The diesel works on a very simple principle. Draw cold air into the engine during the piston’s induction stroke, shut valves, then compressed air extremely hot, so when fuel is injected into the cylinder, it h as no option other than to ignite. The resulting force drives the piston down on its power stroke, and we’re running. Because even the smallest amount of fuel will burn under these conditions, diesel can be controlled purely by the amount of fuel admitted to the engine, unlike a carburetor petrol unit which is controlled by air admission.
When the diesel fuel ignites, it pushes the cylinder pressure even higher, causing an audible knock as each cylinder fires the familiar diesel rattle. The high compression ratio needed to compress air in the cylinder, is part reason for the diesel’s fuel efficiency. But it puts extra mechanical strain on the engine, so generally, diesels are more heavily built.
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