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.