Paul, I am not taking issue with the comparative power produced in a power stroke.
Given equal cylinder displacement, a two-stroke engine will produce less than twice the power produced by a four-stroke engine running at the same speed, but it will produce more power than the four-stroke engine because it fires twice as often.
[quote user=“M636C”]
VGN Jess
Why has GE never had to build a 20 cylinder prime mover to achieve higher horespower, but EMD has had to build two (SD45 and SD80MAC) to do so? Even now, GE gets more HP out of a 12 cylinder GEVO than EMD does with a 16 cylinder 70ACe. What does GE know that EMD doesn’t?
It isn’t just a matter of the number of cylinders;
The 20 cylinder 710 is more powerful than the 16 cylinder FDL or the 12 cylinder GEVO, however.
The two sixteen cylinder engines, the GE HDL and the EMD 265H were both rated at the same 6000 HP. The experimental EMD 12-265H was the same power as the 12 cylinder GEVO. EMD chose for good reasons to sell the 16-710 instead, not least because that’s what the customers wanted.
EMD have an experimental 12 cylinder four stroke engine and it is expected that this will develop 4500 HP.
In export locomotives, an Alco 12-251 developed 2000 HP and was a competitor with the 16-645E, and had the advantage of generally lower fuel consumption, but the EMD outsold the Alco (except in India, where the ALCO could be built locally).
It is true that the 20-645E3 was necessary to match the 3600 HP of the FDL16, but the GE engine was not more successful than the EMD. At the time many more 3000 HP locomotives were built than 3600 HP.
The 20-710G3 was more powerful than any GE engine of the time but only sold a few examples.
In general, EMD engines last longer than GE engines. In time the cast crankcase of the GE FDL cracks and requires replacement, after ten to twenty years depending on the duty cycle. EMD 645 engines have lasted more than 40 years and many are still in service. These older engines might not be as economical
IN THE 70s WE PURCHACED A CLEVELAND 16 278a. FROM THE NAVY AT ANAPOLIS MD. WAS A EXPEREMENTAL ENGINE WITH A 12 CYL. ROOTS BLOWER & A LARGE ELECTRIC BLOWER ON THE FLOOR ABOVE. WE PURCHACED IT & PUT A 16 CYL BLOWER BACK. IT RAN IN A DREDGE FOR MANY YEARS AFTER. NOT MANY LEFT TODAY. BUT THATS 70 YEARS AGO. HERBYGD@AOL.COM
As for SD45s being derated, Wisconsin Central did reset the fuel racks on all of their units to 3450 horsepower, never heard of many failures…
Thank you to all who responded to my questions; I learned much. That said, I still don’t feel the crux of my query was answered. I was asking for opinions (hopefully from EMD/GE experts), why would EMD use two stroke engines at 900-950 max RPMs (over 4 strokes at 1,050 RPMs), when GE gets more HP from using (in some cases) 4 less cylinders? It just seems to me, in looking back over time, GE has always produced a prime mover w/more HP, during the same time period, than EMD. Why is EMD always seemingly behind GE in the HP “game”? Just curious. If someone thinks they already answered that, I apologize for not recognizing it. Merry Christmas to all! 
Generally, conservatism. This is what gives EMD its reputation for reliability and longevity. There are some exceptions, but EMD was hesitant to push the limits of their design, because it had the potential to create problems. Look at the SD50, for example. Railroads tend to value reliability just as much as horsepower. GE caught up with the -8s and -9s in terms of reliability and longevity.
Thanks; I understand that (conservatism) as a probable reason.
GE only entered the market around 1960 with the U25.
At that time EMD produced the SD24 with the same number of cylinders but 100 HP less.
Apart from the SD45 and SD45-2 with 20 cylinders, to match the U36C, EMD and GE had matching engines, the 12-645E3 in the GP39 matchng the FDL-12 in the U23B and the 16-645E3 in the SD40 matching the FDL-16 in the U30C. So apart from the most powerful locomotives in the range (which were not the most popular) EMD and GE had matching engines.
Later with the 710 engine, the 12-710G3 in the GP59 matched the increased power of the FDL-12 in the B30-7A and later the 16-710 at 950 rpm in the SD75 was only 80HP less than the FDL-16 in the Dash9-44CW.
In the 6000 HP locomotives, the 16-265H matched the HDL-16.
It is only with the current GEVO-12 compared to the 16-710 that there has been a consistent period where GE has had a locomotive with fewer cylinders. EMD could have built the SD89MAC but customers asked for the the SD70ACe instead.
The EMD 16-710 engine pretty much matches the fuel consumption of the GEVO-12. The EMD engines are kbnown to last much longer than the GE FDL engines. Most of the Dash 8s rebuilt recently have new engines, while most rebuilt EMD locomotives retain their original engine, rebuilt with new power assemblies. In the long term, the EMD is cheaper to own.
To be fair, the GEVO is yet to establish whether it will last as long as an an EMD two stroke.
As from now, it appears that EMD and GE will again have equivalent engines with the same number of cylinders, with the new EMD four stroke engine against whatever GE are going to call their Tier 4 engine, with both producing 4500HP.
Best answer yet; thanks! Generally, I was primarily considering the 1965 period on, and should have been more specific in my query. Specifically, I just couldn’t (can’t) understand why EMD would use a 16 cylinder 2 stroke (SD70ACe) with less HP than a GE 4 stroke (ES44AC) w/only 12 cylinders and why customers would buy it (16)? Wouldn’t 16 cylinders burn more fuel than 12?
