Face to face with engine room

What, that is heart for humans is the engine room for the ship. It is what which is most important something which keeps it alive to sail across. Its loud and hot and you have to watch your steps on stairs to avoid any trouble.

What the book says is: On a ship, the engine room, or ER, is the propulsion machinery spaces of the vessel. To increase a vessel's safety and chances of surviving damage, the machinery necessary for operations may be segregated into various spaces. The engine room is generally the largest physical compartment of the machinery space. It houses the vessel's prime mover, usually some variations of a heat engine - diesel engine, gas or steam turbine, or some combination of these (such as CODAG; see Category: Marine Propulsion). On some ships, the machinery space may comprise more than one engine room, such as forward and aft, or port or starboard engine rooms, or may be simply numbered.

On a large percentage of vessels, ships and boats, the engine room is located near the bottom, and at the rear, or aft, end of the vessel, and usually comprises few compartments. This design maximizes the cargo carrying capacity of the vessel and situates the prime mover close to the propeller, minimizing equipment cost and problems posed from long shaft lines. The engine room on some ships may be situated mid-ship, especially on vessels built from 1900 to the 1960s. With the increased use of diesel electric propulsion packages, the engine room(s) may be located well forward, low or high on the vessel, depending on the vessel use.

What is it all about( Easy explanation/ UN-bookish): It is the machinery compartment situated at the aft of the ship below waterline. It consists of 3 decks having different machineries mounted on it. The lowest most floor or platform is called the third deck below which are the bilges a place where all the drains from the engine room other than of oil containing sources. 
                           Third deck is commonly called as machinery deck in the ship. It has main engine, Auxiliary engines, Auxiliary boilers, Hot well, Fresh water generator, Bilge and blast Pump,Main engine sea water Pump, Ejector pump, Main engine jacket water pump, Main engine lube oil cooler, Main engine jacket water cooler, Main engine lube oil storage tank, Main engine lube oil clarifier and purifier, Reciprocating bilge pump, Oily water separator, Main air bottle,Main air compressor, Hand air compressor, Emergency air bottle, Fuel oil transfer pump, General service pump, Fire pump, Fuel oil bunkering valve chest and bilge and blast valve chest.

Block diagram of location of machinery on 3rd or bottom deck of ship.
Block diagram of location of machinery on 3rd or bottom deck of ship.
Second deck is commonly known as the utility deck in the ship and compromises of control room, Electrical stores, Spare gear stores, Injector testing bay, Various display table, Emergency fire pump, Emergency air compressor, Workshop, Incinerator, Fuel oil mixing column, Air conditioning and refrigeration plant, Filters, Changing room for crews, Fresh water hydrophore, Boiler reciprocating pump, Feed water tank, Fresh water tank, Fuel oil tank, Main engine expansion tank, Auxiliary engine expansion tank, Auxiliary engine fuel oil service tank.


So far we have discussed about bottom or third deck and middle or second deck platforms. Now we will talk a very little about the first deck, it is at the top most and mainly contains engine control room and various other compartments and machines stated in the given diagram. It is commonly known as the weather deck on the ship.

-For any query or suggestions please comment down below.

Author marineGuru


TURBOCHARGERS & ITS SURGING

Turbocharger sketch
Turbocharger
Shown in the sketch is a section of turbocharger fitted on a large 2 stroke engine. It consists of a single stage, axial flow exhaust gas driven turbine mounted on a common shaft with centrifugal air compressor.

Turbine : The exhaust gas enters through the nozzle ring and is then directed to the turbine rotor blades at high velocity. The nozzle ring converts the energy in the exhaust gas to kinetic energy. The turbine blades are firmly fitted on the wheel by fir tree shaped roots which give positive fixing and minimum stress concentration.
The blades are held together at the free end by lace wire to dampen vibration. The nozzle ring, turbine wheel, blades and rotor shaft are manufactured from heat resisting nickel chrome alloy steel to withstand high working temperatures. The turbine casing is of cast iron with adequate water cooling spaces. In modern slow speed 2 stroke engines with relatively low exhaust gas temperatures the casings are un-cooled.

