One of the most popular HowStuffWorks articles is How Car Engines Work, which explains the basic principles behind internal combustion, discusses the four-stroke cycle and talks about all of the subsystems that help your car's engine to do its job. For a long time after we published that article, one of the most common questions asked (and one of the most frequent suggestions made in the suggestion box) was, "What is the difference between a gasoline and a diesel engine?"

If you haven't already done so, you'll probably want to read How Car Engines Work first, to get a feel for the basics of internal combustion. But hurry back! In this article, we unlock the secrets of the diesel!