Fuel Mixer

The fuel mixer is an air-fuel metering device and is completely self contained. The fuel mixer does not require linkage or an idle vacuum line connected to the intake manifold. The mixer is an air-valve design, utilizing a relatively constant pressure drop to draw fuel into the mixer from cranking to full load. During normal engine operation, the fuel is drawn from the secondary chamber of the low pressure regulator by the vacuum created as the air passes through the fuel mixer. This pressure drop is most commonly referred to as air valve vacuum. As the air valve vacuum increases or decreases, the amount of fuel drawn from the secondary chamber will increase or decrease. In the fuel mixer, the CNG vapor is combined with air to form a combustible air/fuel mixture.

The vacuum applied to the air valve, working against a spring located on top of the valve, correctly positions the air valve to meter the proper amount of fuel for any given engine speed and load. The pressure drop that is controlled by the air valve spring provides the force to draw fuel into the air stream. The upward movement of the diaphragm controls the fuel flow in the venturi air valve.

A pressure drop under the air valve of approximately 0.2 psi (6 in H2O) of pressure is required to lift the air valve of its seat. Approximately 0.5 psi (13.8 in H2O) lifts the valve to the top of its travel in the full open position. Lowered pressure communicated to the top of the diaphragm varies with engine speed and the position of the throttle valve opening. The air valve assembly measures the air flow into the engine by moving precisely in response to the demands of the engine and throttle valve position.

The controlled pressure drop of 0.2-0.5 psi (6-13.8 in H2O) set up by the metering spring provides the signal or force necessary to draw fuel into the air stream within the mixer. The gas metering valve is attached to the air valve assembly and is shaped to admit the correct amount of fuel from the gas jet to mix with incoming air at any opening of the air valve.