10 Section 1 Introduction to Automotive Technology
Figure 1-12. Note the three basic types of fuel systems. Compare differences.
Air enters
When open, fuel injector
(fuel valve) sprays fuel
toward intake valve
Throttle
valve
Wires to
engine
sensors
Computer
Electric
fuel pump
Spark plug
ignites mixture
Gasoline
from tank
A—Gasoline injection system. Engine sensors feed information (electrical signals) to computer about engine conditions.
Computer can then open injector for right amount of time. This maintains correct air-fuel ratio. Spark plug ignites fuel.
Mechanical injection nozzle sprays fuel
into combustion chamber
Air enters
No throttle used
Air compressed so tight
it becomes red hot
Only air flows past intake valve
and into combustion chamber
Diesel fuel
from tank
High-pressure
mechanical pump
Fuel ignites as it
touches hot air
Injection line
B—Diesel injection system. High-pressure mechanical pump sprays fuel directly into combustion chamber. Piston squeezes and
heats air enough to ignite diesel fuel. Fuel begins to burn as soon as it touches heated air. Note that no throttle valve or spark plug
is used. Amount of fuel injected into chamber controls diesel engine power and speed.
Air enters filter
Carburetor
Fuel pulled into airstream
by vacuum
Throttle controls airflow
and engine speed
Air-fuel mixture flows
to cylinder
Mixture ignited
by spark plug
Gasoline
from tank
Low-pressure
mechanical fuel
pump
Fuel line
C—Carburetor fuel system. Fuel pump fills carburetor with fuel. When air flows through carburetor, fuel is pulled into engine in
correct proportions. Throttle valve controls airflow and engine power output.