船舶輪機英語lesson 5

1、Lesson FiveText Fuel oil systemFuel oil is thought to be one of the main factors having much to do with the operation and maintenance of an engine. When selecting a fuel oil, there are more than ten factors to be considered, among those which affect combustion are the fuel o i l s v i s c o s i t y,

2、 c e t a n e n u m b e r ( 十 六 烷 值十 六 烷 值 ) a n d calorific value(熱值熱值); the sulphur(硫分硫分) in it and its carbon residues(殘?zhí)恐禋執(zhí)恐? and ash(灰分灰分) are factors that decide the formation of combustion products;and the engines maintenance has a lot to do with its flash and setting points(閃點和凝點閃點和凝點), speci

3、fic gravity(密度密度), viscosity, water content(水分水分) and the mechanical impurities(機械雜機械雜質(zhì)質(zhì)) in it.The work that fuel does in an engine not only depends upon the fuel oil itself, but also upon its working condition, which here means the fuel system. The fuel oil system for a diesel engine can be consid

4、ered in two partsthe fuel supply and the fuel injection systems. Fuel supply deals with the provision of the fuel oil suitable for use by the injection system.Fuel oil supplyA slow-speed two-stroke diesel is usually arranged to operate continuously on heavy fuel or residual oil(渣油渣油) and have availa

5、ble a diesel oil supply for maneuvering conditions. The whole fuel system will then embody two almost entirely separate systems, one for diesel fuel and one for high viscosity fuel. The latter will embody heating arrangements and means to control the temperature of the fuel to ensure that it is adeq

6、uately fluid when stored, transferred, cleaned and injected. In a typical fuel installation on board a ship for a modern diesel engine, separate filling connections for the diesel and heavy fuel tanks are provided. In use, the filling connections on deck are connected to shore hoses and the fuel oil

7、 bunkers(燃燃料艙料艙) are then distributed to various double bottom, deep, wing and side tanks(雙層底艙，雙層底艙，深 艙 ， 舷 側(cè) 艙 和 邊 艙深 艙 ， 舷 側(cè) 艙 和 邊 艙 ） a s necessary. Steam heating coils(蒸汽加熱盤蒸汽加熱盤管管) are installed in the various tanks to ensure that the temperature of the oil can be raised to reduce the viscosity

8、 to a level that will ensure easy pump-ability. Pipes used for transferring high viscosity fuel should be well lagged(加保溫層加保溫層) and long runs of piping(管道系統(tǒng)管道系統(tǒng)) should have steam-tracing pipes(蒸汽伴熱管蒸汽伴熱管) fitted.The fuel oil is drawn from the bunker tanks through a duplex strainer(雙聯(lián)過濾器雙聯(lián)過濾器) by a

9、transfer pump and thence to dirty oil storage or setting tanks. Leaving the fuel in the setting tanks whilst keeping it hot to reduce its viscosity allows the heavier impurities and any water present to settle to the bottom of the tank. The sediment(沉淀物沉淀物) and water are drawn off leaving the remain

10、der ready for cleaning. I t i s t h e n p a s s e d t o a purification(凈化凈化) system for treatment and from there to the clean heavy fuel tank, which known as the service tank.From the clean heavy fuel tank the oil gravitates through a heated buffer(緩沖柜緩沖柜)、 or balance tank to the booster pumps(增壓泵增壓

11、泵)and is discharged through a fuel heater and filter to a viscosity regulator and from there to a duplex fine filter on the suction side of the main engine fuel pumps.Fuel excess to requirements is spilled back into the system via the buffer tank. The viscosity regulator controls the fuel oil temper

12、ature in order to provide oil at the c o r r e c t v i s c o s i t y f o r combustion. A pressure-regulating valve ensures a constant pressure at the fuel main. The valve can be opened to warm through the system by circulating with heated oil. Regular attention to the d r a i n i n g o f h e a t e d

13、 settling(setting tank) and ready use tank(service tank) is advisable to eliminate the r e s u l t s o f c o n t i n u o u s condensation which can be very heavy under certain climatic conditions. Usually the settling and ready use tanks are lagged to reduce heating losses.The system will include va

14、rious safety devices such as low level alarms and remote operation of tank outlet valves in the events of fire. The diesel oil supply system similarly uses transfer pumps to draw oil from the bunker tanks. The oil is then purified and stored in service tank. The diesel oil enters the system through

15、a three way valve which permits the supply of only one type of oil to the system. The engine must be changed over to running on diesel oil for 30 minutes or more before a long period of standstill(停止停止). Diesel oil required less heating, and thus the change from one fuel to another should take place