Blower : The air blower casing is fitted with filters and silencers at the air inlet of the casing. A inducer is fitted just before the impeller to direct the flow of air to the centre of the impeller without any shock. The impeller is made of light aluminum alloy. The impeller takes in air axially and delivers it radially through a diffuser to the volute casing. The kinetic energy is converted into pressure energy and air is delivered to the air cooler for cooling and then to scavenge manifold. Compressor casing is of cast aluminum and un-cooled.

Labyrinth Seals
: Two labyrinth seals are fitted to the shaft, one between thrust bearing and air compressor and the other between turbine and bearing. They are sealed with air under pressure from the compressor discharge through internal passages. The seals prevent possible oil leakage into the turbine and compressor and also prevent exhaust gas leakages into bearing oil.

Bearings : Two shaft bearings are fitted, one at each end. End thrust is taken at the compressor bearing, allowing the turbine bearing free thermal expansion of the shaft. Bearings may be of either plain sleeve types with copper lead bushes on hardened steel sleeves or ball and roller type.

Lubrication : Ball and roller bearings may be lubricated by self contained gear type pumps operated from the shaft and drawing oil directly from the independent bearing sump.
For sleeve type bearings either the lubricating oil from engine lubrication system is used or a complete different system can be used exclusively for the turbochargers. In which case additional pumps, motors, filters and cooler will be required.

Maintenance on Turbochargers :
  • Regular checking of oil level in bearing sump and changing oil after 1000 hrs
  • Cleaning of air filter after 1000 hrs
  • Renewal of bearings after 16000 hrs and gear pumps to be renewed or reconditioned after 16000 hrs
  • The cooling water chamber to be cleaned at every 8000 hrs.
  • Regular water washing of compressor and turbine.

Water washing of Turbocharger compresso
Water washing of Turbocharger compressor
Turbocharger  Cleaning : Under operating conditions turbocharger systems may become fouled, causing reduced efficiency, loss in power and surging.
Compressor :
Oil mist and dust drawn from engine room may get deposited on the compressor surface.  Dirt deposits should be dislodged by injection of water during operation.
A small container is provided which is filled with water to clean the compressor. Water is injected using air from the compressor. Cleaning is carried at full load and performed once every day.
1.  Open filler of the tank and fill with fresh water. Close vent.
2.  Open air supply valve A
3.  Open injection valve B and wait for 30 seconds.
4.  Close valve A and B and open vent.
5.  Check to ensure tank is empty.

Turbine :

Fouling of the turbine can occur due to products from combustion of fuel, ash and any other non-combustibles present in the fuel.
Water Washing of Turbine side: The dirt deposits on turbine side can be reduced by periodic cleaning (water washing) during operation. Dirty turbines lead to higher temperatures of exhaust gas and higher stresses on bearings due to imbalance.

  • The engine speed must be reduced to reduce the exhaust temperature and prevent thermal shock of the turbine.
  • Once the exhaust temperature is at or below the manufacturer's limit, the turbocharger drain can be opened and freshwater admitted to the turbine casing.
  • Water should be admitted slowly until water appears at the drain, then the water flow can be increased.
  • Water supply and drain to be closed once fairly clean water starts flowing from the drain.
  • After the cleaning is completed the engine must be run on same speed for about 5 mins until all parts are dry.
  • This operation is usually carried out on a weekly basis.
Arrangement for turbine water-washing
Arrangement for turbine water-washing
Dry Cleaning : The turbocharger speed does not have to be reduced when dry cleaning. A container is filled with correct amount of cleaning material, either ground nutshells or small grains of rice. The valve from the container is then opened to blow the material into the turbine casing. This is carried out normally every two days.

