An enclosed high-speed steam engine connects its piston to the crankshaft through a connecting rod and supplies oil to the moving bearings. Explore the slider-crank motion and calculate cycle period, mean piston speed and rod angularity.
High-Speed Engine Slider-Crank Calculator
Enter piston stroke, connecting-rod/crank ratio and shaft speed. The worksheet reports exact cycle timing, mean piston speed and maximum ideal rod angle; it does not rate the engine or specify lubrication pressure.
Equation Used
- The mechanism is an in-line rigid slider crank with zero offset.
- Stroke equals twice crank radius and the entered rod/crank ratio exceeds one.
- Shaft speed is constant and one revolution equals one piston cycle.
- Steam pressure, indicated power, valve events, masses, balance, bearing loads, oil pressure, friction and safe speed are excluded.
Stroke, rod/crank ratio and shaft speed determine the ideal motion quantities shown. The green oil loop illustrates circulation only; oil pressure and flow require machine-specific data.
Enclosed slider crank and circulated oil
The piston, connecting rod and crankshaft form a slider-crank mechanism. Historical high-speed engines enclosed the moving gear; surviving Belliss equipment and period descriptions also document forced oil circulation to bearings.
The animation solves the in-line rigid slider-crank position at every phase. The green oil loop identifies circulation topology only, not pressure or flow.
Calculating slider-crank motion
Use the worksheet to convert an entered stroke and rpm into cycle period and mean piston speed and to inspect rod angularity. Actual engine operation requires maker drawings, valve setting, balance, bearing and lubrication data.
Cycle timing and piston motion
Mean speed averages the full out-and-back path over one revolution. In the speed equation, use stroke in metres to obtain metres per second; the calculator converts the entered millimetres. Instantaneous piston speed varies through the cycle.
Kinematic example
For 200 mm stroke, rod/crank ratio 4 and 500 rpm, crank radius is 100 mm, period is 0.120 s, mean piston speed is 3.33 m/s and maximum rod angle is 14.5 degrees.
Motion quantities and operating limits
Mean piston speed describes motion, not an operating limit. Bearing life, safe shaft speed and lubrication requirements depend on the engine's geometry, masses, materials, bearings, lubrication system and maker limits.
High-speed-engine motion questions
Is mean piston speed the peak speed?
No.
Does rpm determine required oil pressure?
No. The lubrication system is machine-specific.
Does the animation include valve timing or steam forces?
No.
Historical and kinematic references
- Science Museum Group, High Speed Engine with Forced Lubrication: 1891 Belliss enclosed stationary steam engine with dynamo and pressure gauge.
- MIT OpenCourseWare, Topics in Machine Elements: slider-crank loop equations and geometry.
- Encyclopaedia Britannica 1911, High-Speed Direct-Acting Engines: enclosed crankcases and forced lubrication in Belliss and Morcom engines.
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