Tuesday, December 31, 2019

Measuring of K-value of T\C



  • K- From bearing flange face to end face of shaft.
  • K1- for measuring K1 , slacken compressor side bearing by around 5 to 6 mm and pull it out using extractor tool .Then push the shaft towards compressor side.
  • Screw the extractor device on to the inner bearing bush of the compressor end and pull out the bearing about 5 to 6 mm
  • Push the rotor towards the compressor side measure K1.
  • Same way for measuring K2  , pull the rotor towards turbine side measure the dimension K2

L=K-K1              M=K2-K

  • In manual required valus of K ,L and M will be given .
  • Basically we are measuring the end play  ie, distance between turbine wheel and casing on either side.
  • K value will give an indication of thrust bearing weardown

Labels:

Lacing wire , Damping wire and Binding wire of T\C

 

Lacing wire

It is fitted at anti node provided very effective form of dampening.
It passes through blades and are braced or welded in blades.

Damping wire

All same purpose of Lacing wire , but free moving through holes and crimmed  at either end.
Centrifugal force of wire when it gets thrown out , dampens the vibration , but can cause fretting in blades and need to be dynamically balanced.

Binding wire 

It is used to strengthen the trailing edge of the blade

Labels:

Miller cycle


  • Only for 4stroke  engines.
  • In Miller cycle inlet valve closes early.
  • NOx reduction , As inlet valve close early when the piston moves down little bit of expansion of inlet air will occur , exhaust temp drops and NOx emission reduces.
  • Normally inlet valve should close around 29 degree after BDC , as the miller cycle introduces , the inlet valve closing is earlier.

Draw back of Miller cycle.

Since the closing of inlet valve is early , the amount of air inside the cylinder is reducing . So further we have to combine it with multistage T\C (To compensate the loss in air )

Labels:

Why A\C compressor is belt driven but Air compressor is directly coupled?

  • Safety against liquid
  • RPM is less in A\C compressor
  • Heat generated in motor armature is not trannsferred to crankcase

Labels:

Monday, December 30, 2019

Air bottle pressure testing How?

All hydraulic test has to done by water because in pressure testing we are checking for weakness in air bottle .Hydraullic pressure test to be done above 50% at design pressure . If the air bottle was actually having a hole , then it will take atleast half hour  for the pressure to be released , till that time the weak air bottle is pressurised .But in hydruallic pressure test even one drop escapes , the pressure is released because the water is incompressible

Labels:

Stern tube


  • Seal is gripping on to the chrome liner.Chrome liner is bolted on to propeller boss(aft)
  • Fwd chrome liner is fitted on to a clamp ring . Clamp rings are of 2 halves and have holes.
  • Aft  sealing assembly consist of 2 main and 1 aux sealing rings.All sealing rings are spring loaded .Fwd sealing ring prevent oil leakage to sea .Lip seals hold oil within Stern tube and accepts small misalignment
  • Chrome liner act as rubbing surfaces for lip seals .The chrome liner at the aft end protects the steel shaft from seawater and corrosion .Grooving will not happen on the shaft because of liner, so that the chrome liner can be machined or can be shifted axially by putting spacer.If grooving occurs leak will start.
  • As per diagram the space between  #2 and #3 is connected to header tank ,#3s is the spare seal 
  • If water content found on the stern tube that means along with #1 and #2 , then #3 seal is also leaking.Then we have to put #3s seal in use.

Labels:

Thrust pad lubrication

  • By LO branching pipe coming from main LO pump through the nozzle and sprayed on to the thrust collar.
  • Rotation of thrust collar causing the formation of LO wedge.
  • Hydrodynamic fluid film to be formed between rotating and stationary part .
  • This film prevents metal to metal contact .ie between the thrust pad and collar .
  • Pad is same material as white metal bearing

Labels:

Advantage of fitting thrust block inside engine

  • Ship structure already is strengthened for engine seating , so no need of additional strengthen
  • There are more no: of nodal points
  • Cross sectional area is more , so strengthening required is less.
  • No need of separate LO arangment as the chain\ gear LO supply can be tapped for using in thrust bearing.
  • Thrust collars outside is having the sproket , so space saving.
  • Both side of the collar have thrust pads

Advantages of Jack bolts

  • Jack bolts are used in Sulzer RTA engines
  • Tie rod should always be as close as possible to the crankshaft
  • Adv of bringing tie rod closer is to reduce the bending moment on transverse girder.
  • If there is bending moment on transverse girder cracks would propagate ie why Sulzer has employed a jack bolt so that the bearing top cover is held in position by the jack bolts.
  • In B & W main bearing top cover is in two pieces.ie bearing cover  or keep in of 2 pieces.

