LESSON 9 LESSON 9 TEXT STARTING SYSTEMTEXT STARTING SYSTEM

第第 99 课 起动系统课 起动系统

Diesel engines are started by Diesel engines are started by supplyingsupplying compressed aircompressed air into into the cylindersthe cylinders in the appropriate in the appropriate sequence for the required sequence for the required direction. direction.

A supply of compressed air is A supply of compressed air is stored in stored in air reservoirsair reservoirs or or bottlesbottles or or receiversreceivers at pressures at pressures about 30 or 40 bar ready for about 30 or 40 bar ready for immediateimmediate use.use.

Some times compressed air presSome times compressed air pressure is dropped to a lower value sure is dropped to a lower value by means of a by means of a reducing valve(reducing valve( 减减压阀压阀 )) for other uses. The receiv for other uses. The receivers are charged byers are charged by compressors. compressors.

The design of starting air systems, The design of starting air systems, including the number and capacity including the number and capacity of compressors and receiversof compressors and receivers, the , the pprovision rovision （规定）（规定） of features and of features and drainage facilities are the subject odrainage facilities are the subject of f stringent(stringent( 严格严格 )) requirements by requirements by Classification Societies(Classification Societies( 船级社船级社 ))..

Up to 12 starts are possible with Up to 12 starts are possible with the stored quantity of the stored quantity of compressed air. The starting air compressed air. The starting air system usually has system usually has interlocksinterlocks to to prevent starting if any thing is prevent starting if any thing is not in order.not in order.

The compressed air is supplied The compressed air is supplied by a large bore pipeby a large bore pipe to a to a remote oremote operating non-return or automaticperating non-return or automatic valve and then to the valve and then to the cylinder aicylinder air start valves(r start valves( 气缸起动阀气缸起动阀 )). .

The opening of each cylinder The opening of each cylinder air start valves will admit air start valves will admit compressed air into the compressed air into the correspondingcorresponding cylinder. cylinder.

The automatic valve and the The automatic valve and the cylinder start valves are cylinder start valves are controlled by a controlled by a pilotpilot airair systemsystem. .

Each cylinder start valve will be Each cylinder start valve will be opened opened immediately after immediately after the top the top dead centre(TDC)dead centre(TDC) position has position has been passedbeen passed and closed and closed just just before the exhaust ports are before the exhaust ports are duedue to open to open according to the according to the direction of rotation required.direction of rotation required.

Thus, when compressed air from Thus, when compressed air from the the mainmain supply is supplied to supply is supplied to the starting system of an engine the starting system of an engine at rest it enters those cylinders at rest it enters those cylinders in in which the pistons are in a position which the pistons are in a position corresponding to some part of the corresponding to some part of the power stroke,power stroke, the resulting the resulting pressure on the pistons causes pressure on the pistons causes the engine to rotate.the engine to rotate.

When a sufficiently high speed, When a sufficiently high speed, say about 20 r/min,say about 20 r/min, has been has been achieved the air supply is cut achieved the air supply is cut off and fuel is injected causing off and fuel is injected causing the cylinders to fire and the cylinders to fire and continue to run in the normal continue to run in the normal way.way.

Cylinder airCylinder air start valvestart valve Air distributorAir distributor

Master valve (automatic valve)

Air bottleAir bottleAir start Air start leverlever

a pilot air a pilot air control valvecontrol valve

The pilot air is drawn from the The pilot air is drawn from the large pipe and passes to a pilot large pipe and passes to a pilot air control valve air control valve which is which is operated by the engine air start operated by the engine air start leverlever. .

When the air start lever is When the air start lever is operated,operated, supply of pilot air supply of pilot air enables the pilot air control enables the pilot air control valve to open either valve to open either manuallymanually or or with a pneumatic cylinderwith a pneumatic cylinder when a bridge control system is when a bridge control system is fittedfitted..

Pilot air for the appropriate Pilot air for the appropriate direction of operation is also direction of operation is also supplied to an supplied to an air distributorair distributor(( 空气分配器空气分配器 )). .

This device is usually driven This device is usually driven by the engine camshaft and by the engine camshaft and supplies pilot air to the supplies pilot air to the control cylinders of the control cylinders of the cylinder air start valves.cylinder air start valves.

The pilot air is then supplied The pilot air is then supplied in appropriate sequence for in appropriate sequence for the direction of operation the direction of operation requiredrequired. .

