🔧 Spark Timing & Cylinder Pressure Curve

About this simulation

This model reimplements a single-cylinder spark-ignition engine's real slider-crank kinematics — piston position is computed from the finite connecting-rod-length equation, not a plain sine wave — and pairs it with a live cylinder-pressure-vs-crank-angle curve, drawn on the scrolling plot to the right of the cylinder. Combustion is modelled with a Wiebe-style mass-fraction-burned curve that starts at the spark event and releases heat over roughly 60° of crank rotation, exactly the way real engine simulation software approximates flame propagation.

How it works

• Compression & expansion — pressure without combustion follows a polytropic relation P·Vⁿ = constant as the piston moves through top dead centre (TDC).
• Spark advance — the plug fires a set number of degrees before TDC; because the flame takes time to spread, this timing shifts where the pressure curve peaks.
• Compression ratio — raises both the baseline compression pressure and how much extra pressure combustion adds, but also raises the risk of the unburned end-gas auto-igniting.
• Knock — if spark advance and compression ratio combine to push pressure past the auto-ignition threshold before top dead centre, the sim flags a knock event with a red flash and shockwave ring.

Controls

• Engine speed — crankshaft RPM; faster speeds compress the same burn duration into less real time.
• Spark advance — how many degrees before TDC the plug fires (0–40° BTDC).
• Compression ratio — cylinder volume at bottom dead centre divided by volume at TDC.
• ↺ Reset engine — restarts the crank angle and clears the pressure trace. Drag to rotate, scroll to zoom.

Did you know?

Formula 1 and other race engines run knock sensors that listen for detonation on every single combustion event and retard timing on that cylinder within one engine cycle — a feedback loop far faster than any human could react.