Fuel Delivery and Air Induction: Description and Operation

Influence Of Air/Fuel Ratio On Power, Economy And Emissions:

PURPOSE
The fuel injection system delivers the correct amount of fuel to each cylinder under various engine speeds and load conditions.
The theoretically ideal air/fuel mixture (stoichiometric ratio) is 14.7 : 1. This means the chemical minimum for complete combustion is 14.7 kg of air to every 1 kg of fuel.
Most contemporary engines operate at maximum fuel economy and least emissions output with a mixture of 15.0 : 1.
Because the vehicle engine usually operates in the partial load condition, it is designed for maximum fuel economy in that range. For the other conditions, such as cold start, idle and full load, the fuel mixture is enriched.

Generic Power Comparison Between Turbo And Non Turbo Engine Variants:

This engine incorporates a turbo charger in the air induction system. The turbo charger compresses the intake air to provide a higher cylinder fill rate. This higher fill rate will result in an overall power increase. The normal fill rate of a cylinder in a naturally aspirated engine is about 85%, compared to the turbo engine which can fill the cylinder to a rate of approx. 95 - 120% (depending on boost pressure).

Fuel System Schematic:

BASIC FUEL SYSTEM OPERATION
The fuel injection system used on this engine is called the Bosch LH 2.2-Jetronic. This fuel injection system is manufactured by Bosch and is based on the pulsed multi-port fuel induction system.

The operating principle is simple:
Two fuel pumps (a feed and a main) supply the fuel through the fuel filter into the fuel rail. The fuel rail is equipped with the injectors and incorporates a pressure regulator. This regulator maintains a constant fuel injection system pressure.
During operation, the fuel injectors inject the fuel in front of the intake valve. This injection occurs in a pulsed form. The fuel injectors open and close at a frequency, known as the "injection duration". The longer they stay open, the longer the "duration", therefore, more fuel is supplied to the engine. The "injection duration" is determined by the fuel injection ECU. The ECU uses several input signals (coolant temperature, engine speed, intake air mass... ) to calculate the optimal "injection duration" (air/fuel mixture) for any given engine load. For more information on the fuel injection ECU and its operation, see COMPUTERIZED ENGINE CONTROLS.
The fuel pumps supply a larger amount of fuel then is ever needed by the system. The excess fuel is returned to the gas tank via the pressure regulator and its return line. This constant flushing with cool fuel enables the overall system temperature to drop. This helps to avoid the formation of vapor bubbles and enables good hot starting characteristics.

The components addressed for the intake air and fuel delivery are:
^ Accelerator pedal
^ Air filter
^ EVAP system
^ Fuel filter
^ Fuel injectors
^ Fuel pressure regulator
^ Fuel pumps
^ Fuel pump relay ([1][2]system relay)
^ Fuel rail
^ Fuel return line
^ Fuel supply line
^ Fuel tank
^ Intake air hoses
^ Suppressor relay
^ Throttle body
^ Throttle cable

Turbo System Schematic:

BASIC TURBO CHARGING SYSTEM OPERATION
The turbo charger can be compared to an air pump which pumps air into the engine at higher than ambient pressure.
The turbo charger consists basically of a turbine wheel and a compressor wheel which are connected via a shaft.
The exhaust gases from the engine drive the turbine wheel and consequently the compressor wheel. When the engine speed increases, so does the speed of the compressor wheel, which in turn pumps more air into the engine.
A wastegate valve is incorporated to limit the maximum boost pressure in the intake manifold.

The components for the turbo charging system are:
^ By-pass valve
^ Intercooler
^ Turbo charger
^ Turbo over-boost pressure switch
^ Turbo pressure delay valve
^ Wastegate valve