Air Intake System

Air Intake and Exhaust System
Purpose of Intake System

Diesel engines require sufficient quantities of air to burn the fuel.
Air induction systems must provide enough clean air for combustion, consequently the design of the air induction
system must be adequate to prevent leakages into the system and minimise restrictions. Any reduction in the flow of
air or combustion gases through the Air Intake system will reduce engine performance.
COMPONENTS AIR INTAKE and EXHAUST SYSTEM
Natural Aspirated Engine

1. Pre cleaner 2. Air cleaner 3. Intake Manifold 4. Exhaust Manifold 5. Muffler 6. Exhaust stack
Turbo Charged Engine
1. Pre cleaner 2. Air cleaner 3. Turbo Charger 4. Intake Manifold 5. Exhaust Manifold 6. Muffler 7. Exhaust stack
Pre-cleaner
Many engines use a pre-cleaner this is located before the inlet to the main air cleaner (Figure 7). The purpose of the pre-
cleaner is to collect as much of the heavy contaminants as possible in the intake air before it reaches the air cleaner.
Air Cleaner
Dry element air cleaners (Figure 10) are by far the most common type of air cleaners used on Caterpillar engines.
Dry element air cleaners are typically composed of a pleated paper filter media that is used to remove the dirt from
the incoming air.
Inlet Manifold
From the air cleaner and turbocharger/after-cooler, if equipped, the incoming air enters the inlet manifold (Figure 18) and is
directed to the inlet ports for each cylinder.
Air Cleaner Service
Many air cleaners are equipped with a service indicator. The indicator monitors the amount of restriction through the
air cleaners.
Filter Indicator
When the yellow indicator has reached the red zone of the filter indicator, it is time to replace the air cleaning element.
EXHAUST SYSTEM
The purpose of the exhaust system is to remove the spent combustion gases from the engine and discharge them
into the atmosphere. The design of the system must ensure that there is minimum restriction to gas flow and ensure
that the noise level is reduced to satisfy appropriate standards.
Components Exhaust System
Exhaust Manifold
Exhaust gases, leaving the cylinder through the exhaust ports, enter the exhaust manifold and are then routed to the
exhaust system.
The exhaust manifold on turbocharged engines is similar in construction to those on naturally aspirated engines.
The significant difference on turbocharged engines is that the exhaust manifold is connected to the turbine housing of
the turbocharger; to direct the hot pressurised gases to the turbine. The exhaust gases, are removed from the centre
of the turbine housing, via an elbow, to the exhaust stack.
Mufflers
The diesel engine uses a muffler or silencer to reduce the noise level of the gases as they exit from the exhaust
system.
As the gases flow through the muffler, internal baffling causes the gases to reduce their velocity and increase their
pressure, this in turn lowers the noise level, therefore the correct muffler will reduce the noise to an acceptable
level but not have excessive back pressure which may effect engine performance.
There are basically two types of muffler design,
1. Straight Through mufflers
2. Reverse Flow mufflers
Straight-through Muffler
Straight through mufflers consist of cylindrical body with an inlet and outlet pipe at each end, the pipe inside the
muffler body is perforated along it’s length and surrounding this pipe will be some sound absorbing and heat
resisting material such as glass wool
Reverse-flow Muffler
Reverse flow mufflers are made up of a number of chambers that force the exhaust gases to flow in a forward and
backward motion as they pass through the muffler, this has the effect of lowering the gas velocity and acting as an
expansion chamber thus reducing the exhaust gas noise.
This type of muffler also acts as a spark arrester by allowing any hot particles to cool and be temporarily trapped in the
muffler and so as not to ignite any combustible materials nearby
Exhaust Stack
The exhaust stack connects directly to the muffler and carries exhaust gases into the atmosphere, away from the
operator’s compartment.
Some models use exhaust stacks that are fitted with a rain trap. This rain trap prevents rain entering the engine via
the muffler and turbocharger when the machine is parked. Exhaust pressure forces the trap open when the machine
is operating.
After- Coolers
After-coolers are fitted to high performance turbocharged diesel engines. After-coolers are used to cool the engine
incoming air so that the volume of air available is increased. (The cooler the air – the denser it becomes).
Some engine manufacturers refer to the after-cooler as an intercooler. After-coolers are required because intake air, which
is compressed by a turbocharger Hot air occupies a larger space than cold air, therefore more air can be forced into the
combustion chamber when colder.
There are two basic after cooler designs: one uses engine coolant for cooling of the intake air, and the other uses
the air flow by vehicle movement and cooling fan to create an air draft.
TURBOCHARGER
The turbocharger is made up of three sections, the rotor assembly, the turbine housing (exhaust driven) and the
compressor housing (intake side). The rotor assembly contains two plain bearings, piston-ring-type seals, retainers,
a thrust bearing and the turbine and compressor wheel. There are also passages for the supply and dumping of oil
to and from the housing.
Turbochargers serve two functions:
1. Normalising air supply

2. Boosting air supply to engines.
Normalising means keeping air supply the same as is normal for a naturally aspirated engine at sea level. When
engines operate at altitudes above sea level, the air becomes less dense and a turbocharger is needed to supply
more of the thinner air.
The second function of a turbocharger is boosting air supply to give the engine more than normal oxygen. This
enables increased fuel settings while still providing better combustion and quieter exhaust. Improved combustion
means not only better fuel economy, but also cleaner exhaust emissions.

Air Intake System

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Air Intake System

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Air Intake and Exhaust System

Purpose of Intake System

COMPONENTS AIR INTAKE and EXHAUST SYSTEM

Natural Aspirated Engine

Components Exhaust System

Turbochargers serve two functions:

1. Normalising air supply

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