AIR INDUCTION AND EXHAUST SYSTEMS
Introduction
Combustion requires air, fuel, and heat; certain ratios of all three are necessary if an engine is to
operate. Air induction and exhaust system deals with AIR as it is required to support combustion in
the cylinder of an engine.
AIR INDUCTION SYSTEM
The function of the air induction system is to allow air to reach your car engine. Oxygen in the air
is one of the necessary ingredients for the engine combustion process. A good air intake system
allows for clean and continuous airflow into the engine, thereby achieving more power and better
mileage for your car.
How Does the Air Induction System Works?
The air enters into the system through the special holes created in front of the car. The first step is
to clean the air, removing the unwanted air born particles with the help of an air cleaner. The
amount of air entering the engine is a function of engine load. Air is drawn in through the air
intake; a long plastic tube which has the main purpose to guide the air into a fairly steady stream
until the air filter housing. After the filter, the air will go, in order, through an Air Flow Meter,
Throttle Body with an Air Valve, then Air Intake Chamber, Intake Manifold, and finally will get
to the Cylinders.
AIR INDUCTION SYSTEM COMPONENTS
1. Air Cleaner
The air cleaner actually contains an air filter which
removes solid particles such as dust, pollen, and mold
from air that enters the engine. Air enters the engine
through the air intake or air induction system. The grit
and dust particles in this air must be removed before it
enters the engine. If not, engine wear and damage can
result.
The intake air passes through air cleaner before entering
the engine. The air cleaner has a ring or panel of filter paper or other material. This traps dust
and dirt as the air passes through.
Types of Air filter:
• Filter paper
Pleated paper filter elements are the most common air cleaners nowadays, because they
are efficient, easy to service, and inexpensive. One drawback can be the fact that those
paper filters sacrifice the air flow, but as long as a pleated paper is sized appropriately for
the airflow volumes needed, this will not be a real issue until the filter become significantly
clogged with dirt.
Type of filter element
▪ Ring type filter element
▪ Panel type filter element
• Foam Oil
A wetted polyurethane foam element was in the past used in small engines on power
equipment and lawnmowers, but paper filter supplanted oil wetted foam in these
applications. Nowadays, those are preferred in off-road rallying and other motorsport
competition, because, depending on the grade and thickness of the foam employed, can
offer very high dirt capacity. Also, it can be washable and reusable.
• Cotton
In the past, oiled cotton gauze saw limited use in original-equipment automotive air filters.
Oiled cotton gauze is employed in a small number of aftermarket automotive air filters
nowadays, marketed as high-performance items. It also can be washable and reusable.
• Oil Bath
The general principle of an oil bath air cleaner is that incoming air is sucked through the
system towards a bowl containing a pool of oil, and forced to make a vertical U-turn near
the surface of the oil. Prior to 1960s, it was the most common type of air filter used in
automotive and small engine applications, until the adoption of the pleated, disposable
•
paper filters. Today, such air cleaners are found in application where very high levels of
dust are encountered, because oil bath cleaners can retain a great deal of dirt.
Air Ionizers
An air ionizer is a device that uses high voltage to ionize air molecules. Air ionizers use
fibers or elements with a static electric charge, which attract airborne dust particles in an
effect similar to static electricity.
2. Air Flow Meter
An Air Flow Meter is a device that measures the amount of air flowing through a tube. These
devices convert the amount of air drawn by engine into an electrical signal send to the
Electronic Control Unit. The ECU needs to know intake air volume to calculate how much fuel
to inject into the cylinders in order to provide optimum combustion and low emissions.
Types of air flow meters:
▪ The vane type (Vane air flow sensor) –This type has a flap that is pushed by the
incoming air. The more air coming in, the more the flap is pushed backed. There is also
a second vane behind the main one that fits into a closed camber that dampens the
movement of the vane giving a more accurate measurement.
▪
The hot wire AFM (hot wire sensor) –The hot wire uses a series of wires strung in
the air stream. The electrical resistance of the wire increases as the wire's temperature
increases, which limits electrical current flowing through the circuit. When air flows
past the wire, it cools, decreasing its resistance, which in turn allows more current to
flow through the circuit. However, as more current flows, the wire's temperature
increases until the resistance reaches equilibrium again.
▪
The Cold Wire Type – (Cold Wire MAF sensor)
The cold wire MAF sensor uses thin metal strips that
vibrate as the air passes by. This vibration changes the
inductance of a tiny sensor which is part of an oscillator
circuit. In that way, the frequency is related to the amount
of air passing over. This oscillating electrical signal is then
sent to the engine’s ECU.
▪
Kármán Vortex Air Flow Meter - This air flow meter provides the same type of
information (intake air volume) as the Vane Air Flow Meter. This type of airflow sensor
is named after the Karman-Vortex principle that says turbulent swirls or "vortices" will
form behind an object if it is placed in the path of a moving stream or column of air.
As the air bumps into the object and passes around it, little swirls form behind the object
much like the wake behind a boat. The number or frequency of these vortices will vary
in proportion to the velocity of the airflow.
3. Throttle Body
The throttle body is the part of the air intake system
that controls the amount of air flowing into an
engine's combustion chamber. It consists of a bored
housing that contains a throttle plate that rotates on
a shaft.
When the accelerator is depressed, the throttle plate
opens and allows air into the engine. When the
accelerator is released, the throttle plate closes and effectively chokes-off air flow into the
combustion chamber. This process effectively controls the rate of combustion and ultimately
the speed of the vehicle. The throttle body is usually located between the air filter box and the
intake manifold, and it is usually located near the mass airflow sensor.
4. Intake Manifold
After intake air passes through the throttle body, it passes
into the intake manifold, a series of tubes that delivers air
to the intake valves at each cylinder. Simple intake
manifolds move intake air along the shortest route, while
more complex versions may direct air along a more
circuitous route or even multiple routes, depending on
engine speed and load. Controlling air flow this way can
make for more power or efficiency, depending on demand.
