Fuel Oil System — Most Asked Questions
40 questions asked about fuel oil system across the General and Fn 3 and Fn 4b and Fn 6 papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Slide type fuel injector?
Answer
The slide-valve (zero-sac) injector closes the nozzle without leaving a pocket of fuel to dribble after injection — killing smoke, NOx and wasted fuel.
- Old nozzles kept a sac volume below the needle that dribbled fuel after effective injection, making black smoke, NOx and pure waste.
- The slide type eliminates the sac: injection ends crisply with zero trapped volume.
- Typical two-stage opening: primary valve lifts at about 10 bar, secondary at about 300 bar against its spring.
- Benefits the surveyor wants: cleaner combustion, lower NOx, no after-dribble carbon on nozzle tips, measurable fuel saving.
Surveyor follow-up: exhaust shows black puffs at load change with slide valves fitted — injection or air side, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
2 Fuel pump timing
Answer
Fuel timing is checked at compression TDC by the hairline method and set by plunger height, barrel position or cam shims.
- Lock the turning gear, run the LO pump, open indicator cocks, bar the unit toward compression TDC on its upstroke.
- Read timing where the plunger hairline meets its mark — spill-port closing is injection beginning.
- Wrong timing announces itself: hard starting, abnormal exhaust temperatures, black smoke, irregular running.
- Adjust by plunger-versus-barrel height, barrel shims, lead or pmax shims, or cam-to-camshaft position; advance the cam to raise pmax.
Surveyor follow-up: exhaust temperatures high on one unit with normal timing marks — timing or injector, and what proves it?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
3 Fuel oil properties
Answer
Bunker properties decide heating, purification and injection: density, viscosity, flash, pour, residue, asphalt, sulphur and water.
- Density 991 kg per cubic metre maximum at 15°C — sets gravity-disc choice and energy content.
- Viscosity 700 cSt at 50°C maximum — heated to 10–14 cSt at the injector for atomisation.
- Flash point 60°C minimum for machinery-space safety and tank-heating limits; pour point guards pumpability.
- Residue limits: Conradson carbon 22% and asphalt 14% maximum; sulphur 5% maximum, water 1% maximum.
Surveyor follow-up: viscosity correct at the injector but combustion still smoky — which property do you blame next?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
4 Bosh type fuel pump working parts ?
Answer
The Bosch jerk pump meters with a helical plunger in a barrel: ports, helix and delivery valve turning lift into timed injection.
- Plunger sliding free in its barrel with no measurable clearance — wear here drops pressure, quantity and power.
- Suction and spill ports plus the control helix set start and end of injection as the rack turns the plunger.
- Delivery, suction and puncture valves hold pressure between shots and cut fuel on demand.
- Timing adjusts by plunger-versus-barrel height, shims and cam position; advance the cam to raise maximum pressure.
Surveyor follow-up: delivery pressure falling on one pump with timing correct — plunger, valves or cam, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
5 Fuel oil low pressure
Answer
Low fuel pressure is starved suction, worn pump or thin leaking oil: filters, tank level, viscosity and relief valve in that order.
- Suction first: low tank level, choked filters, stuck suction valve or air ingress collapsing delivery.
- Pump next: worn plunger and barrel leaking past clearance drops quantity and pressure together with smoke and lost power.
- Oil condition: cold high-viscosity oil chokes flow, hot thin oil slips past — prove temperature against the 10–14 cSt band.
- Relief and puncture valves passing, burst lines and wrong rack setting complete the hunt.
Surveyor follow-up: pressure low with the relief lifting at normal setting — pump worn or relief weak, and what proves it?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
6 related to MARPOL annex vi brief on regulation on fuel oil availability , quality , BDN and assistance provided by the states to the stake holders
Answer
Annex VI fuel rules put compliant oil on the ship and proof in hand: availability, quality, delivery notes and state help when bunkers fail.
- Ships must be able to buy compliant fuel in port — states report availability and the organisation tracks shortfalls.
- Quality sits with the supplier: sulphur and grade within the ordered spec with retained samples against disputes.
- The bunker delivery note states quantity, density and sulphur for port-state checks and record-keeping.
- Where compliant fuel is genuinely unavailable, the ship reports, logs and notifies the next port instead of burning her way into detention.
