Could someone explain the fuel rack on a diesel locomotive ? I’m reading a book about GE’s. The book makes it sound like every time GE wanted to raise the horsepower on their U-series, they “adjusted the fuel rack” for increases.(?) I picture a guy at Goober’s garage, with a screwdriver, adjusting the fuel rack. If it was that simple, why didn’t they adjust it to start with? I’d appreciate some explanation. (Bear in mind that I’m not mechanically inclined-talk to me like I’m 4!) Thanks
Picture goober at the Mayberry garage twisting a few injector rack knobs and you pretty much got the idea.
In addition to resetting the rack it you would also need all the electrical equipment to handle the increased kilowatts. A wheel slip system to keep the wheels from spinning gets more important as horsepower increases.
As far as the 7FDL goes… give her a few more turns !!!
Randy
The rack meshes with a pinion gear on the “barrel and plunger” inside the unit injector (EMD)or high pressure fuel pump (GE and just about everything else).
The plunger is pushed up and down by the camshaft/rocker to inject the fuel. A helix cut in the plunger determines when the injection event starts and stops - there are ports in the plunger that are covered/uncovered by the plunger. As the rack moves in, the duration of injection gets longer and more fuel is delivered.
You set the rack, to match the governor quadrant so that you get the fuel delivery the governor thinks it’s calling for. You also want to make sure the rack is set the same for all the cylinders. There are precision tools to help do this, but then, I’ve seen mechanics set the rack on Dash 7s by ear (maybe that’s why they ran so poorly!).
Murphy Siding, I’m going on the assumption you have a basic understanding of diesel engines. Where I work at night we occasionally “rack” diesel engines. The process involves adjusting the “lash” (the space between a valve tip and the rocker arm that actuates it) with regard to crankshaft position. It is like setting the timing on a gasoline burning engine (sort of). The injectors on a diesel also have la***hat needs to be maintained/adjusted the same way. In as far as getting more power out of any engine, typically you add more fuel and air and then adjust the variables like valve timing or turbo boost. Hope this helps a bit.
? If it’s that easy to adjust the fuel rack ( it sounds like simply thowing more logs on the fire?), why didn’t they start with a U-36?
main generator
Yea, the problem has never been how to increase HP of the diesel, but how to design a reliable electrical system that would fit within body of the locomotive + the traction control to get that HP to the rail.
That being the case, why didn’t the builders start with smaller engines, and adjust the fuel rack up to match the electrical systems? I’m not meaning to sound dumb, but it’s almost like putting a v-8 in a car, with a 2 barrel carbuerator, when a V-6 with fuel injection would work. What am I missing?
Thanks
Murphy, they are trying to keep it simple. But raising the horsepower is a bit more complicated than just adjusting up the rack, at least if you don’t want there to be a downside. For example the GP9 (1750hp) was uprated from the GP7
(1500hp) The rack was adjusted and the RPMs were increased and viola 250 more hp. The only problem was that the exhaust valves were burning out way to fast, the rings weren’t lasting and the cylinder liners weren’t lasting as long either. So engine oils had to be improved, GM had to develop a new metal alloy
for the exhaust valves, and they had to change the design and arrangement of the piston rings.
OK. Now I’m starting to get a clearer picture. Thanks
Sayeth mudchicken, accurately:
"QUOTE: Originally posted by Murphy Siding
? If it’s that easy to adjust the fuel rack ( it sounds like simply thowing more logs on the fire?), why didn’t they start with a U-36?
main generator"
The U36b did have at least an adequate main generator, but never had a wheel-slip detection and correction system that could handle 900HP per axle.
In areas where the railroad was relatively flat and speeds high, the U36b was reasonably satisfactory.
On the SCL, the U36b was rated on 1% grades for the same tonnage as a GP30 - 2050 tons. The GP30 would do a much better job of handling the tonnage than the U36b. If speed dropped below 22MPH, which with that tonnage it always would, the U36b was not very useful. As the crews said, they’d “slip out of a sandhouse”. Rain just made it all that much worse.
Old Timer
Don’t know how they say it in railroad terms, but in trucking terms, a 2 stroke diesel gets it’s rack adjusted, a four stroker like a Cummins gets it “Overhead” adjusted. So, the GE is a 4 stroke diesel, it gets an adjustment on it’s “Overhead” not its rack, why because it doesn’t have a rack it has an “overhead.”
Jim
Also if you stop and think about it, the GE FDL in the first U25’s, other than being upgraded is the same engine as an AC4400
“turn up the fuel…”
Basicly what I did for my F-250. The powerstroke is done with computer tuning though. Older models like the 7.3L IDI and Cummins 12v are done by turning a screw on the lift pump.
This comes at a penalty though. The rest of the drivetrain was designed around a certain (usually stock) power level. They have to be beefed up to handle the extra power to last the same life interval.
A bigger engine running not at full or near full capacity will last longer and be more reliable than a smaller engine doing the same job.
Adrianspeeder
True , I recall a serious problem with piston crown failures in the 4400s, a change in metallurgy was in order.
In addition ALL the electrical gear including the traction alternator was changed with each progressive upgrade.
DC generators had SERIOUS limitations.
Randy
Without a doubt Randy. I was just refering to the prime mover only.
I’ll pile on. Every time the builder’s turned up the HP, bad things happened that required design changes to the diesel engine. This, in spite of all the testing they did prior to release.
The bore and stroke changes to the engines (e.g. 567 to 645 and 645 to 710) tended to cause fewer new problems than just turning up the rack or engine speed (e.g. 567C to D and 645E to F) on an existing engine.
And lets not forget to change all the traction motors too !!!
Randy
D77s for everyone! On the house!
Ultimately it’s a trade off between getting more power out of the prime mover and the increased maintenance and likelyhood of failure due to increased stresses in the components.
I have two cents too.