Exam Question

### (a) Purpose of Tie-Rods in a 2-Stroke Main Engine (6 Marks)
Tie-rods, also known as tie-bolts, are critical structural components in large, slow-speed 2-stroke marine diesel engines. Their primary function is to hold the main engine structure together under high compressive stress to counteract the tensile stresses generated by combustion forces.
* **Counteracting Firing Forces**: The peak firing pressure inside a cylinder can exceed 200 bar. This immense force acts upwards on the cylinder cover and downwards on the piston, but via the connecting rod and crankshaft, it exerts a significant upward tensile load on the engine structure (bedplate, A-frame/entablature, and cylinder block/jackets).
* **Material Limitations**: The main structural components (bedplate, A-frames, cylinder blocks) are typically made of cast iron or fabricated steel. Cast iron is exceptionally strong in compression but relatively weak in tension. If subjected to the high, cyclical tensile forces from combustion, these components would be prone to fatigue cracking and catastrophic failure.