Power Plant Engineering

DIESEL POWER PLANT 241

8.9 Fuel System of Diesel Power Plant

The fuel is delivered to the plant by railroad tank car, by truck or by barge and tanker and stored
in the bulk storage situated outdoors for the sake of safety. From this main fuel tank, the fuel oil is
transferred to the daily consumption tank by a transfer pump through a filter. The capacity of the daily
consumption should be atleast the 8-hour requirement of the plant. This tank is located either above the
engine level so that the fuel flows by gravity to the injection pump or below the engine level and the fuel
oil is delivered to the injection pump by a transfer pump driven from the engine shaft, Fig. 8.3. Fuel
connection is normally used when tank-car siding or truck roadway is above tank level. If it is below
tank level, then, an unloading pump is used to transfer fuel form tank car to the storage tank (dotted line).

Foot Valve

and Strainer

Unloading

Pump

Sounding Well

Fill Connection

Manhole

Vent

Day Tank

To

Engine

Transfer

Pump

Strainer

Suction

Line

Crain

Ta n k

car

Fig. 8.3. Fuel System.

The five essential functions of a fuel injection system are:

1. To deliver oil from the storage to the fuel injector.


2. To raise the fuel pressure to the level required for atomization.


3. To measure and control the amount of fuel admitted in each cycle.


4. To control time of injection.
   5.To spray fuel into the cylinder in atomized form for thorough mixing and burning.
   The above functions can be achieved in a variety of ways. The following are the systems, which
   are usual on power station diesels:

1.Common Rail.

2.Individual Pump Injection.

3. Distributor.


4. COMMON RAIL INJECTION

A typical common rail injection system is shown in Fig. 8.4. It incorporates a pump with built in
pressure regulation, which adjusts pumping rate to maintain the desired injection pressure. The function
of the pressure relief and timing valves is to regulate the injection time and amount. Spring-loaded spray
valve acts merely as a check. When injection valve lifts to admit high-pressure fuel to spray valve, its
needle rises against the spring. When the pressure is vented to the atmosphere, the spring shuts the
valve.