Starting and reversing system of an electronically controlled diesel engine compared with a camshaft engine:

In a conventional camshaft engine, the starting air is admitted to the cylinders by an air distributor driven by the crankshaft, and the fuel injection and exhaust valve timing are set by the camshaft. To reverse, the camshaft is axially shifted (or the cams rotated) to bring the correct ahead/astern profiles into line, and the air distributor is driven in the reverse direction. The starting sequence is mechanical.

In an electronically controlled (camshaftless) engine (e.g. MAN ME, WinGD X), there is no camshaft. The fuel injection and exhaust valve timing are controlled by the engine control unit (ECU) which commands hydraulic actuators (via solenoid valves) to open the fuel injection valves and exhaust valves at the correct crank angles. The starting air is admitted to the cylinders by the ECU controlling the starting air valves (or via a distributor), and the firing order and timing are set in software. To reverse, the ECU simply switches the injection and valve timing and the firing order to the astern sequence - there is no mechanical camshaft to shift, so reversal is fast and simple.

In a camshaft engine, the starting air is admitted to each cylinder for a fixed period (set by the distributor) during the starting stroke, and the air is admitted even when the engine is already turning, wasting air. In an electronically controlled engine, the ECU can control the starting air admission precisely:

1. The starting air is admitted to each cylinder only for the exact period needed to turn the engine, and is cut off as soon as the engine fires (when the first cylinder ignites), so less air is used.
2. The ECU can start the engine with a smaller number of cylinders receiving air (e.g. starting on a reduced number of cylinders) and can optimise the air admission timing, reducing the total air consumption.
3. The injection can begin at the correct instant on the down-stroke, so the engine fires sooner and the starting air is used for a shorter time.
4. The starting sequence is controlled to give the minimum air consumption while ensuring reliable starting.

The result is a significant reduction in starting air consumption (up to 30-40% less), which reduces the size/load on the air receivers and allows more starts from a given air supply.

In a camshaft engine, reversing requires the mechanical shifting of the camshaft, which takes time, and the starting air and fuel timing must be re-established for the astern direction. In an electronically controlled engine:

1. Reversal is almost instantaneous: the ECU switches the injection and valve timing and the firing order to the astern sequence without any mechanical movement, so the engine can be reversed quickly.
2. The starting air is admitted correctly for the astern direction immediately, and the fuel injection begins at the correct time, so the engine accelerates astern quickly.
3. During a crash astern (a rapid reversal from full ahead to full astern), the ECU can control the sequence precisely - cutting off fuel, applying the astern starting air, and re-establishing astern firing - to achieve the fastest safe reversal, reducing the time and distance to stop the ship.
4. The precise control of injection and valve timing during the astern manoeuvre gives smoother, more reliable operation and reduces the risk of the engine stalling or over-speeding.

The result is markedly improved astern starting and crash astern performance, which is important for safety in manoeuvring.