The Detroit Diesel Series 71 is a two-stroke Diesel engine series, available in both inline and V configurations. The primary fuel pump is gear driven from the engine and the fuel pressure output is ~45 to ~65 PSIG at 1600 to 2100 RPM. This low pressure fuel pump supplies filtered Diesel fuel into the cylinder head fuel ducts, and into each injector fuel port of a constant stroke pump plunger injector, which is overhead camshaft operated. UIs are employed (Unit Injector is an integrated direct fuel injection system for Diesel engines, combining the injector nozzle and the injection pump in a single component. The plunger pump used is driven by a shared camshaft. In UI, the device is often lubricated and cooled by the fuel itself.), with one injector per cylinder, with no high fuel pressure outside of the injector body. This design of the UI eliminates the need for high-pressure fuel lines, and with that their associated failures, as well as allowing for much higher injection pressure to occur. The unused fuel that has been employed to cool the UI’s is returned to the fuel tank heating the remaining fuel in the tank.
The forward fuel flow (volume over time) and return fuel flow is dependent on multiple factors:
• Fuel specific gravity (varies with temperature etc.)
• The fuel supply system, e.g. filter(s)
• The UIs (type)
• UIs and engine condition
• Engine RPM
• Engine loading
• Environment (temperature and humidity)
• Others factors
In general, as engine RPM increases the primary fuel pump maintains supply fuel pressure, the UI’s deliver more fuel to the engine increasing forward fuel flow as well as return fuel flow.
What is your exact engine model number and when fabricated?
What exact UI’s are installed?
Assume you have considered installing positive displacement fuel flow transducers in the forward and return lines for empirical data gathering over RPM etc.
