System Description

Alternative Fuel Engine Control Module (AF ECM) controls fuel system when vehicle is operating on CNG. CNG is stored in a tank at pressures up to 3600 psi. A High Pressure Lock-Off (HPL) solenoid located in the tank and a Low Pressure Lock-Off (LPL) located in fuel line, prevent fuel flow. When ignition is turned on, AF ECM commands HPL open for one second to charge fuel system, and allows Fuel Pressure Sensor (FPS) to monitor tank pressure. When engine is cranking or running, AF ECM opens both HPL and LPL. This fuel delivery system utilizes 2 different pressure stages in order to lower fuel pressure from tank pressure down to an injector delivery pressure.

1. High Pressure Regulator Stage
   
   When AF ECM commands HPL solenoid open, fuel begins to flow through High Pressure Regulator (HPR). HPR reduces fuel pressure to 110-210 psi (758-1448 kPa). The outlet of HPR is the intermediate pressure stage.
2. Intermediate Pressure Regulator Stage
   
   With pressure between 110-210 psi (758-1448 kPa), fuel exiting HPR flows through intermediate fuel line to LPL solenoid. LPL solenoid is controlled by AF ECM. Fuel flows out of LPL and into Intermediate Pressure Regulator (IPR). IPR reduces fuel pressure to 43-46 psi (246-317 kPa). Fuel flows out of IPR and into fuel rails.