intro fuel systems (1)

Aims and Objectives

Aim

•To be able to recognize the main components within a basic engine fueling system and its function within an internal combustion engine

Objectives

•Recognize the main components within an engine’s fueling system•Be able to identify the correct air and fuel ratio for an internal combustion engine•Be able to list the main components within an engine’s fueling system•To list the main differences between diesel and petrol fueling systems

Introduction to Fuel Systems

Introduction to fuels

Petrol and Diesel are fuels that are particularly suitable for use in internal combustion engines

Fuel is mixed with air and introduced into the engines cylinder in order to be burnt within the engines Otto cycle


Mixture strength

“The mixture strength is the proportion of air that is mixed with the fuel required to produced the engine’s power”

Hiller’s Fundamentals of Motor Vehicle Technology 5th ed. V.A.W Hiller and Peter Coombes

The ideal mixture for a petrol internal combustion engine is 14.7:1 (14.7 air to 1g fuel)


Ideal, rich and lean

14.7:1 (14.7 air to 1g fuel) =ideal (stoichmetric ratio)

10:1 = rich mixture (more fuel than air)

20:1 = lean mixture (more air than fuel)


Question

What is stoichmetric ratio ? And what is the ideal fuel to air mixture for a petrol engine ?


Exhaust gas emissions

If the engine burns the chemical correct mixture the following gases are produced:-CO2 H2O N2

As an engine will never be 100% efficient harmful gases are produced CO, HC. O2 and NOx

A richer mixture produces more CO which is harmful for the environment ( produces a sooty black exhaust gas )

A technician can analyse the vehicles exhaust gases using an exhaust gas analyser


Vaporization and Atomization

VaporizationIt is important to remember that petrol burns in vapour form so it must be like this before it enters the cylinder

Diesel, however must be subjected to heat and compression for it to burn

AtomizationHelps brake the fuel into vapour form before it goes into the cylinder

This is achieved by either subjecting it to turbulent airflow or by pumping the fuel through holes in an injector before it goes into the main air stream of the cylinder


The main fuelling components

Fuel tank


Fuel lines

Fuel filter

Carburettor or injectors

Fuel gauge

The difference between Petrol and Diesel


Petrol

Petrol is lighter

More volatile

Contains hydrocarbons with around 8 carbon atoms per molecule

A petrol engine is a spark-ignition engine

Utilises a spark to ignite the volatile petrol/air mixture

Diesel

Diesel oil is heavier Less volatile

Greater lubrication qualities, contains hydrocarbons with around 10 carbon atoms per molecule

A diesel engine is a compression-ignition engine

Utilises high compression to create the high temperatures in which diesel oil will burn

Question

Can you list the main differences between diesel and petrol ?


Summary – Have we ?

Recognized the main components within an engine’s fueling system ?

Been able to identify the correct air and fuel ratio for an internal combustion engine ?

Been able to list the main components within an engine’s fueling system ?

Listed the main differences between diesel and petrol fueling systems ?


Any questions ?


intro fuel systems (1)

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