Internal Combustion Engines Components 2 (automobile engineering)



in the previous section we had discuss :

Classification of Internal Combustion Engines and Engine Components (Course)

 

 that  we had discussed in :

-Classification of Internal Combustion Engines

-Internal Combustion Engine Components

 

 

lets begin our section which we will discuss :

-Describe individual pump, distributor, and common rail fuel injection systems for a diesel engine.

-Explain the purpose and describe the operation of superchargers and
turbochargers

-Describe the cooling systems, function operation, inspection, and service.

 

 

 SECTION 2



Objective 3

Describe individual pump, distributor, and common rail fuel injection systems
for a diesel engine.


THE FUEL INJECTOR

The diesel engine, unlike some gasoline engines, does not use a carburetor to mix the fuel and air nor does it use a spark to ignite the fuel-air mixture. Instead, the diesel uses an injection system to spray the fuel into the engine cylinder. The fuel must enter against the pressure of the air that has been compressed in the cylinder by the engine piston. The air may be at a pressure of 3100 kPa and at a temperature of 540°C. Therefore, when the fuel is injected into this high temperature air, it will ignite and burn. This type of fuel injection is called a solid injection system, as the fuel is pumped directly into each cylinder.

The solid injection method has three different designs or variations. They are:

(1) The individual pump system

(2) The distributor system

(3) The common rail system


The Individual Pump System

The basic components of this system are shown in Fig.17.

This system has an individual high-pressure pump for each cylinder fuel
nozzle. The fuel is supplied to the high-pressure pumps from a storage tank by a low-pressure
transfer pump not shown in the diagram. The high-pressure pumps are operated by the engine through a camshaft arrangement and are of the plunger type. The camshaft controls the
timing of each plunger so that injection takes place at the proper time. The control rod
controls the amount of fuel injected by each plunger.


The Distributor System

In the distributor system shown in Fig. 18, the fuel is pumped from the storage
tank to a single high-pressure pump by a low-pressure transfer pump. The high-pressure
pump then injects the fuel to each cylinder nozzle in the proper firing order by means of
a distributor. The distributor contains a rotating channel, which lines up the pump discharge
with the fuel line to the desired fuel nozzle or injector.

The Common Rail System

The common rail system is illustrated in Fig. 19. A low-pressure pump, pumps the
fuel from the tank to the injectors. A separate injector is located at each engine
cylinder. Most of the fuel returns from the injector to the tank via the drain orifice B in the
injector and via the drain manifold. Some fuel, however, passes through the metering orifice C into the cavity D

under the injector plunger. When the proper firing point occurs in each
cylinder, the injector lever, driven by the camshaft, pushes the injector plunger down and forces the fuel under high pressure into the cylinder.

Fuel Pumps and Injectors

Individual fuel pumps are mounted on the top face of the frame at each cylinder
and are directly actuated by the camshafts. This allows individual adjustment of each
pump to equalize the load over all the cylinders. The proximity of each pump to its
corresponding fuel injector and the use of short connecting pipes ensure that equal distribution of  the load is maintained under all conditions. The individual fuel pumps are of the reciprocating plunger type. Each has a rotating outer sleeve, which controls the fuel delivered per stroke. An anti-dribble, spring loaded, non return

delivery valve is part of the fuel pump discharge. The pump is designed to allow
easyadjustment of both timing and quantity of fuel injected. A large diameter
skirt over the cam

follower prevents fuel from leaking into the lubrication system. Injectors are of the multi-hole nozzle type, centrally located in the cylinder heads, and connected to the fuel pumps by short, rigid lengths of fuel delivery pipe. Atomization of the fuel at the nozzle is a result of passing through a spring-loaded needle valve.



Objective 4

Explain the purpose and describe the operation of superchargers and
turbochargers.


SUPERCHARGING

Supercharging involves the use of a blower to force more air into the cylinder
of a diesel engine or more air-fuel mixture into the cylinder of a gasoline engine. In both
cases the result is an increase in the power output, because the amount of fuel burned is
increased.The blowers used are usually the rotary lobe type or the centrifugal type.
Gearing or a belt connects the lobe type blower to the engine shaft. The centrifugal type blower
may be similarly driven or it may be driven by an exhaust gas turbine in which case it
is called a turbocharger.

The arrangement in Fig. 20 involves a rotary lobe blower used to supercharge
a gasoline engine. The air-fuel mixture is compressed to from 35 to 140 kPa by the blower,
which is driven from the engine shaft. The lobes in the compressor do not touch each
other. They are constructed to fine tolerances so leakage is minimal. Similarly, there is no
contact between the lobes in the blower and the blower casing. The lobe type blower requires
little maintenance. Fig. 21 shows a similar type of lobe blower with 3 lobes per rotor.