The cylinder air start valves are The cylinder air start valves are held closed by springs held closed by springs when not when not in usein use and opened by the pilot and opened by the pilot air enabling the compressed air air enabling the compressed air direct from the receivers to enter direct from the receivers to enter the engine cylinder.the engine cylinder.

As soon as the engine As soon as the engine firesfires the air the air starting lever is brought back. starting lever is brought back. The pilot air control valve The pilot air control valve returns to the off position, returns to the off position, venting venting the pilot air lines and the the pilot air lines and the remote air starting valveremote air starting valve and and allowing it to close.allowing it to close.

A number of interlocks are A number of interlocks are provided in connection with the provided in connection with the air starting system to air starting system to safeguardsafeguard the engine and personnel. These the engine and personnel. These are: are:

1. The 1. The turning gear(turning gear( 盘车机盘车机 ) ) intinterlock valve which is arranged terlock valve which is arranged to shut off the starting air pilot lio shut off the starting air pilot line when the turning gear is ne when the turning gear is engaengaged(ged( 啮合啮合 )), thus preventing the , thus preventing the engine being started.engine being started.

2.2. To prevent operation of the To prevent operation of the starting air system whilst the starting air system whilst the engine is runningengine is running a pilot air a pilot air interlock valveinterlock valve is operated by is operated by the main control lever. the main control lever.

The valve remains open The valve remains open during during the starting sequence, i.e. until the starting sequence, i.e. until the main control lever is the main control lever is removed just beyond the starting removed just beyond the starting positionposition, but remains closed , but remains closed after this pointafter this point and does not and does not open again open again until the main lever until the main lever is moved back to the stop is moved back to the stop positionposition..

3. A mechanical interlock is 3. A mechanical interlock is provided in the control box to provided in the control box to prevent the main control lever prevent the main control lever being moved beyond the being moved beyond the starting position starting position while the while the starting air lever is either the starting air lever is either the aheadahead or or asternastern starting position. starting position.

4. Another mechanical interlock 4. Another mechanical interlock is provided to prevent the main is provided to prevent the main control lever being moved until control lever being moved until starting air is admitted to the starting air is admitted to the cylinders. This prevents fuel cylinders. This prevents fuel being admitted to the cylinders being admitted to the cylinders when the engine is at rest.when the engine is at rest.

Lubricating oil Lubricating oil from the from the compressorcompressor will pass along the will pass along the air lines and deposit on them. In air lines and deposit on them. In the event of a cylinder air the event of a cylinder air starting valve leaking, hot gases starting valve leaking, hot gases would pass into the air pipes would pass into the air pipes and and igniteignite the lubricating oil. the lubricating oil.

If starting air is supplied to the If starting air is supplied to the engine this would further feed engine this would further feed the fire and could lead to an the fire and could lead to an explosionexplosion in the pipelines. in the pipelines.

In order to prevent such an In order to prevent such an occurrenceoccurrence, cylinder starting , cylinder starting valves should be valves should be properlyproperly maintained and the pipelines maintained and the pipelines regularly regularly draineddrained. Also oil . Also oil discharged from compressors discharged from compressors should be kept to a minimum, should be kept to a minimum, by careful maintenance.by careful maintenance.

In an attempt to reduce the effe reduce the effects of an explosion, cts of an explosion, flame trapsflame traps(( 阻 焰 器阻 焰 器 )), , relief valves(relief valves( 安 全安 全阀阀 )) and and bursting caps or discsbursting caps or discs (( 防爆帽防爆帽 )) are fitted in the pipel are fitted in the pipelines.ines.

In addition an In addition an isolatingisolating non-non-return valvereturn valve (the automatic (the automatic valve) is fitted to the system, valve) is fitted to the system, which prevents further which prevents further compressed air by the engine compressed air by the engine into system.into system.

The loss of cooling water from The loss of cooling water from an air compressor could lead to an air compressor could lead to an an overheatedoverheated air discharge and air discharge and possibly an explosion in the possibly an explosion in the pipelines pipelines leading to the air leading to the air reservoirreservoir..

A high temperature alarm or a A high temperature alarm or a ffusible plug(usible plug( 易溶塞易溶塞 )), , which will which will melt(melt( 融化融化 ,, 熔化熔化 )), is used to gu, is used to guard against this ard against this possibilitypossibility..

