{"id":5915,"date":"2023-06-23T16:57:54","date_gmt":"2023-06-23T16:57:54","guid":{"rendered":"https:\/\/seadonna.com\/blog\/?p=5915"},"modified":"2023-06-23T17:04:35","modified_gmt":"2023-06-23T17:04:35","slug":"fuel-valve-questions-asked-by-mmd-surveyors-meo-class-4-class-2-marine-engineer-study-guide-mechanical-engineering","status":"publish","type":"post","link":"https:\/\/seadonna.com\/blog\/fuel-valve-questions-asked-by-mmd-surveyors-meo-class-4-class-2-marine-engineer-study-guide-mechanical-engineering\/","title":{"rendered":"FUEL VALVE | QUESTIONS ASKED BY MMD SURVEYORS | MEO CLASS 4 \/ CLASS 2 | MARINE ENGINEER STUDY GUIDE | MECHANICAL ENGINEERING"},"content":{"rendered":"

\"\"FUNCTIONS<\/strong>
\nFuel valve is one of the vital parts of the Diesel Engine due to their high precision in manufacturing and the intricate duties it has to perform, to atomiser, penetrate and distribute as swirling action achieved.<\/p>\n

Atomisation<\/strong>
\nAtomisation is the splitting up of the fuel into very small droplets by the fuel injector, forcing fuel at high pressure through small atomiser holes.
\nThe droplet size will depend upon the size of holes and the pressure difference between fuel pump discharge and that of the compressed air in the combustion chamber, and consequently the size of droplets may vary.
\nAtomised droplets have a high surface area to mass ratio, giving good heat transfer and causing efficient combustion with minimum of unburnt fuel.
\nAtomization<\/strong> \u2013 to ensure that each minute particle of fuel is surrounded by particle of oxygen with which it can combine.
\nAtomization. Is the break up of the fuel charge into very small particles it is injected into the cylinder.
\nPenetration refers to the distance that the fuel particles travel or penetrate into the combustion chamber.<\/p>\n

Why fuel is required to atomise ?<\/strong>
\n\udbc0\udc56 To get complete (fully) combustion of charge fuel within a short time.
\n\udbc0\udc56 To ensure that each minute particle of fuel is surrounded by particle of oxygen<\/p>\n

Excessive Atomisation<\/strong>
\n1) Smaller oil particles have insufficient KE, to go through combustion chamber
\n2) Dense compressed air has high resistance to the motion of oil particles
\n3) Smaller particles tend to cluster around injector tip, and oxygen-starved during combustion
\n4) Can cause after-burning<\/p>\n

Insufficient Atomisation<\/strong>
\n1) Oil particles become larger and will have more KE and travel further into combustion chamber, and some may rest on cylinder liner and piston crown.
\n2) Carbon built-up around the top of cylinder and piston crown
\n3) Lower rate of combustion and after burning<\/p>\n

Penetration<\/strong>
\nIt refers to the distance the oil droplets travel into the combustion space before mixing with the air and igniting.
\nThis will depend upon droplet size (atomisation), velocity leaving the injector and the conditions within the combustion chamber. It is desirable that fuel should penetrate into the whole of the combustion space for efficient space utilisation and good mixing, but droplets should not impinge on the internal surfaces before burning. The number of atomiser holes and their position will decide the spray pattern.<\/p>\n

Low Penetration<\/strong>
\n1) Less intimate mixing of air and fuel particles in combustion chamber
\n2) Fuel cluster around injector tip causing after burning<\/p>\n

High Penetration<\/strong>
\n1) Fuel particles travel further into the combustion chamber and some may rest on the cylinder liner and piston crown
\n2) Lower rate of combustion and after burning<\/p>\n

Turbulence<\/strong>
\nIt is the movement of compressed air and fuel within the combustion space before combustion occurs. This may have several causes. Swirl is imparted to the air during its entry at scavenge ports. It may be further agitated by the furl spray pattern and the shape and movement of the piston crown.
\nTurbulence will improve the mixing of fuel and air for effective and rapid combustion. It is particularly desirable for rapid combustion of heavy fuels in medium or higher speed engines.<\/p>\n

Propose of cooling to nozzle tip<\/strong>
\n\udbc0\udc09 To prevent carbon trumpet (or) formation & needle valve seizure
\n\udbc0\udc09 To maintain the tip region temperature within acceptable limit
\n\udbc0\udc09 To avoid the malfunction of operation mechanism<\/p>\n

How to check the fuel valve is OK or Not ?<\/strong>
\n\udbc0\udc31 Set pressure (on pressure gauge)
\n\udbc0\udc31 Atomization (visual check & listening jarring noise)
\n\udbc0\udc31 Spray pattern (by maker supply spray pattern plate, holes on it must not touch the oil or paper method @ right angle to valve)
\n\udbc0\udc31 Dribble (sensing hand feel after correct pressure test)<\/p>\n

