Compressed Air Engine using Slider Crank

Before electric motors took over, compressed air drove real machinery — and the slider-crank engine that converts a piston's push into rotation is the same mechanism at the heart of every internal-combustion engine. This project rebuilds that idea as a clean student prototype: instead of fuel and spark, a double-acting pneumatic cylinder fed by shop air drives the piston, a solenoid valve times the air admission to each stroke, and the crankshaft and flywheel turn it into smooth rotary motion. The student assembles the mechanism, times the valve, measures RPM and brake power, and learns first-hand why air engines are simple and clean but inefficient — the thermodynamics of expanding air is unforgiving, and the report discusses the measured numbers honestly instead of hiding them.

1. Shop air at up to 8 bar enters the FRL unit, which filters, regulates (4–6 bar working range) and lubricates it.
2. The 5/2 solenoid valve, timed to crankshaft position, admits air to one side of the double-acting cylinder while exhausting the other.
3. Air pressure drives the piston through its stroke; the connecting rod pushes the crank pin, converting linear motion into crankshaft rotation.
4. Half a revolution later the valve switches ports, pressurizing the opposite side for the return power stroke.
5. The flywheel stores energy through the stroke and returns it at dead centres, keeping rotation smooth; the tachometer reads steady-state RPM.
6. With the rope brake applied, the buyer measures torque at several pressures and speeds, computing brake power (P = 2πNT/60) and air consumption per run for the report's honest efficiency discussion.

Tech stack:

• Double-acting pneumatic cylinder (~32 mm bore class)
• 5/2-way solenoid valve with crank-timed switching
• Machined crankshaft, connecting rod, crosshead assembly
• Flywheel (cast/machined)
• FRL unit + pressure regulator (4–6 bar working range)
• Digital non-contact tachometer, rope-brake dynamometer
• MS fabrication frame with bearing pedestals

• [Double-acting pneumatic cylinder] A standard pneumatic cylinder (bore ~32 mm, stroke ~100 mm class) admits air alternately to both sides of the piston, giving a power stroke in each direction — twice the work per revolution of a single-acting layout.
• [Slider-crank mechanism] A machined crankshaft, connecting rod and crosshead/piston assembly convert the linear stroke into rotation — the exact mechanism the student studies in theory of machines, made tangible.
• [Timed solenoid valve] A 5/2-way solenoid valve, switched in sync with crank position, routes air to the correct cylinder port each half-stroke; valve timing is adjustable so the student can experiment with its effect on running.
• [Flywheel] A cast/machined flywheel smooths the pulsating crank torque into steady rotation and carries the engine through dead-centre positions.
• [FRL unit and regulator] A filter-regulator-lubricator conditions the shop air and sets the 4–6 bar working pressure; the regulator lets the student map RPM against supply pressure.
• [RPM measurement] A digital tachometer (non-contact) measures crankshaft speed directly, giving the primary performance number of every test run.
• [Brake-drum power measurement] A simple rope-brake dynamometer on the output shaft lets the buyer measure torque and compute brake power from their own readings — no pre-claimed power figure.

• Working compressed-air engine (cylinder, slider-crank, flywheel, valves, FRL, frame)
• Digital tachometer and rope-brake dynamometer setup
• Build and timing manual: assembly, valve-timing procedure, test protocol, power-calculation worksheets
• Project report PDF (background, slider-crank kinematics, pneumatic circuit, buyer-run test results, efficiency discussion)
• PPT presentation for final review
• Viva Q&A preparation document (slider-crank analysis, dead centres, valve timing, air-engine thermodynamics)
• Setup and safety guide (pressure limits, hose ratings, eye protection, leak checks)

• Air engines are inherently inefficient — expanding air cools and most input energy is lost; the report discusses the measured efficiency honestly and no power figure is pre-claimed.
• A shop compressor is required and is not included; the engine cannot run without a 6–8 bar air source.
• The prototype is noisy (exhaust pulses) and the exhaust air carries oil mist from the lubricator — run it in a ventilated workshop, not a classroom.
• Speed and torque depend on supply pressure, hose length and valve timing; results vary between setups and must be reported with their test conditions.
• This is a demonstration prototype, not a practical power source — it will not run a vehicle or a generator meaningfully.