CHAPTER 4 GASOLINE FUEL SYSTEMS

LEARNING OBJECTIVE: Describe the different types of gasoline fuel systems, how the components function to provide fuel to the engine in proper quantities, and servicing of the gasoline fuel system.

The purpose of the fuel system of the internal combustion engine is to provide a combustible mixture of fuel and air to the engine cylinders. The ratio of fuel to air must always be in correct proportions regardless of the speed and load of the engine.

GASOLINE FUEL SYSTEMS

LEARNING OBJECTIVE: Identify the properties of gasoline and the components of a fuel system. The function of both the carburetor fuel system and the fuel injection system is to supply a combustible mixture of air and fuel to the engine. Major elements of the gasoline fuel supply system include the following: fuel tank and cap, fuel system emission controls, fuel lines, fuel pump, fuel filter, carburetor or fuel injection system, air cleaner, and exhaust system. Before discussing the components of a gasoline fuel system, you should understand the composition and properties of gasoline.

GASOLINE

Gasoline is a highly volatile flammable liquid hydrocarbon mixture used as a fuel for internal- combustion engines. Acomparatively economical fuel, gasoline is the primary fuel for automobiles worldwide. Chemicals, called additives, such as lead, detergents, and anti-oxidants, are mixedinto gasoline to improve its operating characteristics.

Antiknock additives are used to slow down the ignition and burning of gasoline. This action helps to prevent engine ping or knock (knocking sound produced by abnormal and excessively rapid combustion). Leaded gasoline has lead antiknock additives. The lead allows a higher engine compression ratio to be used without the fuel igniting prematurely. Leaded gasoline is designed to be. used in older vehicles that have little or no emission controls.

The fuel used today is unleaded gasoline. Unleaded gasoline, also called no-lead or lead-free, does NOT contain lead antiknock additives. Congress has passed laws requiring that all vehicles meet strict emission levels. As a result, manufacturers began using catalytic converters and unleaded fuel.

The properties a good gasoline should have are as follows:

Proper volatility (how quickly the gasoline vaporizes)

Resistance to spark knock, or detonation

Oxidation inhibitors to prevent formationof gum in the fuel system

Antirust agents to prevent rusting of metal parts in the fuel system

Anti-icers to retard icing and fuel-line freezing

Detergents to help keep the fuel system clean

Dye for identification

PROPERTIES OF GASOLINE

For a gasoline fuel system to function properly, it is necessary that the fuel have the right qualities to burn evenly no matter what the demands of the engine are. To help you recognize the qualities required of gasoline used for fuel, let's examine some of the properties of gasoline and their effects on the operation of the engine.

Volatility

The ease with which gasoline vaporizes is called VOLATILITY. A high volatility gasoline vaporizes