Engine Room · Demo
One crank driver, three cycles compared — in step, side by side.
fires every 2 revolutions · 720° cycle
fires every 2 revolutions · 720° cycle
Right now every selected cycle is in the same phase.
Why these cycles differ
Two ways to light a fire, two ways to breathe. Petrol (Otto) sucks in fuel and air already mixed and lights it with a spark. A Diesel squeezes plain air so hard it gets hot enough to ignite fuel on contact — no spark plug at all. And the two-stroke squeezes the whole four-step dance into one revolution, firing twice as often as either.
Higher compression ⇒ more efficiency. For the ideal Otto cycle the thermal efficiency rises with the compression ratio as (with ). That is the core reason the high-compression Diesel is the most efficient engine here — in engineer mode, watch its PV loop tower over Otto’s as you raise its compression.
Different heat-addition shapes. Otto adds heat at almost constant volume — a sharp pressure spike at TDC. The Diesel adds it at roughly constant pressure while the piston already descends — the flat-topped loop. The two-stroke breathes through piston-uncovered ports with symmetric timing, so during scavenging some fresh charge escapes straight out the exhaust, lowering the trapped compression ratio below the geometric one.
Idealised models. These are air-standard Otto and Diesel cycles with simple smooth combustion — qualitatively right, and they respond correctly to compression ratio, but they are teaching idealisations, not engine-dyno predictions.