Reading materialReading material

A. STARTINGA. STARTING

As previously explained, the As previously explained, the ignitionignition of the fuel in diesel of the fuel in diesel engine is caused by the heat of engine is caused by the heat of compression of the air compression of the air previously admitted into the previously admitted into the cylinder.cylinder.

Thus, Thus, for the engine to begin for the engine to begin firing,firing, air must first be drawn air must first be drawn or pumped into the cylinder and or pumped into the cylinder and this air must be compressed by this air must be compressed by the upward movement of the the upward movement of the piston to obtain the high piston to obtain the high temperature necessary to burn temperature necessary to burn the fuel the fuel when it is injectedwhen it is injected..

Hence the engine must be Hence the engine must be driven for a few revolutions by driven for a few revolutions by some outside source before some outside source before allowing the fuel into the allowing the fuel into the cylinders.cylinders.

In heavy marine engine the In heavy marine engine the practice is to drive the engine practice is to drive the engine on compressed air on compressed air which has which has previously been stored (at previously been stored (at pressure pressure rangingranging from 20 to 40 from 20 to 40 bar depending upon the type of bar depending upon the type of engine) in starting-air reservoirsengine) in starting-air reservoirs. .

The compressed air is admitted The compressed air is admitted to each cylinder through a cam to each cylinder through a cam operated starting-air valve operated starting-air valve when the piston has just passed when the piston has just passed its top center and commence its its top center and commence its power stroke and remaining power stroke and remaining open until the piston has open until the piston has traveled part of that stroke.traveled part of that stroke.

The period of opening depends The period of opening depends upon(on) the number of upon(on) the number of cylinders and whether it is cylinders and whether it is four-stroke or two-stroke four-stroke or two-stroke engine. engine.

When the starting-air valve When the starting-air valve closes on one cylinder, another closes on one cylinder, another starting-air valve already starting-air valve already opened on another cylinder opened on another cylinder whose piston has just commenced whose piston has just commenced its downward strokeits downward stroke..

Thus no matter in what Thus no matter in what position the engine stops there position the engine stops there will always be at least one of will always be at least one of the cylinders with its starting-the cylinders with its starting-air valve open to admit air valve open to admit compressed air to start the compressed air to start the engine.engine.

When the engine obtains When the engine obtains sufficient speed, the fuel pumps sufficient speed, the fuel pumps and valves are brought into and valves are brought into operation and the starting air operation and the starting air valves put out of commission.valves put out of commission.

B. Engine B. Engine reversingreversing

Where running at maneuvering Where running at maneuvering speedspeed

1. Where manually operated 1. Where manually operated auxiliary blowers are fitted they auxiliary blowers are fitted they should be started.should be started.

2. The fuel supply is shut off and 2. The fuel supply is shut off and the engine will quickly slow the engine will quickly slow down.down.

3. The direction handle is 3. The direction handle is positioned astern.positioned astern.

4. Compressed air is admitted to 4. Compressed air is admitted to the engine to turn it in the astern the engine to turn it in the astern direction.direction.

5. When turning astern under 5. When turning astern under the action of compressed air, the action of compressed air, fuel will be admitted. The fuel will be admitted. The combustion process will combustion process will take take overover and air admission and air admission ceasecease..

When running at full speedWhen running at full speed

1. The auxiliary blowers, where 1. The auxiliary blowers, where manually operated , should be manually operated , should be started.started.

2. Fuel is shut off from the 2. Fuel is shut off from the engine.engine.

3. 3. BlastsBlasts of compressed air may of compressed air may be used to slow the engine be used to slow the engine down.down.

4. When the engine is stopped 4. When the engine is stopped the direction handle is the direction handle is positioned astern.positioned astern.

5. Compressed air is admitted 5. Compressed air is admitted to turn the engine astern and to turn the engine astern and fuel is admitted to fuel is admitted to accelerateaccelerate the engine. The compressed air the engine. The compressed air supply will then cease.supply will then cease.

Speed regulationSpeed regulation

In order to control the engine In order to control the engine speed, it is now common speed, it is now common practice to fit a speed regulator practice to fit a speed regulator or governor to make balance or governor to make balance between the fuel injected into between the fuel injected into the engine and the engine load.the engine and the engine load.

The governor maintains the The governor maintains the engine speed at the desired value engine speed at the desired value by continually by continually positioningpositioning the the metering devicemetering device in the fuel in the fuel system to control the amount of system to control the amount of fuel fuel being injected into each being injected into each cylinder per cycle.cylinder per cycle.

