The engine listed here as Berrenburg appears as “Berrenberg” in Hiscox’s historical reference. Its two opposed cylindrical pistons pass through cavities in a separate synchronized rotary valve. The calculator estimates mean shaft output from entered effective pressure, displacement and mechanical efficiency.
Berrenburg Rotary Engine Interactive Calculator
Estimate mean torque, work and power while viewing the opposed-piston rotor and its synchronized cavity valve. The four original performance inputs are retained.
Equation Used
- Entered displacement includes the complete working cycle per shaft revolution.
- Mean effective pressure already represents the pressure-work cycle.
- Mechanical efficiency converts indicated work to mean shaft work.
- The visualization is slowed; cavity profiles are illustrative clearance envelopes and not a build drawing.
The original torque/work relationships and horsepower conversion remain. The mechanism depiction is corrected to Hiscox movement337; no unsupported service-life, wear-rate or commercial-performance claims are retained.
Two pistons and a synchronized cavity valve
Hiscox’s movement337 describes two intersecting cylindrical shells. Rotor D carries two cylindrical pistons on opposite sides. They enter corresponding cavities in rotary valve E. Equal external gearing synchronizes the shafts. Hinged supplementary sectors on the pistons improve contact with the outer shell.
The rebuilt cutaway follows those distinguishing features. The main rotor and cavity valve turn at equal and opposite angular speeds. A separate small end view identifies the timing gears. The previous sliding-abutment explanation described a different arrangement and has been removed.
The pocket outlines are generated from an illustrative swept-clearance envelope of the piston pair, not from recovered production dimensions. The small sectors indicate the historical sealing feature. Port locations are schematic; this animation does not calculate steam admission, cutoff or leakage.
A historical rotary steam-engine arrangement
The historical drawing is useful for studying how a rotary abutment can accommodate passing pistons. It does not provide a tested operating envelope for a modern machine. This page makes no claim about a particular surviving installation, service life or commercial efficiency.
Mean work, torque and power
Mean effective pressure multiplied by total effective displacement per revolution gives indicated work per revolution. With psi and in³, divide by12 to express work in ft·lbf, then multiply by mechanical efficiency η as a fraction. Mean shaft torque is that shaft work divided by2π.
Power follows mean torque and speed. The retained calculation uses hp = T × rpm /5252, with torque in ft·lbf; 5252 is the conventional rounded conversion constant. Kilowatts use0.7457 kW per horsepower. These are cycle-averaged outputs, not the torque at the instantaneous pictured rotor angle.
Inlet pressure alone cannot replace mean effective pressure without a pressure-volume analysis. The displacement input must count every working event in one shaft revolution; do not add another factor for the two visible pistons.
Worked mean-output example
At150 psi mean effective pressure,50 in³ total effective displacement per revolution and75 percent mechanical efficiency, calculated shaft work is150 ×50 ×0.75 /12 =468.75 ft·lbf per revolution. Mean torque is74.6 ft·lbf. At300 rpm, the retained rounded conversion gives approximately4.26 hp or3.18 kW.
These values follow the entered assumptions. The geometry illustration does not establish that the historical engine achieved them.
What the model leaves open
The pressure-work relation is useful for comparing assumptions, but it does not resolve sealing losses, the pressure history in either shell, structural loads or contact stress. Mechanical efficiency is entered rather than predicted. Real pocket, piston, sector and port geometry would be needed for those analyses.
Rotary-engine questions
Why do the shafts turn in opposite directions?
The reference specifies equal external gearing. A pair of equal external gears gives equal angular speed in opposite directions.
Does changing displacement resize the drawing?
No. The scalar displacement does not uniquely determine rotor diameter, axial width or port timing. The drawing is illustrative while the work and power outputs use the entered displacement.
Is mean effective pressure the inlet pressure?
No. Mean effective pressure represents net indicated cycle work divided by effective displacement. Admission, expansion and exhaust conditions affect it.
Are the cavity outlines manufacturing profiles?
No. They are a schematic swept-clearance construction for showing the passing piston pair. The original dimensional, sealing and port details have not been reconstructed.
Historical reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, movement337 on printed page93, identifies the “Berrenberg” rotary engine and its opposed pistons, cavity valve, equal external gearing and hinged supplementary sectors.
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