16、 gradually to allow temperatures in the system to stabilize.Fuel InjectionThe function of the fuel injection system is to provide the amount of fuel at the right moment and in a suitable condition for the combustion process. That means, the fuel injection system for diesel engines must be able to su

17、pply a metered(定量定量) amount of fuel to each cylinder for each power stroke according to the load on the engine, and must include a timing mechanism to ensure that d e l i v e r y o f t h i s f u e l commences at the correct moment, and must have a means to atomize(將將噴成噴成霧狀霧狀) the fuel. The type of i

18、njection system most commonly used in modern diesel engines is the jerk pump(脈動泵脈動泵) system. In the system, a separate injection pump is provided for each cylinder which operates once every cycle.The barrel and plunger， together with the cam, are dimensioned to displace (discharge) fuel at the rate

19、it is required in the combustion chamber. P o r t s i n t h e b a r r e l i n combination with slots in the p l u n g e r, o r s e p a r a t e mechanically operated spill valves(回流閥回流閥), determine the amount of fuel delivered and the timing of its entry to the cylinder. Plunger barrelEach pump is co

20、nnected to the injector, or injectors, serving one cylinder. These injectors have spring loaded differential needle valves which are set to ensure that the fuel is raised to a sufficiently h i g h p re s s u re t o c a u s e atomization(霧化霧化) when they automatically open to admit it to the cylinder.

21、Fuel Oil QualityViscosity is not a measure of the fuel quality, but determines the complexity of the fuel heating and handling system, which should be considered when estimating installation economy. The standard engine fuel system is designed for fuels up to the viscosity class 55 mm2/s. When the d

22、ensity exceeds 0.991g/ml at 15, water, and to some extent solid matter, can no longer be removed with certainty by a centrifuge(離心離心分離機分離機). Centrifuging systems that are claimed to be able to clean fuel oils with densities up to 1.010g/ml at 15 are available. If such systems as the so called contro

23、lled discharge design are installed, fuels with densities up to 1.010 g/ml at 15 may be used.Note: Fuel oils having high density in combination with low viscosity may have low ignition quality. High sulphur content increases the risk for corrosion and wear, particularly at low loads, and may contrib

24、ute to high-temperature deposit formation. The lubricating oil specification must be matched to this. High ash content causes abrasive(研磨的研磨的) wear, and may cause high temperature corrosion and contributes to formation of deposits. T h e m o s t h a r m f u l a s h constituents（成份）（成份） are vanadium(

25、釩釩) sodium(鈉鈉) combinations(化合物化合物). High vanadium content causes hot corrosion on exhaust valves particularly in combination with high sodium content. The corrosion increases with increased temperatures (increased engine output).High Conradson carbon(康拉康拉特遜殘?zhí)贾堤剡d殘?zhí)贾? may cause deposit formation in c

26、ombustion chamber and exhaust system, particularly at low engine output. High content of asphalt (瀝青瀝青) may contribute to deposit formation in combustion chamber and exhaust systems (at low loads). Asphalt may under certain circumstances, precipitate(使使沉淀沉淀) from the fuel and block filters and/or ca

27、use deposits in the fuel system, precipitating asphalt may also cause excessive centrifuge sludge(油油泥泥). Heavy fuels may contain up to 1% water at delivery. Water may also originate from the installation in bunker tanks. To avoid difficulties in the engine fuel injection system water must be removed

28、. Although low ignition quality produces long ignition delay, advancing the ignition timing makes things only worse; fuel is injected at a lower compression temperature and this will produce even longer ignition delay. Aluminum(鋁鋁) and Silicon(硅硅)Fuels may contain highly abrasive particles composed

29、of aluminum and silicon oxides(氧氧化物化物) known as catalytic fines(催化粉末催化粉末) from certain refining(精練精練) processes. If not removed by efficient fuel treatment, wear down of high pressure fuel pumps, nozzles and cylinder liners in a few hours may expected. Reading MaterialA. Dual purpose plus(additive)

30、descriptionDual Purpose Plus is a concentrated combustion improver(集中燃燒促進劑集中燃燒促進劑) for heavy fuel oils. It also has fuel conditioning properties. Product PropertiesThe catalysts(催化劑催化劑) in Dual Purpose Plus react with heavy f u e l p a r t i c l e s d u r i n g combustion. The fuel ignition temperat

31、ure is reduced, resulting in increased combustion efficiency with less carbon left to form smoke and soot(煙灰煙灰). Engine and exhaust systems are kept cleaner with longer service life and less maintenance. Anti-polymerization(反聚合作反聚合作用用) agents inhibit(抑制抑制) sludge formation, while dispersants(分分散劑散劑)

32、 stabilize the fuel. This results in a cleaner fuel system and better fuel flow, g i v i n g i m p r o v e d f u e l atomization and greater combustion efficiency.Sulphuric acid(硫酸硫酸) corrosion caused by condensing exhaust gases may be seen in any of the cooler parts of the boiler or engine system.

