auto maintenance January 14, 2018

Diesel Cars

This is an update of an article I originally entitled “DIESELS ARE DEAD,” which was published over a decade ago in a response to the perennial claim that diesels are about to make a major surge in the U.S. car market. I still don’t believe this is likely to happen, in spite of the fact the manufacturers, particularly the European ones, have made great strides in getting diesel engines to mimic the behavior of gasoline engines – at great expense, I might add.

History and theory of operation
The diesel engine was invented by a German man named (you guessed it) Diesel. Unfortunately for him, he disappeared while attempting to travel to England on the eve of World War I. It is believed that the German Secret Police had something to do with this.

The diesel engine is much simpler in theory than the gasoline engine. Whereas a gasoline engine draws in fuel and air and ignites it with a spark plug, causing the fuel to burn, a diesel engine draws in diesel fuel (a very light oil) and compresses it until it gets so hot it simply explodes, driving the piston down, creating that distinctive noise diesels make. This eliminates the complex and fickle ignition system that had to provide just the right spark at just the right time, constantly varying in an era when these things had to be done mechanically. The fuel system was also simpler, as diesels do not require a tremendous variation in the amount of fuel compared to engine speed and load.

So why did the gasoline engine become dominant in cars? First, in spite of the need for an ignition system, it was cheaper to build and easier for the average person to operate. In the early automotive era of manually cranking a car to start (literally putting a hand crank in the front of the engine), cars had relatively low compression (4 to 1). Even at that low compression you could break your arm if the engine kicked back. Diesels require 20-to-1 compression to get the heat to ignite the fuel. You would have needed an effective electric starting system in a 6-volt era. And even if you had the electric starter, starting a diesel in very cold weather can be difficult even today.

Second, in order to withstand the 20-to-1 compression and the battering of fuel exploding, a diesel engine has to be built very strong out of very good metals costing several thousand dollars more to make than a comparable gasoline engine in today’s dollars.

Third, the operating characteristics of a gasoline engine, such as rapid acceleration and wide rpm range, made it more suitable for the way cars and light trucks are used. Diesels have a narrow rpm band at which they produce power, so if you just needed to drive at a steady 60 miles per hour they were perfect. But diesels did have a use. The engines produce lots of torque (pulling power), making them perfect for large trucks. A company buying a fleet of trucks could easily see the benefit of a powerful engine that could last hundreds of thousands of miles, and the awkward driving characteristics were not a problem for a skilled driver, especially at a steady 65 miles per hour. A big truck could carry a tank of special gas for cold-starting, and once the truck was started it could stay running until it reached home. So cars and light trucks were gasoline-powered, and heavy trucks and locomotives used diesel engines. As intended by the heavens.

A different evolutionary path
If you studied dinosaurs, you know that all land masses on Earth were once joined, but as the continents drifted apart, the dinosaurs took different evolutionary paths. So it was with cars. At the end of World War II, Europe was a wretched impoverished place. Most governments favored mass transit and collected huge taxes on gasoline, creating a bias towards diesel engines. And coming out of the ruins of war, people weren’t likely to be too picky about performance (anything beats walking), so diesels, in spite of their high cost and low performance, became popular. In the seventy years since then, diesel-engine cars have evolved in Europe that are smoother, more powerful, easier to drive, and somewhat quieter. But the cost for those improvements is great, and you could avoid it all by simply burning gasoline. So it is unlikely diesels will become popular in American cars and light trucks, nor would it be desirable.

Then there is the problem of cultural memory. The number 1984 may evoke thoughts of George Orwell’s forecasts of Big Brother and totalitarian government. But actually it was the peak year for diesel car sales in the U.S. Now Americans may have short political and cultural memories, but when you screw them as consumers they don’t forget. Diesel had been growing steadily in popularity among the American automakers, not as an efficiency tool, but as an emissions evasion tool. (Diesels were not subject to the same emissions scrutiny that gasoline cars were). Suddenly every car sold in America was available with diesel. For the small cars, GM and Ford simply bought diesels from their Japanese partners and cobbled them into existing cars. The Escort, Tempo, and Chevette were all available with diesel. At best they were sluggish, forgettable cars. At worst they became nightmares no one could keep running or start.

Diesels are dead
But the mother of them all was GM, with their diesel full-size cars. GM took an Oldsmobile gasoline engine and “converted” it for diesel use. The conversion evidently involved removing the “Unleaded Fuel Only” sticker from the gas cap and putting a “Diesel Fuel Only” sticker in its place. They sold a lot of them, they wouldn’t start, and Lord help you if they did, because that old 307 block just wasn’t up to 18-to-1 compression. They cracked, blew, exploded, or just lay there. Entire industries were created yanking out Olds diesel engines and replacing them with gasoline engines.

Then the EPA announced that if diesel sales continued to grow, emissions standards would have to be applied, which sort of defeated the purpose as far as the American manufacturers were concerned. American manufacturers ran away from diesels quicker than the German Army fled the Caucus region after Stalingrad.

Return of the living dead                    
Diesels have since made a slow recovery. The addition of electronic engine controls, catalytic converters, and a mystery fluid (believe me, you want it to remain a mystery) that is sprayed into the exhaust from a special holding tank has solved the emissions problem. But the expense problem has only grown. To get any level of acceptable performance out of a diesel, a turbo charger is required, and that adds expense to an already expensive engine.

With fuel prices looking low for the foreseeable future, there’s not much push for diesel cars. Still, if I were buying a truck for any kind of work use, towing or plowing or an extremely large SUV, I would certainly consider a diesel engine.

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