Saturday, August 29, 2009

A Global Warming Issue: Automotive Physics

Magical thinking is not the answer.

Repeatedly, people have been offered (and repeat online) assorted schemes for obtaining a fantastic new way to travel willy-nilly in their own vehicle. I have seen boycotts, additives and a variety of biodiesel, hydrogen and hydrogen fuel-cell devices claimed as The Solution to:

a) high prices
b) dependency on foreign oil
c) excessive profits by oil companies
d) pollution
e) Global Warming.

I'd like you to study the issues. That way, you can avoid supporting some liar seeking public office, as well as make some decent decisions of your own as to what to do with your own money.

You may be tempted to dismiss the whole Global Warming thing, simply because you don't want to be told you can't drive somewhere on a whim. Also, you might be confused, or think it is too much effort to understand what is being presented. It's simple, and it's obvious: cars are being driven today, and they have not been before in terms of Earth history, because the idea that one lives a distance away from one's work is a recent development. It is hotter in the city, where automotive and service energy is expended. You can see this for yourself in pictures from space, like this one. Yes, that light represents terawatts of energy expended on the surface of the Earth.

All of the gases generated by the combustion of fossil fuels, and all of the energy generated by those fuels and by nuclear plants is released directly into our living environment.

There are arguments about what to do about this - but those arguments do not change the physics of heat transfer at all.

Okay. What has this to do with cars?

You own a vehicle with an internal combustion engine. Whether it is gas or diesel, it performs a number of conversions to get the energy stored in a pound of fuel to do a certain amount of work moving the vehicle.

Let me digress for a minute.
Energy is a measure of the ability to do work.
Work is the expenditure of energy against a load.
Power is the amount of work done per unit time.
Weight is a force, derived from the action of gravity on mass.
Mass is a quantity of matter. Note that this doesn't depend on gravity at all.
Combustion is a particular kind of exothermic oxidation, where something combined with oxygen reacts and produces high temperature.
Temperature is a measure of the kinetic energy possessed by a substance. It is NOT "heat".
Heat is the flow of energy from a heat source to a heat sink as a result of their difference in temperature.

When your vehicle was built, it was designed with literally hundreds of compromises in place. The term, "blueprinting", known to gearheads, means simply to make an engine conform perfectly to the design document; in the process, the engine gains efficiency, which lets it make more power.

How does your engine make power?
First and foremost, your engine is an air pump. It must pump air to provide oxygen to the cylinders for combustion. Cylinders are a convenient place to combine fuel and air, burn them, and extract the resulting energy by allowing the expanding gases to act on the piston. As the piston is forced outward, an assortment of rods, levers and gears turns the fuel's kinetic energy into mechanical energy - the motion of hard car parts like wheels. The end result is to let you do four things:
1) Accelerate your mass to a convenient velocity
2) Overcome rolling resistance
3) Climb an incline, increasing your store of potential energy
4) Literally "pump" your car or truck through the wind.

Regardless of the fuel used, these tasks are FIXED by the configuration of your vehicle and the load it carries. You CANNOT dismiss any of these tasks and still move your vehicle.

What can you do?
Strictly speaking, you can only change the way you drive: go slower, avoid hills, drive less. The rate at which you do these things has a tremendous impact on energy consumption.

There is a spectacular table of obscure things at this link.
A compact car uses 94HP worth of chemical energy to yield only 20HP of mechanical energy - forward motion.
Wow. Why holler about a "miracle carburetor"? That's why - if only we could recover some of that wasted power!

Wait a minute. The engine design depends on the fuel supply. I CAN'T burn radically smaller amounts of fuel in that engine. Gasoline only burns within a few percentage points by volume, mixed with air.

Can you change fuels? Within limits set by the design of your engine, yes. Obviously, you are not swapping diesel and gasoline without destroying your engine; each engine is designed for its own fuel. Manufacturing variation may make a change of fuel brand or grade useful, but you have to take careful records to make sure you're not fooling yourself. ("Super" gasoline has anti-knock additives which suppress combustion. You actually get less energy from a gallon of it. Engines designed for it compensate for this in their design.)

So, can you get another engine in your next car?
What kind is best? The turbodiesel, until electric storage batteries are improved further. All of the technology is well established, and special manufacturing techniques do not include the high environmental costs of battery manufacture.

Take a look at this link about fuel.
So, forget alcohol. Notice the 66% yield vs. gasoline? Yes, that's a 50% mileage hit, along with a bunch of other problems with water entrainment and cold starting problems.
See the Hydrogen's 279%? No wonder people are clamoring about it.

But can you use it? No. Your engine's not designed for it; you can make it run, but not well. Your engine design is wasteful of heat. The production of H2 - the gas, hydrogen, occurs as a pair of atoms - is well known, but it's expensive to make.

Take a look at the Treadwell site, and you'll see the company which makes oxygen generators for the US Navy; I used to maintain two of them on a ballistic missile submarine. Their 7L16 model used about 65KW to make ~100CFM oxygen and therefore about 200CFM hydrogen. Now - go back to the link above and figure out how much H2 that really is. (Spoiler: about 18 grams)

In short, the lesson is clear: no matter what people say, you're not driving a Suburban or a pickup truck cheaply, because energy is not cheap. The production of energy depends on completely rigid natural laws. You have mistaken convenience for economy or efficiency, because manufacturers have made it so easy for you to zip around town in two-plus tons of steel. 
This bulk is not necessary, and when refinements arrive, you'll appreciate them. After all, a modern Corvette, complete with catalytic converters, will run away and hide from a Plymouth Superbird - while getting twice the mileage, running the A/C, displaying GPS info and listening to the stereo. 
Other examples abound!