Electronically controlled unit injector

An electronically controlled unit injector (EUI) is a unit injector (UI) with electronic control. It performs the same function as a conventional unit injector in an internal combustion engine, such as in an on-road or off-road vehicle or a diesel-electric locomotive. The pressurized delivery of fuel is camshaft-driven, but the timing of the injector's internal operations are controlled by the engine control unit so as to achieve certain advantages.

Central to the EUI is the built-in plunger pump, which, just as in a UI, allows for low-pressure fuel delivery and return to all injectors, yet provides exceptionally high pressure and concomitant injection and atomization of the fuel to a cylinder during the engine's power cycles. As in a UI, the injector is connected to common banks of fuel supply and fuel return. Fuel is always circulating within the EUI as two of its functions, other than injection for combustion, are injector lubrication and injector cooling. Connections on UIs are by formed steel tubes. Connections on EUIs are by stainless steel-reinforced hoses.

The controlled part of the injector is a solenoid-operated spill valve. Normally, it is open, allowing the fuel to return to the supply line when the pump plunger descends. When the solenoid is energized, the spill valve closes, and the fuel is forced through the spray tip into the cylinder.

The four phases of EUI operation are:

Thus, although the mechanical plunger pump has a fixed stroke, electronic control can select any part of that stroke to deliver to the cylinder, thereby controlling the volume and timing of fuel delivery.

This system is employed primarily on Electro-Motive Diesel (EMD) locomotive, marine and stationary engines, and primarily on the 710 family of diesel engines.

When implemented in a locomotive, the ECU may also be incorporated into the Locomotive Control Unit (LCU), which performs a variety of functions, such as wheel-slip control, "phone home" for incident reporting and scheduling of delivery of service parts, etc. EMD's LCU is often GPS-assisted, and maintenance personnel can effectively monitor the performance of perhaps thousands of locomotives at all times.

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