How Diesel Engines Work

By: Marshall Brain & Kristen Hall-Geisler  | 

Diesel Improvements and Biodiesel

During the big oil crisis in the 1970s, European car companies started advertising diesel engines for commercial use as an alternative to gasoline. Those who tried it out were a bit disappointed — the engines were very loud, and they would arrive home to find their cars covered from front to back in black soot — the same soot responsible for smog in big cities.

Since then, vast improvements have been made on engine performance and fuel cleanliness. Direct injection devices are now controlled by computers that monitor fuel combustion, increasing efficiency and reducing emissions. The sophistication of these computers turned out to be a double-edged sword, however, when we learned in 2014 that Volkswagen had been using the technology to cheat on emissions testing. The company had to buy back diesel vehicles it had sold with the promise of being a cleaner alternative fuel and pay billions in fines, and in some cases VW executives served jail time.


Since 2010, all diesel fuel in the United States has been ultra-low sulfur diesel (ULSD), which contains very little sulfur. Why does that matter? The devices that lower pollution and emissions from diesel engines can be damaged by sulfur, so having less of that element means cleaner-burning fuel. Modern catalytic converters for diesel engines are 90 percent efficient, so they don't stink or put out clouds of black smoke anymore.

But these changes might not be enough. Diesel still emits a lot of particulates that can harm humans and their environment, especially in dense urban areas. That's why several cities, states, and even countries have decided to ban diesel vehicles within the next decade or so.

You may have also heard of something called biodiesel. Is it the same as diesel? Biodiesel is an alternative or additive to diesel fuel that can be used in diesel engines with little to no modifications to the engines themselves. It's not made from petroleum; instead it comes from plant oils or animal fats that have been chemically altered. (Interesting fact: Rudolf Diesel had originally considered vegetable seed oil as fuel for his invention.) Biodiesel can either be combined with regular diesel or in some engines used completely by itself.

Diesel Engine FAQ

Who invented the diesel engine and when?
­I­n 1878, Rudolf Diesel was attending the Polytechnic High School of Germany when he learned about the low efficiency of gasoline and steam engines. He was inspired to create an engine with a higher efficiency, and devoted much of his time to developing a "Combustion Power Engine." By 1892 Diesel had obtained a patent for what we now call the diesel engine.
How does a diesel engine work?
The diesel engine uses a four-stroke combustion cycle just like a gasoline engine. The four strokes are intake stroke, compression stroke, combustion stroke and exhaust stroke.
What happened to the inventor of the diesel engine?
Rudolf Diesel was traveling from Belgium to England on a steamship in 1913. He disappeared and his body was found floating in the water. Diesel's death was ruled a suicide, but many people believe he was actually murdered.
Is a diesel engine better?
When working on his calculations, Rudolf Diesel theorized that higher compression leads to higher efficiency and more power. He turned out to be right — a gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1.
What type of engine is a diesel engine?
Just like a gasoline engine, a diesel engine is an internal combustion engine.

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