Question

(a) Describe the procedure to be undertaken when, upon a routine schedule for changing fuel injector on a main engine, it is found that the injector body is seized and cannot be removed by conventional means. (10)

(b) Briefly explain the routine tests that are carried out on main engine fuel injectors. (6)

Answer 1

Part (a)

PROCEDURE WHEN A FUEL INJECTOR BODY IS SEIZED AND CANNOT BE REMOVED BY CONVENTIONAL MEANS

Stop the engine and secure the turning gear; isolate the fuel supply to the unit and drain the fuel from the injector/ high-pressure pipe. Tag the unit not-to-run.
Remove the high-pressure fuel pipe and the injector's leak-off/ return connections; remove the injector clamping/ holding-down arrangement (clamp, studs, nuts) so the injector is free.
Attempt gentle freeing: apply a suitable penetrating oil/ releasing agent around the injector body/ bore and allow time to soak. Tap the injector body lightly with a soft-faced hammer (never strike the nozzle) to break the corrosion/ carbon bond.
Use the injector lifting/ extraction tool: fit the maker's injector puller/ extractor (a threaded puller that grips the injector body and applies a steady axial pull) and apply a controlled pull, rocking gently. Do not use excessive force that could damage the cylinder head bore.
If still seized, apply controlled heat: warm the cylinder head bore around the injector (using a hot-air gun/ induction heater or a controlled flame at a safe distance) to expand the head bore relative to the injector, then re-apply the puller. Take care not to overheat or damage the head or the injector.
If the injector is still stuck, use a combination of heat and a hydraulic/ mechanical puller, or a slide hammer/ extractor, working progressively. Where the injector is badly seized, it may be necessary to drill/ tap the injector body to fit a puller, or to machine/ cut the injector out (as a last resort, with the head removed) - this is a workshop operation.
If all else fails, remove the cylinder head and take it to the workshop where the seized injector can be removed by machining (boring out the injector body) without damaging the head bore; the head bore is then re-machined/ sleeved as required.
On removal, inspect the injector bore in the head for scoring, corrosion and damage; clean and, if damaged, re-machine or fit a sleeve/ bush to restore the bore.
Refit a new/ overhauled injector with the correct sealing (copper washer/ O-ring), torque the clamp correctly, reconnect the fuel and leak-off lines, and bleed the system.
Run the engine and check for fuel leaks and correct injection.

Part (b)

ROUTINE TESTS CARRIED OUT ON MAIN ENGINE FUEL INJECTORS

Opening pressure test: The injector is tested on a test rig (injector tester) by pumping fuel/ oil; the pressure at which the needle lifts (opening pressure) is checked against the maker's specification and adjusted (by the spring/ shim) if necessary.
Atomisation/ spray test: The injector is operated on the test rig and the spray pattern is observed - it should be a fine, even, well-atomised spray with no dribble, no streaks, and no uneven distribution.
Leakage/ seat test: The injector is pressurised below the opening pressure and checked for leakage past the needle/ seat (no dripping).
Chatter test: The injector is operated and the needle should "chatter" (open/ close cleanly) without sticking.
Back-leakage test: The amount of fuel leaking back through the injector (leak-off) is checked against the limit.
Visual inspection: The nozzle, needle, spring and body are inspected for wear, carbon, scoring and damage; the nozzle holes are checked for blockage/ enlargement.

✓ Verified Model Answer (Text Solution)

PROCEDURE WHEN A FUEL INJECTOR BODY IS SEIZED AND CANNOT BE REMOVED BY CONVENTIONAL MEANS

ROUTINE TESTS CARRIED OUT ON MAIN ENGINE FUEL INJECTORS