New series of two-stage turbochargers :

Two-stage turbocharging is important for the development of new generation of large-bore diesel engines with reduced exhaust emissions. Reducing engine emissions through internal measures is achieved by increasing the mean effective pressure. This requires high charge-air pressures but cannot be achieved through single-stage turbocharging. Two-stage turbocharging enables the charge-air pressure to be increased substantially while simultaneously reducing exhaust emissions, despite the increased specific engine output. MAN Diesel & Turbo has introduced  two-stage turbocharging to the market with its TCX series.
Two-stage turbocharging systems consist of two turbochargers of different size connected in series. The exhaust gas coming from the engine drives the turbine of the smaller, high-pressure turbocharger (the first stage) which in turn drives the turbine of the larger, low-pressure turbocharger (the second stage).
The low-pressure turbocharger's compressor draws in ambient air and sends it via an intermediate cooler to the high-pressure turbocharger's compressor. Here, the air is compressed once again and, via a further charge-air cooler, sent to the engine. The system adapts to varying operating conditions either through controlled turbine bypass or by variable nozzle rings (VTA).
VTA – Variable Turbine Area, allows charge air delivery to be optimized by using adjustable vanes. By altering the pitch of the adjustable vanes, the exhaust gas pressure is regulated and thus the air amount can be precisely matched to the quantity of injected fuel at all points in an engine’s load and speed range. The result is reduced specific fuel consumption, reduced emissions HC and CO2 and improved engine response.
Although two stage turbocharging is more efficient than single stage, the additional cost and complexity of the system makes it generally unpopular.

Surging
Surging is a phenomenon that affects centrifugal compressor when the mass flow rate of air falls below a sustainable level for a given pressure ratio.
Surging is a condition whereby an imbalance in demand and supply of air from the turbocharger causes a rapid deceleration. When this occurs the pressure downstream of the compressor is relieved to atmosphere backwards through compressor. This is known as surging and it is accompanied by a loud barking noise and vibration. It was not uncommon on pulse systems in heavy weather, it is less prevalent in modern constant pressure designs.
The turbocharger must produce the required scavenge pressure. When the turbocharger cannot maintain pressure and the air flow decreases, the delivered pressure falls below the scavenge pressure which results in reversal flow and surging occurs.
If surging occurs engine speed must be reduced, the compressor should be water washed and air filters cleaned. If this does not solve problems the engine balance should be checked by taking set of indicator cards.
Conditions leading to Surging: 
Surging may occur in heavy weather when propeller comes out of water and governor shuts the fuel almost instantaneously.
Some possible reasons of surging are :
  • For multi blower installations surging can occur due to a difference in maintenance of cleaning causing one or more to operate at pressure ratio's above its capability
  • When governor shuts fuel instantaneously.
  • change in engine speed/ load relationship- say due to hull fouling
  • cylinder power imbalance
  • faulty injectors or timing
  • dirty air filter
  • dirty air cooler (air side)
  • dirty turbine nozzle ring
  • deposits on blades or impeller
  • damage to blades
It is also possible that components downstream from the blower exhaust such as a fouled exhaust gas boiler can also lead to surging



Author marineGuru


SUPERCHARGING IN MARINE DIESEL ENGINE

Supercharging (or Pressure charging) is a process where a greater mass of air is admitted in the cylinder for combustion and consequently a greater amount of fuel is burnt efficiently.
Power output of the engine is increased with higher thermal efficiency without increasing the size of the engine.

Naturally aspirated engines : It is a term applied to engines where air charge is brought into cylinder only by the downward movement of the piston, without any external aids.

Supercharged engines : is the term used to indicate that weight of air supplied to the engine is considerably increased.
Supercharger can be any device (normally exhaust gas driven turbocharger) which increases the pressure of combustion air supply above that which is normally required.

Air Charge Ratio : This is ratio of volume of air contained in the cylinder at the the start of compression to the swept volume of the piston. For naturally aspirated engines it is about 0.85 where as for supercharged engines it is about 2.5 – 4.0.

Advantages of pressure charging :
1. Substantial increase in power for given speed and size of the engine.
2. Better power to weight ratio i.e. reduced engine weight for given output
3. Improved mechanical efficiency with reduction in specific fuel consumption
4. Reduction in cost per unit of power developed.
5. Increase in air supply has a considerable cooling effect leading to reducing the  severe working conditions and improved reliability.

There are 2 types of Supercharging methods :
Pulse type  and
Constant pressure type.