It does not burn more fuel. It burns the same amount of fuel and the engine has been around longer. Everyone knows how to work on it.
As has already been said, the fuel consumption is basically the same or nobody would buy the locomotive with the higher fuel consumption.
Also, the power difference isn’t that great. An AC4400 developed about 4380 HP and an SD75 4300, in theory.
In government emissions trials in California comparing GE and EMD locomotives, an EMD SD70ACe from BNSF was compared with an ES44AC from UP and in order to appear fair, no adjustments were made to the locomotives, and they were tested just as they came out of service.
It was found that the EMD used more fuel, but it also was more powerful than the GE. I think the 4300HP EMD was acually about 150HP more powerful than the 4400 HP GE… It was the GE that was down on power and the EMD was pretty much as advertised. But it could have been the other way around.
One railway tested each of their 16-567C engines, half of which were supposed to be 1750 HP and half were supposed to be 1800 HP. Of course, the most powerful engine, at about 1815 HP was one that was nominally 1750 HP.
So don’t be misled by the advertising. An EMD of
You’re asking the wrong question. My father had a 12-cylinder E38 BMW that was good for over 28 mpg indicated at just over 80 mph, on a road that was far from flat. I have never seen an eight-cylinder model of the same car that would get even remotely similar mileage under the same conditions – from less displacement.
There is a bit more loss, thermodynamic and mechanical, out of more cylinders, and of course the capital cost of more injectors, bearings, valves, etc. is higher. So there are advantages to building engines with fewer cylinders… if you haven’t already costed-down much of your production cost, established a cadre of skilled maintenance people, developed a robust aftermarket for parts and supplies, etc. for an engine design with more cylinders.
The point is not just how many cylinders an engine has. I think most Class I railroads care more about ton-miles and over-the-road reliability (including the ability to work partially disabled without catching fire!) than about pure specific fuel consumption in the prime mover.
There are certainly cases where fuel economy is significant – that’s part of the appeal of older Alcos in shortline service, I believe. But that’s normally a fairly small part of the overall cost of assuring motive power. Again, it’s working reliability that matters, and railroads have (or ought to have) a pretty good idea of how the balance between fewer cylinders and easier maintenance, etc., works out economically.
Now, what the locomotive manufacturers say to the railroads when trying to sell their products is another matter. One that I suspect requires other criteria than straight factual truth to evaluate… [;)]
What difference is there between the hp per cc displacement of an EMD 2 cycle engine and a GE 4 cycle engine?
Does a 2 cycle engine run slower than a 4 cycle engine?
Partial answer to #1 has already been discussed. 2-cycle has more power strokes per unit time, so higher HP; 4-cycle is more efficient (and can use higher peak and mean pressure over a longer stroke) so greater unit power for a given displacement. Then you factor in the injection characteristics, the permissible machine speeds, etc.
M636C can probably provide actual numbers for various kinds of EMD 567/645/710 vs. GE and Alco 4-cycle service engines. If we ask him politely, he might work them up if not already available…
#2 – the rotational speed is determined by a number of factors, ranging from how the engine is balanced net of power thrust on the pistons (which changes during the stroke) to how the firing order, etc. puts torsional strain on the crank. EMD engines were classically designed for the 900 rpm range, and running them even 25 to 50 rpm faster can significantly degrade reliability and engine life. GEs are, in my opinion, being overdriven at 1050 rpm, but I’m not in the industry and don’t have reliability data – under Welch, GE developed the power-by-the-hour guarantee system to cope with the real-world effects of diminished reliability at higher rotational speed.
The recent posts have thouroughly addressed my initial query; thank you very much. The answers have shown me that intuitive thinking is not always relevant in the railroad power industry. While a railroad supporter, I am ignorant of these kinds of technical issues for never having worked on a railroad (though my grandfather was an engineer on the Virginian RR for 35 years). Merry Christmas to all who helped me understand how complex something I thought was relatively simple!!!
[quote user=“Paul of Covington”]
Deggesty
owlsroost
CPM500
The 710 displaces 11.6 litres/cyl vs 15.67 for the GEVO. Doing the math reveals that the total displacement of the EMD is 185.6 litres vs. 188 litres for the GEVO.
Stated design criteria for the GEVO indicates that the 12 cyl was designed for the same output as a 16 cyl. FDL.
General question - since the two engines have similar displacements, but the 710 has twice as many power strokes (at the same RPM) as the GEVO, why isn’t the 710 considerably more powerful ?
Presumably the effective stroke length of a two-stroke diesel is less than on a four-stroke, due to the ports in the cylinder wall being uncovered for part of the stroke ?
I have always understood that every other stroke (movement of the piston) in a two-stroke engine is a power stroke, whereas every fourth stroke in a four stroke engine is a power stroke. Therefore, at the same rpm, a two-stroke engine has twice the power strokes that a four-stroke engine has.
I’m no expert, but I remember reading that because of restricted breathing (the cylinder must be purged and re-charged at the bottom part of each
My dad worked on a 24 cylinder GM diesel while attending the USN’s Diesel Engineering school at Cornell, late 1944 early 1945. He was emphatic that it was a one piece cank as they had to replace a broken one at great expense.
The U.S.Navy does not have any diesel submarines. The last one, Bonefish, had 3 Fairbanks engines.
Indeed, but I’m not in the US Navy…
M636C
That’s true but FM opposed piston engines were the standard auxilary power for U.S Nuclear submarines up until quite recently and the older boats still have them installed…