Heat Engines

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Everything that moves of itself is powered by an engine. Humankind, in our wisdom, invented engines. There are essentially four common kinds of engines (in terms of operating principle) adaptable to serve most of our needs. Of those four only two are significant in most people’s lives, heat engines and electric motors (engines). Some of the machines we operate on a regular basis are powered by electric motors; virtually all others are powered by heat engines.

Heat engines drive cars, trucks, jet planes, rocket ships, motorcycles, lawnmowers, tractors, atomic submarines, bulldozers and chainsaws. If it has a fuel tank it’s a heat engine. If it runs on nuclear power under human supervision it is, in most cases, still a heat engine.

Electric engines, electric motors, are our other common source of motion. Air conditioners, electric drills, Mixmasters, those other chainsaws, subway trains and Chevy Bolts are driven by electric motors.

If you come full circle even most electric motors, most of the time, ultimately draw their power from heat engines, because that’s how most electricity is generated. Coal, oil, natural gas, or nuclear power plants are big heat engines spinning generators. The home generators that get us and our neighbors through power outages are small heat engines spinning small generators. Heat, moving from hot to less hot, causing motion. Hydropower, wind power, and solar electric panels generate electricity without the intervening use of some heat engine.

There is an amazing amount of science related to heat engines, but strangely enough the engines came first and the science followed along to explain them. So leaving aside the science for now, here’s how a heat engine works:

You generate a bunch of heat and you stuff it into a confined space.
Somewhere near to that space it is cooler. The heat forces its way from the hot space to the cooler space, and whatever is in the way has to move.

Early steam engines generated the heat with fire and used steam to move the heat into a closed space. There was a piston somewhere in that space, and on the other side of the piston it was cooler. The piston had to move as the heat pushed its way over to the cooler spot.

That’s it. In every heat engine everywhere: Heat moves some object in order to reach a place with less heat. Energy moves from areas of higher concentration to areas of lower concentration. It is an expression of the second law of thermodynamics: heat flows spontaneously from hotter to colder bodies and never the reverse.* Your pizza gets cold and your beer gets warm.

With early steam power they had a problem where sometimes the heat would push its way out to the cool spot without going through the cylinder and piston. If it couldn’t escape any other way the heat blew right through the walls of the boilers, often killing large numbers of people. Heat will not be denied.

One rarely hears our system described in these terms, but this is literally and exactly what is happening. Heat is moving. The fire, the steam, the Ultra High Test Scientifically Improved gasoline – all that is secondary. The heat is the thing. The energy.

Look at how a car works: no firebox, no steam, no boiler. We just squirt some gasoline into the cylinders and the car magically goes, right?

Well, not exactly. It’s a heat engine. We squirt in some gasoline and we set it on fire. The fire generates heat which, in accordance with the laws of thermodynamics, just has to go to the cool place, which is outside your tailpipe, On the way there the heat pushes a bunch of pistons – because remember, anything that gets in the way of the heat’s journey has to move – and the piston bone attach to the thigh bone, and the thigh bone attach to the tire bone, and down the road we go.

A jet plane works the same way, except instead of pistons they’ve got a big fan. Heat moves, the fan spins, air moves, and all things  being equal and opposite reactions the jet plane takes people to Frisco. Riding on heat engines. On rocket ships the heat squirts right out the tailpipe and the whole rocket ship moves.

Heat moves from a hot place to a not-as-hot place and the 21st Century goes round and round.

What all these heat engines have in common is that the amount of heat equals the amount of power. Oh, there are fancy theorems and proportions and this and that, but the basic fact is, the more heat the more power.

Build a bigger fire and the steam engine runs faster. Step down on the gas pedal and your car goes faster. Push forward the throttle on your tractor and your plow cuts either deeper, faster, or both in your field. The more heat the more power.

Not Richmond. I couldn’t find any pics of the local event. CA somewhere.

Which brings me to a related point: the earth is a heat engine. It’s harder to see the confined spaces where the heat is by looking out your window but they’re there. They don’t have shiny fins on them and say Harley Davidson, but they’re just as real. We call them by names like high pressure area and jet stream, but they are essentially just heat stuffed into restrained areas. It operates on the same principle as your car engine: heat moves from the hot place to the cooler place, and whatever is in between has to move.

Everything on Earth moves, from hummingbirds to mountains, and heat drives it all, but we particularly notice the motion of air and water. We know it as weather. Or climate, depending on the frame of reference.

So that’s why earlier this week a spring breeze blew down a quarter mile of electric poles in my home town, and tore down several buildings. There is more heat than there used to be. Our heat engine has more power. Somebody pushed down on the gas pedal. It’s never going away, not in a human scale of time.

We call it global warming.


*Direct quote from Wikipedia article.

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