What exactly limits the speed of a diesel engine? They usually go to about 70-80 mph and that’s it, but why? Is it that their trucks and wheels are built for speeds below 80mph and wouldn’t handle higher speeds? Surely the prime mover could give the electromotors enough hp to go at 120mph, but why are the motors limited at 70-80mph?
oops, that’s speed not speel
Diesel engines can go up to around 90 or 95 MPH. I guess it depends on the type of loco you are seeing at the time in fact I think locos can even top 100 mph’s to
Three major things limit the speed of a locomotive and its train, the locomotive gearing, the type, condition and contents of the cars, and the track it has to operate over.
With the proper gears, speeds in excess of 120 mph are not hard to achieve, even an old SD40-2 can hit that, but the track they run on and what they are pulling is a different story.
The cost to maintain a high speed track prohibits most US freight railroads from even attempting such speeds.
Remember the “Fast 40s” on the UP?
Matched sets of SD40s geared to run 80 mph under load…
But today’s freight cars were not designed for speed much beyond 80, most are designed for slower speeds, and the condition of most mainline track would prohibit even trying…
Other things to take into consideration would be the traffic flow on a given piece of railroad, the type of freight being moved, and of course, the weak link would be the slow, peddler freight having to use the same track as the hot shot run through…
Ed
The Diesel Engine in a train has very little to do with the speed limit of the locomotive that the Engine is in. In a Locomotive the Diesel engine is connected to a generator that makes Electricity. This Electricity powers the Traction Motors which are hung on top of every axle. The Traction Motors have a certain number of teeth and the axle has a certain number of teeth. The traction motors will spin at a minumum speed and a maximum speed. If they are geared high (57:20 Passenger Gears) they can reach 103 Miles per hour, but will overheat if the train is kept under 20 miles per hour for any lenght of time. Freight trains are geared around 62:15 which is good for 70 Miles an hour. Not the fast freight we want to see but they can pull up a steep mountain at slow speeds and not worry about burning out there Traction Motors. On aside note the Diesel Engine spins at about 800 RPM’s. The first number in the gearing is the teeth on the axle and the second is the teeth on the Traction Motors.
Just because I drive a truck I’ll give a little info on that, applies to a car as well. The top speed of my truck (or a car) is determined by the maximum rpm, the gears in the transmission and the gears in the differential. My truck has a maximum engine rpm of 1900 (car around 6500). In 1st gear my truck goes 2 miles an hour, my car goes about 25 miles an hour. My truck has 13 forward speeds, my car has 6. At 65 miles an hour my truck runs at 1450 RPM, my car 2650 RPM. My truck will do 90 Miles an hour ( I work for a company that has a safe driving record with the DOT) and doesn’t limit the speed of there trucks through the Computer. It is limited by the Max Engine RPM and the gears. Oh my car will do 155 Miles per Hour.
One last note on the “Speed of a Diesel Engine” The bigger the Engine the less RPM it will do. Diesel in a Pick UP Truck 4500 RPM, Tractor Trailer 2000 RPM (Before you complain about numbers each Company that makes Diesels have different max RPM’s, I’m just giving averages)
Amtrak tries for a 79 mph speed limit throughout the majority of the country on lines it does not own. That was part of the problem that Amtrak experienced on its service between Boston and points in Maine. Guilford maintained that its track was in no condition for those kinds of speeds and held out until the money could be found to upgrade the lines for higher speeds.
In the time before Amtrak took over the service, the Illinois Central, on its then doubletracked north-south MainLine had a lot of territory where the speed limit was 100mph [or better] for passenger equipment. The E units were all geared for high speeds, and I know in the MIssissippi Delta areas, the Panama Limited had a schedule that demanded speeds in the 100 mph range, and the track was good enough for that kind of running and the engines could keep those schedules easily. The max speed range of a locomotive is a product of the gear ratio ordered for that locomotive and the type of service it is intended for.
I’m talking about max speed ratings by manufacturers, it’s always "max speed= " between 70 and 80 mph
so what I gather from what all of you are saying…
A diesel-electric like ac4400cw won’t go 120mph simply because the manufacturer didn’t put the same gear ratio in as Bombardier would put for their HHP8. And they didn’t put such gear ratios becuase there is no need for it since it’s ment to pull freight anyway.
right?
I just explained it too you. Read Gearing, you can’t start a 100 car loaded train with gears that can run at 100 miles an hour.
you did and that is what I said in my last post, isn’t it?
Sorry I was replying to the one before your last post. I was writing during your last post
oh, ok then
PURE POWER ! I never heard of any deisel approaching 200mph, tubines get close and only straight electrics achive 200+mph because they have the hp sauce.
440cuin
even thought I’m the one that asked the question in this thread, I must say that this is not true.
A 6000hp diesel-electric is made to go up to 80mph, and a 1500hp EMU bombardier train is set to go 100mph. This defies your logic.
As others said it here, it’s all about gears. A 3000hp diesel does have the power to pull a passanger train at 100mph and more but it’s gears are set to give it a clean start with a 2000t train, and because of that the max rpm of traction motors can only pull any train at up to 80mph at that ratio.
The traction motor RPM is the limiting factor on the locomotive itself. Above a certain RPM the motor starts to fly apart. The gear ratio is set to allow the desired top speed witout exceeding the maximum motor RPM.
There is the real answer to your question !!! The reason different (higher ) gear ratio’s exist is to allow the armatures to turn slower at higher speeds.
Think about it this way, 62:15 the most common EMD gearing, is approx 4-1. at 60 mph, what speed is that big, heavy ball of copper called the armature turning?
Randy
60 mph = 88 feet/second
If we assume a wheel radius of 20 inches, the wheel is rotating at 52.8 radians/second or 504.2 RPM. At 62:15 gear ratio, the shaft of the motor is spinning at 121.98 RPM, unless I have the gear ratio backwards (I should look it up) then it is 2084.04 RPM.
Let’s not forget the guvmint. After a series of bad wrecks in the late 40s the ICC set maximum permissable speeds at 60MPHm 79MPH and 99MPH for “dark” track, atomatic block signal territory and track have ABS and automatic train stop respectively.
The fastest diesel engines I know of operating in REGULAR servcice, not on test runs, are the british high-speed-trains (HST). They run reliably at 125 mph and are advertised as Intercity 125. (In the metric system they would be calle IC 200 which is much better in terms of marketing.) I don’t know of any regular diesel service above 125 mph. . True high speed trains have elctric traction or turbines like the projected Florida Jet-Train. In theory, it should be possible to run high-speed-trains with diesel engines. The French high-speed-trains have to streamlined engines at each end of the train with aproximatively 6000 hp each. A modern diesel can reach this. Most probably, the question is, whether this is possible with the limited axleloads of 17 to 18 tons true high-speed-engines have
In the times of traction control and ac motors gearing is irrelevant.
The reason why locos have - say 70 mph gearing - is to ensure that at that speed the motors will not overspeed themselves and work most efficiently.