Fuel Injection: Injector

The solenoid-controlled injection valve discharges a high-pressure spray into the combustion chamber. The solenoid-controlled injection valve is a retracting-plunger valve characterized by a high level of flexibility in its spray-propagation pattern (angle and shape). The discharge orifices form the high-precision injection pattern. This provides even and consistent propagation.

The retracting-plunger solenoid-controlled injection valve continues to maintain stable propagation properties, even at the temperatures and pressure levels encountered within the combustion chamber. Fuel is injected into the combustion chambers under high pressure (between 50 and 200 bar) during the intake and compression strokes. During the warm-up phase yet another, minute quantity of fuel is injected to assist the catalytic converter reach its effective operating temperature more quickly (catalytic converter heating). During cold starting the fuel is sprayed during the compression stroke in multiple pulses. This strategy provides reliable cold-starts along with substantive improvements in the areas of pollutant emissions and fuel consumption.

Fig 1: Identifying Injector And Two-Pin Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.

The solenoid-controlled injection valve injects the quantity of fuel required under the instantaneous conditions into the combustion chamber. The mass can be adapted based on 2 control variables:

• Rail pressure
• Injector opening period.

The opening period is controlled by the fuel injection signal. The opening period is specified by the Digital Engine Electronics (DME). The opening stroke is determined by the activation duration of the injector. Generally, the stroke is always a maximum stroke.

The DME controls activation of the solenoid-controlled injection valve on the earth side.

The activation can be divided into 4 phases:

• Opening phase
• Intake phase
• Holding phase
• Deactivation phase.

Fig 2: Fuel Injection Signal Graph

Courtesy of BMW OF NORTH AMERICA, INC.

Together with the spark plug, the injector is integrated centrally in the cylinder head between the intake and exhaust valves. This installation position avoids wetting the cylinder walls and the piston crown with injected fuel. Uniform formation of the fuel-air mixture is achieved with the aid of gas movement in the combustion chamber and cone-shaped fuel dispersion. The movement of gas is influenced by the geometry of the intake ports and the shape of the piston crown. The injected fuel is swirled with charge air in the combustion chamber.

Fig 3: Identifying Exhaust Valve Components

Courtesy of BMW OF NORTH AMERICA, INC.