DIESEL ENGINE SUB SYSTEMS

DIESEL ENGINE SUB SYSTEMS
Diesel engines require five supporting systems in order to operate:
· Cooling System
· Lubrication System
· Fuel System
· Air Intake System
· Exhaust System

We shall examine each system in detail.

Purpose of Cooling System The purpose of the cooling system is to circulate the coolant in order to absorp dissipate, and control the heat from fuel combustion and friction. The flow volume which the coolant pump must move through the coolant system, as well as the overall coolant volume, are specifically related to engine
horsepower.

Combustion heat is dissipated in three ways (1) convection by means of air currents: (2) j
radiation, by waves sent out from the vibrating molecules; and (3) conduction, by travelling through the metal into the cooling passages (where the coolant picks up the heat and carries it into the radiator). Heat absorbed by the engine oil is partly removed by conduction. The remainder is removed in the oil cooler and the oil pan by a combination of the methods just described.

The dissipation of heat, in itself, would be relatively simple if it were not essential that the cooling system maintain an even temperature at any torque range, at any engine-speed range, and at varying ambient temperatures.

At maximum engine torque and high ambient temperature, the system is forced to dissipate heat at its maximum capacity in order to maintain the top tank temperature around 180°F [82°C]. When the engine torque and the ambient temperature are low, the system must nevertheless maintain the engine at approximately the same temperature,
Cooling-System Components Beginning at the front of the engine, the components which make up an average cooling system are the radiator, fan, coolant purnp, engine oil cooler, aftercooler, and the connecting pipes and hoses (Fig.3.2). The cylinder block and cylinder head are, of course, also part of the system.

Some engines have additional components, such as a torque-converter oil cooler, a radiator shutter system, a coolant filter, a surge tank, and a second coolant pump.
It is the engine and equipment manufacturers who select the cooling-system components to be used on a given engine. They choose the radiator size, the shroud and fan size, the fan design, its rotating speed, and the coolant capacity and flow. Together, these components ensure that

(1) the cooling temperature in the top tank of the radiator does not exceed maximum prescribed temperature, that is, about 200°F [93.3°C);

(2) the horsepower required to drive the fans does not exceed 6 percent of the engine horsepower;

(3) the speed of the tip of the fan is not greater than 18,000 ft/min [6,000 m/min] and therefore the fan noise remains at an acceptable level;

(4) the air-flow does not exceed 1,600 ft'/min [755.12 L/s], and (5) there is no dead area (unswept core area) on the surface of the radiator.


b) Lubrication System
Lubrication System Design Diesel internal depend on their lubricating system for Design cooling, to reduce friction, to clean inteal engine parts, and to aid sealing between the piston rings and the cylinder walls. This is why the lubricating system must be able to move the volume of oil required to do all of these jobs.
oil

The basic lubrication system components include the oil pump, the inlet nlet 0*1 strainer, one or more pressure relief and/or bypass valves, the oil filter, the oil-level indicator, an oil pressure gauge, the oil pan or reservoir, and the oil pipes and hoses which connect.the
components to each other and to the engine. In addition to these components, most diesel engines use an oil cooler and piston spray tubes (Fig. Al & A2). Some manufacturers have made available electrically driven prelubrication pumps which allow the operator to bring the engine up to full oil pressure before the cranking motor is engaged, thereby greatly g increasin engine
- increasing

Engine manufacturers usually use of two oil pump designs:

an external gear pump or

a rotor pump.

The external gear pump has two closely meshed gears within a cast-iron housing. The rotation of the gears causes oil which is trapped between the teeth and the housing to flow through the outlet port of the pump housing to the oil cooler, if the engine is so equipped, before going on to the oil filter and beyond. The rotor pump moves oil to the engine when the inner rotor and rotor ring rotate and oil is trapped between the inner rotor and the rotor ring. As the rotor continues to turn, the space in the outlet side of the pump becomes smaller, thereby forcing the oil through the outlet port of the pump port of the pump housing to the engine.

We find two types of lubrication oil filtration systems in use today: full-flow filtration or bypass filtration. By far the most common of the two designs is full-flow filtration. With full-flow filtration, all of the lubricating oil must pass through the filter under normal operating conditions.

Oil will by-pass the filter for two reasons:

(1) Cold weather can cause oil to become so viscous that it will not flow through the filter, or
(2) if maintenance of the engine is poor, the filter element can become plugged and restricted.

When this happens the lubricating oil will bypass the filter and go to the engine bearings without
filtration.

In contrast, the bypass filtration system sends only 10 percent of the lubricating oil to the filter, while the rest of the oil goes to the bearings without filtration. Again, maintenance is critical with this type of system.