Locomotives

The difference between 2 stroke and 4 stroke engines of comparable size is that the peak firing pressure of the 2 stroke is half that of the 4 stroke but it does it every stroke whereas the 4 stoke gets around to it every other stroke. The result is the same horsepower output. All the components of the 4 stroke have to be built up to take the extra stress. The result is a substantially heavier engine. If the 4 stroke did not have a turbo it would develop about half the power. That's why it seems that every 4 stroke diesel over 40 hp has a turbo. (I was surprised to see that a 40 foot Beneteau sailboat auxiliary engine had a turbo on it.)

This is very true, and is the reason why the two stroke is generally a smaller, slower engine than it's equivalent powered 4-stroke.

 Remember, with the RPM difference between the two stroke (900) and the four stroke (1050) means that the power stroke delta is something less than 2:1.

 Yet another advantage of the four stroke over the two stroke is better scavenging pf the exhaust (though scavenging may not be the correct term here). This allows for more oxygen in the cylinder, which should further reduce the delta.

Since we are discussing 2cycle vs 4cycle, I have read that the 4cycle engined locomotives don't 'load' as fast as an equivalent 2cycled one, so that acceleration is consequently poorer.
Is this, as a rule, true (or was it at one time)?

chutton01:

Since we are discussing 2cycle vs 4cycle, I have read that the 4cycle engined locomotives don't 'load' as fast as an equivalent 2cycled one, so that acceleration is consequently poorer.
Is this, as a rule, true (or was it at one time)?

Its called turbo lag. EMD unique scavenging system uses an over running clutch and an 18 to step up gear train to turn the impeller at start up and lower speeds an loads where there isn't enough exhaust flow and energy to turn the turbine fast enough to give enough combustion air. Both 4 stroke and 2 stroke diesel are more properly called compression ignition engine where a charge of air is compressed enough to heat it to the point where diesel fuel at the top dead center is sprayed in and ignites. The resultant increase in pressure on the piston is extracted a torque by the crankshaft as the piston descends. Getting air and exhaust out of the cylinder is called scavenging. The piston on the 4 stroke substitutes as an part time air pump where as 2 strokes use a separate blower or the gear drive turbo combination that EMD uses. Positive displacement blowers like root blowers are more efficient at moving air in high volumes and low pressure than centrical blowers and both are better than piston pumps. Thats the reason just about every 4 stroke engine above 40 hp size uses a turbo to get a decent specific horsepower. Now back to turbo lag. EMD generators running at synchronous speed no load have the turbo at 16200 rpm an closing the breaker it quickly goes to full power with the turbo off the gear train at about 18000 rpm for full air box pressure. A 4 stroke at synchronous speed no load has a turbo being dragged around by to low energy exhaust flow and has to gain a great more rotational speed to pick up the full load. Typically 4 stroke can only manage to pick up 35% load without stalling but the EMD can pickup 100%. For locomotives as well as generators the load has to be fed in slowly to avoid smoking which makes them even slower.

When I was a kid the Detroit truck engine used both a blower and a turbo. Scavenging of a cylinders exhaust was not good from an emissions point of view. How did they clean up the 710.

creepycrank:

All the other locomotive builders except Fairanks Morse, lacked the imagination to build anuthing but 4 stroke engines.

You win! That's my laugh for the day! (EMD people were always some of my favorites....)

aut1rml:

When I was a kid the Detroit truck engine used both a blower and a turbo. Scavenging of a cylinders exhaust was not good from an emissions point of view. How did they clean up the 710.

Although EMD and Detroit Diesel Allision were part of GM together the engineer departments never coordinated on anything. The only exception is that Allison made all the engine bearings and I suppose had a lot to do with the turbo design. I know EMD started using CAD fairly early and had enough computer capacity to run prototype designs on the computer rather than build the parts and run the equivalent of several years in the field on test engines. Possibly all this was done on a GM mainframe. I don't know what happened to DDA but I think they just went along with the conventional wisdom rather than have any confidence in there own abilities. Somehow they still offer 2 stroke engines probably for the export market. Everybody and their brother has a different scheme to improve the basic 710. The first thing was to develop new piston rings which at this point reduce lube oil consumption by about 50%. You can get away with this because of the very great improvement in oil additive packages in the last 30 years. For locomotive EMD has electronic unit fuel injectors, 18:1 compression pistons, and a separate cooling system for the after coolers to control the temperature at 120 deg F. There was an experiment done at Southwest Research on a Ingram Barge 12-710-GA engine that include an injector of a patented design o an f after treatment catalyst. It made T2 but with a penalty of raising the bnsf from 0.325lb/hp-hr to about 0.350lb-lb-hr. They didn't replace the original 2 pass aftercoolers or the original 16:1 pistons.

Creepycrank I'm sure you didn't mean:

"The first thing was to develop new piston rings which at this point reduce lube oil consumption by about 50airbox temperature at about 120deg."

There must be something missing between "50" and "airbox".

Also

" It made T2 but with a penalty of raising the bnsf from 0.325 to about 0.350."

Did you mean BSFC (Brake Specific Fuel Consumption) in pounds per horsepower hour?

Detroit Diesel's problem was that with the blowers running at full power, they couldn't get anywhere near the fuel consumption of the competing four strokes, which EMD achieved with the overrunning clutch on their turbo and blower. That was too expensive for the small engines, so they just changed over to four strokes.

M636C

Yes, thank you. I discovered that I can edit after the fact. I think the point I wanted to make was that revising the design to get to Tier 2 isn't all that difficult and but you can rapidly get bogged done in the details, the reports on this subject can run to 50 pages. Of the other 2 stroke manufactures only Fairbanks Morse seems to be building for the new engine market as they announced that they sold some fast start emergency generators to a customer in Australia. Without researching, Bergen Diesel, owned by Rolls Royce, still makes 2 stroke engines.

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

monon99:

probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke!

monon99:

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

monon99:

 The EMD products are nearly all two strokes which wind up very fast on acceleration, but GE's product is a 4 stroke which is quite delayed in response. Old heads tell me that Monon RS-2's and C-420's would load up faster and kick better than an EMD by a long shot - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke! As usual the better, longer lasting product was muscled out of the market by the ones with better financial arms. Must be why they still build new ALCos in India and France.

NYC guys swear by Baldwin S-12's being the absolute best quick-load kicking engine - don't know if the 606 or deLavergne was a two or 4 stroke.

On a practical level in todays railroading a two stroke is the best  on a light intermodal train for maintaining a schedule but on a heavy drag freight in hilly terrain with tough grades I'll take a GE every time - pulls like a bear and won't let you down - the EMDs will be a constant fight with sand and independant brake to get them to quit slipping and lose so much speed that you stall.

 

monon99:

  - probably due to the fuel being injected ahead of the turbo instead of directly into the cylinder - which also caused our favorite ALCO smoke!

 WHAT have you been smoking?

 

 Now I find that I can't edit because I use firefox. So:

1.If the fuel is not injected directly into the cylinder, it is not a Diesel engine

2. IF it ran it would destroy itself due to preignition

3.It would not produce usable power

tdmidget:

 Now I find that I can't edit because I use firefox. So:

 

That's strange, I have no problem editing with firefox (version 3.5.5 running on Solaris 10u8 (SPARC)) but have had problems with paragraph formatting on Safari running on MacOS 10.5 (x86).