Automotive Engine Air and Fuel Management Systems Explained

Air Flow Measurement

The air flow sensor measures the volume of air entering the engine. The ECU uses this data, among other inputs, to calculate the precise amount of fuel to be injected. Its operation is based on measuring the force exerted by the air stream on a palette, which works against a spring mechanism. Air generated by the engine's aspiration passes through the throttle body after being filtered. As it passes through the flow meter, it generates an electrical signal sent to the ECU, which then regulates the fuel injection volume.

Additional Air Device

The additional air valve seals or opens an air duct to provide the necessary air volume during specific engine conditions. During the engine heating phase, the injected fuel volume is increased. This volume is matched by a greater proportion of air provided by the additional valve, which bypasses the throttle butterfly. Once the engine reaches operating temperature, the additional air valve is deactivated.

Cold Start Systems

The cold start device functions by injecting auxiliary fuel into the intake manifold or air box. This provides a fuel supplement for a limited time, regulated by a thermal timer. The timer is in contact with the engine coolant, causing a bimetallic strip to curve. Once the target temperature is reached, the strip bends, opening the contacts and interrupting the command signal to the cold start injector, stopping the fuel supplement.

Lambda Probe and Emission Control

To reduce toxic emissions, fuel injection systems utilize a lambda probe (oxygen sensor). Installed in the exhaust system near the muffler pipe, it measures the oxygen content of the exhaust gases. It generates a signal sent to the ECU to adjust the fuel mixture based on engine requirements. This process ensures more complete combustion, minimizing noxious fumes. The combined use of this device and a catalytic converter is standard in modern fuel injection systems.