Surveyor follow-up: compliant fuel unavailable at the stem port — bunker off-spec or sail short, and what paper saves you?
Full theory: MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning -
7 Fuel injector overhauling
Also asked: “fuel injector overhauling nd pr. Testing”
Answer
Overhaul injectors in clean conditions with special tools: spray, leak, drip and opening pressure proved on the test pump in that order.
- Spray pattern on paper shows blocked or bent holes — a ragged fan condemns the nozzle.
- Leak test just below opening pressure times the pressure fall — fast fall means needle and guide renew.
- Drip test held just below opening pressure must show no droplet at the seat.
- Set opening pressure on the spring, prove clean closing, warn hands clear — spray pressure pierces skin.
Surveyor follow-up: spray ragged with opening pressure correct — lap, renew nozzle or reset spring?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
8 For each ship subject to regulations 5 and 6 of this Annex, details of fuel oil for combustion purposes delivered to and used on board shall be recorded by means of a bunker delivery note which shall contain at least the
Also asked: “For each ship subject to regulations 5 and 6 of this Annex, details of fuel oil for combustion purposes delivered to and used on board shall be recorded by means of a bunker delivery note which shall contain at least the information specified in appendix V to this Annex”
Answer
Every stem lands on paper: the delivery note records ship, port, supplier, product, quantity, density, sulphur and declaration.
- Receiving ship name with IMO number, port and date the delivery starts.
- Supplier name, address and telephone with product names and metric-ton quantity.
- Density at 15 degrees and sulphur content in percent mass with the conformity declaration signed.
- Kept aboard three years for inspection with the retained sealed sample beside it.
Surveyor follow-up: sulphur box blank with density filled — compliant note or not, and what do you do?
Full theory: MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning -
9 The bunker delivery note shall be accompanied by a representative sample of the fuel oil delivered, taking into account guidelines to be developed by the Organization. The sample is to be sealed and signed by the supplie
Also asked: “The bunker delivery note shall be accompanied by a representative sample of the fuel oil delivered, taking into account guidelines to be developed by the Organization. The sample is to be sealed and signed by the supplier's representative and the master or officer in charge of the bunker operation on completion of bunkering operations and retained under the ship's control until the fuel oil is sub”
Answer
Every stem keeps a witness bottle: sealed and signed at delivery, held twelve months until the fuel is gone.
- Drawn to organisation guidelines during bunkering as the representative stem sample.
- Sealed and signed by supplier and master or bunkering officer on completion.
- Held under ship control until the fuel is substantially consumed and at least twelve months from delivery.
- Opened for accredited lab verification when sulphur compliance is disputed.
Surveyor follow-up: sample seal broken with the fuel half burnt — still evidence or just oil, and why?
Full theory: MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning -
10 the fuel oil shall be blends of hydrocarbons derived from petroleum refining. This shall not preclude the incorporation of small amounts of additives intended to improve some aspects of performance; (ii) the fuel oil sha
Also asked: “the fuel oil shall be blends of hydrocarbons derived from petroleum refining. This shall not preclude the incorporation of small amounts of additives intended to improve some aspects of performance; (ii) the fuel oil shall be free from inorganic acid; (iii) the fuel oil shall not include any added substance or chemical waste which either”
Answer
Legal bunker is petroleum hydrocarbon with tiny performance additives only: no acids, no wastes, nothing harming ship, crew or air.
- Hydrocarbon blends from refining with small additive doses for performance allowed.
- Free from inorganic acid outright — acids eat injection gear and liners.
- No added substances or chemical waste risking ship safety, machinery performance, personnel health or extra air pollution.
- Off-spec stems get reported, debunkered or treated — never quietly burnt.
Surveyor follow-up: cheap stem with waste oil blended in — burn it or report it, and under which regulation?
Full theory: MARPOL Annex VI — Air Pollution: SOx, NOx & Exhaust Gas Cleaning -
11 state the purpose of fuel pump on low speed two stroke engine
Answer
The fuel pump meters, pressurises and times every shot: constant nozzle pressure across the injection window at any speed.
- Builds and holds pressure before the nozzle through the whole injection period for even atomisation.
- Varies effective stroke for load while injection pressure and admission rate stay near constant.
