Intake and Exhaust System

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Intake and Exhaust System


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Intake System

Carbureted systems :Air enters through the air cleaner and passes through the carburetor to be mixed with the correct amount of fuel. Air-fuel mixture thenpasses through the inlet manifold, and enters the cylinders.

EFI systems :Electronic fuel injection is controlled by an electronic control unit. Ithas replaced the carburetor on most modern engines. EFI engines runmore smoothly, with lower fuel consumption and emissions, and morepower than carbureted engines.

Diesel induction systems :Diesel engines draw in air only. Speed and power is controlled by theamount of fuel injected at the end of the compression stroke. 2-strokediesels use a blower for induction and to improve scavenging.


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Intake systemAir cleaners : Air cleaners filter the air before it reaches the engine.They remove abrasive particles which cause wear and damage. Thefilter must stop minute particles without restricting air-flow.Carburetor air cleaners : Most air cleaners trap abrasive particlesusing a pleated dry paper element but some use the dust-attractingproperty of oil.EFI air cleaners : The air cleaner on a multi-point fuel injected engineuses a dry-type element. It is connected to the throttle body by a duct.For optimum performance, it needs to be supplied with cool, clean air.Intake manifolds : The intake manifold carries the air of the air-fuelmixture to each cylinder. In spark ignition engines, fuel is either mixedwith the air at the entrance to the manifold, or injected close to thecylinder head.Intake air heating : To maintain ideal combustion conditions andreduce emissions, many air cleaners include a system to maintain air-intake temperature, regardless of outside air temperature.Volumetric efficiency : Volumetric efficiency is a measure of the air-fuel mixture burned in the cylinder, usually expressed as apercentage.Forced induction : Engine performance can be improved using an air pump to force air or mixture into the cylinders. A pump driven by

exhaust gases is called a turbocharger.


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INTAKE SYSTEM


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INTAKE SYSTEMInlet runners :

The length and diameter of the intakemanifold inlet runners also have an effecton volumetric efficiency.

During low engine speeds, longer andthinner inlet runners produce higher volumetric efficiency.

During high engine speeds, shorter andwider inlet runners are more efficient.

More modern engine designs utilize suchinnovations as multi-valve engines andvariable intake systems to increasevolumetric efficiency.


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Intake manifold runner control (IMRC) system :

The intake manifold has two runners per cylinder,feeding each of the intake ports in the cylinder heads. The IMRC assemblies are located betweenthe intake manifold and cylinder heads, providingtwo air passages for each cylinder. The IMRCassemblies are actually the lower manifold, in whatbecomes a two piece intake manifold assembly.One air passage is always open and the other passage switches from closed to open by means of a valve plate.

Intake manifold tuning (IMT) valve :

The IMT valve is an electric actuator controlling avalve plate or shutter device mounted directly to theintake manifold. Below a certain rpm the IMT valveis closed. Above a certain rpm, the IMT valve opensallowing more into the cylinders to improve highspeed engine performance. The engine controlsystem controls the IMT valve.


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INTAKE SYSTEM

Forced induction :

Most vehicle engines draw in the air-fuel mixture from vacuum created by the downwardtravel of the piston, and for this reason are called naturally aspirated engines . Naturallyaspirated engines rely on atmospheric air pressure to supply air to the cylinder.

The power output of an engine is directly linked to its volumetric efficiency. A naturallyaspirated engine usually has about an 80% volumetric efficiency. This means that the

engine draws in about 80% of its displacement. Streamlining passages and increasingport sizes improves volumetric efficiency. The air still has difficulty reaching the cylinder. Aslong as the engine relies on atmospheric pressure to push the air through the intakesystem, the engine does not produce as much power as it is capable of producing. Withoutexternal help, an engine receives only a partial air-fuel charge.

Pumping air into the cylinders can increase the air-fuel charge. This forcing of more air into

the cylinders allows the engine to fill its cylinders with a charge, which meets or exceeds100% volumetric efficiency. This process of pumping more air into the engine cylinders iscalled forced induction.

There are two different methods used to pump air into an engine: turbocharging andsupercharging .


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INTAKE SYSTEM


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INTAKE SYSTEM

Turbocharging :

Because a turbocharger is driven by exhaust gas flow, it does not consume engine power.Some turbocharged engines experience a short interval of time before the turbocharger begins to pump a large amount of air into the engine. This short interval of time is calledturbo lag. During this period of turbo lag, the engine does not deliver the extra power thatthe turbocharger provides at higher rpm. Some turbochargers use a variable inlet design.This design helps the turbocharger reach optimal speed at a lower rpm which increases low-

speed engine performance and reduces turbo lag.

Supercharging :

A supercharger is a type of air pump or compressor. Exhaust gases do not drive asupercharger. The power source of a supercharger is the engine itself. The crankshaft drivesthe supercharger through a belt, gear or chain. Intake manifold pressures of up to 1 3 psi are

typical for supercharged engines. As with a turbocharger, the amount of power availableto drive the supercharger depends upon engine speed. Unlike some turbocharged engines,when accelerating a supercharger immediately delivers extra engine power. Although it takesengine power to drive a supercharger, a supercharger helps produce much more power inreturn. There are different types of superchargers. No matter how a supercharger isdesigned, its main purpose is to force more air into the cylinders and help the engine producemore power.


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Exhaust Systems

An exhaust system must reduce enginenoise and discharge exhaust gasessafely away from the vehicle.

An efficient exhaust system canimprove engine performance.


