Reading about Diesel-Electric rail locomotives, it seems that they are effectively Hybrid vehicles. Are they actually Hybrids in the sames sense that a Toyota Prius is a Gasoline-Electric vehicle?
http://boards.straightdope.com/sdmb/archive/index.php/t-63293.html
Not exactly the same thing. A Prius has an electric motor and a gas engine; it can run on either one, depending on circumstances.
A diesel locomotive uses diesel engines to run electric motors on the wheels. It can’t directly use the diesel engines to move the wheels.
More like a serial hybrid like a Chevy Volt. The diesel engines don’t provide motive power. They just run generators to provide electricity for the electric motors which drive the wheels.
Further, and in opposition to a hybrid vehicle, the diesel engine is always running.
Right. A better analogy for a diesel locomotive would be a gas-powered electric generator, hooked up to the “motor” of an electric car.
The diesel locomotive isn’t using the diesel engine to charge an electric battery, which then is “drawn down” when the engineer needs the locomotive to move (unlike a hybrid automobile); the diesel engine is an “always-on” power source for the electric motors on the axles.
Which is a difference with a serial hybrid car like the Volt, which can manage short trips on its batteries. The Volt’s ICE runs to charge the batteries. Personally, I wouldn’t make “the ICE doesn’t run all the time” as a condition for defining something as a “hybrid” vehicle.
There apparently are (and have been) true “hybrid” diesel locomotives, though most are fairly recent prototypes or experimental designs:
It’s a hybrid drive system, but not for efficiency, more for practicality.
Locomotives dump extra energy (such as from braking), into resistors to generate heat, none of it is stored or even dumped into a 3rd rail AFAIK.
OTOH, in the general article about “hybrid vehicles”, says the following:
It then goes on to link to the “hybrid train” provided above. I would suggest there’s a lot of wiggle room in what one means by “hybrid vehicle”. The one sentence definition that starts the article is pretty broad:
I would argue that a diesel-electric locomotive is NOT a hybrid, because it only has one source of energy (the diesel engine).
A gas-electric hybrid car has two sources of energy: a battery and a gasoline engine. The two are used in a way that maximizes energy efficiency. Namely, when the engine is run, it is run at a RPM and power output that offers good energy efficiency. When more power is needed, the electric motor kicks in, instead of revving up the engine. A diesel-electric locomotive can’t do that; you need to rev up the engine when accelerating, and run the engine at a lower PRM when cruising at a low speed.
The real question is what definition of hybrid do we accept. I think as applied to cars, it came into common usage to describe the Prius and Insight. Diesel locomotives are different. I am not sure who is in a position to say whether they fit the difination or not.
I think the main advantage of diesel-electric isn’t ease of power transmission, but rather that they can run that diesel in a much more efficient manner than if it was directly powering the wheels.
I see your point, but a hybrid car (like a Prius) has one source of energy: the gasoline. The battery is charged only by energy from the generator (powered by the gas engine) and reclaimed from braking. All the energy in the battery comes from energy that the gas engine created to start with.
Years ago, I read that the diesel electric locomotive was a solution to an engineering problem related to the inability to build the strong, efficient transmission necessary to power the multiple drive wheels. Getting power to all the drive wheels was simplified by the use of the multiple electrical motors.
Looking back through some old patents the term Hybrid Drive System has been in use for many decades. Just browsing quickly it seems the term is generally applied in cases where there is more than one way to deliver a driving force to the drive wheels. Looking through these was a bit of an eye opener. I found this patent from the early seventies that is earily close to modern hybrids.
So from that, I would say that locomotives and large off highway vehicles are not hybrids. Just vehicles with a diesel-electric powertrain instead of a mechanical one.
A Volt’s engine can propel the car directly when the batteries are depleted, however, in addition to providing charge to the batteries.
Do you know where you learned that?
I’m not a vehicle engineer, but my understanding is that diesel-electric locomotives came about mainly because it’s a lot easier to run electrical wire from the engine to drive wheels than it is to run mechanical driveshafts with enough power to move a freight train.
Secondarily, the electric motors (unlike diesels) are efficient at low-speed high-torque conditions, so you don’t need the huge gear ranges you would need to start a train with direct-diesel. The less extensive gearing probably helps efficiency a little, but is probably more valuable for simplicity and low-cost.
I believe the real efficiency gains from internal combustion–electric drive come when there’s enough battery storage to smooth the loading on the IC engine; this lets the engine stay in its sweet spot for power output, and be smaller overall, both of which give you a big efficiency gain. (Regenerative braking adds another big dollop of efficiency as well). Since most traditional diesel-electric locomotives don’t store power in batteries, they don’t get these efficiency gains.
But the OP seems to understand how locomotives work, so anything further is just arguing about what ‘hybrid’ means.
What about the dual-mode buses that are in Seattle as well as in at least one town in Switzerland (Fribourg). Also, they are about to introduce dual-mode locomotives for a new commuter line in Montreal. The line will run partly in a tunnel where only electric locomotion is permitted and partly on some non-electrified freight lines. So they will run on diesel (or, it seems more likely, diesel-electric) over the freight line and on pure electricity (with catenaries and pantographs) in the tunnel. These locomotives were developed in conjunction with NJ Transit, which then canceled after the carhead governor canceled the proposed new tunnel under the Hudson.
It’s quite impressive when you see it in action from an engineer/mechanical standpoint.
http://www.ge.com/products_services/rail.html
Then again, I’ve always been a fan of their jet engines for some reason.
http://www.ge.com/products_services/aviation.html
How this could translate into more efficient cars, I dunno. But would love to find out.
A critical reason for using a diesel electric is that the electric motors generate maximum torque at stall. Which is pretty much the opposite of an internal combustion engine. What this means is that you can run the diesel engine at maximum power when the train is stopped and dump all the power into moving the train. You can’t do that easily with a mechanical transmission, and certainly not at the large powers the bigger freight locos provide. Efficiency gains from regenerative braking and the availability of a useful power boost for dragging a train up steep grades are advantages with a hybrid, when you add batteries.
One useful thing about a locomotive, you are not worried about adding mass. In order to get traction they are built heavy in the first place.