustion engines available.

[BLINGMW]

NOW we're talkin. :wink: Thanks! Narrow power band eh? Yeah, obviously those large engines stick with a fairly constant RPM, which I figured was mostly attributed to their extreme size (I'm sure accelerating/decelerating that crank and other rotating mass is a BITCH), but I have to ask, why does the tech lead to such a narrow band? Assuming you could make a small one that made max power at say, 4 grand, why would power fall off so rapidly at anything but that? Seems like fuel injection timing is adjustable (computer controlled, retarded/advanced with RPM), the amount of air entering the chamber can be controlled, I wasn't sure what actually drove the exhaust valve(s), but couldn't that be adjustable as well? 2-stroke diesel V-tek? 8) Is there something static (the cyl/piston size, compression ratio, valve size) that dictates a certian RPM in this case?

[CaptainHenreh]

EGT.

Exhaust gas temperatures skyrocket at high RPM's.

That being the case, the compression-ignition becomes more unstable at high RPM's, causing detonation at a less-than-optimal piston location, causing loss of power, and damage to engine internals.

[BLINGMW]

hey, wouldya look at that! 8)

http://www.deltahawkengines.com/index.htm

....these guys are making them for airplanes! Their tests so far are for a non-intercooled one, making ~240ftlbs/50HP @ 1200 RPM and ~330ftlbs/165HP @ 2700RPM. They predict 200HP with an intercooler. So at least it looks like they don't HAVE to be room sized. Doesn't look like it has much of an RPM range, but it looks like they're making progress....

I just talked to Dean, an engineer there, sounds like exciting stuff. (to me) The 2700 RPM's it turns is mostly a limit of injection technology, he siad there's not much reason it couldn't be designed to turn faster if the injectors could keep up. Make sense since current 4-stroke diesels usually top out at 4-5k, and in a two stroke they have to fire twice as often, so I'd say they're doing pretty good. He did say the for automotive applications, there's more of an emissions hurdle, and their engine currently is too dirty for that. Aviation standards are more relaxed. Neato.

a few highlights from their site:


upright 90 degree V-4, turbocharged, direct drive, two-stroke diesel with oil pump and external air-oil separator/sump

160 and 200 hp models, at 2,700 rpm

currently about 327 lbs including starter, oil pump, fuel pump, water pump, turbocharger, all internal lines and internal exhaust system

lower part count and fewer potential leakage points than the current 4-cylinder gasoline-powered aircraft engines:
no cam shaft or valve train
no head gaskets to blow and no head bolts
fully doweled, four bolt main construction (12 studs)
inherently stout block and compact V-4 design
no ignition system

[Krush]

Hey guys, I'm new here...I go to VT. I'm a diesel nut and I saw this thread and had to reply.

2stroke diesels have been along for MANY years. Yes, there are small twostroke diesels. The older Detroit Diesels are all two stroke. Almost every charter/city bus made before 1985 has a 2 stroke diesel in it. They are also used extensively in boats. Detroits are designated by a great model # convention. I have a bus with a 6v92T, that means 6 cylinders, in V config, with each cylinder being 92 cubic inches, T = turbo. I have another truck with a 4-53 (inline 4, 53 ci each cylinder).

The ole detroits have a distinctive sound...usually it's the assoicated blower whine (they need a supercharger to work). In the late 80's detroit came out with the series 60, which is 4 stroke. It is the most prevelent engine in OTR (Over the road) trucks. 12.7 or 13.8 liters i think. The 2 strokes were used up until recently in boats.

What killed the 2 strokes is emission requirements. However, there are THOUSANDS of these engines around, and parts will be available for many years to come.

Now, BIGASS lowspeed diesels like the one pictured are used in ships. The operate around 100rpm and are directly connected to the propellar (read: no transmission). To go in reverse, the engine is run in reverse. These engines are amazing and approaches 50% efficiency due to their low speed and massive size.

That's enough from me for now (I get easilly excited when it comes to diesels).

check out some pics I took of a ship engine.

<!-- w --><a class="postlink" href="http://www.hurthing.com/day3">www.hurthing.com/day3</a><!-- w -->

[Mike]

wow, way cool info! big motors = mmmmm... do they have vtec? i like how they MUST have a supercharger... mandatory boost = genius.

[JohnC]

Hey guys, I'm new here...I go to VT. I'm a diesel nut and I saw this thread and had to reply.

Welcome!

Now, BIGASS lowspeed diesels like the one pictured are used in ships. The operate around 100rpm and are directly connected to the propellar (read: no transmission). To go in reverse, the engine is run in reverse. These engines are amazing and approaches 50% efficiency due to their low speed and massive size.

That's enough from me for now (I get easilly excited when it comes to diesels).

check out some pics I took of a ship engine.

<!-- w --><a class="postlink" href="http://www.hurthing.com/day3">www.hurthing.com/day3</a><!-- w -->

Awesome. So is there some kind of clutch, or driveshaft disengagement or something?

[Krush]

There is no clutch or disengagement of any type. The motor is direct drive to the prop. To stop, stop engine...reverse, reverse engine. Again, 100rpm TOPS lol.

On the first page of pics (<!-- w --><a class="postlink" href="http://www.hurthing.com/day3">www.hurthing.com/day3</a><!-- w -->), the bottom row has pics inside the engine room (the other pics are in the cargo hold...boring). That biggass pump looking thing is a turbo charger--1 of 3. The cylinder with all the bolts on it is one of the heads, 1 of 9. <!-- m --><a class="postlink" href="http://www.hurthing.com/day3/DSC01324.html">http://www.hurthing.com/day3/DSC01324.html</a><!-- m --> was taken directly underneith where i was standing by the head...that's the block of the engine lol multilevel.

That ship was old (late 60's) and the engine made my Mitsubishi. It burns fuel oil (nasty tar like shit).

There are pictures of replacement cylinder sleeves and pistons too along with the "small" generators....figured you guys would be interested in some big engine stuff.

But yeah, I love diesels and love to explain how they work lol nerd.

[BLINGMW]

oh K! Didn't know Detroit Diesels were 2 stoke. Thanks for joining in. :thumbup: So they've been used in automotive applications before, and they do have a useable range of power, even if it would be best for only a truck (or airplane apparently) until injection tech allows for higher RPMs. Right?

but I guess I don't understand the emissions problem. Why are they prone to higher emissions than a 4-stroke diesel? It seems like the power stroke is identical, so it should burn just as completely, and the FI would do a good job evacuating the cyl, so what's the problem? I want one! :wink:

your thoughts?

[Krush]

Well, the new detroits are 4stroke...in fact now detroit is part of Mercedes Benz, but that's off topic.

The 2 strokes operate at normal diesel speeds (around 1800-2300rpm). They don't really rev any higher. EMD (GM locomotive engines and tug boat engines) are also 2stroke.

The reason the 2 stroke DD's are gone is cause that basica engine design is 60 years old. It was just going to cost too damn much to get the emissions of the 2 strokes down. they also aren't as fuel efficient (overall). And the screaming D's like to puff out blue smoke.

Basically, it's old technology and time to move on (except in HUGE applicatoins ).