With suitable block and line diagrams, describe the starting and reversing systems of a two-stroke diesel engine. Explain the importance of the running direction interlock provided on diesel engines.

[Block/line diagram notes: The starting system consists of: (1) air compressors; (2) air receivers; (3) a main starting air valve; (4) the air distributor; (5) the starting air valves on the cylinders; (6) the control system. The reversing system consists of: (1) the direction selector (ahead/astern); (2) the reversing mechanism (camshaft shift or electronic); (3) the interlocks.]

Starting system: The air compressors charge the air receivers to the working pressure (e.g. 30 bar). To start, the main starting air valve is opened and the air is admitted through the main line to the air distributor. The distributor, driven by the crankshaft, directs the air to the starting air valves of the cylinders in the correct order, turning the engine. When the engine fires, the starting air is cut off. The system has safety valves, drain valves, and a non-return valve.

Reversing system: To reverse the engine, the direction selector is set to ahead or astern. On a camshaft engine, the reversing mechanism axially shifts the camshaft (or rotates the cams) to bring the correct ahead/astern cam profiles into line, and the air distributor is driven in the reverse direction. On a camshaftless engine, the ECU switches the injection and valve timing and the firing order. The engine is then started in the new direction.

Importance of the running direction interlock:

The running direction interlock is a safety device which prevents the engine from being started or run in the wrong direction. It ensures that:

1. The engine cannot be started unless the direction selector and the reversing mechanism are correctly set for the required direction.
2. The engine cannot be reversed while it is running at a high speed (the interlock prevents a dangerous reversal).
3. The fuel is cut off while the direction is being changed, preventing the engine from firing in the wrong direction.
4. The starting air is not admitted to the cylinders in the wrong order.

The interlock prevents damage to the engine and the shafting and prevents a dangerous situation (e.g. the engine running astern when the bridge ordered ahead). It is essential for the safe operation of the engine.