Physics of Internal Combustion Engine

Four-Stroke Cycle (Otto Cycle)

1. Intake Stroke: piston moves to max volume and sucks in vaporized fuel mixture

2. Compression Stroke: piston moves to min volume, compressing the fuel mixture (increase in pressure, temp, density of fuel)

3. Power Stroke: spark plug ignites the fuel mixture; piston moves to max volume; power transmitted to crank shaft

4. Exhaust Stroke: piston moves back to min volume, exhaust valve opens to let exhaust out

Chemical PE, Translational & Rotational KE

High temperature and pressure converted to work

Thermodynamic Limit (Efficiency): 37%

Most engines: average efficiency of 18-20%

NOT Frictionless, Ideal Gases, Perfect Insulator

Direct Injection

—Direct Injection: better dispersion of air/fuel mixture, cylinder and piston cooler

—Better Fuel/Air Ratio (Increase Fuel Efficiency) Higher Compression Ratio (Extract more mechanical energy), Higher Power Output

Supercharging/Turbocharging

—Forced Induction (“Direct Injection” for Air) : compresses air and allows more fuel/air to enter the cylinder

—Turbocharger: uses exhaust gases to power a turbine to spin the compressor (no parasitic effect)

—Supercharger: uses a belt/chain connected to the engine’s crankshaft to power compressor (no lag)

—Increases mass flow-rate and burns more fuel; extract more useful energy per unit of fuel

—Increase Power and Efficiency