I have so far come across to some books, but none of them explained clearly to how gas-turbine locomotives work. What they told were the same; “big blow”, high bunker C consumption ends up similar to diesel cost, etc. Can anyone tell me the principle of gas-turbine locomotive please? A book stated that their horse power range somewhere between 7,900-11,500 hp (if I am not wrong) depend upon the temperature. Why is it? It also looked like there were A and B unit following with a big bunker C tanker. Is that hp figure for both units? Thank you!
Karn[:)]
http://science.howstuffworks.com/turbine.htm explains how they work. But in a rail application the shaft is connected to a gearbox and a high sppd alternator.
The high power is due to the very high rotational speed of the turbine (power is proportional to torque times angular velocity) upwards of 30,000 RPM
The UP gas-turbines and their different generations (the “veranda” turbines, the “Big Blows”) are discussed from a spotting standpoint in the various editions of the Diesel Spotter’s Guides (Kalmbach).
The units you are speaking of are the semi-permanently coupled pairs of C-C locomotives which were the last generation of UP turbines – the Big Blows. Living in Colorado in the late 60’s, I heard railfans talking about them, but they were retired before I got to see one.
These units had a big (initially 8500 HP, later uprated to 10,000 HP) turbine in the “B-unit” while the “A-unit” had the cab, a small Diesel to run accessories, and the like. And then a converted steam-loco tender in the rear carried an ample supply of Bunker C fuel.
I had been told by an engineering prof doing research on such engines that turbines have poor part-load fuel economy. The Big Blows were said to use as much fuel per hour at idle as at full power. The reason for this is that the efficiency of compressors and turbines falls off dramatically as you back off on revs, and when those efficiencies head south, so does the thermal efficiency of the entire engine. I understand that jet airliner are wasting a lot of fuel in the taxi, and it is because jets fly at high altitudes in thin air that they are able to get pretty good cruise efficiences.
You can use heat regenerators on a turbine to keep the part-load efficiency up somewhat – that was the idea behind the Chrysler automotive turbine experiment of the 60’s and the Ford truck turbine of the 70’s. The Chryser turbine never made it to market and the Ford turbine got recalled – probably on account of technical problems with building a good regenerator. The UP Big Blows did not have regenerators.
The idea behind the Big Blow is that you burned Bunker C, which was one grade above road asphalt and for a while was a refinery waste project used by oil-burning steam ships and by some oil-burning steam locomotives. The fuel
But basically, in answer to “how they work”, turbins are a fan or blower in reverse, the expanding stream of vaporised fuel (coal or bunder-C or aviation grade gasoline) froces the turbin’s blade around. In addtion to Jet Trubis, the most popular use for Turbins is electric power generaiton, where their applicaiton is almos universal and operation at full and near full load is continuous and the ususal thing. Most electric generating stations have multiple turbins and generators and part load operation is done by shutting a portion down.
If it helps your understanding any, there are many “turbo-props” flying - they have a jet turbine which is geared to the prop. Most helicopters operate the same way now.
The turbine has also found a home in power generation today, with all of the problems that have been encountered with the commercial grid. The set-up is virtually identical to how the RR turbines were set up, however the load is usually hundreds of computers instead of C-C trucks.
The diesel engine included was for hostling, and also for as an APU for starting. A gas turbine must be cranked to 85% of its top speed before it starts to make power. The top 15% is its total operating range.
Aircraft turbines use the eletrical generator in double duty as a starter.
I think but am not sure, but early units were built with axial turbines, the kind with many rows of blades, and later units were built with radial turbines similar to what you see when you look at a turbo charger. Naval ships with gas turbine propulsion have a cruising turbine in addition to a main turbine, and diesel power for manuevering.
Steam turbines are also made in axial and radial configurations, and have a much wider operating range. Axial turbines are typically used for main propulsion,and radial turbines are used for auxiliary power. Turbines are also classified as reaction or impulse types which has to do with the angle of attack on the blades. Naval ships typically have a high pressure, low pressure and a cruising turbine.
They are are also much more hungry for steam than a piston engine, which is not bad, except in locomotives there is no recovery cycle limiting efficiency to about 7 or 8%. A steam plant with a condensation cycle can have an efficiency as high as 30% if run carefully. The problem with a closed loop system on a locomotive is to condense exhaust steam at a practical rate requires massive cooling capacity. Not a problem for a ship sitting in the ocean, or a power plant next to a lake or river.
To heat one pound of water from 32 degrees to 212 degrees at sea level, takes 180 BTU of heat. To convert that water at 212 degrees to steam at 212 degrees, takes 970 BTU of heat. This is called latent heat. That same 970 BTU must be removed to condense that steam.
Water weighs about eight pounds a gallon, so a thousand gallons weighs about 8,000 lbs. and has almost 8 million BTU of latent heat.
Oh, to explain com
“To heat one pound of water from 32 degrees to 212 degrees at sea level, takes 180 BTU of heat. To convert that water at 212 degrees to steam at 212 degrees, takes 970 BTU of heat. This is called latent heat. That same 970 BTU must be removed to condense that steam.”-jruppert
Is that right?
Your saying it takes 5+ times the amount of energy to make the state change to steam as it does to go between the solid/liquid state change and the liquid/gas state change?
Thats incredible !!!
for the same reason a glass of water with ice becomes either a glass of water or a glass of ice.
To turn one pound of water at 32 degrees in to ice at 32 degrees takes the removal of 144 BTU, to continue to zero degrees takes only 16 BTU.
This is why a Slurpy from 7-11 freezes your brain!!!
The UP turbines were a gas turbine, coupled to a generator through reduction gears. They have a 500 to 800hp diesel for hostling, starting the turbine and exciting the dynamic braking.
The UP turbines were not cycled off during downhill runs for a good reason. The turbine had to be started on diesel fuel. Once up and running it then switched over to bunker C fuel. To shut it down, the engine was first switched back to diesel fuel and run for 10 minutes to purge the fuel lines of bunker C and prevent clogging. The engine then shut down. The starting and shut down procedures were automatic. Once the start or shut down switch had been activated you waited and watched.
Another interesting event sometimes occurred. If during the starting process one of the combustion chambers failed to ignite then the unburned fuel in the exhaust created a flame thrower that made a GE diesel look like an amateur. You then had to shut it down and start over. Starting or shutting down a diesel is much simpler.
As for the poor part load fuel economy, the final modus operandii was to team the big blow with two geeps. The turbine was run in notch 8 wherever possible while speed control was provided by varying the geeps throttle positions.
I recall reading about a running gas turbine unit that UP parked under a highway overpass. Seems it melted the asphalt above and ate a big hole in the roadway!
Good explanation everyone.
This is a very intersting thread.