Effect of trumpet formation ?<\/strong>
\n1) Interfere the spray pattern
\n2) Increase fuel consumption
\n3) Poor combustion resulting in black smoke
\n4) High exhaust temperature<\/p>\n

Fuel valve overhaul ?<\/strong>
\n1) Test & check the old valve
\n2) Slacken the lock nut & adjusting screw to release spring pressure
\n3) Make upside down & remove retaining cap nut, take out nozzle & dowel pin fitting
\n4) Make upright, remove lock nut, adjusting screw, spring, spindle and spring retainer
\n5) Clean all parts with kerosene especially on nozzle holes check all parts thoroughly & renew if necessary<\/p>\n

Check point:<\/strong>
\n\udbc0\udc31 Nozzle hole diameter with pin gauge (Maker supply)
\n\udbc0\udc31 Needle valve surface
\n\udbc0\udc31 Valve lift
\n\udbc0\udc31 Spindle for straightness
\n\udbc0\udc31 Spring tension
\n\udbc0\udc31 Lock nut & pressure adjusting screw wear & tear
\n\udbc0\udc31 Body especially oil passage<\/p>\n

6) Reassemble correct sequence and set the pressure on test pump and check the following<\/strong>
\na. Set pressure (some holding pressure)
\nb. Atomisation
\nc. Spray pattern
\nd. Dribble<\/p>\n

What point do you check when overhaul fuel valve ?<\/strong>
\n\udbc0\udc31 Needle valve lift
\n\udbc0\udc31 Seat clearance (tilted 30 \u00b0 from horizontal position needle must not fall down)
\n\udbc0\udc31 Nozzle atomisation hole
\n\udbc0\udc31 Spindle & spring
\n\udbc0\udc31 Fuel line & Cooling Water line to be clear, dowel pin fitting)
\n\udbc0\udc31 Contact surface of nozzle and body<\/p>\n

Excessive needle valve lift<\/strong>
\n1) Spring failure
\n2) Impact damage between needle shoulder and thrust face & impact damage at the seat
\n3) Combustion gas may blow back into nozzle due to prolonging opening period<\/p>\n

Too low\/small needle valve lift<\/strong>
\n1) Restrict the flow
\n2) May overload the pump<\/p>\n

Anti-dribbling arrangement<\/strong>
\nThe angles of the needle valve and its seat are cut difference about 1 \u00b0 or 2 \u00b0 to achieve point contact thus preventing dribbling and sharp closing.
\nIn other words, weeping and dribbling has been prevented by cutting the needle angle about 2 \u00b0 larger than the seat angle of about 60 \u00b0. This arrangement ensures sharp opening and closing of the fuel valve.<\/p>\n

Worn nozzle hole<\/strong>
\nIt is due to erosion of fuel oil which contains abrasive particles. That is due to insufficient filtration and purification or the fuel valve does not close snappily after injection.
\nIt affects the spray pattern and atomization. It cause burning away of piston crown due to the fuel impingement and secondary burning and seriously effects engine performance.<\/p>\n

How to decide nozzle is suitable for further used ?<\/strong>
\n\udbc0\udc40 By titling the nozzle body & needle valve assemble 30 \u00b0 from horizontal position.
\n\udbc0\udc40 If the needle valve falls from the nozzle body at only a slightly tilting angle the whole sprayer must be renewed.<\/p>\n

Nozzle leakage<\/strong>
\nIt is due to defective needle valve of partial opening of needle valve. It is due to defective delivery valve of fuel pump that causes dribbling of needle valve.
\nIt may causes secondary burning, reduced combustion efficiency and high exhaust temperature. It may cause trumpet formation of carbon on the nozzle tip.<\/p>\n

How to detect leaking fuel valve ?<\/strong>
\n\udbc0\udc40 Loss in power in affected cylinder (Power card)
\n\udbc0\udc40 Smoke at exhaust
\n\udbc0\udc40 Exhaust high temperature
\n\udbc0\udc40 There may be a knock or pressure wave in the injection system
\n\udbc0\udc40 Draw card show fluctuations of pressure during expansion process due to secondary burning of fuel leaking, higher expansion line.<\/p>\n

Affect of leaking fuel valve<\/strong>
\n\udbc0\udc40 Increase fuel consumption
\n\udbc0\udc40 Engine over loading
\n\udbc0\udc40 Knocking
\n\udbc0\udc40 High exhaust temperature
\n\udbc0\udc40 Lifting of cylinder relief valve.<\/p>\n