33、Typical problem areas are cylinder liners (cloverleaf(苜蓿苜蓿葉形的葉形的) corrosion), valve stems and funnel uptakes.D u a l P u r p o s e P l u s catalytically(催化催化) inhibits the formation of acid gases and so reduces the amount of acid present, thereby reducing acid corrosion. Directions for Use and Dose(

34、劑量劑量) RatesDual Purpose Plus is completely oil-soluble and should be added via a metering pump into the suction side of the booster pump. Alternatively, it can be added into the settling tank. If so, the dose rate should be increased by 10%. As a general guide, the average dosage(劑量劑量, 配藥配藥, 用量用量) s

35、hould be 1:4000. Alterations can then be made according to operating experience and results obtained. B. Dieselite(柴油助燃劑柴油助燃劑) descriptionDieselite is a multi-functional fuel treatment containing combustion catalysts and ash modifiers(灰分調(diào)節(jié)灰分調(diào)節(jié)劑劑). It is intended for use in diesel engines and boilers

36、 burning residual fuels.Product PropertiesCarbon residue formation during combustion is inhibited by catalysts that lower the ignition temperature of heavy asphaltic particles. C o m b u s t i o n t i m e i s consequently increased, leading to a reduction of tarry(焦油焦油) deposits and carbonaceous(炭炭的

37、、炭質(zhì)的的、炭質(zhì)的) fire-scale. Ash modifiers combine with fuel combustion ash to raise the sinter(燒結(jié)物燒結(jié)物,熔渣熔渣) and melting points of the ash above the engine or boiler normal operating temperatures. High temperature corrosion is m i n i m i z e d , r e d u c i n g maintenance and extending service life. The

38、 majority of ash formed is ejected with the exhaust gases in a fine, solid state, and any ash remaining in the exhaust system is easily removed by light brushing. The conversion of fuel sulphur to potentially corrosive sulphur trioxide(三氧化物三氧化物) gas is also inhibited. Sulphur trioxide reacts with co

39、ndensed steam in the exhaust trunking, funnel uptakes and other cooler zones to form sulphuric acid. Dieselite is a wide spectrum a d d i t i v e i n t e n d e d f o r continuous use. Directions for Use and Dose RatesFor best results, Dieselite should be dosed automatically using a metering pump to

40、dose into the fuel feed line as near to the injector or burner pump as possible. Where micro carbon residue ( M C R ) ( 微 量 法 殘 炭 值微 量 法 殘 炭 值 ) o r vanadium/sodium analysis is available, use the tables given by the manufacturer. If no analysis is available, use an initial dose rate of 1:4000 and ad

41、just according to results obtained. C. TEST OF FUEL INJECTION VALVE For injection test on fuel injection valve, perform with use of the fuel injection valve tester(噴油嘴試驗臺噴油嘴試驗臺). Adjustment of Fuel Injection PressureCheck fuel injection initial pressure by use of the fuel injection valve tester, and

42、 adjust this pressure to the designated value. For this adjustment, remove the cap nut first, and then adjust by means of the adjusting bolt. If components (needle Valve, spring, etc.) of fuel injection valve are replaced as well as the valve is disassembled, be sure to check the fuel injection pres

43、sure. If the injection nozzle is clogged, remove the carbon sticking to the nozzle part, using either carbon removing agent or cresol solution(甲酚溶液甲酚溶液); never use sandpaper(砂紙砂紙) or the like. Remember that shape of the n o z z l e g r e a t l y a f f e c t s atomization of fuel oil. Atomization Tes

44、tTurn the hand lever of the fuel injection tester at the rate of 1-3 turns per second, and check f o r c o n d i t i o n o f f u e l atomization under this circumstance. Confirm that fuel oil is evenly spread out as it is injected and that there is no abnormality(異異常常; 變態(tài)變態(tài)) due to clogged nozzle. Since the tip part of this needle valve is in double cone shape, if the rate of the lever is slowed down, atomization becomes m u c h c o a r s e r t h a n a conventional needle valve. However, in actual engine operation, fuel oil is no