Fuel Delivery and Air Induction: Description and Operation
PURPOSEThe fuel injection system delivers a precise amount of highly atomized fuel to the intake system to ensure optimum performance and emissions compliance.
The air induction system, a sub-system of the fuel injection system, provides the pathway by which filtered air is introduced to the intake system. This pathway includes devices to measure regulate the intake air flow.
OPERATION
The Fuel System consists of four major sub-systems:
- The fuel storage system,
- Fuel injector with the supporting fuel injection control system,
- The fuel delivery and return system, including a vapor recovery sub-system.
- Air induction system.
Fuel Storage
The fuel storage system consists of a fuel tank, fill pipe and filler cap.
Fuel Injection And Control
The injector is a solenoid operated valve designed to deliver fuel in an appropriate spray pattern to promote total fuel atomization in the intake air stream
The fuel injection control system consists of the Electronic Control Module (ECM) and all of the engine and operating condition sensors. Using the information from the sensors to determine the proper fuel amount and delivery time, the ECM varies the injector "ON" time to adjust the amount of fuel delivered during each individual firing cycle.
For a more detailed description of the fuel injection system operation, refer to Computers And Control Systems.
Fuel Delivery And Return
Fuel is pumped up by the fuel pump, which flows through the fuel filter under pressure through the fuel pipe to the delivery pipe where it is distributed to each injector. Fuel is injected into the intake manifold according to signals from the ECM.
The fuel pressure regulator adjusts the pressure of the fuel from the fuel line (high pressure side) to a pressure 250 kPa (2.55 kgf/cm2, 36 psi) higher than the pressure inside the intake manifold, and excess fuel is returned to the fuel tank through the return tube. The pulsation damper absorbs the slight fluctuations in fuel pressure caused by the operation of the injectors.
When the engine is hot, the fuel pressure is increased to control percolation in the fuel system and improve restartability and idling stability. A check valve in the fuel pump holds pressure in the system after engine shutdown to prevent vapor lock and to ensure adequate pressure is available during warm engine re-start conditions.
The fuel delivery components consist of fuel supply lines, a high pressure fuel pump (mounted in the fuel tank), a fuel filter assembly and a fuel pressure regulator.
The fuel return system recovers excess fuel vented by the fuel pressure regulator (mounted on the fuel rail) and returns it to the fuel tank. The fuel return line is low pressure and returns directly to the fuel tank. The fuel return system consist of lines and couplings
Fuel Vapor Recovery
The fuel vapor recovery system provides a route for the recovery of fuel vapors (from the fuel tank) either for storage in the charcoal canister, or for evacuation through the purge control system. The vapor recovery system also consists of lines and couplings. These components function as evaporative emissions control devices and are therefore covered in detail in Emission Control System.
Air Induction
Air filtered through the air cleaner passes through the Mass Air Flow (MAF) meter and the amount flowing to the air intake chamber is determined by the throttle valve opening in the throttle body and the engine speed.
The MAF meter measures the intake flow to the engine by the swirl frequency.
The throttle valve, located in the throttle body, regulates the volume of air intake to the engine. Intake air, controlled by the throttle valve opening, is distributed from the intake chamber to the manifold runner of each cylinder and is drawn into the combustion chamber.
At low air temperature the Idle Air Control (IAC) valve opens and the air flows through the IAC valve, as well as the throttle body, into the air intake chamber. During engine warm up, fast idle is accomplished by air flowing into the intake chamber via the IAC valve, even when the throttle valve is closed.
The air intake chamber prevents pulsation of the intake air, which reduces MAF meter accuracy. It also prevents intake air flow interference in each cylinder which increases the air intake volume.
The air induction system on this engine incorporates a turbocharging system. Two turbochargers and an intercooler are used to supply the engine with a denser air charge than normally aspirated engines are capable of producing.
Intake air is drawn into the exhaust gas driven turbochargers where it is compressed and then routed through the intercooler. Much like a radiator for air, the intercooler cools the air, which further increases it's density before it passes into the intake system. To accommodate the extra air in each cylinder, additional fuel is injected as well. The extra air and fuel present in each combustion cycle, results in a higher power / displacement ratio than a normally aspirated engine.