Lesson 4 Fuel Oil System 第 4 课 燃 油 系 统

The common system covers the entire fuel oil flow from storage tank to injection into the engine cylinders. The ‘Unifuel’ System ( 单燃料系统 )

With regard to centrifuge recommendations( 推荐 ), fuel oils should always be considered as contaminated( 污染 ) upon delivery ( 运送 ) and should therefore be thoroughly cleaned to remove solid as well as liquid contaminants( 污染 物 ) before use.

The solid contaminants in the fuel are mainly rust( 铁锈 ), sand, dust( 灰尘 ) and refinery( 炼油厂 ) catalysts( 催化剂 ). Liquid contaminants are mainly water, i.e. either fresh water or salt water.

Impurities in the fuel can cause damage to fuel pumps and fuel valves, and can result in increased cylinder liner wear and deterioration( 变坏, 损毁 ) of the exhaust valve seats.

Also increased fouling( 脏污 ) of gasways( 气路, 气道 ) and turbocharger( 涡轮增压器 ) blades( 叶片 ) may result from the use of inadequately cleaned fuel oil.

Effective cleaning can only be ensured by using a centrifuge ( 离心分离机 ). Results from experimental work on the centrifuge treatment of today’s residual fuel( 渣油 ) qualities have shown that the best cleaning effect,

particularly in regard to the removal of catalytic fines( 催化 粉末 ), is achieved when the centrifuges are operated in series ( 串联 ), i.e. in purifier( 分 水机 ) /clarifier( 分杂机 ) mode.

This recommendation is valid( 有 效的, 正确的 ) for conventional centrifuges. For more modern types, suitable for treating fuels with densities higher than 991 kg/m 3 at 15 ℃, it is recommended to follow the maker’s( 制造商, 生 产厂家 ) specific instruction.

In view of ( 考虑到 )the fact that some fuel oil standards incorporate ( 包括 ) fuel grades( 等级, 分级 ) without a density( 密度 ) limit, and also the fact that the traditional limit of 991 kg/m 3 at 15 ℃ is occasionally( 非经常发生的, 偶尔 ) exceeded on actual deliveries( 交付 ),

some improvements in the centrifuging treatment have been introduced to enable the treatment of fuels with higher density.

With such equipment, adequate separation of water and fuel can be carried out in the centrifuge, for fuels up to a density of 1010 kg/m 3 at 15 ℃. Therefore, this has been selected as the density limit for new high density fuel grades.

Thus high density fuels are fully acceptable for our engines provided that( 如果 ) appropriate centrifuges are installed. They should be operated in parallel( 并 联 ) or in series according to the centrifuge maker’s instructions.

Design features and working principle 设计特点和工作原理 The fuel oil system is a common, pressurized( 加压 ) system in which both heavy fuel oil and diesel oil can be used.

The purpose of pressurization is primarily to avoid boiling and cavitation( 气蚀, 气穴 ) in the system, which may occur when the heavy fuel oil is heated to achieve the viscosity of cSt required for injection (Fig. 4-1 ).

Operation at sea The fuel from the bunker tanks( 燃 油舱 ) must be treated in centrifugal separators before entering the service tanks( 日用柜 ). From the service tanks, the fuel enters the supply system.

In the supply system, the fuel is pumped by the supply pumps, into a circulating system at a pressure of 4 bar. The supply system may include a fine filter( 细滤器 )..

All overflow( 溢流 ) from the supply pumps is recirculated in the by-pass piping, which incorporates the overflow valve shown in order to keep the inlet pressure in the circulation loop constant, irrespective of( 不管, 与 --- 无关 ) the actual consumption.

The pumps in the circulation loop, raise the pressure of the fuel oil from the supply system to a constant inlet pressure of 7- 8 bar before the engines.

The inlet pressure is maintained at the specified level by a spring- loaded overflow valve located on the main engine. The temperature or viscosity( 粘度 ) controlled preheater( 预热器 ) heats the heavy fuel oil until it reaches the necessary viscosity.

To safeguard the injection system components on the main engine, a full-flow( 全流量 ) 50 μm filter, must be installed as close to the main engine as possible. Such a filter is already built onto the auxiliary engines.

Excess fuel oil supplied to the engines is recirculated via the venting box( 放气箱 ), where gases, if any, are released by a deaerating( 除气, 排气 ) valve, to avoid cavitation in the system.

The flexibility( 灵活性 ) of the system makes it possible, if necessary, to operate an auxiliary engine on diesel oil by means of remote controlled 3-way valves( 三 通阀 ), which should be located close to the auxiliary engines.

A separate booster pump( 增压泵 ) supplies diesel oil from the diesel oil service tank to the auxiliary engines and returns any excess oil to the tank. In order to ensure operation of the booster pump in the event of a black-out( 全船失电 ),

the booster pump must have an immediate possibility of being powered by compressed air( 压缩 空气 ) or by power supplied from the emergency generator( 应急发 电机 ).

A 3-way valve is installed immediately before each auxiliary engine for change-over( 转换 ) between the pressurized and the open( 开式的 ) MDO (Marine Diesel Oil 船用柴油 ) supply system.

In the event of a black-out, the 3-way valve at each auxiliary engine will automatically change over to the MDO supply system.

The internal piping on the auxiliary engines will then, within a few seconds, be flushed( 注满, 充满 ) with MDO and be ready for start up.

Operation in port During operation in port, when the main engine is stopped, but power from one or more auxiliary engines is still required,

the supply pump should be running. One circulation pump should always be kept running when there is heavy oil in the piping.

The by-pass line with overflow valve between the inlet and outlet of the main engine serves the purpose of by-passing the main engine if, for instance, a major overhaul( 检修 ) is required on the main engine fuel oil system.

During this by-pass, the overflow valve takes over( 取代 ) the function of the internal overflow valve of the main engine.