Labels:

Synthetic oil and Mineral oil

  • Mineral oil are exracted from crude oil in distillation process.
  • Mineral oil contain lot of contamination or substances which are no lub oil property to oil.
  • Hydrocarbon molecule are non -uniform in crude oil.
  • Synthetic oil is not distilled from crude oil .It is made through a chemical process known as Fischer Troph process.Starting with raw material like , methane ,CO,CO2 doesnot contain any contaminants and hydrocarbon molecule are uniform

Labels:

Advantages of main engine exhaust valve W seat

  • Reduce surface temperature
  • Reduce errosion and wire drawing.
  • W seat has 2 narrow concentric contact area , crushed and squeezed out and eliminate without any dents
  • TBO increases ,
  • Cost reduced and running hr increased

Labels:

Batch purification

  • Engine stop, Immobilization permit from port authority
  • Entire oil charge should be pumped by Px or transfer pump to LO settling tank.
  • It is allowed to settle for 24 hrs with heating about 60 degree celcius,
  • Water and Sludge should be drained out periodically.
  • Cleaning of interior sump tank and careful examination.
  • The oil should be passed through the Px at its optimum purification efficiency and then pumped back into the sump tank.

Batch purification is required when
If oil is suspected containing strong acid.
  • High insoluble content due to poor combustion or water due to leak in cooling system
  • Suspecting biological contamination

Labels:

Super long stroke

Long stroke: 3.2 - 4.0
Super long stroke:4.0 -4.7
Ultra long stroke :>4.7

Advantages of super long stroke:

  • Power to weight ratio is more.
  • Reduced fouling, smoke, NOx
  • Increased thermal efficiency: Simple geometric relationships show that an engine cylinder with longer stroke-to-bore ratio will have a smaller surface area exposed to the combustion chamber gasses compared to a cylinder with shorter stroke-to-bore ratio. The smaller area leads directly to reduced in-cylinder heat transfer, increased energy transfer to the crankshaft and, therefore, higher efficiency.
  • Low quality fuel can be burnt as more time is available for fuel combustion.
  • Slow rpm is possible so large diameter propeller can be used and hence propeller efficiency increases.
  • More time for heat dissipation to cooling water.
  • Better scavenging: Scavenging is the process in which the exhaust products in the cylinder are replaced by fresh air. As the stroke-to-bore ratio increases, so fresh air has to travel larger distance between the intake ports at one end of the cylinder and the exhaust ports at the other end. This increased distance results in higher scavenging efficiency and, as a result, lower pumping work because less fresh air is lost via charge short circuiting.
  • Higher compression ratio can be achieved and hence reduced exhaust temperature

Labels:

Ship Implementation plan (SIP)

The Ship Implementation plan addresses issues related to preparing the vessel for use of compliant fuel oil and includes items such as risk assessment and planning for actions needed to ensure compliance on 1 January 2020. Preparing a good plan can enable a smoother transition into 2020.

The plan is not mandatory and is not subject to endorsement by the flag state or a recognized organization (RO). However, PSC may consider the preparatory actions described in the SIP when verifying compliance.
Items covered by the plan can include, as appropriate, but are not limited to:
  • Risk assessment and mitigation plan (impact of new fuels)
  • Fuel oil system modifications and tank cleaning (if needed)
  • Fuel oil capacity and segregation capability
  • Procurement of compliant fuel
  • Fuel oil changeover plan (conventional residual fuel oils to 0.50% sulphur compliant fuel oil)
  • Documentation and reporting
Benefits of the web-based Ship Implementation Plan app:
  • Save time & effort with a user-friendly tool for developing ship implementation plans.
  • Helps you focus on preparing quality plans by making informed decisions
  • Instant overview of your fleet and the progress of your plans
  • A solid implementation plan ensures a smoother transition into 2020 and can serve as documentation for charterers and authorities

Labels:

Reasons for avoiding atomisation test in slide valves

  • Small lift
  • High frequency
  • Large pressure drop
  • High contact pressure
  • Thin oil

Labels:

Camshaft timing check and adjustment

  • Checked by pin gauge.
  • Pin gauge must be fitted between the camshaft and engine frame housing wall poop marks.
  • Max allowed variation is 2 degree ie 4.8mm
  • If >2 degree , then adjust the camshaft by hydraullic pressure and the special spanned attached to the tackle
  • Position of the engine is no:1 cylinder in TDC, confirm in flywheel.

Labels:

How to run main engine with piston cracked?

  • Cut out the fuel pump by lifting and securing the roller guide.
  • Put the exhaust valve out of action , so that valve remain closed.
  • Dismantle the starting air pipe.ie Blank the main pipe and Control air pipe for the cylinder.
  • Suspend piston and crosshead.
  • Take connecting rod out of crankcase
  • Blank off the oil inlet to the crosshead.
  • Set the cylinder lubricator for the unit to zero discharge.

Labels:

Tri - Metal type thin shell Bearing

1st layer(Flash)       - 1 micron thickness of lead\tin for corrosion prevention before installing.
2nd layer(Overlay)  - 20 micron thick white metal.
3rd layer(Inter lay)  - 5 micron thick nickel\Ag helps to reduce corrosion of white metal
4th layer(Bearing)   - 1mm thick lead\bronze ,tin\Al
5th layer (Steel backing shell)-5-15mm for strength and stiffness

Labels:

Air Purging method in Refer system.

