Spring 2008 Forward to a Friend



Sequential Multi-Port Fuel Injection System

Impreza

THE CONCEPT OF FUEL INJECTION FOR AUTOMOBILE ENGINES HAS BEEN PART OF AUTOMOTIVE HISTORY FOR MORE THAN A CENTURY. FOR ALMOST THREE DECADES, AUTOMOBILES HAVE BEEN EQUIPPED WITH FUEL INJECTORS AS PART OF THEIR FUEL SYSTEMS.

Although fuel injection has been used in diesel engines since the 1920s, it didn’t have viable commercial application in gasoline-powered automobiles until the 1950s. By the early 1990s, all gasoline automobile engines had fuel injection.

FUEL INJECTOR
FUEL SUPPLY SYSTEM

Fuel injectors are part of an engine’s intake system. In Subaru engines, injectors are located in the path of air entering the engine’s cylinders, where they spray gasoline that mixes with the air. That mixture is trapped in the engine’s cylinders, where it’s ignited by spark plugs, thereby providing power. (For an overview of a gasoline engine’s 4-stroke cycle, see the “Active Valve Control System (AVCS)” article in the Winter 2005 issue of Drive.

FUEL DELIVERY IN THE AGE OF ELECTRONIC CONTROLS

At the end of the 20th century, demands for cleaner air necessitated finer control over engine functions, accomplished by the use of microcomputers called Engine Control Modules (ECM). Powerful and sophisticated, they manage such things as valve position, ignition timing, and engine response based on information from increasing numbers of sensors along the powertrain.

Sensors provide ECMs with information concerning:

  • The mass of the intake air
  • The amount of oxygen in the exhaust system
  • The position of the electronic (“drive-by-wire”) throttle
  • The temperature of the engine coolant
  • The amount of voltage being used
  • The air pressure and temperature in the intake manifold
  • The speed of the engine and vehicle

Among an ECM’s functions is management of the fuel injection system.

A fuel supply system regulates and monitors gasoline to the injectors. Its components include the gas tank, fuel pump, fuel injectors, fuel lines, fuel pressure regulator, and intake manifold. (Other components are used to regulate the system to help lower emissions, to perform system checks and balances for proper operation, and to help supply the exact amount of fuel required by the engine.) Gasoline enters the injectors under high pressure from the fuel supply system.

A VALVE BY ANY OTHER NAME

A fuel injector is an electronically controlled valve with a plunger that opens to allow fuel to pass into the engine. Based on information gathered by the various sensors in the vehicle, the ECM determines how long and how often the plunger should remain open to enable the engine to perform as requested by the driver.

An electrical field within an injector surrounds the plunger and acts like an electromagnet. The ECM varies the injector’s electrical ground signal. Complete grounding lifts the plunger off its seat. Then the pressurized fuel sprays through the injector’s tip in a pattern determined to mix it well with the intake air flowing into the cylinder. The duration of plunger openings is measured in milliseconds and is called “pulsewidth.”

The air/fuel mixture enters the cylinder through an intake port. The injectors spray in sequence according to the multiple cylinders’ firing order, giving the system the name “sequential multi-port fuel injection.”

Along with the other electronically controlled systems found in Subaru engines, fuel injection enables Subaru to meet the increasing demand for fuel efficiency and low emissions.