- Times by cam-peak position with plunger-height trim — raise the plunger for earlier cut-off, lower for later.
- Low-speed running injects inside maximum plunger acceleration so load swings never starve the nozzle.
Surveyor follow-up: pressure sagging at low load with timing correct — plunger, valves or cam, and what proves it?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
12 Fuel oil should be free from solid and liquid contaminants. Presence of these impurities results in poor combustion, wear of cylinder liner and damage to exhaust valve seats, fuel pumps and fuel valves
Also asked: “• Fuel oil should be free from solid and liquid contaminants. Presence of these impurities results in poor combustion, wear of cylinder liner and damage to exhaust valve seats, fuel pumps and fuel valves”
Answer
Dirty fuel burns dirty and wears everything it touches: solids grind, salts corrode, water kills combustion.
- Solids and cat fines abrade liners, rings, pumps and valves into early overhaul.
- Dissolved vanadium and sodium survive centrifuges to hot-corrode valves, blades and boiler firesides molten near 500 degrees.
- Water cuts heat release, pops in injectors and pits journals through stuffing-box paths.
- Answer is bunkers bought clean, treated hard and watched on exhaust, drains and analysis.
Surveyor follow-up: valves guttering with centrifuges running clean — fuel, cooling or timing, and what analysis proves it?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
13 Fuel oil used onboard should be of good quality for good performance of engines and boilers. In order to make it good quality it has to be settled in settling tank and purified to remove impurities
Also asked: “• Fuel oil used onboard should be of good quality for good performance of engines and boilers. In order to make it good quality it has to be settled in settling tank and purified to remove impurities”
Answer
Good fuel is settled, spun, heated and filtered: gravity tanks drop sludge, purifiers spin water, heaters thin for injection.
- Settling tanks rest bunkers so water and sludge fall for daily draining.
- Purifiers and clarifiers in series spin the rest out hot toward 24 cSt separation viscosity.
- Heaters with viscometer control land 10–14 cSt at the injector with fine filters guarding pumps.
- Sludge to heated sludge tanks for disposal — soluble metals pass through regardless, so buy clean.
Surveyor follow-up: sludge rising with bunkers unchanged — settling, purifier or heater, and what proves it?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
14 Inadequate preheating results in high viscosity which leads to high injection pressures, causing excessive mechanical stresses in the fuel oil system. This affects combustion, increases wear of cylinder liner and piston
Also asked: “• Inadequate preheating results in high viscosity which leads to high injection pressures, causing excessive mechanical stresses in the fuel oil system. This affects combustion, increases wear of cylinder liner and piston ring and damages the exhaust valve seats”
Answer
Cold fuel is thick fuel: injection pressures spike, sprays jet instead of misting, liners and seats pay.
- High viscosity resists pump and injector flow into pressure spikes that strain drives and lines.
- Jets instead of mist burn late and smoky with afterburning and carbon beds growing.
- Liner, ring and seat wear climb together with exhaust temperatures spreading unit to unit.
- Cure is heat to the viscometer band, not pressure — prove 10–14 cSt at the injector.
Surveyor follow-up: pressures normal yet one unit smokes cold — heater, injector or air, and what proves it?
Full theory: Fuel Oil System — Interactive One-Line Diagram -
15 Increasing the atomization pressure of fuel injectors
Also asked: “• Increasing the atomization pressure of fuel injectors”
Answer
Higher atomisation pressure means finer mist: small holes, fast needle lift and hot dense air burn it clean.
- Pressure acts on the needle shoulder against spring compression to snap the valve open.
- Lift exposes the mitre fully so flow jumps — holes sized and patterned to spread the spray.
- Finer drops mix faster for lower particulates, but drive energy, leakage and heat must stay low.
- Mean and peak hole pressures must both climb or extra pump work buys nothing but wear.
Surveyor follow-up: pressure up with smoke unchanged — holes, timing or air, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
16 Show the layout of a 2S slow speed propulsion engine fuel oil system with short notes on components
Answer
Draw bunker to injector in order: transfer, settling, purifier, service, booster, heater, viscometer, filter, pumps, injectors.
- Transfer pump moves bunkers to the settling tank for heating and gravity separation.
- Purifiers take suction through purifier heaters and discharge clean oil to the heated service tank.