Indication

  1. High condensor pressure.
  2. Small bubble in sight glass of condensor\reciever.
  3. Compressor discharge pressure and temp high.
  4. More super heat.
  5. Pressure fluctuations,
  6. Insufficient working(Temp of room is not coming in time)
  7. Pressure temp relations at compressor discharge and reciever would not match with P-T chart of the refrigerant.

Procedure for Purging

  • During normal running , measure liquid refrigerant pressure , temp at outlet of condenser\receiver.
  • Check corresponding saturation temp for the recorded pressure from P-T chart of the refrigerant
  • Compared the measured temp with the determined saturation temp for any sub cooling \under cooling.Adjust the flow of cooling water through condenser to achieve the saturation condition.

Purging of Air.

  • Close condenser outlet valve, 
  • Circulate cooling water .
  • Pump refrigerant to the condenser/receiver till the compressor trips on LP cutout.(Reduce the LP cut out setting above the atmosphere pressure)
  • Circulate cooling water till inlet and outlet temp becomes equal .Ensure complete refrigerant has pump down.
  • Check condensor sea water outlet temp. Check the refrigerant pressure corresponding to this temp from P-T chart of refrigerant has pump down.
  • Due to the  pressure of air they don't agree .
  • Release air from the condensor through the vent and collect it on to a recollecting bottle until the pressure of the refrigerant in the condenser corresponds to the saturation pressure at the cooling water outlet temperature

Labels:

How to test leaking Air start valve?

How to test leaking Air start valve?

  • Open all the valves for starting main engine except distributor valve.
  • Open all units indicator cocks.
  • Start the main engine from ECR by moving the telegraph of AHD direction.
  • Now the engine wont start , but automatic main air starting valve will open and starting air will be available to all units air start valve.
  • If any air start valve leaks , then the air will go to units and comes out from indicator valve.
  • For checking this personnel should be employed near all indicator cocks

Labels:

Slow turning

Slow turning

  • If a slow turning valve is fitted , then this will open instead of the main automatic valve if the engine has been stopped for more than 30 minutes during maneouvring.
  • It will only supply enough air to turn the engine over very slowly . This is a precaution in case a cylinder has oil or water leak into it which would cause damage to engine when starting.
  • If the engine completes a full revolution on slow turn , then the main automatic valve opens and engine will not start

Labels:

Friday, December 27, 2019

Suction valve purpose in MAN B &W

  • Oil is supplied to the barrel through the spill port and a suction valve
  • The suction valve situated at the top of the barrel opens when the pressure in the barrel falls below the supply pressure.ie during the downward stroke of the plunger , while spill ports are covered by plunger

Labels:

Advantages of Chain drive

  • Flexibility in positioning of camshaft , so fuel pump is located near to cylinder head and HP pipe leakage is reduced
  • Can cope up with some amount of misalignment
  • High transmission efficiency ie 98%
  • Easier to adjust camshaft timing.
  • Less spare requirement
  • Factor safety is high 40-50

Labels:

Piston pressure testing

  • Fill the piston and piston rod with LO.
  • Mount the pressure testing tool at the base of piston rod
  • Connect air supply and apply air pressure to 7 bar( 10 minutes)
  • Check the contact surfaces of piston crown , piston skirt , piston rod and sealing rings for tightness
  • Check no crack on piston crown

Labels:

Inerting ,Gas freeing ,Purging ,Topping up

Inerting

Replacement of hydrocarbon in a cargo tank by using inert gas

Gas freeing

The process of creating normal atmosphere condition inside the tank where oxygen level is 21%

Purging

Inerting inert gas in the tank when it is already having less than 8% oxygen to reduce oxygen and hydrocarbon value even further that.

Topping up

Inerting inert gas into an already inerted tank just for raising the pressure to positive level wit respect to atmosphere

Labels:

Parametric rolling

Parametric rolling is an unstable phenomenon, which can quickly generate large roll angles that are coupled with significant pitch motions. The rolling occurs in phase with pitch, and on containerships introduces high loads into the containers and their securing systems

