A car comes equipped with an electric starter. Simple deal: battery powers an electric motor that spins the engine up to some speed where combustion can take over and bring things up to a steady idle RPM.
18-wheelers, I believe, typically have two options:
electric starter as described above, or
air-start. The have compressed air on board for operating the air brakes, so they can use this to spin the engine. Unclear whether some special valvetrain management is needed, or whether (on an in-line 6-cylinder) there’s always going to be at least one cylinder with its intake valves open, and so you can just pressurize the intake manifold and start spinning.
So how about diesel locomotives, with displacements on the order of 120 liters (your car is more like 2-5 liters)? It would take a humungous electric starter and battery to spin this engine over. Barring that, do they have compressed air on board for any purpose? Moreover, do they have enough compressed air on board to start the engine?
Finally, take it all the way to the limit: large-scale, marine diesel engines, with displacements up to 25,000 liters. My understanding is that these engines are almost never shut down unless something is seriously wrong with them. because they’re capable of extremely low-speed operation (I’m talking about single-digit RPM’s), it’s even possible to completely overhaul one cylinder at a time without shutting down the engine. But at some point, somehow, they must have started the engine, and they must have the capability to do it again if they ever shut it down. Anyone know how?
They certainly have compressed air on board – that’s what powers the whole braking system for trains! And given the amount needed for that, I suspect it would be enough to start the engine.
Also, those are diesel-electric locomotives. The diesels just power electric generators, which charge batteries that power electric motors that drive the wheels. So they have a real big supply of electricity stored in batteries onboard. Certainly enough to power an electric starter for the diesel engines if they did it that way.
I serviced an older Caterpiller dozer years ago that had a two cylinder gasoline engine that was pull-rope-started. When you had the two-cylinder running, you used a hand-actuated clutch to turn the big diesel engine.
why would there need to be batteries which add weight and loose energy? the generators power the motors directly (with control and rectification in between).
The diesel engines are set to run at a constant, most-efficient speed. But the energy needed by the train varies, depending on whether they are accelerating, going up a hill, down a hill, coming to a stop, etc.
Even if the engine is held at constant RPM, the fuel injection can be varied to meet load demand. Not only is there no need of batteries for this purpose, but it would be impossible to carry enough battery capacity in the locomotive to meaningfully affect the performance of the train as a whole. I suppose a battery may be present for starting purposes, but as has been noted (I don’t know why I didn’t realize this :smack:), a locomotive will have a ready supply of compressed air on board for brake operation, and so an air-start is a trivial add-on.
It’s still not certain to me that this is the case for the super-big marine diesels. Locomotives and OTR trucks have compressed air systems for braking purposes, but what about the big container ships? And if they do have compressed air available, wouldn’t it take a freakin’ humungous tank of it to get an engine spun up?
Back in the days of DC generators and electrical systems, a diesel locomotive was started by running battery current throught the generator itself, making it a DC motor.
Modern, Tier 3 compliant diesels are air start. A dead locomotive with the air bled off requires another locomotive or an external air compressor to charge the reserviors.
Unless you’re talking about the Green Goat style switchers based on hybrid technology, this is baloney. There ain’t enough battery made to do this in the standard long haul locomitive you see pulling a train. Batteries in those serve much the same purpse as those in IC cars and trucks, power when the engine is not running, not propulsion.
Various Googling suggests that storage batteries are not common in trains. As JFF notes, they would certainly have to be big, heavy and expensive in order to store train-scale amounts of useful energy.
I recall asking this here a long time ago (and forget the answer) but seems to me when a train is accelerating with a big load you can hear the rumble of the diesel engines get low and strained. You can feel/hear the engine struggling. If the engine could just run at a constant speed this would not be the case. You’d just hear one constant hum from the engine regardless of what the train was doing. Somehow the effort of the electric motors goes back to the diesel engine making it struggle (which I think was my question ages ago…how did this effort translate through the electric motors to make the diesel strain?).
One scheme I’ve read about involves a relatively small motor that slowly (say, over the course of 20 seconds or so) cranks one cylinder up to full compression. When this cylinder is fired it kicks the whole engine to life.
The principle invloved (I forget the name, and I’m an electrical enginer; shoot me) is that electrical power isn’t free. if you need a kilowatt to run a load, you need to generate a kilowatt plus the transmission losses to deliver it. Therefore, should the traction motors on the locomtive bog down under load, the increased load will be transmitted back to the alternator, and in turn slow down the prime mover, which you hear.
IIRC, built in your Gigantic Engines and Such Factory (GESP), disassembled, shipped to the wharf (with engine assembly crew), reassembled, then lowered into the beast. Life!
You ever hear a train start the engines will rev up at it starts to move. The output of a generator running at a constant speed will vary according to the load, no batteries are needed.
Excluding diesel electric ships or ships with variable pitch props, a marine diesel engine is directly coupled to the prop shaft. To change speed of a ship the engine’s rpms are incrreased or slowed down. A slow bell might be 20 RPM with a full ahead bell being around 120 RPM.
The engines are started with high pressure air. Each cylinder will have a valve just for starting air. If the prop is not turning then the engine is not turning. If the ship is on any ahead bell and a reversing bell is given, the engine is stopped the valve guides lifted, the cam shaft is shifted to the reverse position, the valve guides are dropped and starting air is introduced into the clinders. When the engine is up mim rpms the air valves are closed and the injectors begin operating.
If a cylinder needs to be worked on the engine is stopped first, woth a pistion and valves moving you can not work on a cylinder.
Air is provided through air compressors and air tanks. Some of the older ships had an air compressor built into the main engine with auxalliary compressors.
When manuvering into port some times a ship can get a show boat Mate or Captian who likes to use a lot of bells forward and astern. If too much air is being used the engineering watch officer will call the bridge and tell them that they have only so many more ahead to astern bells that they can do in the next 20 minutes. If the bridge exceeds the number and uses all the air the enginroom will ring up STOP, and call the bridge and tell them that they will not be answering bells for the next time period. When the air pressure is back up they will ring up stand by engines.
Normally the engine is assembled as the ship is being built.