FULE VALVE TESTING<\/strong>
\n\udbc0\udc31 To pressure-test a fuel valve:
\n\udbc0\udc31 The valve is connected to a test pump with pressure gauge.
\n\udbc0\udc31 The passages are primed by pumping oil freely and all air forced through the valve air vent when the spring tension is low.
\n\udbc0\udc31 The correct lifting pressure is stated on the adjustment sheet for the engine.
\n\udbc0\udc31 The adjusting screw for the spring is now set so that the spindle lifts at this pressure: the screw is then locked in position and the lift pressure rechecked. If everything is in order, the needle valve will open suddenly when the correct pressure is reached.
\n\udbc0\udc31 Next, the nozzle is wiped thoroughly clean and pressure reapplied, this time to 10 kgf\/cm2 below the injection working pressure. If the pressure remains steady for a few minutes, the valve is tight. A trace of oil at the nozzle holes is of no importance, as the valve will normally be worked-in completely after a few minutes of running. However, should the nozzle become wet or should drops appear, then replacement or regrinding of the valve is necessary.
\n\udbc0\udc31 Condition of the spray holes can be checked by placing a piece of cardboard just below the Tip (not held by hand) and depressing the tester handle briskly once.
\n\udbc0\udc31 The pattern (for a symmetrical nozzle) should be symmetrical.
\n\udbc0\udc31 Observe whether the nozzle ‘chatters’ whilst the fuel is discharged.
\n\udbc0\udc31 Injectors should be tested when removed, as a diagnostic check on their condition, and after recondition.
\nOpening pressures set too high can result in spring failure. If the opening pressure is adjusted low, combustion gas can blow back into the injector and build up lacquer and carbonaceous deposits.<\/p>\n

Atomization test<\/strong>
\nTest handle is to be pushed hard two or three times.
\nTo see fuel spray pattern is uniformly
\nNot dripping
\nListing jarring noise.<\/p>\n

Pressure drop test (Set pressure test)<\/strong>
\n300 kg\/cm2 \udbc0\udcc6 200 kg\/cm2 (30 to 90 sec)<\/p>\n

Dribbling test<\/strong>
\nMaintain oil pressure of 10 kg\/cm2 below opening pressure
\nCheck nozzle tip<\/p>\n

Spray pattern test<\/strong>
\nOriginal test bench has hole plate (same number with nozzle hole) when the spray can enter into the hole without touching the plate.
\nPaper method \udbc0\udcc6 fuel valve and paper right angle position.<\/p>\n

Incorrect spring pressure setting<\/strong>
\nIt is due to
\n1) Broken spring
\n2) Loose pressure adjusting nut and loose lock nut
\n3) Incorrect initial pressure setting
\n4) Sticking of spring
\n5) Worn out spring<\/p>\n

It may cause<\/strong>
\nEarly injection (low pressure setting)
\nLate injection (high pressure setting)
\nEarly injection may causes knocking the engine unit. Shock heavy load on bearings.
\nLate injection may causes high exhaust temperature with reduced engine output and fouling of exhaust system.<\/p>\n

How to know fuel valve spring is broken ?<\/strong>
\n\udbc0\udc31 Over fuelling
\n\udbc0\udc31 Engine knocking
\n\udbc0\udc31 Black smoke from funnel
\n\udbc0\udc31 Exhaust temperature high.<\/p>\n

Chocked nozzle cooling space<\/strong>
\nIt is due to insufficient pressure of cooling liquid (if in separate system). It is due to choked cooling line due to internal corrosion that is resulted from failure of anti-corrosive liquid to be added into cooling water system.
\nIt may be due to incorrect alignment of nozzle holder and nozzle. The choked nozzle cooling carbonization of nozzle tips and clogging of nozzle holes.
\n* scale formation, sticking of nozzle needle*<\/p>\n","protected":false},"excerpt":{"rendered":"

FUNCTIONS Fuel valve is one of the vital parts of the Diesel Engine due to their high precision in manufacturing and the intricate duties it has to perform, to atomiser, penetrate and distribute as swirling action achieved. Atomisation Atomisation is the splitting up of the fuel into very small droplets by the fuel injector, forcing […]<\/p>\n","protected":false},"author":1,"featured_media":5916,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[79],"tags":[],"class_list":["post-5915","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-marine-engineering-competency-exams-study-blogs"],"_links":{"self":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5915","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/comments?post=5915"}],"version-history":[{"count":1,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5915\/revisions"}],"predecessor-version":[{"id":5917,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5915\/revisions\/5917"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media\/5916"}],"wp:attachment":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media?parent=5915"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/categories?post=5915"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/tags?post=5915"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}