Causes of Parametric Rolling
  • The size of container ships is increasing drastically as companies are looking forward to monster ships; for e.g. Maersk’s Triple-E Vessels. The new container ships coming to the market have large bow flare and wide beam to decrease the frictional resistance which is generated when the ship fore end passes through the water, making it streamlined with the hull.
  • As the wave crest travels along the hull, it results in flare immersion in the wave crest and the bow comes down. The stability (GM ) varies as a result of pitching and rolling of the ship. The combination of buoyancy and wave excitation forces push the ship to the other side.
  • The similar action takes place as the bow goes down in the next wave cycle resulting in synchronous motion which leads to heavy rolling up to 30 degree in a few cycles. This type of rolling is known as Parametric rolling.
  • This phenomenon occurs only when the sea condition is in head / stern or anywhere near to them. There are two pitch cycles- maximum and minimum. The period of roll is half the natural rolling period which coincides with large phase angle and maximum roll always occurs when the ship is pitching down i.e. bow is down.
Three conditions for parametric rolling :-
  • Sufficient wave height for bow immersion
  • Wave length at least the length or two times the length of ship
  • The ship should pitch atleast two times for every roll
Effects of Parametric rolling :-
  • Heavy stresses in ship structure especially in fore and aft parts
  • Extreme stresses on container and their securing system resulting in failure of the same and even loss of containers
  • Unpleasant for the crew of the ship
  • Variation in the load of ship’s propulsion engine

Labels:

Rudder checks

  • Remove plug for any water
  • Hammer test to check condition of plates.
  • Gauging of vessel more than 5 years.
  • Condition of Zn block
  • Pintle and Jumping clearance
  • Wear down and Rudder drop.
  • Corrosion , Pitting cracks
  • Rudder pressure test 2.4 m water height.
  • Check position correct or not..

Differance between flame screen and Flame arrestor?

Flame Arrestor

Prevent the passage of flame complying with all relavant requirement of this schedule
It is based on the principle of quenching , made of permiable matrix of metal , ceramic or other heat resisting material which can cool a flame.

Flame Screen

A portable device incooperating corrosion resistan wire of very small mesh which used for preventing sparks from entering tank or vent opening for short time preventing passage of flame.

Labels:

Sounding Pipe regulations

  • Deck sounding pipe  - Screw type
  • Engine room sounding pipe - self closing type
  • Minimum diameter 32mm
  • If it is passing through refrigerated space below zero degree then minimum diameter 65mm
  • It should have a stricker plate

Labels:

Why semibalanced rudder is used commonly ?

The top part is unbalanced . It helps in giving structural support to the rudder from vertical displacement .Balanced part is bottom . It render less torque in swinging the rudder as a result semi balanced rudder return to centre line on its own ie, if steering gear fails during turn

Labels:

Onboard pressure vessel testing interval

Fixed CO2 -10 years
DCP - 10 years
SCABA -5 years
Fire extinguisher container - 10 years
Medical Oxygen cylinder -5 years
Water mist sprinkler tank - 10 years
Main air bottle - 5 years

Labels:

Crane rocking test

  • Slewing bearing weardown measurement.
  • 6 months
  • 4 point checks
  • The deflection taken with jib up and down the valve should be certain limit.The gauge should be placed opposite.

Labels:

Gas checking procedure for tanks

Bottom-H2S , CO2

Middle - CO

Top- Lighter  gases

Labels:

Continous Survey of Machineries (CSM).

  • All classification society or IACS requires tha all machinery under their rules must be surveyed every 5 years due to heavy load .
  • They allow some items to be surveyed in rotation curve of anual cycle (20%) .Then survey will over by 5 years . So it is called CSM.
  • Class will allow C\E to survey that class surveyor to credit the survey at anual levels

Labels:

Why IG cannot be less then 1% ?

  • Alarm and change over set at 2%.
  • Because at below this % , unburnt combustion particles increase which can lead to contamination of cargo
  • Plus soot will start coming out from scrubber

Labels:

How to close non confirmity ?

  • Take corrective action.
  • Take precaution not to come again.
  • Send photograph of work.
  • Close it . ie,Identification , Documentation , Evaluation , Disposition ,Notification

Labels:

Substance prohibited from incineration

  1. Residues of cargo subjected to Annex 1 , 2 & 3.
  2. Poly Chlorinated benyl(PCB)
  3. Garbage of Annex V , contain more than traces of heavy metal.
  4. Refined petroleum compounds like halogen compounds.
  5. Sewage sludge and sludge oil either of which is not generated onboard.
  6. Exhaust gas cleaning system residues.
  7. PVC proibited

Labels:

CO2 bottle stamping

  • Manufacturing 
  • " * " means 10 year pressure test . If no " * " then pressure test 5 years.
  • Hydraullic test pressure and date
  • Weight and cylinder capacity.
  • Serial no:
  • Standard
  • Non flammmable
  • Empty bottle height

Labels:

CO2 bottle level measurement

  • Check temp of the room
  • Put sensor on the bottle and keep moving it up and down until it indicates 100 on the panel by using ultrasonic level sensor.
  • Measure the height
  • Put values in the calculation sheet and final values

Labels:

Position 1 & 2 of a ship

Position 1

Any location upon exposed free board deck and raised quater decks and exposed super structure with forward 0.25L

Position 2

Exposed superstructure deck situated aft 0.25L from forward perpendicular and poop deck , bridge deck

Labels:

Difference between ISM external and internal audit?

Internal Audit

  • After July 2010 mandatory
  • 12 months , 3 months can be extended.
  • Tool to monitor how SMS is maintained onboard.
  • Helps to check whether company safety and enviroment policy is continously compliance with requirement of this code , changes in SMS system.
  • Helps to do external audit survey.
  • Company DOC validation.

