Engine Types, Components, and Construction
Core concepts
Candidates should recognise the major reciprocating engine configurations and their components. Types include horizontal and vertical, single- and double-acting, simple and compound (two-stage) or triple-expansion, and uniflow versus counterflow exhaust arrangements. Uniflow engines exhaust at mid-stroke through ports, giving better thermal efficiency and more uniform cylinder temperature; counterflow engines exhaust through the same valve used for admission.
Principal components: cylinder and liner, piston and rings, piston rod, crosshead and guides, connecting rod, crankshaft, flywheel, stuffing box/gland, and the valve chest. Understand the function of each and typical failure modes: ring wear and blow-by, cylinder scoring, crosshead guide wear, crankshaft bearing wear, and gland leakage. Know the role of the flywheel in smoothing torque pulsation, especially in single-cylinder engines where torque is highly cyclic.
Traps in questions
- Assuming uniflow engines use exhaust valves; they use ports uncovered by the piston.
- Confusing crosshead engines (separate piston rod and connecting rod, gland seals the cylinder) with trunk-piston engines.
- Believing a flywheel increases power; it stores and releases energy to smooth speed variation.
- Missing that double-acting cylinders produce work on both strokes but still have a cyclic torque profile.
Worked example / rule of thumb
Coefficient of fluctuation of speed = (maximum speed - minimum speed) / mean speed. A larger flywheel moment of inertia reduces this coefficient. Rule of thumb: flywheel energy variation per cycle equals the area between the torque curve and the mean torque line; size the flywheel from that area and the permitted speed fluctuation.