Electric Car Debate

[johnny watt]

http://tinyurl.com/qd77m

Edit;

This link brings you to U-Tube "Top Gear GM Highwire"

Johnny if you use 'Tinyurl' please give some indication of what the link is.

 

[suemarkp]

I think the main problem with hydrogen, whether fuel cell or you make a hydrogen engine, is the fuel itself. You can not mine hydrogen, you have to extract it from water or hydrocarbons (oh golly, another way to use oil or alcohol or nat gas). This takes a lot of energy. Hydrogen is difficult to move and store. Liquid would be better than gas, but I don't think hydrogen can be liquified very easily (very cryogenic). So its high pressure vessels. It is also a very small molecule, so it permeates easily and will disappear from its container.

I think the greenie approach is to use "free" solar to break down water into hydrogen and oxygen. But the distribution of hydrogen requires a massive infrastructure change. And then there will be some incident somewhere and we'll hear how idiot planners decided to use Hindenberg fuel for the masses...

 

[iwire]

It's not commonly known, but the reason electric traction motors are used for locomotives is because diesels don't work in that application.

Yeah that is a well kept secret

I have no idea why you are trying to make this all about blinding acceleration.

John Force's car has blinding acceleration but that does not make it a practical car for my Mom.

 

[iwire]

I think the main problem with hydrogen, whether fuel cell or you make a hydrogen engine, is the fuel itself.

IMO one of the problems with Hydrogen is people think it is a fuel like Gasoline when it is much more of storage medium like a battery.

 

[don_resqcapt19]

Bob,

IMO one of the problems with Hydrogen is people think it is a fuel like Gasoline when it is much more of storage medium like a battery.

I don't understand...hydrogen is a fuel gas.
Don

 

[iwire]

But as I understand it you do not just pump it out of the ground.

You have to make it, and the making of it uses more power than is returned.

 

[iwire]

Here is one version of the 'truth' about hydrogen.

www.popularmechanics.com/technology/industry/4199381.html?page=1

 

[tallgirl]

Yeah that is a well kept secret

I have no idea why you are trying to make this all about blinding acceleration.

John Force's car has blinding acceleration but that does not make it a practical car for my Mom.

I'm not -- I'm pointing out that what's required from gasoline engines isn't from electric motors.

Fer instance -- a 140HP 4 cylinder isn't producing 140HP when you're cruising down the highway in top gear at low RPMs. So why do you need 140HP for an electric motor? And a 140HP 4 cylinder isn't producing 140HP when you're pulling away from a traffic light.

What accelerates a car is not horsepower, it's torque, and electric motors are very efficient at creating torque. So, the OPs comment about a 140HP gasoline motor is irrelevant -- who cares how many horsepower a car needs out of a gasoline motor?

 

[iwire]

who cares how many horsepower a car needs out of a gasoline motor?

Who cares how much torque an electric motor can make when the power supply is inadequate?

 

[Bob NH]

"While it might be a symbolic gesture now, would it be if it caught on? Would folks realize that real WVO fuel can be used for pennies on the dollar compared to conventional fuel sources?"

Waste Vegetable Oil for diesel fuel will never be more than a symbolic gesture because there is not enough of it and it is not the best and highest value use for waste vegetable oil.

The total waste vegetable oil available in the US is estimated to be 0.13% of the diesel and heating fuel oil burned in the US. And there are other, more economically attractive, uses for waste cooking oil.

From Wikipedia:
Many advocates suggest that waste vegetable oil is the best source of oil to produce biodiesel. However, the available supply is drastically less than the amount of petroleum-based fuel that is burned for transportation and home heating in the world. According to the United States Environmental Protection Agency (EPA), restaurants in the US produce about 300 million US gallons (1,000,000 m?) of waste cooking oil annually.[1] Although it is economically profitable to use WVO to produce biodiesel, it is even more profitable to convert WVO into other products such as soap. Therefore, most WVO that is not dumped into landfills is used for these other purposes. Animal fats are similarly limited in supply, and it would not be efficient to raise animals simply for their fat. However, producing biodiesel with animal fat that would have otherwise been discarded could replace a small percentage of petroleum diesel usage.

The estimated transportation fuel and home heating oil used in the United States is about 230 billion US gallons (0.87 km?) (Briggs, 2004).

 

[George Stolz]

Who cares about any of this stuff?

Bob, I'd tend to agree with Julie's take on it - If a smaller sized electric motor would have the same sensation to the driver as a larger gasoline engine would, I think it's worth noting in the context of the discussion. If a car is unresponsive enough, even the most long-haired yada-yada would not drive it for fear of getting hit in the rear.