External Audit

  • Done by classification society.
  • 5 years or 2-3 years
  • Provide DOC and SMC after this audit.
  • Will cehck internal audit details

Labels:

Damage Control booklet


  • Gives idea to show how to control the effect of damage , specific actions
  • Sounding of alarms to alert the crew.
  • Closing of all watertight doors and compartment,
  • Sounding of tanks , rate of flooding.
  •  Ways to reduce the flooding , pumping out.
  • Some ship have a flow chart.
  • If the ship is seaworthy will full fill intact and damage stability

Labels:

Damage Control plan

  • Layout of all compartment such as cargo tank , ballast tank , fuel tank etc.
  • Means of clossure such as valves water tight doors, hatches or cofferdams and its position.
  • Arragment for correction of the list during flooding , location and capacity of fire and  ballast pump.

Labels:

Condition of assignment.

  • All opening on weather deck are water tight.
  • Height of the coaming , air pipes and door sills above weather deck.
  • The change in freeboard depend on degree of water tightness.
  • Water in deck should be removed immediately , bulwark need freeing ports , scupppers.
  • In type A ship due to small freeboard open rails should be fitted instead of bulwark.
  • Hatch coaming , hatch cover , Air pipes should be strong enough to resist pounding from sea

Labels:

Cargo hold fire CO2


  • Remote detector fitter at CO2 room can detect smoke on concerned cargo space.
  • Operation done by master order.
  • After ensuring no person left in cargo space .Seal off the cargo space ie, close ventilation fan , fire damper , hatch cover.
  • Operate  3 way valve for concerned hold and manually open required bottles

Labels:

Fuction requirement of ISM


  1. Safety and enviromental protection.
  2. Instruction and procedures for safe operation and protection of enviroment.
  3. Defined lines of authority and lines of communication between shore and ship.
  4. Procedures for reporting accident.
  5. Procedures for emergency situation.
  6. Internal and External audit

Labels:

Why OMD is M/E not in A/E?


SOLAS Chapter 11-1 regulation 47 says
  • Internal combustion engines of 2250KW and above or having cylinders of more than 300mm bore shall be provided with crankcase detector or engine bearing temp: monitor

Labels:

Pillars of IMO

  1. MARPOL
  2. SOLAS
  3. STCW
  4. MLC

Labels:

Purpose of IG.


Even with no cargo on hold there may be harmful flammable gases.
When vapour produced by an oil cargo is mixed wit certain concentrations of air primarly containing Oxygen , it can result in explosion

Labels:

Weather tight door
  • location above waterline of vessel.
  • Prevent ingress of water from outside to inside.
  • Designed to open outwards.

 Water tight door
  • Prevent ingress of water from both sides.
  • Location below deck level.

Labels:

Rescue boat launching procedure

  • Take off canvas cover of boat.
  • Prepare davit for launching.
  • Switch on pump to operate davit
  • Close drain plug.
  • Prepare painter.
  • Remove lashings
  • Boat ready for lauching

Labels:

PROCEDURE FOR RENEWAL OF INDIAN CDC

  • Use windows  Mozilla Firefox for better resolution.
  • Go to google and type dgshipping. and open dgshipping website.
  • Click on the egovernance link and select Seafarers registration, a new page will open.
  • if you are a new user then register first enter INDoS no & DOB.
  • If already registered then use your INDoS no as user ID, Password ( INDoS no followed by digit 1 or changed password)
  • Before apply for CDC renewal make sure you have updated your seafarer profile if not updated. Update seafarers profile fill out all your documents details and voyage related details.
  • Go to “CDC management and CoC as a cook ”new page will open.
  • However on “Submit Application” Select your desired option as explained above “Renewal CDC (New)”, “Replacement of the CDC”, “Duplicate CDC ”.
  • Fill out all the data & Generate Application No.
  • Under office Select “ SHIPPING MASTER OFFICE MUMBAI”( nearest shipping master) and fill the remaining fields including passport details and click “CONTINUE”
  • Enter Permanent Address and Contact Details and click “CONTINUE”.
  • Under pay fees click “CONTINUE”.
  • Pay Fees online.
  • Take print out of the application, sign on it and upload along with other required documents.
 DOCUMENTS REQUIRED
  • Scan copy of online application.
  • Passport size photograph 3.5cm x 3.5cm
  • Self attested copy of CDC , first and last pages.
  • Self attested copy of proof of indian citizenship better Passport
  


Labels:

Wednesday, December 25, 2019

Safeties in Refer System

Safeties in Refer System
  1. LP cut outs
  2. HP trip
  3. LO differiential trip
  4. Low LO pressure trip
  5. Relief valve in condenser.
  6. Belt driven
  7. Cooling water high temp alarm'
  8. Cooling water non flow alarm
  9. Motor overload
  10. Drier
  11. Oil separator
  12. Sight glass
  13. Crankcase heater
  14. Unloader
  15. Safety spring loaded liquid shock valve on compressor head
  16. Superheat setting on expansion valve.
  17. Master solinoid 


Labels:

Short cycling in refer compressor

Short cycling in refer compressor 

  1. Undercharged.
  2. LP cut out not properly adjusted.
  3. Filter/Drier chocked.
  4. Moisture in system.(icing of exp v/v or Exp v/v filter chocked)
  5. Unloader not working properly.
  6. Expansion valve not properly adjusted.
  7. Solenoid valve malfunction.

