Multec 3.5 Fuel Injector Application Manual
Fundamentals
Delphi Energy and Chassis Systems
Revision:
11/05-1
2-21
2.3.1 Minimum Fuel Pump Flow Output
The minimum fuel pump output must provide enough fuel to maintain
regulated fuel pressure during all engine running modes. Regulated fuel
pressure is defined as the pressure reached when the fuel pressure
regulator has enough fuel passing through it to adequately control the fuel
pressure in the rail. The fuel pressure regulator is normally mounted at the
rail for recirculating fuel systems, and at the fuel pump for demand (or
returnless) fuel systems.
Typically, the minimum fuel pump flow output is determined by taking
the maximum required flow for the injector multiplied by the number of
cylinders. Additional flow is added to ensure that there is always some
minimum amount of flow for proper operation of the pressure regulator.
The minimum flow through the regulator is a characteristic of each
regulator design. Refer to the MPFI Fuel Rail Assembly Manual for more
details.
This relationship should be maintained for all engine running mode
system voltages. The required fuel pump supply pressure at minimum
pump flow is determined by the set-pressure of the regulator at minimum
flow and the supply line pressure-drop between the pump and regulator.
2.3.2 Nominal Fuel Pump Output
Nominal fuel pump output and nominal system voltage and conditions
should be determined with consideration for the following:
•
Minimum flow requirements for the system must be met. See above
section for details on minimum flow requirements.
•
Output must not be so large (especially for recirculating fuel systems)
that large amounts of heated fuel are returned to the fuel tank, resulting
in increased vapor generation. This will cause the fuel vapor pressure
in the tank to increase and will also increase the demands on the
evaporative canister storage and purge system.
•
Output must not be so large as to exceed, at worst case maximum flow
conditions, the maximum fuel pressure regulator flow rate for safe
operation.
•
Since the injector is a pressure-differential-sensitive device, avoid
pump-induced pressure variations.
Note:
The information provided on fuel pump specification is provided only as
an overview. For further information on fuel pump application criteria,
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