Most governors are hydraulic aMost governors are hydraulic actuating types and ctuating types and self-containeself-contained(d( 独立的独立的 )) units. The mechanis units. The mechanism can be divided into two parts, m can be divided into two parts, a speed sensing portion and an a speed sensing portion and an actuating portion.actuating portion.

A common form of sensing deviA common form of sensing devices is the ces is the ball headball head. It consists o. It consists of a f a revolving carrier(revolving carrier( 旋 转 支旋 转 支架架 ))on which are mounted two won which are mounted two weights having eights having crankedcranked levers levers. .

They are They are pivoted(pivoted( 装在枢轴上装在枢轴上 )) so that the levers compress a spso that the levers compress a spring as the weights fly out undering as the weights fly out under centrifugal force.r centrifugal force.

The force The force exerted by the springexerted by the spring is controlled by the pressure of is controlled by the pressure of an adjustment on its other end an adjustment on its other end which is decided by the main which is decided by the main control lever mechanism of the control lever mechanism of the engine.engine.

This adjustment is the speed This adjustment is the speed control for the engine. control for the engine. Wherever this is setWherever this is set the weights the weights will assume a corresponding will assume a corresponding position according to the speed position according to the speed at which they are rotated.at which they are rotated.

This position is signaled to the This position is signaled to the actuating portion of the governactuating portion of the governor by the position of the control or by the position of the control spindle.spindle.

The control spindle is connected The control spindle is connected to a pilot valve which admits oil to a pilot valve which admits oil as requiredas required to the actuating to the actuating piston and cylinder. piston and cylinder.

The position The position taken up by this actaken up by this actuating pistontuating piston is ‘ is ‘fed back(fed back( 反反馈馈 ))’to pilot valve so that the oil ’to pilot valve so that the oil is controlled to give the actuatois controlled to give the actuator the desired final position.r the desired final position.

The actuator spindle is The actuator spindle is connected to a lever connected to a lever output from output from the governorthe governor. This lever is . This lever is connected to the linkage connected to the linkage which which controls the fuel quantity.controls the fuel quantity.

For any speed setting of the goverFor any speed setting of the governornor there will be a range of fuel there will be a range of fuel output according to whether the output according to whether the load load torque(torque( 扭矩扭矩 )) is high or lo is high or low. w.

It will vary from full at one end It will vary from full at one end of the travel of the actuator of the travel of the actuator piston to no fuel at the other.piston to no fuel at the other.

These two positions correspond These two positions correspond to two slightly different values oto two slightly different values of the speed. The difference betwf the speed. The difference between these values is known as the een these values is known as the governorgovernor dropdrop. It is usually exp. It is usually expressed as a ressed as a percentagepercentage of the set of the set speed.speed.

Electronic governors are coming Electronic governors are coming into use on modern engines. into use on modern engines. They give quicker response and They give quicker response and a more powerful output. a more powerful output.

The speed-sensing device is a sThe speed-sensing device is a small electric mall electric generator(generator( 发 生发 生器器 )) or small machine which pr or small machine which produce a signal, usually in the fooduce a signal, usually in the form of a pulsed current or voltarm of a pulsed current or voltage ge having a frequency proportiohaving a frequency proportional to engine speed.nal to engine speed.

This is compared with a desired This is compared with a desired speed setting and any difference speed setting and any difference produces an output signal. The produces an output signal. The output signal output signal energizes(energizes( 激活，激活，使 …活 跃使 …活 跃 )) the actuating equip the actuating equipment ment which operates the fuel conwhich operates the fuel control mechanism.trol mechanism.

With all governors it is usual pWith all governors it is usual practice to provide a manual ractice to provide a manual ovover-ride(er-ride( 优势，优先权优势，优先权 ) ) by whiby which the linkage can be returned ch the linkage can be returned to the no fuel position in an emto the no fuel position in an emergency or should the governoergency or should the governor fail in any way.r fail in any way.

The engine is stopped for The engine is stopped for normal maneuvering purposes normal maneuvering purposes by bringing the main control by bringing the main control lever to the no fuel position.lever to the no fuel position.