Labels:

Turbocharging Principles and Construction

Turbocharging Principles and Construction

By turbocharging an engine, the following advantages are obtained:
  • Increased power for an engine of the same size OR reduction in size for an engine with the same power output.
  • Reduced specific fuel oil consumption - mechanical, thermal and scavenge efficiencies are improved due to less cylinders, greater air supply and use of exhaust gasses.
  • Thermal loading is reduced due to shorter more efficient burning period for the fuel leading to less exacting cylinder conditions.

The turbocharger consists of a single stage impulse turbine connected to a centrifugal impeller via a shaft.
The turbine is driven by the engine exhaust gas, which enters via the gas inlet casing. The gas expands through a nozzle ring where the pressure energy of the gas is converted to kinetic energy. This high velocity gas is directed onto the turbine blades where it drives the turbine wheel, and thus the compressor at high speeds (10 -15000 rpm). The exhaust gas then passes through the outlet casing to the exhaust uptakes

On the air side air is drawn in through  filters, and enters the compressor wheel  axially where it is accelerated to high velocity. The air exits the impeller radially and passes through a diffuser, where some of the kinetic energy gets converted to pressure energy. The air passes to the volute casing where a further energy conversion takes place. The air is cooled before passing to the engine inlet manifold or scavenge air receiver.

 
The nozzle ring is where the energy in the exhaust gas is converted into kinetic energy. It is fabricated from a creep resistant chromium nickel alloy, heat resisting moly-chrome nickel steel or a nimonic alloy which will withstand the high temperatures and be resistant to corrosion.

 Turbine blades are usually a nickel chrome alloy  or a nimonic material (a nickel alloy containing chrome, titanium, aluminium, molybdenum and tungsten) which has good resistance to creep, fatigue and corrosion. Manufactured using the investment casting process. Blade roots are of fir tree shape which give positive fixing and minimum stress concentration at the conjunction of root and blade. The root is usually a slack fit to allow for differential expansion of the rotor and blade and to assist damping vibration.  On small turbochargers and the latest designs of modern turbochargers the blades are a tight fit in the wheel.


Lacing wire is used to dampen vibration, which can be a problem. The wire passes through holes in the blades and damps the vibration due to friction between the wire and blade. It is not fixed to each individual blade. The wire can pass through all the blades, crimped between individual blades to keep it located, or it can be fitted in shorter sections, fixed at one end,  joining groups of about six blades. A problem with  lacing wire is that it can be damaged by foreign matter, it can be subject to corrosion, and can accelerate fouling by products of combustion when burning residual fuels. Failure of blading due to cracks emanating from lacing wire holes can also be a problem. All the above can cause imbalance of the rotor.
The turbine casing is of cast iron. Some casings are water cooled which complicates the casting. Water cooled casings are necessary for turbochargers with ball and roller bearings with their own integral LO supply (to keep the LO cool). Modern turbochargers with externally lubricated journal bearings have uncooled casings. This leads to greater overall efficiency as less heat energy is rejected to cooling water and is available for the exhaust gas boiler.


The compressor impeller is of aluminium alloy or the more expensive titanium. Manufactured from a single casting it is located on the rotor shaft by splines. Aluminium impellers have a limited life, due to creep, which is dictated by the final air temperature. Often the temperature of air leaving the impeller can be as high as 200°C. The life of the impeller under these circumstances may be limited to about 70000 hours. To extend the life, air temperatures must be reduced. One way of achieving this is to draw the air from outside where the ambient air temperature is below that of the engine room. Efficient filtration and separation to remove water droplets is essential and the impeller will have to be coated to prevent corrosion accelerated by the possible presence of salt water.

The air casing is also of aluminium alloy and is in two parts.
Bearings are either of the ball or roller type or plain white metal journals. The ball and roller bearings are mounted in resilient mountings incorporating spring damping to prevent damage due to vibration. These bearings have their own integral oil pumps and oil supply, and have a limited life (8000 hrs). Plain journal bearings are lubricated from the main engine oil supply or from a separate system incorporating drain tank, cooler and pumps. Oil is supplied in sufficient quantity to cool as well as lubricate. The system may incorporate a header tank arrangement to supply oil to the bearings whilst the turbocharger comes to rest should the oil supply fail. A thrust arrangement is required to locate and hold the rotor axially in the casing. In normal operation the thrust is towards the compressor end.

