Fuel Systems: Intake & Exhaust

Intake & exhaust systems	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 then passes through the inlet manifold, and enters the cylinders.
	Electronic fuel injection systems	Electronic fuel injection is controlled by an electronic control unit. It has replaced the carburetor on most modern engines. EFI engines run more smoothly, with lower fuel consumption and emissions, and more power than carbureted engines.
	Diesel induction systems	Diesel engines draw in air only. Speed and power is controlled by the amount of fuel injected at the end of the compression stroke. 2-stroke diesels use a blower for induction and to improve scavenging.
	Exhaust systems	An exhaust system must reduce engine noise and discharge exhaust gases safely away from the vehicle. An efficient exhaust system can improve engine performance.

Intake system components	Intake system components	The primary components of the automotive intake system are: intake manifold, throttle body/carburetor, and air induction components such as air cleaner and ducting.
	Air cleaners	Air cleaners filter the air before it reaches the engine. They remove abrasive particles which cause wear and damage. The filter must stop minute particles without restricting air-flow.
	Carburetor air cleaners	Most air cleaners trap abrasive particles using a pleated dry paper element, but some use the dust-attracting property of oil.
	EFI air cleaners	The air cleaner on a multi-point fuel injected engine uses 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-fuel mixture to each cylinder. In spark-ignition engines, fuel is either mixed with the air at the entrance to the manifold, or injected close to the cylinder head.
	Intake air heating	To maintain ideal combustion conditions and reduce 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 a percentage.
	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.

Exhaust system components	Exhaust system components	The primary components of the automotive exhaust system are: exhaust manifold, engine pipe, catalytic converter, exhaust brackets, muffler and components such as the resonator and tail pipe.
	Exhaust manifold	The exhaust manifold collects exhaust gases as they leave each cylinder and directs them into the exhaust system.
	Exhaust pipe	The exhaust pipe carries the hot exhaust gases to where they can be discharged into the atmosphere.
	Extractors	Extractors are sometimes known as 'headers'. They are used to assist in the fast extraction of exhaust gases in engines.
	Mufflers	The muffler reduces exhaust noise by dampening the pulsations in the exhaust gases and allowing them to expand slowly.
	Catalytic converters	The catalytic converter provides a chemical reaction with the exhaust gases to reduce the level of exhaust pollutants entering the atmosphere.
	Flexible connections	Flexible connections are used to allow movement between components.
	Ceramic coatings	Ceramic coatings are being used as a barrier between dissimilar metals to reduce friction, which in turn reduces wear in internal engine components. The most common applications for ceramic coatings are on the exhaust system, intake manifolds, and exhaust headers.
	Electronic mufflers	The function of a vehicle’s muffler is to minimize the sounds coming from the vehicle exhaust system. Electronic mufflers are designed to produce anti noise without restricting exhaust flow.
	Thermal expansion	Thermal expansion refers to the way some materials expand when they are heated.
	Superchargers	A supercharger compresses the air intake to above atmospheric pressure which increases the inlet air density to the engine.
	Intercoolers	The purpose of an intercooler is to reduce the intake air temperature by up to 390 degrees Fahrenheit, or 200 degrees Celsius, before it enters the intake manifold.
	Frequency	Sound travels through the air by producing pressure waves - areas of high pressure and areas of low pressure. The rate at which these waves reach our ears is called frequency.
	Back-pressure	Back-pressure in an exhaust system refers to a build-up of pressure in the system that interferes with the outward flow of exhaust gases.

Intake system procedure	Checking & changing an air filter	The objective of this procedure is to show you how to check, remove, and replace throttle body and plenum type engine air filters. If the filter element is not fitted correctly and does not seal properly, air will bypass the filter and enter the engine directly.

Topic group	Topic	Summary