The primary function of the intake manifold is to evenly
distribute the combustion mixture (or just air in a direct injection engine) to each intake port
in the cylinder head(s). Even distribution is important to optimize the efficiency and
performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel
injectors and other components of the engine. The Intake manifold connects to the throttle
body with the intake ports in the cylinder head. The manifold has a set of passages of runners
through which air or air-fuel mixture flows. With port fuel injection, only air flows through.
Fuel is injected into the air as it flows through the intake ports. With a carburetor or throttle
body injection, fuel mixed with the air as it enters the intake manifold.
THE EXHAUST SYSTEM
A vehicle’s exhaust system is designed to direct harmful gases away from the driver and
passengers, reduce the emissions the vehicle releases into the environment, control the delivery of
hot exhaust, provide information to the vehicle’s computer to improve vehicle performance, and
significantly reduce the amount of noise the vehicle makes.
All exhaust systems produce six gases as emissions, three of which are toxic, including carbon
monoxide, nitrogen oxide, and nitrogen monoxide. While the main task of the exhaust system is
to dissipate harmful gases produced by the engine’s combustion chamber, it is also tasked with
muffling the sound. A vehicle with a poor exhaust system will exhibit issues such as lower fuel
efficiency, rumbling noises from the exhaust pipe or muffler, dangerous gases, and may emit a
rotten egg smell.
How Does An Exhaust System Work?
1. As your car emits fumes, the exhaust manifolds—the part of the system connected directly to
the engine—harness the gases into the system.
2. At this point, your car’s catalytic converter takes charge. It takes the gases in the system,
analyzes them, and transforms them into matter that is either less harmful or not harmful at all.
3. This is a noisy process. Your vehicle’s muffler is what helps keep it quiet.
4. What’s left of the gases exits your car through the tailpipe.
EXHAUST SYSTEM COMPONENTS
1. Exhaust Manifold
Exhaust gases leaving the engine first travel through
the exhaust manifold. The manifold collects the exhaust
gases from the individual ports in the engine’s cylinder
head, then routes those gases to the rest of the exhaust
system.
It is possible, depending on the size of the engine, for
there to be two exhaust manifolds. The manifold,
comprised of smooth curving passages to improve the
flow of exhaust, can be made of steel, aluminum, stainless steel, or more commonly, cast iron.
Cracking, warping, and leaking due to broken mounting bolts are common manifold ailments.
2. Oxygen Sensors
Oxygen sensors can be found on both sides of a
catalytic converter. They are used to measure how
much oxygen is in the exhaust system. Once an oxygen
sensor has the measurement, it then will increase or
decrease the amount of fuel in the combustion process.
By doing this, it allows for the best mixture of fuel to
air.
Modern vehicles have both upstream and downstream oxygen sensors. Upstream oxygen
sensors are located before the catalytic converter, while downstream sensors are located after
the converter.
The engine computer, which is often referred to as the powertrain control module (PCM), uses
data from the upstream oxygen sensor to regulate the engine’s fuel mixture. Meanwhile, the
PCM primarily uses the signal from the downstream oxygen sensor for monitoring the health
of the catalytic converter.
3. Catalytic Converter
The catalytic converter is an emissions control device that
converts harmful exhaust gases into water, carbon dioxide,
and nitrogen. The converter is mounted between the
exhaust manifold and the muffler.
The catalytic converter reduces harmful emissions from
engine exhaust. The converter uses a combination of heat
and metals that act as catalysts. A catalyst is a metal, or sometimes a chemical, that causes
other chemicals to go through a reaction without being affected itself. The inside of the
catalytic converter consists of materials such as platinum, palladium, and rhodium. These
materials are the catalyst that causes the carbon monoxide and hydrocarbons to react and
produce water vapor and carbon dioxide which are much less harmful to the atmosphere.
4. Resonator
After going through the catalytic converter, the transformed
gases, along with sound waves from the engine, travel along
the resonator. This is a steel tube that helps to reduce sound
waves. The resonator is like a mini muffler with less
restriction. It is an empty echo chamber the exhaust travels
through where the exhaust energy bounces around, resonates,
and some of the noises cancel each other out. A resonator
doesn’t just remove sound, it changes it to be more
acceptable. The resonator can be either before or after the
muffler in the exhaust system.
5. Exhaust Pipes
Exhaust pipes connect all the components of the exhaust
system. They are designed to route the exhaust in the most
efficient way possible as it travels toward the rear of the
vehicle, and to keep the hot exhaust away from heat sensitive
components in the engine compartment and along the
undercarriage of the vehicle. Exhaust piping is usually made
of steel, but can be aluminized steel tubing, or stainless steel,
which lasts longer due to its corrosion resistance. Connections are generally made with clamps,
gaskets, or welds.
6. Muffler
Next, exhaust gases and sound waves travel through exhaust
pipes to the muffler. A muffler is also widely known as a
silencer. It is situated near the end of an exhaust system. The
function of a muffler is to reduce any noise which is caused
by the fuel combustion process. It also guides the fumes
outside of the exhaust system. This can be done by using
perforated tubes. The tubes create different sound waves
which cancel each other out.
7. Tailpipe
The tailpipe is the final link in the exhaust system—it
routes the exhaust gases, which have been cleaned up by the
catalytic converter, away from the vehicle and into the
atmosphere.
Some vehicles may have more than one tailpipe. The
tailpipe often ends with just a straight or angled cut, but may
include a fancy tip. The tailpipe is often larger in diameter
than the rest of the exhaust system. This produces a final
reduction in exhaust pressure, and is sometimes used to enhance the appearance of the vehicle.