METHANE PRESSURE REDUCTION UNIT

2.0 16V · Methane

CONSTRUCTION SPECIFICATIONS

The diagram below shows the pressure reduction unit.

The pressure reduction unit is fitted in the engine compartment. It includes the actual pressure reduction unit (1) and a cut out solenoid valve (2); a methane pressure sensor (3) is also fitted on it.The high pressure pipe (5) conveys the methane from the canister to the pressure reduction unit inlet, whilst the low pressure pipe (6) is connected at the unit outlet.

Pressure reduction unit operation

The pressure reduction unit has the task of reducing the pressure of the methane from the value in the canister to the supply valve for the methane injectors (9 ± 1 bar), in all engine operating conditions.

The pressure reduction takes place in one stage where the pressure is decreased from 200 to 9 bar.When the pressure in the canister decreases to approximately 15 bar, the CNG control unit automatically switches from methane to petrol operation because at a pressure of below 15 bar at the reduction unit inlet this would automatically result in a pressure of below 9 bar at the oulet and this pressure would be too low for the engine to run smoothly.Since the temperature of the methane decreases considerably as a result of its expansion due to the sudden increase in pressure, the engine cooling circuit has a branch (7) that allows the engine coolant to heat the pressure reduction unit in order to prevent any problems due to the rise in temperature. (The diagram shows the assembly seen from above).

Cut out solenoid valve

The methane cut out solenoid valve is the normally closed type. This means that it only allows the flow of methane when it is energized. It is electrically supplied by the ignition key by means of a special relay and is earthed directly.When the solenoid valve is not supplied, the flow of methane from the canister to the engine is prevented.With the solenoid valve supplied (ignition key in ON position and petrol/methane switch released) the methane passage between the two stages of the pressure reduction unit is open and consequently there is a flow to the injectors.Methane pressure sensorThere is a pressure sensor/transducer (3) fitted on the reduction unit casing, connected to the upstream high pressure pipe (6), that sends a signal to both the methane canister level gauge in the instrument panel and to the CNG control unit which uses it for the operating logics (see electrical/electronic circuit).