Home▸Engineering & Materials▸Steam Engine

🚂 Steam Engine

Interactive reciprocating steam engine simulator. Watch the piston, slide valve and flywheel run a Rankine-style cycle while a live PV indicator diagram shows admission, expansion, exhaust and compression. Tune boiler pressure, cutoff and load.

Engineering & Materials3DAdvanced60 FPS

About this simulation

This simulator models a real single-acting reciprocating steam engine cycle: a slide valve admits boiler-pressure steam until the cutoff angle, the trapped steam then expands roughly as PV = constant while pushing the piston, the valve opens to release exhaust, and the returning piston compresses residual cushion steam — all converted to rotation through a crank-slider and smoothed by a flywheel. The enclosed area of the live PV indicator diagram is numerically integrated (∮p dV) every frame to compute real indicated power, mean effective pressure, torque, and thermal efficiency referenced against the Carnot limit.

🔬 What it shows

How a reciprocating steam engine converts the pressure of expanding steam into continuous rotary motion, and why the four phases of the cycle — admission, expansion, exhaust, and compression — trace out a closed loop on a PV diagram whose enclosed area is exactly the mechanical work done per cycle.

🎮 How to use

Choose a Preset (Full throttle, Economical, Heavy load, Condensing) or adjust Boiler pressure, Cutoff ratio, and Speed/load directly; switch Exhaust between Atmospheric and Condenser to change back-pressure; watch the piston, slide valve, and flywheel animate in sync with the live PV loop, and track Indicated power, Work/cycle, Thermal efficiency, Torque, Steam use, and MEP in Stats.

💡 Did you know?

Cutting off steam admission early (a low cutoff ratio) lets the trapped steam do extra work through expansion alone rather than continuously admitting fresh high-pressure steam — this single idea, exploited by engineers like James Watt, dramatically improved fuel efficiency over earlier engines that ran steam at full pressure for the entire stroke.

Frequently asked questions

What does the cutoff ratio control?

It sets the crank angle at which the slide valve stops admitting fresh boiler steam; a lower cutoff means steam is admitted for a shorter fraction of the stroke and then expands on its own for the rest, which improves thermal efficiency at the cost of some peak power.

Why is the area inside the PV loop meaningful?

The enclosed area of the pressure-volume diagram equals the net indicated work done by the steam on the piston over one complete cycle, since work is the integral of pressure with respect to volume change (∮p dV) around the closed cycle.

Why does switching to a condenser improve efficiency?

A vacuum condenser lowers the exhaust back-pressure well below atmospheric, which increases the pressure difference the expanding steam works against throughout the stroke, extracting more useful work from the same admitted steam and raising the thermal efficiency toward the Carnot limit set by the boiler and condenser temperatures.

What is the flywheel actually doing?

Since torque from a single-acting piston varies sharply through the cycle (strong during the power stroke, near zero elsewhere), the flywheel stores rotational kinetic energy during high-torque phases and releases it during low-torque phases, smoothing the engine's rotational speed into something close to constant.

Why does the compression phase matter at the end of the return stroke?

Compressing the small volume of residual "cushion" steam left in the cylinder before the next admission cycle gently decelerates the piston near the end of its stroke and pre-pressurises the cylinder, reducing the mechanical shock of the next admission and improving overall smoothness and efficiency.

⚙ Under the hood

A reciprocating steam engine with a slide valve, crank-slider and flywheel, plotting its PV indicator diagram. Set boiler pressure and cutoff and read indicated power, work per cycle and thermal efficiency.

EngineeringSteam EnginePV DiagramRankine CycleThermodynamics

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install