The roots or lobe type of blowers are positive displacement air pumps. The
airflow is proportional to engine speed. This is an advantage at low engine speeds, but may
be a disadvantage if the engine starts to overload and slow down. The blower also
slows down,further reducing power output.

Supercharging should not be confused with scavenging. Scavenging refers to
the removal of the exhaust gases from the cylinder by blowing air through, as in Fig. 4A. The
air left in the cylinder when the compression stroke commences, however, is not already
compressed to any extent as it is with the supercharger. Roots blowers are used on some
two-stroke diesels for scavenging.

TURBOCHARGERS

In the turbocharger, Fig.22, exhaust gases from the engine drive the gas
turbine, which drives the centrifugal blower as they are connected to the same shaft. This arrangement forces more air into the engine. As the engine load and speed increases the speed of the turbocharger increases. Turbochargers on medium size diesel engines turn at speeds of 70 000 r/min. At peak load the turbocharger speed can go as high as 130 000 r/min.

As the turbocharger rotor speed increases the compressor forces more air into
the engine. As more air is forced into the engine more fuel can be burned. The maximum power of an engine

may be increased by up by 50%-70% using a turbocharger. The heat of compression
is removed from the air in the intercooler and this reduces the specific volume of
the air and allows a greater weight to be forced into the cylinder. The engine depicted is a
four-stroke cycle diesel.

By using a turbocharger the exhaust temperature can be reduced by 200°C (for
large diesels up to 300°C). The combination diesel engine plus exhaust gas turbine is an
efficient heat engine. Its efficiency is over 40%. Fig. 23 shows the internal details of a
turbocharger for a diesel engine.The materials used in turbocharger construction must be able to withstand high temperatures

(up to 600°C) and centrifugal forces. The compressor components are often
constructed of aluminum alloys. The turbines are constructed of nickel or cobalt steel or
ceramics. Most turbochargers use floating friction bearings. They are designed to rotate in
operation at about one third of the shaft speed. They have a film of oil on both sides of the
bearing. A thrust bearing limits the axial movement of the turbine rotor.


Objective 5

Describe the cooling systems, function operation, inspection, and service.


COOLING SYSTEM

Function of the Cooling System
The main function of the cooling system is to regulate engine temperature.
This ensures that the engine runs at the most efficient range and that the engine has a long
service life. This means that the system prevents both overheating and overcooling, which are
harmful. Overheating causes some of engine parts to. fail. Overcooling causes the engine
to operate inefficiently. The amount of energy that the cooling system rejects is about 30%
of the total energy consumed by the engine. Approximately 25% to 39% of the energy consumed
by the engine goes to usable HP at the flywheel. This varies, depending on the
efficiency of the engine. The rest of the energy is lost to friction and the heat of exhaust.

The cooling system works to reject heat in three basic ways:


o Conduction

This is the transfer of heat from molecule to molecule that occurs when the heat
from the block, heads, and liners is transferred to the coolant.


o Convection

Convection is the transfer of heat by movement of a medium such as coolant and
air. Heat is transferred by circulating the coolant with the water pump and/or by the fan
moving air through the heat exchanger.


o Radiation

This is the transfer of heat through space by electromagnetic waves, from one
object to another, even if they are apart. The sun is the best example of radiant heat
transfer. The darker the colour of an object the more readily it radiates and absorbs heat.

The temperature in most engines is kept at 82°e to 95°e (180oP to 200°P).
Temperatures above this point create engine problems, including pie-ignition, detonation,
burnt pistons, burnt valves, scored liners and lube oil breakdown. Running the engine below
these temperatures leads to problems such as sludge and water accumulation in the
crankcase, poor fuel economy, and unnecessary engine wear.


Cooling Systems Types

Air-cooled engines have fins on cylinders and heads to increase surface area so
that a forcedair fan can remove the heat. There is an increased fin size in hot points of the
engine. The fan creates airflow, which is directed to hot points by shrouding and baffles.
Temperature regulation may be controlled by fin size or airflow or by a thermostatic valve
controlling airflow or fan speed. The liquid cooling or open system is an engine with water jackets, similar to the closed system, except that the coolant is not recirculated. The coolant is taken from a lake or reservoir and dumped backing to the same place. This system is used for some marine applications.Liquid cooling (closed systems) is recommended over the open system and is the most

common system used. The coolant is recirculated or reused by sending the coolant
from the engine to a heat exchanger (radiator) to reject the heat. By reusing the coolant, the
coolant can be conditioned to allow for a minimum of scale buildup and can receive
additives to ensure longer cooling system life. The liquid in the block surrounds the hot.
Points in the heads ane water jackets to absorb heat, which is later, dissipated. A water pump
creates the coolant flow and a thermostat regulates the flow to the heat exchanger




in The next section we will discuss :
-Describe and explain the operation of a typical cooling system for an industrial ICE.
-Describe and explain the operation of a typical lubrication system for an industrial ICE.


see you

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