The main propulsion diesel engines on your uninspected fishing industry vessel are fitted with mechanically operated and controlled unit injectors. In order for the engine to run properly, the injectors must be properly timed relative to the camshaft and properly synchronized relative to the other injectors. In terms of timing and synchronization, what statement is true?
• Injector timing – when (in crank/cam degrees) injection starts in each cylinder relative to the camshaft and piston position • Injector synchronization – making sure all cylinders get the same amount of fuel for a given power setting • How cam follower height and control rack position each affect a unit injector’s operation
• Think about which adjustment changes when the injector plunger starts and stops its pumping stroke relative to cam rotation. • Think about which adjustment changes how much fuel is injected for a given stroke, and lets you balance power between cylinders. • Ask yourself: on a mechanically controlled unit injector, does the rack move the timing of injection, or the quantity of fuel delivered?
• Be clear that timing = start/end of injection in the cycle, not fuel quantity. • Be clear that synchronization = equal fuel quantity between cylinders, not crank angle. • Match cam follower height with the function that depends on the cam profile (mechanical stroke and timing), and control rack with the function that depends on fuel metering (quantity/engine speed control).
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