Heck, my dad is a firm believer that restrictor plates are what killed Dale Earnhardt, believe it or not.

The battery-weight issue currently dooms all the electric cars, from what I understand. Also, all decisions are currently dominated by money and politics, so it's not as though our little discussion here is going to develop into something tangible.

So, if someone dreams up the perfect car that's waiting for the perfect battery to supply it, that's interesting too.

 

[Bob NH]

What accelerates a car is not horsepower, it's torque, and electric motors are very efficient at creating torque. So, the OPs comment about a 140HP gasoline motor is irrelevant -- who cares how many horsepower a car needs out of a gasoline motor?

What accelerates a car is indeed horsepower. The transmission translates the horsepower to torque and speed. Those unlimited class dragsters need HORSEPOWER that is converted to the torque that is converted to the force required to accelerate them. Acceleration = Force/mass still applies.

Electric motors can deliver much more torque, over a wider range of speed, than an internal combustion engine.

Diesel driven trains use traction motors for the same reason. The generator, cables and motors comprise the transmission that distributes the engine power to the wheels. Can you imagine the gearbox that would be required to connect a diesel engine to all of those driver wheels, and deliver the necessary horsepower over the range of speed of a train?

 

[Bob NH]

Who cares about any of this stuff?

The battery-weight issue currently dooms all the electric cars, from what I understand. Also, all decisions are currently dominated by money and politics, so it's not as though our little discussion here is going to develop into something tangible.

So, if someone dreams up the perfect car that's waiting for the perfect battery to supply it, that's interesting too.

In the end, most of the decisions revolve around the conflict of politics and social engineering on one side, versus physical science, engineering and economics on the other side.

1. A diesel engine automobile will get you from Boston to Los Angeles and back with less fuel than a hybrid that will carry the same payload, but the politically correct hybrid gets a tax subsidy.

2. Drilling for gas off the Florida coast is more economical than importing LNG from the middle east, but Saudis don't vote in US elections.

3. Ethanol costs more than gasoline which could be extracted from ANWR, but farmers in the Midwest have more clout than Alaskans who want the drilling.

4. Nuclear power is more economical than wind and solar, which are expensive because of capital costs, but the anti-nuclear lobby makes more noise and the tax on the rest of us to subsidize solar and wind is not very noticeable.

 

[George Stolz]

And Dereck thought we could keep religion and politics out of this...

 

[iwire]

And Dereck thought we could keep religion and politics out of this...

LOL ....................

 

[tallgirl]

Who cares how much torque an electric motor can make when the power supply is inadequate?

Well, that's an entirely different issue!

 

[tallgirl]

What accelerates a car is indeed horsepower. The transmission translates the horsepower to torque and speed. Those unlimited class dragsters need HORSEPOWER that is converted to the torque that is converted to the force required to accelerate them. Acceleration = Force/mass still applies.

Correct -- a = F/m

What's the units for F? Torque. What's the F in the equation for the accelleration of a vehicle? Drive wheel torque minus drag divided by pound-mass. What's the equation for the velocity of that dragster? The integral of the equation for the accelleration with respect to time (a dt = v dv, solve that puppy and you've got your dragster). No where in there does shaft horsepower appear. At any instant in time, the accelleration of a vehicle (including when the accelleration is zero ...) is determined by an equation that doesn't have "horsepower" in it.

Horsepower sells cars because it can be made more cheaply in a gasoline engine than torque.

Horsepower = Torque * RPM / 5252

To make a "more powerful" car, manufacturers look for ways to extend the
upper limit of the torque curve because the torque is fixed based on engine geometry and combustion chamber pressures (it's the average of the circular integral of combustion chamber pressure times the lever arm, FWIW).

Here's the dyno slip from my car (just after the engine was broken in, before it was tuned or the exhaust replaced) --

That top line in the upper box is torque, the sloped line is horsepower. Everything I've done to my car since that dyno run has been about extending that torque curve so it remains flatter longer. The added horsepower comes along for the ride because of the fixed mathematical relationship between the two.

 

[Bob NH]

Correct -- a = F/m

What's the units for F? Torque. What's the F in the equation for the accelleration of a vehicle? Drive wheel torque minus drag divided by pound-mass. What's the equation for the velocity of that dragster? The integral of the equation for the accelleration with respect to time (a dt = v dv, solve that puppy and you've got your dragster). No where in there does shaft horsepower appear. At any instant in time, the accelleration of a vehicle (including when the accelleration is zero ...) is determined by an equation that doesn't have "horsepower" in it.

Horsepower sells cars because it can be made more cheaply in a gasoline engine than torque.