- Booster pumps push service oil through heaters to injection viscosity with the viscometer trimming steam.
- Heated filters guard injection pumps and injectors; mixing tank steadies temperature across load swings.
Surveyor follow-up: draw the loop and point at purifier suction and discharge — which tanks sit each side?
Full theory: Fuel Oil System — Interactive One-Line Diagram -
17 Stop fuel oil booster pump
Also asked: “STOP LUBE OIL PUMP”, “Stop-fuel oil booster pump”
Answer
Stop the booster by unloading first: change over, cool the change, then stop and isolate with valves made up.
- Reduce load and change fuel over toward diesel before stopping so lines never clog on heavy oil.
- Stop the pump with suction and discharge proved shut and pressure vented to zero.
- Isolate, lock and tag the drive with the permit in the key safe until work completes.
- Prove standby cut-in on falling pressure before boxing the stopped pump up.
Surveyor follow-up: booster stopped with HFO still in the lines — changeover, heating or tracing, and what first?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
18 The ability to separate water from fuel oil depends on the specific gravity, viscosity, flow rate and separation temperature of the fuel oil. The ability to separate abrasive particles from fuel oil depends on the size a
Also asked: “• The ability to separate water from fuel oil depends on the specific gravity, viscosity, flow rate and separation temperature of the fuel oil. The ability to separate abrasive particles from fuel oil depends on the size and specific weight of the particle”
Answer
Separation follows physics, not hope: density gap, thin hot oil, slow flow and right temperature split water; size and weight split grit.
- Wide specific-gravity gap between oil and water with low viscosity at high separation temperature.
- Slow throughput giving droplets time to settle or spin out in settling tanks and purifiers.
- Abrasives separate by size and specific weight — big dense cat fines first, flour-fine last.
- Prove by interface position, sludge volumes and outlet clarity against the gravity-disc table.
Surveyor follow-up: water passing with settings correct — flow, temperature or disc, and what do you change first?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
19 Worn out fuel pump, cam and roller
Also asked: “Worn out fuel pump cams”
Answer
Worn pumps, cams and rollers lose lift, timing and pressure together: quantity falls, smoke rises, power fades.
- Worn plunger-to-barrel clearance leaks past pressure — delivery quantity and pressure fall together.
- Worn cams and rollers retard and soften lift, shifting timing late with incomplete injection.
- Symptoms stack as hard starting, black smoke, lost power and uneven exhaust temperatures.
- Prove by pump lead, pmax and timing marks; renew plunger sets, cams and rollers to maker figures.
Surveyor follow-up: timing correct with pressure low on one pump — plunger, cam or valves, and what proves it?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
20 if turbocharger increases fuel consumption by 10-15%; it still reduces the overall fuel consumption than a large engine with more cylinders. This leads to much efficient fuel consumption in turbocharged engines
Also asked: “• if turbocharger increases fuel consumption by 10-15%; it still reduces the overall fuel consumption than a large engine with more cylinders. This leads to much efficient fuel consumption in turbocharged engines”
Answer
Turbocharging spends a little air power to save a lot of engine: smaller boosted plant beats a bigger lazy one.
- Blower work costs fuel to compress charge air — the 10–15% the question quotes.
- Dense charge burns more fuel per stroke with better thermal efficiency and mechanical efficiency together.
- Smaller boosted engines replace thirsty multi-cylinder giants at the same output.
- Modern efficient turbochargers stretch expansion further down the stroke for the same bunkers.
Surveyor follow-up: boosted engine thirstier than her natural sister — matching, fouling or overload, and what proves it?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
21 she's speed increased by 20% above normal for hours, reduced by 10% below normal ‘for 10 hours and fe the remai ing 6 hours of the day the speed s normal, Calculate the ‘percentage variation in fuel consumption in that d
Also asked: “she's speed increased by 20% above normal for hours, reduced by 10% below normal ‘for 10 hours and fe the remai ing 6 hours of the day the speed s normal, Calculate the ‘percentage variation in fuel consumption in that day from normal. (10”
Answer
Fuel follows the cube: power near speed cubed, so a day split fast, slow and normal burns about 13% more than steady steaming.
- Apply power proportional to speed cubed with consumption tracking power at constant plant efficiency.
