Why are tractor-trailer rig so much more fuel efficient

[njlou]

Originally Posted by Duffman

1) Diesel Engine is more efficient and there is more energy in the fuel
2) Big rig engines operate in an efficient narrow band
3) Low power to weight ratio
4) Better Driving habits and bulk of the time spent cruising
5) Aero Drag is smaller on a per pound basis (being both heavy and long are advantages here)
6) Semis are optimized to reduce cost of operation above all other criteria.

You are correct - Here are some more:
- The big Diesels are more efficient and use more powerful fuel. Since they need big engines anyhow, they can use large/efficient ones.
- They have (little) pollution controls
- Gearing is a major helper and the big rigs have the room and the budget for them.
- they are on the highway at highway speeds. If they drove to the grocery store or around town they would get gallons to the mile.
- yes they drive more conservatively simply due to size.
- BTW locomotives use the diesel/electric propultion systems. the diesel is computer controlled to run a generator at peak efficiency. In effect it IS a hybrid. It is a multi ton Prius???LOL.

Here is another comparison - Why do some old British tiny cars including sports cars get miserable (teens) MPG?

[jamesqf]

Originally Posted by njlou

BTW locomotives use the diesel/electric propultion systems. the diesel is computer controlled to run a generator at peak efficiency. In effect it IS a hybrid. It is a multi ton Prius???LOL.

Not so. The electric part of a standard diesel-electric locomotive is just a transmission, so calling one a hybrid is like claiming an automatic transmission makes a car a hydraulic hybrid.

There apparently are a few experimental hybrid locomotives used as switching engines. And in some places in Europe (I remember seeing one in Finland some years ago), there are hybrid diesel-electric systems that pull power from overhead wires when available, but run on the diesel engine otherwise.

[njlou]

Originally Posted by jamesqf

Not so. The electric part of a standard diesel-electric locomotive is just a transmission, so calling one a hybrid is like claiming an automatic transmission makes a car a hydraulic hybrid.

There apparently are a few experimental hybrid locomotives used as switching engines. And in some places in Europe (I remember seeing one in Finland some years ago), there are hybrid diesel-electric systems that pull power from overhead wires when available, but run on the diesel engine otherwise.

Please do some research. start with: Diesel-electric locomotive engines & how they work

or google for additional information
The diesel electric technology is VERY old however with newer technology such as computer controls they are getting more efficient.

[jamesqf]

Originally Posted by njlou

Please do some research. start with: Diesel-electric locomotive engines & how they work

Do what research? That article says "...the diesel-electric uses a diesel engine to drive an electric generator, which then supplies the current to traction motors, which are geared directly to the locomotive's wheels", which is exactly what I said. The electric part is just a transmission. Nothing hybrid about it at all.

If you want to see examples of actual hybrid locomotives, look here: Hybrid locomotive - Wikipedia, the free encyclopedia or here: GE Ecomagination: Hybrid Locomotive

[SmartTrucker]

"They have (little) pollution controls"

Train engines have little pollution controls as compared to highway trucks and it's a gap that gets bigger and bigger every year or two with the government piling on more and more emission controls.

What's the governments way of making trucks green?

Hey let's put this EGR thing on these trucks and it'll make them run a lot hotter and burn this bad stuff off.

So how do they make them burn excessively hot? Why by using up crazy amounts of diesel fuel now and again to clean out the new fandangled particulate filter they come with. Yes because refining diesel doesn't pollute??

\rant off

[instarx]

Originally Posted by jamesqf

Not so. The electric part of a standard diesel-electric locomotive is just a transmission, so calling one a hybrid is like claiming an automatic transmission makes a car a hydraulic hybrid.

That makes no sense. A generator is not a transmission. A motor is not a transmission, wiring to connect the two is not a transmission. Frankly, I don't know if there is a transmission between the drive motor(s) on a locomotive and the drive wheels, but even if there were it would be mechanical.

[RH77]

Originally Posted by instarx

That makes no sense. A generator is not a transmission. A motor is not a transmission, wiring to connect the two is not a transmission. Frankly, I don't know if there is a transmission between the drive motor(s) on a locomotive and the drive wheels, but even if there were it would be mechanical.

Instarx is correct in the assumption that locomotives are hybrids...

They are "Series" or "Serial" hybrids. The ICE turns a generator that produces electricity for electric traction motors that turn the axles through gears. These motors are pre-geared from the factory. Locos used for higher-speed operation between terminals are geared differently than those used to shuffles cars in railyards. The amount of torque involved would make "shifting gears" too strenuous on components, so the ratio is fixed. With the current technology, railroads are required to purchase models with pre-configured gear ratios.

To spare brake linings, overheating, and a potential runaway condition, many of these locomotives have the ability to switch their motors into generators for "Dynamic Braking". When activated, the system forces the motors to become generators themselves, in-turn creating their own electricity and producing a braking effect. The spent electricity is dissipated as heat in large, air-cooled, resistor grids. The Diesel engine is accelerated to increase the resistance through the generator.

The advent of AC traction motors has made it possible to to manage larger loads in one locomotive unit more efficiently and accurately (the vast majority of these motors have been DC over the last 60 years). Depending on your location, you may see 2 engines at the front, and one "pusher" at the rear of a coal train. These are newer, carefully configured AC units designed to transport an abnormally heavy configuration.

Hybrid cars like the Prius are "Parallel" hybrids, where the energy can be stored in some fashion and make use of a transmission-like device to change gear ratios and/or the power source for propulsion, and are preferred for efficiency in vehicle operation.

There are other hybrids (hydraulic/electric, etc.) that can be compared.

RH77

[jamesqf]

Originally Posted by instarx

That makes no sense. A generator is not a transmission. A motor is not a transmission, wiring to connect the two is not a transmission.

Certainly it makes sense. Is automatic transmission fluid a transmission? Are the various parts inside a torque converter a transmission? No, but you put them all together, and they BECOME a transmission.

What's the purpose of a transmission? To transmit the power developed by the engine to the wheels, no? That job can be done with a bunch of gears and a friction clutch, in which case you have a mechanical transmission. You can do it with fluids and a torque converter, as with an automatic transmission. Or you can do it with an electric generator & motor, as with the locomotive. EXACTLY the same task is being accomplished.

Now if a locomotive were to be a hybrid, it would have to have two (or more) SOURCES of power, as do the hybrid switching locomotives that I linked to, which have diesel engines and battery storage. The standard diesel-electric locomotive only has the diesel engine transmitting power to the wheels via the electric system, so it's not a hybrid.

[jamesqf]

Originally Posted by RH77

...many of these locomotives have the ability to switch their motors into generators for "Dynamic Braking". When activated, the system forces the motors to become generators themselves, in-turn creating their own electricity and producing a braking effect. The spent electricity is dissipated as heat in large, air-cooled, resistor grids.

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 :-)

[instarx]

Originally Posted by jamesqf

Certainly it makes sense. Is automatic transmission fluid a transmission? Are the various parts inside a torque converter a transmission? No, but you put them all together, and they BECOME a transmission.

What's the purpose of a transmission? To transmit the power developed by the engine to the wheels, no?

No, it makes no sense. You are confusing THE transmission of power with A transmission (gearbox). One is a process, the other is a device. True, power is "transmitted" from engine to drive wheels in a locomotive, but that doesn't make a locomotive a transmission. LOL