Horsepower = Torque * RPM / 5252

To make a "more powerful" car, manufacturers look for ways to extend the
upper limit of the torque curve because the torque is fixed based on engine geometry and combustion chamber pressures (it's the average of the circular integral of combustion chamber pressure times the lever arm, FWIW).

I respect electrical engineers. They do a lot more math than I had to do in civil and mechanical engineering. But we studied more mechanics.

The unit of force in a=F/m is pounds.

The unit of torque is ft-pounds.

The accelerating force is the torque at the axle divided by wheel radius, which is related to engine torque and gear ratio.

The unit of horsepower in the the same system of units is 1 HP = 550 ft-pounds per second.

You can make a large force with a very small engine, but as soon as it starts moving, you need power, as in horsepower or kilowatts or whatever kind of units you want to use.

The reason you want to extend the torque curve is because more torque at higher speed means more POWER.

As soon as the dragster or other car starts moving, you need that horsepower to sustain the acceleration.

To accelerate a car with a mass of 100 slugs (3217 pounds) at 1 g (32.17 ft/sec^2) requires 3217 pounds at the road surface + enough to overcome drag. If it is going 100 ft/second at that time, you need 3217 pounds x 100 ft/sec = 321700 ft-lbs per second, which is (321700 ft-lbs/sec)/(550 ft-lbs/Hp-sec) = 585 Hp.

That is why those dragsters have big engines (much horsepower), and why your typical family sedan has lousy acceleration when trying to pass on those 80 MPH speed limit Texas interstates.

 

[dereckbc]

Julie,

HP is relevant to the discussion. The reason is HP is an integral part of torque equations. You cannot have without the other. It is like saying you can have current without watts, not possible and violates laws of physics. T=(5252 x HP)/rpm. Without HP or rpm, you do not have torque period.

Here are some useful motor formulas at:
http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

 

[tallgirl]

I respect electrical engineers. They do a lot more math than I had to do in civil and mechanical engineering. But we studied more mechanics.

Well, I'm not an electrical engineer. What I know about engines is from building and racing them. I've had enough mechanical, marine and electrical engineering to be dangerous.

The unit of force in a=F/m is pounds.

The unit of torque is ft-pounds.

The accelerating force is the torque at the axle divided by wheel radius, which is related to engine torque and gear ratio.

The unit of horsepower in the the same system of units is 1 HP = 550 ft-pounds per second.

Correct so far.

You can make a large force with a very small engine, but as soon as it starts moving, you need power, as in horsepower or kilowatts or whatever kind of units you want to use.

As soon as the dragster or other car starts moving, you need that horsepower to sustain the acceleration.

What's the equation for the acceleration you want to sustain? Horsepower doesn't appear as a term. Horsepower is derived -- drive wheel TORQUE times drive wheel RPM / 5252.

To accelerate a car with a mass of 100 slugs (3217 pounds) at 1 g (32.17 ft/sec^2) requires 3217 pounds at the road surface + enough to overcome drag. If it is going 100 ft/second at that time, you need 3217 pounds x 100 ft/sec = 321700 ft-lbs per second, which is (321700 ft-lbs/sec)/(550 ft-lbs/Hp-sec) = 585 Hp.

Correct -- but the horsepower comes along for the ride. What you absolutely must have is a means of producing the force.

That is why those dragsters have big engines (much horsepower), and why your typical family sedan has lousy acceleration when trying to pass on those 80 MPH speed limit Texas interstates.

No, those engines are all about maintaining torque.

Go look at that dyno slip -- if I can get my engine to hold that 300 ft-lb line after the secondaries open at 4,400 RPM, I get more horsepower. Everything that can be done to that engine is going to be about holding that line because without changing from normally aspirated to forced induction, I'm not going to increase average combustion chamber pressure by all that much.

Back when I raced motorcycles, I had a bike where the power curve tanked around 8,000 RPM. The "fix" wasn't a bigger motor, it was a new valve train (titanium for the reciprocating upper end parts -- neat stuff) to move the "flat" part of the torque curve out to the right. Then, like magic, more horsepower is produced because that flat spot, which on my Corvette is 300 ft-lbs up until 4,400 RPM, allowed that torque to continue being produced up until somewhere around 10,000 RPM. That's a 25% increase in "horsepower", but a 0.00% increase in accelleration for every foot travelled up until the engine reached 8,000 RPM. Feel free to check my math on this example -- I used to check my math at the Gulfport International drag strip

I went out and google'd "torque wins races" and found this interesting website --

http://www.rbracing-rsr.com/orcadyno.htm

Give the article a good read.