Labyrinth seals or glands are fitted to the shaft and casing to prevent the leakage of exhaust gas into the turbine end bearing, or to prevent oil being drawn into the compressor. To assist in the sealing effect, air from the compressor volute casing is led into a space within the gland. A vent to atmosphere at the end of the labyrinth gives a guide to the efficiency of the turbine end gland. Discoloring of the oil on a rotor fitted with a roller bearing will also indicate a failure in the turbine end gland.
A labyrinth arrangement is also fitted to the back of the compressor impeller to restrict the leakage of air to the gas side

Labels:

Slow Steaming

Slow Steaming
Slow steaming has become more of  a normal operating procedure due to the following factors:

The worldwide downturn in the global economy leading to reduced demand for manufactured goods. This has led to reduced capacity demand. Shipowners are reluctant to lay up vessels and there are also  a large number of new ships being delivered.

  • Increase in fuel and other operating costs such as lubricating oil and maintenance
  • Falling freight rates

The simplest way to reduce operating costs is to reduce the fuel bill. Most vessels are propelled by a slow speed two stroke engine directly coupled to a fixed pitch propeller. If the speed of the engine is reduced, then although the vessel will slow down, the amount of fuel required to travel each nautical mile is reduced. This is because the correlation between speed and shaft power is not linear, but cubic. (PaV3D2/3)

For example, reducing the ship speed by about 20% will reduce the engine power to 45% of its nominal output. This will result in a reduction in the fuel burnt per hour by about 60%.  Reduce the speed by 33% and the fuel saving could be 75% . Of course the voyage will take longer and so the actual fuel saving will be up to about 60%

A two stroke engine operates  at its optimum overall efficiency at about 80% load. When the engine is designed, the auxiliary and ancillary systems are optimised for the engine running at between 70 -85% load. If the load drops below 60% then other problems will begin to show which will interfere with engine performance and operation: These are outlined below.

 Fouling of exhaust systems and  turbochargers due to poor fuel injection, atomisation and combustion. This is more relevant to the camshaft engines where the fuel pump is driven by a cam. The slower the engine runs, the slower the fuel pump plunger moves to deliver fuel to the injector. Electronic engines with various forms of camshaftless fuel injection are better at coping with this, and engines fitted with slide injection valves reduce the quantity the unburnt fuel from the sac  of the injector nozzle from entering the cylinder and causing fouling and poor emissions. Decreasing the viscosity of the fuel to about 13cSt at the nozzles will also improve combustion at low loads.

 Cold corrosion caused by condensation of sulphuric acid on the liner surface and in the exhaust gas heat exchangers. This can be combated to some degree by raising the cooling water temperature to give an outlet of around 90°C and maintaining the Air cooler inlet temperature at about 35°C to keep scavenge temperatures at an optimum. Sulzer maintain that exhaust temperatures must be kept above 250°C to prevent cold corrosion in the uptakes and in the exhaust gas economiser.


Excess cylinder oil fouling and gumming up ring grooves leading to sticking piston rings. Also fouling of the turbocharger nozzle ring and turbine blades. Unburnt cylinder oil can build up in the exhaust manifold leading to a danger of an exhaust manifold fire and uncontrolled overspeed and subsequent failure of the turbocharger. It is recommended that when slow steaming, the engine load is increased to full power for at least 30 minutes daily, or at a minimum of 1hour twice weekly to help burn off these deposits. Engines fitted with either the MAN Alpha lubrication system or the Sulzer pulse lubrication system which both use computers and crank angle sensors to deliver the oil between the ring pack are better at providing adequate lubrication for low load running.
 
Excessive liner wear due to slower piston speeds. This is partly linked to the cylinder lubrication. If this is reduced by too much to combat the effects described above, then the rings will not build up an oil film between ring and liner. But overall lower piston speeds will reduce the effective hydrodynamic film that build up between ring and liner.





Labels:

Sulphur Limits For Ships in EU Ports

Sulphur Limits For Ships in EU Ports
 
From 1st January 2010 the European Parliament Directive2005/33/EC came into force. As well as reinforcing the limits of sulphur for vessels operating in SECAs, and limiting the sulphur content of fuels used ashore in the EU, it also introduced legislation governing the maximum sulphur content of fuels used by inland waterway vessels and ships at berth in Ports which are part of the European Community. The limit placed is 0.1% Sulphur, which is the maximum sulphur content of Gas Oil

The rules state that the limit applies for ships at berth in EU ports allowing sufficient time for the crew to complete any necessary fuel change over operation as soon as possible after arrival at the berth and as late as possible before departure. The change over must be recorded in  ships log books.

It does not apply to ships in port for less than 2 hours, to vessels who "cold iron" i.e. change over to shore power in port. Certain vessels operating in the territory of the Hellenic Republic are exempt until 1st January 2012.

