Compression ignition may be ending in the age of environmentalism.
Diesel engines have been around for over 120 years, and in that time, they have proven to be the most efficient form of internal combustion engine for applications as varied as large cargo ships, trucks, trains and even airplanes. Compared to spark ignited gasoline engines, they are more thermally efficient and deliver lower fuel burn per horsepower. Like all internal combustion engines, however, increasing stringent environmental regulations and the need to reduce CO2 emissions means that their days are numbered in many applications. That’s especially true in light trucks. They’re still available, but won’t be for long.
But is there an alternative to diesel fuel? You can watch that video here.
And, access all episodes of End of the Line on Engineering TV along with all of our other series.
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Episode Transcript:
In 1893, Rudolf Diesel, a student at the Polytechnikum in Munich, Germany, attended the lectures of Carl von Linde, where he learned that steam engines as they then existed were capable of converting under 10 percent of the energy applied into work. The Carnot cycle promised much more efficiency, and in 1893 after years of work, Diesel published an essay called “Theory and Construction of a Rational Heat Motor.”
It was a flawed work, but by 1895, he better understood the basic concepts of compression ignition, and by 1897, a test engine operated at better than 26 percent efficiency. A year later, Diesel became a millionaire.
The engine he invented has powered everything from small cars to airplanes and ships, but in terms of units built, small diesels as commercial power units and vehicle engines made diesels the powerplant of choice for billions of people around the world.
It’s not hard to see why. With thermal efficiencies in the high 30 percent range for the very difficult passenger car applications, up to 45 percent for large truck and bus engines and over 50 percent for large two-stroke marine engines, diesels extract literally the most bang for the fuel buck, and that fuel historically was lower grade, cheaper to refine and lower in cost.
In North America, gasoline has always been cheap, and passenger car diesel engines have never really taken off, despite a major effort by German firms such as Mercedes-Benz and Volkswagen. They’re more efficient, yes, but they’re also more expensive to build, requiring very close tolerance machining in injection systems and higher durability in everything from the engine block to the crankshaft. For most people in North America, the extra savings just aren’t worth it.
With one exception: pickup trucks.
There’s a mystique about diesel engines in light trucks, a cult-like status that was really ignited by Chrysler’s introduction of Cummins straight six diesels in 1989 Dodge Ram pickup trucks. The Cummins 6BT engine was ridiculous overkill for a light truck application, but they were so popular that it took Chrysler three years to catch up with demand. People love them, primarily for towing capacity in three-quarter and one-ton applications.
Over the last decade or so, however, increasing pressures for improved fuel economy from light trucks has led to the introduction of smaller diesels for half-ton pickups. All of the big three offered them, in three-litre turbocharged form: a straight six for General Motors and V6s for Ford and Ram.
But in July of 2021, Ford’s Power Stroke three-litre V6 diesel was dropped. And in 2023, Ram will be withdrawing their three-litre EcoDiesel V6. General Motors has withdrawn their two-point-eight litre Duramax four-cylinder from the Colorado/Canyon pickups.
GM’s full-size pickups still have a small diesel option, for now. But I don’t expect it to last long. Why? Global political conditions have resulted in the extraordinary situation where pump prices for diesel fuel are substantially higher than gasoline, negating the fuel efficiency benefits of diesel power. And significantly, strict EPA emissions regulations requiring complex after-treatment involving urea injection and sophisticated computer control of combustion means engines that are expensive to buy, expensive to maintain and are very expensive to repair when they break.
In a word, for light trucks at least, diesel just isn’t worth it. And as batteries improve, I expect the same fate to both follow gasoline engines, as well.
Automotive technology is moving quickly now. Compression ignition is going away in light vehicles, and in a few years, the closest most of us will get to a diesel engine is aboard a cruise ship.