Automatic shutdown systems Automatic shutdown systems are also provided to stop the are also provided to stop the engine in the case of failure of engine in the case of failure of lubricating oil or of cooling lubricating oil or of cooling water or if the engine speed water or if the engine speed exceeds the maximum exceeds the maximum allowable r/min.allowable r/min.

c. Starting air systemc. Starting air system

The engine is started with The engine is started with compressed air of max. 30 bar. compressed air of max. 30 bar. Minimum pressure required is Minimum pressure required is 15 bar. 15 bar.

A pressure A pressure transmitter(transmitter( 变 送变 送器器 )) PT301 PT301 mounted on the startmounted on the starting air line before the main starting air line before the main starting valveing valve has an indicator in the has an indicator in the instrument panel.instrument panel.

The supply line The supply line from the starting from the starting air bottleair bottle is provided with a is provided with a non-non-return valvereturn valve and a drain valve. and a drain valve.

The The solenoid valve(solenoid valve( 电磁阀电磁阀 )) is e is electrical (remote control) or malectrical (remote control) or manual (on the engine) operated anual (on the engine) operated and sends nd sends after after activation(activation( 带电带电 )) a pilot air signal to the main staa pilot air signal to the main starting air valve. rting air valve.

Interruption(Interruption( 阻断阻断 ,, 中断中断 )) of th of the control air closes the main stae control air closes the main starting air valve.rting air valve.

After the main starting air After the main starting air valve is activated, the air flows valve is activated, the air flows through the through the flame flame arresters(trap)arresters(trap) to the starting to the starting air valves in the cylinder heads.air valves in the cylinder heads.

Part of air flows via the Part of air flows via the starting air distributor to each starting air distributor to each of the main starting air valves of the main starting air valves in the cylinder heads. The in the cylinder heads. The starting air distributor controls starting air distributor controls the timing of opening and the timing of opening and closing of the main starting air closing of the main starting air valves.valves.

On the moment the main startiOn the moment the main starting air valve is operated the ng air valve is operated the govgovernor booster(ernor booster( 调速器升压器调速器升压器 )) i is also energized. s also energized.

The main starting air line is prThe main starting air line is provided of a safety valve. Interloovided of a safety valve. Interlock valve is a safety device to ck valve is a safety device to avavoidoid an engine start an engine start with engagewith engaged d turning gearturning gear..

Starting air distributorStarting air distributor

The starting air distributor is The starting air distributor is of the piston type with of the piston type with precision-machined precision-machined inter-inter-changeablechangeable liners. liners.

The liners as well as the pilot The liners as well as the pilot pistons are of pistons are of corrosioncorrosion resistantresistant materials. The pilot materials. The pilot pistons are controlled by a cam pistons are controlled by a cam connected to the camshaft endconnected to the camshaft end..

When the main starting valve When the main starting valve opens, the pilot pistons are opens, the pilot pistons are pressed onto the cam, wherebypressed onto the cam, whereby the pilot piston for the engine the pilot piston for the engine cylinder cylinder which is in starting which is in starting positionposition admits control air to admits control air to the main piston of the starting the main piston of the starting valve.valve.

The starting air valve opens The starting air valve opens and admits compressed air into and admits compressed air into the engine cylinder forcing that the engine cylinder forcing that piston down. piston down.

Shortly before the exhaust Shortly before the exhaust valves are openedvalves are opened the pilot valve the pilot valve interrupts the control air interrupts the control air to the to the starting air valvestarting air valve and starting and starting air air to that cylinderto that cylinder is stopped. is stopped.

This procedure will be repeated This procedure will be repeated as long as the main starting as long as the main starting valve is activated or until the valve is activated or until the engine speed is so high that the engine speed is so high that the engine engine firesfires. .

After the main starting air valvAfter the main starting air valve is closed, the main starting air e is closed, the main starting air system is system is deaerated(deaerated( 释 放 ， 泄释 放 ， 泄压压 )), the pressure drops quickly , the pressure drops quickly and the springs will lift the piloand the springs will lift the pilot t plungersplungers off the cam. off the cam.

This means that pilot plungers tThis means that pilot plungers touch the cam only during the stouch the cam only during the starting process and thus wear is arting process and thus wear is iinsignificant(nsignificant( 可忽略的可忽略的 ))..

If a pilot liner is worn out, presIf a pilot liner is worn out, press it out. It may be necessary to s it out. It may be necessary to heat the distributor up till abouheat the distributor up till about 200 as ℃t 200 as ℃ LoctitesLoctites (a sealing ag (a sealing agent) is used for fixing and sealinent) is used for fixing and sealing.g.