In the U.S., diesel engines are often only associated with huge work trucks, whereas elsewhere around the globe, you’ll find the technology in tiny city cars. That might make you wonder: how different are these engine types, anyhow? Here’s Car Throttle with a little refresher to help you out.
The video below explains only the very basics of how diesels are different than gas motors. If you need a refresher, it’s worth a watch.
One of the differences between the two thermodynamic cycles, Car Throttle mentions, is that diesel engines squeeze their air charge much harder than gas engines do (that is to say, they have higher compression ratios), meaning oil burners require no spark plug to catalyze the combustion reaction, relying simply on—essentially—the ideal gas law (pressurizing air yields a higher temperature).
This higher compression ratio (which yields better thermal efficiency), combines with lower pumping losses (thanks to the lack of a throttle body) and the fuel’s higher energy density to give diesel vehicles significantly better fuel economy than their gasoline counterparts.
This high fuel economy is one of the main reasons why many Volkswagen owners miss the crap out of their cheating TDIs. Fifty MPG on a highway road trip is a beautiful thing any way you slice it. I’d miss that, too.