Diesel components and starting air system

A diesel power plant consists of a CI engine coupled to an alternator, together with the systems that supply air, fuel, cooling, lubrication and starting energy, and that remove exhaust.

Main components

 Air filter -> Supercharger --+
                              v
 Fuel tank -> Inj. pump -> +--------+
                           | DIESEL |==> ALTERNATOR
 Compressor -> Air bottle->| ENGINE |
             (starting)    +--------+
                            |  |   |
      Lube oil tank, cooler-+  |   +-> Silencer -> Stack
                               v
             Jacket water -> Heat exch -> Cooling tower

Components: engine, alternator, air intake, exhaust, fuel, cooling, lubricating, starting and governing systems.

Function of the starting air supply system

A diesel engine cannot start on its own: the crankshaft must first be turned fast enough that compression raises the air temperature above the fuel's self-ignition temperature. The starting air system supplies this initial cranking energy for medium and large engines.

Parts: motor- or engine-driven air compressor, air receivers (bottles) at about 17–25 bar (some up to 30 bar), pressure gauges and safety valves, main starting valve, air distributor and cylinder starting valves.

Working:

1. The compressor charges the air bottles and keeps them full; enough air is stored for several starts.
2. To start, the main starting valve is opened. The air distributor (driven from the camshaft) admits compressed air to the cylinders whose pistons are just past top dead centre, in firing order.
3. The air pushes the pistons down and rotates the crankshaft like an air motor.
4. When the engine is turning fast enough for compression ignition, fuel is injected, the engine fires, and the air supply is cut off.
5. The compressor then recharges the bottles for the next start.

It gives a quick, reliable start for large engines where electric starting is not practical; small engines use a battery-driven electric starter instead.