An individual fuel injection pump is designed for variable beginning and constant ending of injection. For diesel engines operating a generator at constant speeds, the start of injection will __________.
• Fuel injection timing in diesel engines driving generators at constant speed • Meaning of variable beginning and constant ending of injection in an individual pump • Relationship between engine load, amount of fuel injected, and timing in constant-speed operation
• Think about what must change in the fuel injection event when the engine load increases but the speed is held constant. • If the end of injection is fixed in crank angle, what must happen to the start of injection when you need to inject more fuel per cycle? • Consider whether starting injection exactly at top dead center (TDC) is practical when varying the quantity of fuel to meet different loads.
• Be clear on the difference between constant-speed operation (like a generator) and variable-speed propulsion engines. • Visualize the injection period on a crank angle diagram: as you inject more fuel, does the duration increase forward (earlier), backward (later), or stay centered? • Eliminate any option that would require the end of injection to shift, since the design specifies a constant ending.
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