How an Internal Combustion Engine Works, Built Up From First Principles

Bartosz Ciechanowski’s interactive explainer reconstructs the internal combustion engine from scratch, starting with the simplest way to produce rotational motion — a hand crank that converts linear force into torque — and asking what could replace human muscle as the force source. The answer is controlled explosion. A cannon delivers a strong, directed push but wastes it: fire once and the projectile is gone. Swapping the cannonball for a piston tied to a crankshaft by a connecting rod solves this, since the piston is bounded within a cylinder and returns for another push as the shaft keeps turning.

From there the piece derives the four-stroke cycle. Liquid fuel replaces solid powder so intake can be metered by valves, and openings at the top of the combustion chamber are gated by intake and exhaust valves with a spark plug between them. The four strokes — intake (fuel-air drawn in), compression (mixture squeezed to raise thermal efficiency), power (spark ignites, expanding gas drives the piston and turns the crankshaft), and exhaust (spent gas vented) — take two full crankshaft revolutions per cycle. A single cylinder produces power only about a quarter of the time, which is why the article then scales up to a realistic inline-four car engine.

The back half walks through real hardware: the cast engine block with its four cylinders, stiffening ribs, a flat deck for the head, and hollow passages for coolant to carry combustion heat away; and the crankshaft, with five on-axis main journals, four off-axis rod journals, and the connecting webs between them. Multiple cylinders smooth out the otherwise lumpy, vibration-prone power delivery. The value of the piece is pedagogical — its draggable, animated cross-section demonstrations make an everyday but genuinely intricate machine legible by building each part up from the problem it solves.