Some confusion has arisen over the interpretation of the Directive. It does not mean that the main engine has to be changed over to gas oil, but the generator engines must be changed over "as soon as possible". MIN 376 issued by the MCA as an interim measure
gives guidance on this point for ships at UK ports.  Because the directive states that ships at berth for up to two hours are exempt it can be inferred that a reasonable time for change over can be considered as 1hour after arrival and 1hour before the ship sails.

The MIN also gives guidance on the definition of "at berth", and states it applies to ships at anchor within port limits. Outside port limits, then Annex VI of MARPOL applies.

 Because the limit will also apply to boiler fuel used whist alongside, Companies have applied for exemptions until their boiler burners can be adapted to burn gas oil. This affects not only burner design but also purge times for the boiler.

Vessels must arrive at the port with supplies of the 0.1% sulphur fuel on board. They cannot arrive and then take on the fuel.

some companies have misinterpreted the directive and have issued instructions to change over to 0.1% sulphur fuel on entry to a SECA.

It does not apply to ports within a SECA but outside the EU (for example ST Petersburg) although individual countries outside the EU may have their own regulations. It also applies to ports within the EU but outside a SECA  (for example Lisbon).

Labels:

The Miller Cycle and Emissions Reduction

The Miller cycle was developed by Ralph Miller in the 1940s. With the introduction of turbocharging to the 4 stroke diesel engines, the Mean Effective Pressure and thus the power output of 4 stroke engines rose by 50 - 60%. However this was about the limit; If the  inlet air pressure was increased further, then the charge air reached excessive pressures and temperatures on compression causing burning of the LO film and thermal stressing.

Miller challenged the thinking of the day by closing the inlet valve before the piston reached bottom dead centre. This had the effect of lowering the cylinder pressure as the piston continued downwards, as well as dropping the temperature of the air (Boyles and Charles' Law). Although the engine is still doing work as the piston is descending on the inlet stroke, there is a saving in work during the compression stroke, and the maximum air temperature and pressure is reduced on compression. The timing of the inlet valve of  Miller's engine was governed by a mechanical link arrangement, and varied automatically with engine load. Miller's engine doubled the MEP of the engine when compared with a naturally aspirated engine.

Advances in design and materials led to more efficient turbochargers, higher compression ratios and more efficient cooling of marine diesel engines. However, with the introduction of MARPOL VI, manufacturers had to look more closely at lowering NOx and smoke emissions.

One of the methods used is to reintroduce the Miller cycle using variable inlet closing, so that at full load, the maximum cylinder temperature is reduced. (NOx formation occurs at temperatures in excess of 1200°C). This is combined with higher compression ratios and slightly later fuel injection timing.

Miller relied on mechanical methods to vary the timing. Modern methods linked to a computer controlled engine management system use a hydraulic push rod.


 Low load operation: The throttle valve opens against a spring as the follower moves up the cam and oil is displaced under the push rod piston, opening the valve. When the follower comes off the cam, the throttle valve is closed and oil can only flow through the throttle orifice, delaying the closing ofthe inlet valves.
At full load operation, an air signal opens the throttle valve. This means that as soon as the follower descends from the cam peak, the pushrod piston moves downwards, allowing the inlet valves toclose
In this second method of control, the Variable Inlet Closing consists of two hydraulic cylinders connected by two passages, the flow through one of these passages being controlled by a valve, and the other by the position of the hydraulic piston driven by the cam follower.

When the follower moves up the slope of the cam the oil in the lower cylinder moves to the upper cylinder displacing the push rod piston and opening the valves. When the follower is on the peak of the cam, the hydraulic piston is covering the passage between the  cylinders.

When the VIC control valve is open, the pushrod follows the follower immediately, which results in early valve closure. When the control valve is closed, the downward movement of the pushrod is delayed until the piston actuated by the tappet reveals the passage between the two cylinders.

Make up of oil is from the main engine Lub Oil supply via a non return valve. Build up of air is prevented by an air release in the push rod hydraulic cylinder.

By increasing the compression ratio, giving a higher air temperature the ignition delay is reduced. Later injection over a shorter period combined with improved fuel atomisation and combustion space design result in lower NOx formation.


 
TWO STROKE ENGINES
The two stroke engine cannot utilise the Miller cycle. However they can use variable exhaust valve closing; easily achieved with an electronically controlled camshaftless engine or by involving hydraulic valves as in the case of the modified Sulzer RTA


NOTE
Supercharged petrol engines also make use of a form of Miller cycle in which the inlet valve is left open during the first part of the compression stroke, so that compression only occurs during the last 70% of the compression stroke. Over the entire compression range required by the engine, the supercharger is used to generate low levels of compression, where it is most efficient. The air is then cooled in the air cooler. Then, the piston is used to generate the remaining higher levels compression, operating in the range where it is more efficient than a supercharger. Thus the Miller cycle when used in a petrol engine uses the supercharger for the portion of the compression where it is best, and the piston for the portion where it is best. In total, this reduces the power needed to run the engine by 10% to 15%.

Labels: