Wednesday, January 30, 2008

Knock Knock

Theodore Sturgeon was very taken with his own four word description of the four stroke internal combustion engine: Suck, Squeeze, Pop, Fooey. I do admit, it was pretty clever. He then went and spoiled it by asking why a heat engine would need a cooling system, as if that were some sort of profound insight. Actually, automobile engines need both a cooling system to keep the engine block from overheating, and also a heat sink (which, in the case of automobiles, is the outside air), just like every other heat engine. “Heat engine” is, in that sense, a misnomer, since they are actually “heat flow engines,” and need for heat to flow from a higher temperature to a lower one in order to do work.

Still, Suck, Squeeze, Pop, Fooey. In the Suck (intake) stroke, the piston moves out from the cylinder head, pulling in external air in the case of diesel engines, or an air fuel mixture, in the case of gasoline engines. Both diesels and modern gasoline engines use fuel injection, but the diesel engine doesn’t do the injection until the top of the compression stroke.

For the Squeeze (compression) stroke, the intake valve closes and the piston rams the column of air/fuel toward the cylinder head. That compresses the air and heats it up. Compression ratios for gasoline engines go from about 10:1 as high maybe 18:1; for diesels, it’s more like 25:1, and diesels have to be much more ruggedly constructed to avoid being damaged by the higher pressures and temperatures.

At about the top of the stroke a spark plug triggers the ignition of the air fuel mix in a gasoline engine; in a diesel, the fuel is injected at high pressure, and ignition occurs because the air is already hot enough to ignite the fuel. The increase in temperature and pressure in both engines then pushes the piston away from the head. That’s Pop, or the power stroke.

Once the piston has reached its limit, the exhaust valve opens, and the final stroke (Fooey or exhaust stroke), clears the combusted gases from the system, which is now ready to start all over again.

All well and good. But it turns out that things don’t always work so well on the compression/ignition side of things for the gasoline engine. Because gasoline is easier to ignite than diesel fuel, sometimes the heat of compression alone will ignite the air/fuel mixture on the compression stroke, before full compression is achieved. That’s bad, because then some of the engine power winds up fighting itself, which reduces efficiency. Moreover, it puts more strain on the engine parts, and can damage the engine.

You could just back off on the compression when this sort of thing occurs, but then you’re also reducing efficiency, because lower compression ratios mean lower peak temperatures for your heat engine, and thermodynamics always wins in the end. So typically, you tune an engine to as close as you can get to the pre-ignition point.

Pre-ignition is also called “knock,” and it’s why we have “octane ratings” for gasoline. The name derives from an isomer of octane, 2,2,4 tri-methylpentane, and it’s defined as the ability to resist knocking of a fractional mixture of this octane isomer and n-heptane, heptane having a defined octane number of zero. The octane isomer has a good ability to resist premature detonation of an air fuel mix.

Real fuel mixtures are much more complex, of course, and the octane rating isn’t just a summation of all the individual components of the fuel. Instead, each component of gasoline has a “blending number” that better describes how it changes the octane rating.

Then there are “octane boosters,” things that are added to gasoline specifically to bring up the octane rating, despite your having put a lot of other low-octane trash into the fuel.

As higher compression IC engines began to really move in the 1920s, the need for octane boosters became apparent. Previously, when high compression engines were primarily for motor racing and aviation, specially blended fuels were used, but mass markets meant mass solutions.

There were two hydrocarbon octane boosters that were first suggested for fuels, alcohol and benzene. Alcohol was the better of the two. Benzene required almost 40% in fuel to really allow for high compression engines; ethyl alcohol only 20%. For a while, it looked like the fuel of the future was “Ethyl” meaning ethyl alcohol.

But then research showed that a number of inorganic elements could reduce engine knock. Iodine and selenium were too corrosive, but lead did the trick. Eventually, tetra ethyl lead (TEL) was developed, and it had the additional advantage that it was patentable, and thereby under corporate control for corporate profit. At first, TEL was blended in with gasoline at garages, or by the motorists themselves, but that wound up with a few too many cases of lead poisoning. After that, it was done at refineries, where it also produced lead poisonings, but those could be hushed up better. It also helped that the public health services helped to suppress the idea that there was a danger.

In other countries, particularly European countries, TEL had something of an uphill battle, because ethanol production was tied to farm policy. But with the weight of the U.S. Government behind it (and then, as now, U.S. foreign policy was at the disposal of those making money), TEL became the octane booster of choice.

Time passed and a lot of airborne lead got emitted into the environment. Fact is, tailpipe lead was in the form of very fine particles that stayed suspended for very long periods, under the right circumstances. Those circumstances were common enough so that detectable amounts of lead wound up in the Arctic even.

Then, in the 1970s, California passed some very tough clean air laws, and suddenly, automobile manufacturers were having trouble meeting them. In fact, the only way to meet them seemed to be to install catalytic converters on automobiles. (Actually, there was a while when lean burn engines such as the Honda CVCC could still meet the California regs, but, I mean really, you couldn’t hold Detroit to standards that the Japanese could meet, could you?).

Lead is toxic to people, but that’s nothing to the way it poisons catalysts. A single tankfull of leaded gasoline would reduce a catalyst’s efficiency by more than 50%. So unleaded fuel was born (fun fact: in Mexico, unleaded fuel is called Magna Sin).

The oil industry fought it, but maybe not as much as you’d think. I suspect that what they were doing was to manage the changeover, and to profit from it as much as possible. And they did profit, largely because the elimination of lead created a squeeze on refining capacity, and any time there is a capacity squeeze in the industry, profits increase, owing to the magic of inelastic demand. Sell less, make more money. Such a deal. They also get so squeeze out some independent refiners and distributors when expensive regulations take effect.

But the industry was also working on alternative octane boosters, again ones that weren’t ethanol, because, well, ethanol is evil, isn’t it? I mean, after all, demon rum.

Anyway, in the nick of time, they began producing MTBE, another oxygenated hydrocarbon, an ether instead of an alcohol, and it had all the good aspects of ethanol, with the added benefit (from an oil industry perspective) that it was made from natural gas.

Oxygenated fuels like ethanol and MTBE also have some interesting combustion characteristics in that they reduce the amount of carbon monoxide (CO) and nitrogen oxides that come from automobiles before the catalysts warm up (after they warm up you don’t even get enough CO to kill yourself in a closed garage). So some localities, like Denver, had been mandating oxygenated fuels in winter, in order to reduce their CO problem.

Then MTBE began to leak into the water supplies of some cities.

Refinery operations are a lot more sophisticated now than they were in the 1920s, and can generally turn almost anything into almost anything else – for a price. The oil industry has also become pretty good at using whatever comes their way, be it hurricanes, environmental regulations, or war to their advantage. I knew that the cheap oil prices in the late 1990s were transient and that there would be a big windfall coming, though I had no idea it would be built on so much blood. Even so, I didn’t put any money into oil stocks, because it just seemed like bad karma, and I can be such a prig sometimes.

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