Fundamentals of Internal Combustion Engines
What is tested
Fundamentals of Internal Combustion Engines tests engine terms, cycles, breathing, combustion and power relationships. You should be able to distinguish petrol spark ignition from diesel compression ignition and four-stroke from two-stroke operation.
Core rules
- Bore is cylinder diameter; stroke is piston travel between TDC and BDC. Swept volume = cylinder area × stroke. Compression ratio = (swept volume + clearance volume) ÷ clearance volume.
- Four-stroke cycle: intake, compression, power, exhaust, completed in two crankshaft revolutions. A two-stroke cycle has a power stroke each revolution but needs scavenging and careful port timing.
- Diesel engines draw air only, compress it to a high ratio, and inject fuel near TDC; ignition is by heat of compression. Petrol engines mix fuel and air and use a spark plug.
- Volumetric efficiency is actual air intake divided by theoretical swept volume. Restriction, poor valve timing or a dirty filter reduces it.
- Torque is turning effort; power depends on torque and speed. A governor controls fuel delivery to hold engine speed under changing load.
Worked example
A four-cylinder engine has a bore of 100 mm and a stroke of 120 mm. Area = π/4 × 0.100² = 0.007854 m². Swept volume per cylinder = 0.007854 × 0.120 = 0.000942 m³ = 942 cm³. For four cylinders, total displacement = 942 × 4 = 3,768 cm³, about 3.77 litres. The reasoning uses bore and stroke in the same units and multiplies by cylinder count; it does not include clearance volume.
Traps
Confusing displacement with compression ratio, saying a diesel engine has a spark plug, and counting a four-stroke cycle as one revolution. Another error is treating rated horsepower as the same as drawbar horsepower; the latter is measured at the hitch and includes transmission losses.