The port-and-helix metering pumps, used in...

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Question 1 of 205eccefa2bacbc34ba4d478a5

The port-and-helix metering pumps, used in diesel fuel injection systems, are usually designed to produce a constant beginning and a variable ending of fuel injection. These pumps are usually __________.

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🔍 Key Concepts

• Port-and-helix metering pump operation – how rotation of the plunger changes the end of injection • Difference between start of delivery and end of delivery in fuel injection • How injection timing is usually referenced in relation to plunger/port position

💭 Think About

• Ask yourself: in a constant beginning / variable ending system, which event must always occur at the same crank angle – the opening or the closing of the spill port? • Think about what actually stops fuel injection in a port-and-helix pump: is it when the port is uncovered or covered by the helix? • Consider whether engine timing is normally set from the instant injection starts or when it finishes.

✅ Before You Answer

• Be clear on which port event (opening vs closing) corresponds to start of injection in a port-and-helix pump • Verify how rotation of the plunger helix changes the duration of injection without changing its start point • Confirm whether cam or plunger stroke changes timing, or just the quantity of fuel delivered

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