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DIESEL FUEL INJECTION

There are both electronic and mechanical types of injection found on diesel engines; all are multi-port in design. The electronic types function essentially the same as the gasoline multi-port fuel injection system. There are four main types of mechanical diesel injection systems:

  1. Inline or rotary distributor pump
  2. Individual control pump
  3. Common rail
  4. Unit injection

    The inline or rotary distributor pump is one of the most common types of diesel injection found. This type of pump pressurizes and distributes fuel for each of the cylinders. Fuel from the fuel filter flows from the transfer pump (usually a vane type pump attached to the distributor pump assembly) to the distributor pump itself. The fuel is pressurized inside the distributor pump to approximately 1800 psi (12,411 kPa). This high pressure fuel is then directed to an injector at the appropriate cylinder. The injector atomizes the fuel for proper combustion.

    Fig. 1: Rotary type distributor pump

    Fig. 2: Inline distributor pump injection system

    Fig. 3: Rotating the pump plunger meters the amount of fuel delivered to the cylinder

    The individual control pump system use a separate high pressure pump and metering unit for each cylinder. The high pressure pumps are fed fuel from a transfer pump. The plungers have helix cut grooves which allow them to meter fuel. By rotating the plunger, the effective stroke is changed and the amount of fuel fed to injectors is metered. The plungers themselves are cam operated. The injector atomizes the fuel for proper combustion.

    On common rail systems, a high pressure pump feeds fuel to the injectors through a common rail. The injectors are actuated by a cam, pushrod and rocker arm assembly. The amount of fuel delivered depends on how long the injector is open. A wedge mechanism varies the effective length of the pushrod, which controls how long the injector is open. The injector also atomizes the fuel for proper combustion.

    Unit injections systems also use an individual injector for each cylinder. The injector also contains a high pressure pump and metering assembly, fed by a transfer pump. The injectors are cam operated. Rotating the pump plunger in the injector meters the amount of fuel delivered to the cylinder. In addition, the injector atomizes the fuel for proper combustion.

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