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Exhaust system components

Exhaust manifold :The exhaust manifold collects exhaust gases as they leave eachcylinder and directs them into the exhaust system.Exhaust pipe :The exhaust pipe carries the hot exhaust gases to where they can bedischarged into the atmosphere.Extractors :Extractors are sometimes known as headers. They are used to assistin the fast extraction of exhaust gases in engines.Mufflers :The muffler reduces exhaust noise by dampening the pulsations in theexhaust gases and allowing them to expand slowly.Catalytic converters :

The catalytic converter provides a chemical reaction with the exhaustgases to reduce the level of exhaust pollutants entering theatmosphere.Flexible connections :Flexible connections are used to allow movement betweencomponents.


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Exhaust Systems


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Exhaust system components

Exhaust manifold Exhaust pipe Extractors

Catalytic converters Flexible connections


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Fuel Systems


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Fuel system basics

Petrol / Gasoline :Petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines.

Gasoline fuel :

Gasoline is a mixture of nearly 300 different components,mainly hydrocarbons, which vary widely in physical andchemical properties. The properties of gasoline must bebalanced to give satisfactory engine performance over a widerange of operating conditions including heat, altitude, anddriving patterns.The more effectively liquid gasoline is changed into vapor, the

more efficiently it burns in the engine.

Controlling fuel burn :Detonation is a violent collision of flame fronts in the cylinder,caused by uncontrolled combustion. The sudden rise inpressure can cause a knocking sound.


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O ctane ratingThe most important characteristic of petrol is its Research Octane Number

(RON) or octane rating, which is a measure of how resistant petrol is topremature detonation (knocking). It is measured relative to a mixture of isooctane ( 2 ,2 ,4 -trimethylpentane) and n-hepta ne. So an 87 -octane petrolhas the same knock resistance as a mixture of 87% isooctane and 1 3% n-heptane.There is another type of Octane, called "Motor Octane Number" (MON),which is a better measure of how the fuel behaves when under load. Itsdefinition is also based on the mixture of isooctane and n-heptane that hasthe same performance. Depending on the composition of the fuel, the MONof a modern petrol will be about 1 0 points lower than the RON. Normallyfuel specifications require both a minimum RON and a minimum MON.Using a fuel with a higher octane allows an engine to be run at a higher compression ratio without having problems with knock. Compression isdirectly related to power, so engines that require higher octane usuallydeliver more power. Some high-performance engines are designed to

operate with a compression ratio associated with high octane numbers, andthus demand high-octane petrol.It should be noted that the power output of an engine also depends on theenergy content of its fuel, which bears no simple relationship to the octanerating. Some people believe that adding a higher octane fuel to their enginewill increase its performance or lessen its fuel consumption. This is false -engines perform best when using fuel with the octane rating they weredesigned for .


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Carbureted systems principles A basic carbureted system consists of the fuel tank to store the fuel.

Fuel lines or pipes carry fuel in the system. A pump moves fuel fromthe tank to the engine. A filter cleans the fuel. An air cleaner suppliesclean air. A carburetor mixes the air and fuel and controls how muchmixture enters the engine. An intake manifold carries the mixture tothe engine.The carburetor has to supply the correct mixture of air and fuel to suitall operating conditions.The downdraft carburetor is the most common kind. Its mounted onthe intake manifold. The side-draft model is less common.

The carburetor turns liquid fuel into a fine spray and mixes it with air.It also controls how much air-fuel mixture is delivered to the engine.This is done by the throttle valve near the bottom of the carburetor,which is connected to the accelerator pedal.This down-draft carburetor has a float bowl for fuel. One end of a tubeis immersed in the fuel. The other end is a fuel discharge nozzle, inthe venturi. As the piston moves through intake, it makes a lowpressure area and as a result, air from the atmosphere flows throughthe venturi. The venturi here is narrower than the rest of the barrel,and it is shaped to make the air speed up as it passes through.It creates a low pressure area where the end of the nozzle protrudesinto the airflow. Atmospheric pressure on fuel in the float bowl is nowgreater than the pressure on the end of the nozzle. This forces fuel toflow from the nozzle. It mixes with the passing air, breaking up intodroplets, or atomizing.

A light vehicle under normal conditions needs an air-fuel ratio, bymass, of about 1 5 to 1. By volume, thats 11, 000 to 1.This ratio can vary to suit engine operating conditions.

Too much fuel for the air will waste fuel and cause pollution.Too little, will cause loss of power and possible engine damage.


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Carburetor components

The carburetor :The carburetor atomizes the fuel and mixes it with air, andcontrols the delivery of the correct mixture to the engine.Carburetor systems :Low speed and idling ports allow the engine to operate with alow throttle opening before the main system is operating fully.Metering jets :The main jet size is selected to provide the best mixture for fueleconomy. An extra jet supplies additional fuel for maximumpower.Accelerating :For acceleration, suddenly depressing the accelerator deliversextra fuel into the airstream.Carburetor barrels :A 2-stage carburetor has a primary throttle open only from idleto medium speeds. At higher speeds, the secondary throttleopens to admit more air-fuel mixture.


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Carbureted system components

Mechanical fuel pumps :The mechanical fuel pump has a diaphragm separating 2 chambers. Moving thediaphragm down draws fuel into the pumping chamber. A spring then movesthe diaphragm up, forcing fuel from the pump, into the carburetor.Electric fuel pumps :An electric fuel pump operates with the ignition switched on. It can becontrolled so that it operates only if the engine is runningTachometric relay :The tachometer indicates engine RPM.Tanks & lines :Most fuel tanks are in 2 parts joined by a weld around the flanges where theparts fit together. Baffles make the tank more rigid, prevent surging of fuel, andensure fuel is available at the pickup-tube.Fuel lines :The fuel tank is connected to the engine by fuel lines. A return line may carry

excess fuel back to the tank, to keep fuel system components cool. \Charcoal canister :Used in some emission systems as a means of preventing pollution to theatmosphere.Carburetor filters :Used to prevent particles from entering the fuel carburetion/injectioncomponents.

Intake and Exhaust System

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