Video narration
How can a diesel engine make power without a spark plug? Think of a bicycle pump: push its handle, and air gets packed into less space. Inside one cylinder, a piston moves between two valves; an injector sits above it, and a connecting rod joins it to the crankshaft. On intake, the piston drops as the intake valve admits air alone. On compression, it rises and squeezes the air. Near the top, fuel is injected. The key: compression heats the air enough to ignite the fuel-no spark. That pushes the piston down on the power stroke. On exhaust, it rises, driving gases out through the exhaust valve. The rod turns the crankshaft, changing up-and-down movement into rotation; one full cycle takes two crankshaft revolutions. So, no spark: the piston compresses air until it is hot enough to ignite injected diesel fuel.