- Assume 8 hours at 1.2 speed to fill the 24-hour day: 1.728 × 8 gives 13.82 leg-units.
- Ten hours at 0.9 speed gives 0.729 × 10 or 7.29, plus 6 hours normal gives 6.00 — day total 27.11 against 24.00.
- Variation is (27.11 − 24.00) / 24.00, about +13% — state the 8-hour assumption aloud since the question drops that figure.
Surveyor follow-up: +20% for 12 hours instead of 8 with the rest as stated — recompute the day total before answering?
Full theory: Fuel Consumption & Speed Relationship -
22 AE Fuel injector overhaul and testing
Also asked: “Fuel.injector overhaul testing”
Answer
An auxiliary injector is stripped, examined, cleaned and lapped — no part is assumed good and no reassembly is without a test.
- Dismantle completely and examine every internal part visually; if all is in order, clean thoroughly and reassemble to the builder’s manual.
- Immerse the needle guide in clean diesel oil, take the needle out, and check it for bending and signs of overheating.
- Repair a damaged nozzle-body to valve-body seat with fine lapping paste, then flush it thoroughly with clean diesel and blow dry with compressed air.
- Check the spring, the leak-off pipes, the shims and the packing, and clean the cooling pockets with compressed air on a water-cooled valve.
- On reassembly test the injector and adjust the opening pressure; on some small engines the spring compression is fixed and cannot be altered.
Surveyor follow-up: rebuilt injector holding pressure but spraying asymmetrically on the bench — the hole, the guide or the seating?
Full theory: Marine Fuel Injectors — Atomisation Dynamics, Slide Valves & The Seven Workshop Bench Tests -
23 Bunker tank to settling tank transfer. What type of pump? Can't centrifugal pump be used?
Answer
Bunker transfer is a screw pump: heavy oil will not give a centrifugal pump its prime, so a positive-displacement pump moves it.
- A positive-displacement pump — screw or rotary — moves heavy fuel irrespective of the suction head available.
- A centrifugal pump cannot prime reliably on cold, viscous bunker oil; it aerates and cavitates rather than delivering.
- The transfer pump is a screw pump with its own relief valve, and the line is heated and vented before it is started.
- One effect is the need for a settling tank and heating: the oil is warmed before it can be handled at all.
Surveyor follow-up: bunker transfer pump replaced with a centrifugal and now losing prime — is the pump, the suction or the heat?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
24 Faulty fuel valve (Excessive injector spring setting
Answer
Too much spring on the fuel valve raises the injection pressure and the opening point, and the nozzle then drips and smokes.
- A high spring setting lifts the valve at greater pressure, so the needle does not seat cleanly and fuel passes the seat.
- The symptoms are a leaky valve, loss of power on that cylinder, high exhaust temperature and a pressure wave.
- Reset the spring to the maker’s pressure and re-lap the needle and seat before increasing anything.
- The trap is that a drip is treated by more spring — which makes the atomisation worse and the fuel consumption higher.
Surveyor follow-up: injector opened at 400 kg/cm² after a previous repair — is the spring, the needle or the pump first?
Full theory: Marine Fuel Injectors — Atomisation Dynamics, Slide Valves & The Seven Workshop Bench Tests -
25 Fuel injector atomization
Also asked: “• injected fuel's atomization”
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26 Fuel injector dripping indication
Answer
Dripping injectors show as smoke, heat and lost power on one unit: the fuel is going past the nozzle instead of into the cylinder.
- Symptoms are loss in power, high exhaust temperature with smoke, and knock or a pressure wave in the injection system.
- Power card and draw card together show the pressure fluctuation during expansion, which points at the injection.
- Causes are contamination choking the atomiser holes, a leaky injector letting hot gas blow back, and an overheated nozzle.
- Remedies are a new fuel valve, a clean fuel system, correct centrifuging and filtering, and correct fuel valve cooling temperature.
Surveyor follow-up: one cylinder smoking with the injector on the bench dripping at set pressure — re-seat, replace or clean?
Full theory: Marine Fuel Injectors — Atomisation Dynamics, Slide Valves & The Seven Workshop Bench Tests -
27 Fuel injector testing , fuel injector valve dia. Value
Answer
An injector is proved on the bench in four motions: spray pattern, leak, drip and opening pressure, with the hole gauged.
