Why are tractor-trailer rig so much more fuel efficient

[instarx]

Originally Posted by jamesqf

If instead of wasting that electricity in producing heat, it was stored in batteries, high-speed flywheels, or even sent back into the grid via overhead electric wires, the locomotive would be a hybrid. But it isn't, so it's not, no more than dissapating the energy as heat in brake linings would make them friction hybrids. The energy's not reused, it's gone. Simple, really: all you have to do is think about it :-)

First, let me say that I never said a locomotive was a hybrid - in fact it is pretty clear it is not, because it has only one source of power - the diesel engine. However, the definition of a hybrid does not include the requirement that it re-capture any energy. Therefore your particular argument is fallacious.

What I think you are trying to say (and did say in a previous post) is that if it did use any of those means (flywheel, batteries, grid) then it would have two sources of power and be a hybrid. I agree with that. The Prius is a hybrid because it has two power sources: the gas engine and the batteries, not because it has regenerative braking.

Your position that a locomotive is not a hybrid is correct, but the arguments you use to support that conclusion are sometimes poor ("regenerative braking makes a hybrid", and "a locomotive is a transmission").

[jamesqf]

Originally Posted by instarx

True, power is "transmitted" from engine to drive wheels in a locomotive, but that doesn't make a locomotive a transmission. LOL

But that is not what I wrote. Apparently I wan't clear enough, so I'll try again. Forget about locomotives for a second, and just think of the general process. You have an engine producing power, and wheels on the ground. If the engine can't drive the wheels directly (as with e.g. wheel-hub motors), you need some sort of device to get the power from the engine to the wheels, right?

That device is a transmission. It can be mechanical, with gears and a clutch. It can be hydraulic, as with an automatic transmission. Or it could be electric, with the engine turning a generator, and the current running motors at the wheels. You could, with a decent engineering shop, swap the mechanical transmission of your current car for an automatic, no? (Or vice versa, depending on what you have to start with.) That swap wouldn't turn your car into a hybrid, would it?

You could swap whichever transmission you have for a motor-generator, and have an electric transmission. Your car would still run, but would it be a hybrid? Not by any reasonable definition, so why would a locomotive be one?

[jamesqf]

Originally Posted by instarx

However, the definition of a hybrid does not include the requirement that it re-capture any energy. Therefore your particular argument is fallacious.

You missed the point of what I wrote. I was not saying that the recapture of energy DEFINED a hybrid, but rather that recapturing energy and storing it in batteries is ONE WAY that it could be turned into a hybrid. Of course there are others, such as having batteries that were recharged at stations, and not by regeneration (though of course that would be missing the chance for major energy savings).

[jonr]

Here is a "way out there" idea. Create a system where cars can link up on the highway to create a "train". Computers control the brakes and the disconnects when someone wants to get off at an exit.

Some of the engines can be turned on and off so that they run at higher loads (better efficiency).

Even 2 or 3 cars running bumper to bumper would be a big savings - far less wind drag, more efficient engine operating range.

I'd love to be able to safely tail gate a truck and would be happy to pay them to use their more efficient diesel engine to pull me along. And going up a hill - my car could help push.

[RH77]

Let me point you to a Wiki entry....

Serial Hybrids

Most of what I've read, indicates that that a traditional locomotive is a series hybrid by definition -- which is what I am working off of: the definition.

From the article:

The power from the combustion engine must run through both the generator and electric motor, so the engine-to-transmission efficiency is 70%-80%, which is less than a conventional mechanical clutch having an engine-to-transmission efficiency of 98%. During long-distance highway driving, the combustion engine will need to supply the majority of the energy, in which case a series hybrid will be 20%-30% less efficient than a parallel hybrid.
...
Electromotive locomotives have used this concept for over 60 years.

Although less "efficient" than light-duty conveyances, it has a design to handle the tractive effort.

The argument of "recapturing energy", goes beyond the definition of "energy from two distinct sources" -- a hybrid is just that.

The argument of a "transmission" being a source of energy is inaccurate -- it is a transfer of energy. One can make an argument that a locomotive generator produces electricity.

I get both points, but the definition has been established in common discussion.

RH77

[instarx]

Originally Posted by RH77

Let me point you to a Wiki entry....

Serial Hybrids

[...]Electromotive locomotives have used this concept for over 60 years.

Most of what I've read, indicates that that a traditional locomotive is a series hybrid by definition -- which is what I am working off of: the definition.

Neither your wiki quote nor the wiki article itself says that locomotives are hybrids, serial or otherwise. You cut and pasted sentences out of context and their meaning got turned on its head. In fact, the "concept" that the wiki article says has been used by locomotives for years is wheel-motors, not hybridization. So you aren't working off the definition of a hybrid provided by wiki at all.

One cannot just cut and paste sentences together until they say what one wants them to say.

[trebuchet03]

Originally Posted by instarx

Neither your wiki quote nor the wiki article itself says that locomotives are hybrids, serial or otherwise. You cut and pasted sentences out of context and their meaning got turned on its head. In fact, the "concept" that the wiki article says has been used by locomotives for years is wheel-motors, not hybridization. So you aren't working off the definition of a hybrid provided by wiki at all.

One cannot just cut and paste sentences together until they say what one wants them to say.

Seriously, it needs to explicitly state it? Can we not take definition and use a tiny bit of brain power for pattern recognition?

If you really need explicit statements, here's the wiki article on hybrid vehicles, that explicitly states and backs up what RH77....

Hybrid vehicle - Wikipedia, the free encyclopedia



Here's the text, all of it from the section, not just a few sentences (emphasis added)

Heavy vehicles
Hybrid power trains are used for diesel-electric or turbo-electric railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery, and ships. Typically some form of heat engine (usually diesel) drives an electric generator or hydraulic pump which power one or more electric or hydraulic motors. There are advantages in distributing power through wires or pipes rather than mechanical elements especially when multiple drives—e.g. driven wheels or propellers—are required. There is power lost in the double conversion from typically diesel fuel to electricity to power an electric or hydraulic motor. With large vehicles the advantages often outweigh the disadvantages especially as the conversion losses typically decrease with size. Presently there is no or relatively little energy storage capacity on most heavy vehicles, e.g. auxiliary batteries and hydraulic accumulators—this is changing.

[jamesqf]

Originally Posted by trebuchet03

Seriously, it needs to explicitly state it? Can we not take definition and use a tiny bit of brain power for pattern recognition?

Hey, that's just what I've been asking you to do :-) But if you look at the whole pattern, not what some well-chosen article happens to say, it leads to a different conclusion: that the diesel/electric locomotive does not fit any reasonable definition of hybrid.

[trebuchet03]

Originally Posted by jamesqf

Hey, that's just what I've been asking you to do :-) But if you look at the whole pattern, not what some well-chosen article happens to say, it leads to a different conclusion: that the diesel/electric locomotive does not fit any reasonable definition of hybrid.

Well, it's already been explicitly stated for you...

Trolling services for this bridge are no longer necessary

[tasdrouille]

Back on big rigs...

They operate in a quite narrow rpm range. When you look at a big rig's bsfc map you'll usually see a huge minimum bsfc island covering most of the useful operating range.

Even at highway speeds, rolling resistance is more significant than aero drag. Incidentally, the rolling resistance coefficient of big rig tires is lower than most cars lrr tires (<0.005)