Supercharging in marine engine
Supercharging Techniques
PULSE SYSTEM : IN PULSE PRESSURE SYSTEM THE ENERGY OF THE EXHAUST FROM THE CYLINDER IS TRANSFERRED TO TURBOCHARGER BY PRESSURE WAVES OR PULSES.
Pulse Turbo-charging System with Twin entry Blower
Pulse Turbo-charging System with Twin entry Blower


  • THESE WAVES TRAVEL THROUGH THE MANIFOLD TO THE TURBINE NOZZLES WHERE THEY ARE CONVERTED TO KINETIC ENERGY AT HIGH VELOCITY TO ROTATE THE TURBINE BLADES.
  • THIS GIVES A RAPID BUILDUP OF TURBINE SPEED WHEN AN ENGINE IS STARTED OR DURING MANOEURING.
  • TO MAINTAIN THE PULSES, RAPID OPENING OF EXHAUST  VALVE, EXHAUST CONNECTIONS OF LIMITED DIAMETER, NO SHARP BENDS & THE TURBOCHARGER IS FITTED CLOSE TO THE ENGINE.
  • TO PREVENT BACK FLOW INTO  THESE, THE EXHAUST IS SUBDIVIDED BETWEEN A NUMBER OF MANIFOLDS, EACH CONNECTED TO A SEPARATE NOZZLE BOX AT THE TURBINE.
  • UPTO THREE CYLINDERS USE EACH MANIFOLD WITHOUT INTERFERENCE DEPENDING ON THE FIRING ORDER.
  • DUE TO SMAL VOLUME OF EXHAUST DUCTING AND DIRECT LEADING OF EXHAUST TO TURBINE INLET THE SYSTEM DOES NOT REQUIRE ANY FORM OF SCAVENEGE ASSISTANCE AT LOW SPEEDS OR WHEN STARTING.
ADVANTAGES :
UTILIZES HIGH KINETIC ENERGY OF EXHAUST GASES
DOES NOT REQUIRE AUX BLOWERS AT LOW SPEEDS OR DURING STARTING OF THE ENGINE.

DISADVANTAGES :
MORE NO OF TURBOCHARGERS NEEDED
EXHAUST PIPING IS KEPT STRAIGHT AND SMALL SO LOCATION OF TURBOCHARGER IS VERY CRITICAL
ACCURATE MATCHING OF EXHAUST REQUIRED TO PREVENT BLOWBACK.

CONSTANT PRESSURE : IN THIS SYSTEM THE EXHAUST GASES FROM EACH INDIVIDUAL CYLINDER IS LED TO A COMMON MANIFOLD OR RECEIVER WHERE THE PULSE ENERGY IN LARGELY DISSIPATED.

THE PRESSURE PULSE IS DAMPED OUT BY EXPANDING THE GAS IN THIS CHAMBER WHICH IS MAINTAINED AT CONSTANT PRESSURE.THE EXHAUST GAS FROM MANIFOLD IS LED TO TURBOCHARGER AT CONSTANT PRESSURE.

THE VOLUME OF THE MANIFOLD MUST BE LARGE ENOUGH TO ACCOMMODATE GAS FLOW AND PREVENT LOCALISED PRESSURE RISE.

ADVANTAGES :
1. STEADY PRESSURE BEFORE TURBINE,EFFICIENT OPERATION
2. BETTER AND MORE RATIONAL UTILISATION OF EXHAUST HEAT
3. COMPRESSOR CAPACITY CAN BE INCREASED AS MORE ENERGY IS AVAILABLE
4. EXHAUST PIPING IS SIMPLER
5. EXPANSION IN CYLINDER CAN BE CARRIED OUT LONGER AS NO PRESSURE PULSE IS REQURED.THIS RESULTS IN EFFECTIVE INCREASE IN STROKE SO MORE OUTPUT.
6. DUE TO EFFECTIVE SCAVENGING SFC CAN BE REDUCED

DISADVANTAGES :
THIS SYSTEM IS SLOWER IN ITS BUILDUP OF PRESSURE WHEN STARTING, & INSUFFICIENT AIR IS AVAILABLE FOR ENGINES DURING MANOEUVRING OR OPERATING AT LOW SPEED.

TO OVERCOME THIS DIFFICULTY ENGINES HAVE ELECTRIC DRIVEN AUXILLARY BLOWER.


Author marineGuru