- Spray pattern: hold a sheet below the injector and give a jerk — the pattern tells you the state of the holes.
- Leak test: raise pressure to just below opening and time the fall; a fast drop means renew the needle and guide.
- Drip test: hold just below opening pressure for a few seconds and confirm no droplet forms at the nozzle.
- Opening pressure is normally 280 to 380 kg/cm² within ±10; an early opening is corrected by tightening the top screw, and hole size is go and no-go gauged.
Surveyor follow-up: injector passing the drip test but short 15 kg/cm² on opening — is it the spring, the screw or the plunger?
Full theory: Marine Fuel Injectors — Atomisation Dynamics, Slide Valves & The Seven Workshop Bench Tests -
28 Fuel valve overhaul?
Answer
Overhaul the fuel valve to restore atomisation: strip, decarbonise, lap the nozzle, and prove the pattern and the leak.
- Strip the valve completely and clean the nozzle and body carbon from hot gas blow-back.
- Lap the needle to its seat and polish the guide, checking the spring and the spring seat for set.
- Check the nozzle hole size with go and no-go gauges and reset the opening pressure with the top screw.
- Reassemble, bench-test for pattern, leak and drip, and record the result against the cylinder it came from.
Surveyor follow-up: valve lapped and still dribbling with the spring set — is it the spring, the guide or the opening pressure?
Full theory: Marine Fuel Injectors — Atomisation Dynamics, Slide Valves & The Seven Workshop Bench Tests -
29 In the system shown in Figure , the oil is stored in tanks in the double bottom from which it is pumped to a settling tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily servic
Also asked: “In the system shown in Figure , the oil is stored in tanks in the double bottom from which it is pumped to a settling tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily service tank. From the daily service tank the oil flows through a three-way valve to a mixing tank. A flow meter is fitted into the system to indicate fuel consumption. Booster pumps are”
Answer
The heavy fuel train is: double bottom, transfer pump, settling tank, purifiers, daily service tank, mixing tank, booster and heater.
- Fuel is pumped from the double bottom bunker tank by a transfer pump to the fuel oil settling tank, where it is heated.
- The purifiers or centrifuges take suction from the settling tank via purifier heaters and remove water and impurities.
- Cleaned and heated oil passes to the service tank, which has its own heating coils, then via a flow meter to the mixing tank.
- Booster pumps take suction from the mixing tank and discharge to the fuel oil heaters, achieving the correct temperature and viscosity.
Surveyor follow-up: fuel arriving at the engine with a low viscosity and a warm settling tank — where in that run did it go wrong?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
30 Incorrect fuel pump timing (Slow or late combustion of fue!
Answer
Late pump timing means late injection: the fuel arrives after the air is hot, combustion runs long, and the unit runs dirty and hot.
- Slow or late combustion gives high exhaust temperature, smoke, rising afterburn and a knocking pressure wave.
- The card and the draw card show the injection point moving later relative to the compression line.
- The causes are pump timing, the VIT setting, a stretched chain, or a delivery valve that will not hold the line charged.
- Correct it by re-timing the pump or resetting the VIT, then prove it on the card at the same load.
Surveyor follow-up: late timing on one cylinder with the chain within limits and the valve holding — where else?
Full theory: Variable Injection Timing (VIT), Super-VIT & Engine Emissions -
31 Incorrect fuel pump timing and wrong V.I.T setting
Answer
VIT exists to move the firing point so peak pressure lands near 85% MCR — set wrong, the engine runs rough, hot or knock-knocking.
- The reason for variable injection timing is economy, achieved by advancing injection so maximum combustion pressure sits at about 85% MCR.
- Advanced VIT raises peak pressure and efficiency; retarded VIT softens combustion but costs fuel and raises exhaust temperature.
- A pump out of timing shows the same symptoms as a wrong VIT setting, so both are proved on the card at the same load.
- The fuel quantity and VIT linkages work together — a free or seized linkage turns a timing setting into a quantity fault.
Surveyor follow-up: exhaust temperature high with VIT proved advanced and the chain tight — is the pump, the linkage or the load?
Full theory: Variable Injection Timing (VIT), Super-VIT & Engine Emissions -
32 Injection viscosity too low
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33 Is there any delivery valve present in fuel pump, purpose of the delivery valve
Answer
Yes — the delivery valve sits on the delivery side and holds the fuel column in the line between pump and injector.
- It opens against its spring on the delivery stroke, filling the line and holding it charged to the next injection.
- When the delivery stroke ends, the short-circuiting between suction and delivery drops the pressure on the plunger top.
- The fuel in the line is then drawn back rather than being left standing in the pipe between injections.
- That column of fuel is what makes the injection pressure at the nozzle, so the valve is part of the timing, not just plumbing.
Surveyor follow-up: injector dribbling with the delivery valve leaking on the pump — is the valve, the nozzle or the pressure?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
34 It's main function is to form the top part of the combustion space; while supporting all necessary valves required for the operation such as inlet, exhaust and fuel injector. 10 ) Inlet and Exhaust Valves The function of
Also asked: “It’s main function is to form the top part of the combustion space; while supporting all necessary valves required for the operation such as inlet, exhaust and fuel injector. 10 ) Inlet and Exhaust Valves The function of inlet valves in a four stroke marine diesel engine is to inject a charge of fresh air in the combustion space; while the work of exhaust valves all marine engines is to eject out”
Answer
The cylinder head forms the top of the combustion space and carries the valves and the injector that work in it.
- Its main function is to form the top part of the combustion space while supporting the valves the engine needs.
- The inlet and exhaust valves, their seats, guides and springs, plus the fuel injector, are all carried in or on the head.
- Water passages run through it for jacket and head cooling, and the head gasket seals the combustion space against the liner.
- The head therefore takes the highest gas temperatures in the engine — which is why it is the part most often cracked.
Surveyor follow-up: head removed with a crack round the injector boss and the valve seats unmarked — which came first?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
35 Settling tank > Maintain temperature at least 14'C below flash point. > Drain out water & sludge
Answer
The settling tank is kept warm enough to flow and far enough below the flash point to be safe — that is the whole of the routine.
- Maintain the temperature at least 14°C below the flash point, so the fuel is flowing and still not making vapour.
- Drain out the water and sludge on the schedule — the water is what ruins the pump and the valve before anything else.
- The settling tank gives the fuel time to separate by gravity, so the purifier works on already-settled oil.
- Log the temperature, the level and what was drained; an untended settling tank puts water into the booster.
Surveyor follow-up: fuel to the pumps with water in it and the tank near flash point — is the heat, the drain or the purifier first?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
36 Sulzer fuel pump
Also asked: “Fuel pump (Sulzer”
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37 Tell me about construction of fuel pump and all parts of fuel pump
Answer
A fuel pump is a plunger in a barrel with a jerk device, a delivery valve, a suction valve and a spring to retract the plunger.
- The four definitions of stroke are beginning of injection, end of injection, total stroke and effective stroke.
- The plunger and barrel are the metering pair, and their clearance decides what the pump can deliver at pressure.
- The delivery valve holds the line charged, the suction valve admits from the settling tank or the booster discharge.
- The jerk device — a cam or eccentric — converts rotation into the fast plunger stroke that sets the injection rate.
Surveyor follow-up: pump delivering at pressure but with the suction valve passing — is the valve, the filter or the tank level?
Full theory: The Valve Gear and Fuel Injection — Valves, Camshaft Drive, Pumps and Injectors -
38 The viscosity regulator controls the fuel oil temperature in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, and a pre-war
Also asked: “The viscosity regulator controls the fuel oil temperature in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, and a pre-warming bypass is used to heat up the fuel before starting the engine”
Answer
The fuel train manages the oil so the pump sees the right viscosity and the right pressure — heat it, regulate it, then pre-warm it.
- The viscosity regulator controls the fuel oil temperature to give the correct viscosity for combustion.
- A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, whatever the suction conditions.
- A pre-warmer unit heats the oil before it reaches the pump, so a cold start does not shock the injection system.
- Together they are what keeps the fuel atomising properly — and every one of them is a setting to prove, not assume.
Surveyor follow-up: fuel pressure dropping with the regulator proved in balance — is the suction, the filter or the booster?
Full theory: Lube Oil & Fuel Systems — Properties, Treatment & Changeover -
39 flash point and fire point
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40 no fuel oil in service tank
Also asked: “• no fuel oil in service tank”
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