Omds, Crank Explosions And Scavenge Fires

Front 1

explain how a scavenge fire is caused

Back 1

FUEL SOURCE - EXCESSIVE LUBRICATING OIL ACCUMULATED IN SCAV SPACE, MIXED WITH COMBUSTION PRDCUTS TO REDUCE FLASH POINT//DEFECTIVE STUFFING BOX CARRYING OIL UP

AIR - ABUNDANCE OF AIR, HEATED CLOSE TO FLASH POINT

IGNITION SOURCE- BLOWBY DUE TO COMBUSTION SPACE WEAR, RINGS, LINERS, PISTONS AND DUE TO OVERLOAD

//BLOW BACK FROM CYLINDER DUE TO POORTIMING// DEFECTIVE STUFFING BOX GENERATING HEAT

Front 2

how it is bought to the attention of the duty engineer?

Back 2

LOSS OF POWER, ERRATIC RUNNING

SCAVENGE SPACE TEMPERATURE ALARM

TUBROCHARGER SURGING

BLISTERING PAINT

SMOKY EXHAUST

Front 3

describe the action which should be taken in order to extinguish a scavenge fire

Back 3

INFORM BRIDGE, RAISE FIRE ALARM, SLOW DOWN ENGINE WITH A VIEW TO STOP AS SOON AS SAFE AS POSSIBLE, REDUCED FUEL, COMBUSTION PRESSURE, EXCESS AIR, TEMPERATURE OF FRICTION HOTSPOT

PHONE CHIEF ENGINEER, BRIEF SBAR

LIFT FUEL PUMP ON EFFECTED UNIT, INCREASED CYLINDER LUBRICATING OIL AVOID SEIZURE, SHUT SCAVENGE DRAINS TO PREVENT LEAK INTO E/R SPACE

RETURN TO ECR

ENGINE STOPPED, SMOTHER T/C INLETS, FIXED FIRE FIGHTING MEDIUM, PREPARE BOUNDARY COOLING

Front 4

explain how scavenge fires may be prevented.

Back 4

1. Scavenge space should be inspected and cleaned routinely as per PMS to prevent excessive build up of deposits. Drains should be kept clear

2. Cylinder lub oil consumption should be monitored to ensure excessive lubrication is not provided which could fuel a fire.

3. fuel injection equipment should be maintained and time correctly to ensure unburnt fuel doesn't collect and fuel a fire due to blowsy.

4. cylinder liner, piston, rings and stuffing box should be maintained accordingly to prevent blowby or seizure which could lead to an ignition sour

5. correct power balance maintained to prevent overload in units and increased wear which could lead to blowsy

Front 5

With reference to crankcase explosions:describe how a primary explosion occurs and how this may lead to a secondary explosion;

Back 5

Oil is supplied in abundance to the engine in order to cool, clean and lubricate. As it is circulated and splashed around, the droplets are broken up into varying sizes but are all too big at this point to support combustion.

The moving components within the engine rely on effective lubrication to reduce friction load and remove any heat generated. A breakdown in lubrication, or a misaligned/worn component may result in relative movement which will lead to the generation of a hot spot. Any oil in contact with the hotspot will vaporise and the circulate to a cool part of the engine where it will condense into a fine oil mist. Here the oil droplet size is smaller and so this huge increase in surface area is now sufficient to support combustion. The mixture of oil mist/air may now find its way back to the hotspot and ignite, causing a primary explosion.

This primary explosion causes a turbulent pressure front to travel down the crankcase, at high velocity, further breaking up oil droplets and igniting them. The pressure generated can be great enough to blow the crankcase doors off, allowing the flame front to escape into the engine room.

The massive drop in pressure now causes a vacuum in the crankcase, where there is a massive in rush of air, that mixes with the oil mist and creates a secondary, more destructive explosion

Front 6

explain the action to be taken in the event of an oil mist detector alarm sounding

Back 6

***emergency response as per SMS***

1. call bridge, ask to reduce RPM. By removing load from the engine you are reducing frictional load from any potential hotspot, and minimising risk of an explosion.

2. evacuate engine space, clear of doors.

3. transfer electrical load from shaft alternator if applicable.

4. Ask bridge to reduce to minimum RPM and stop engine as soon as possible.

5. Cylinder lubrication rates should be increased to maximum, to prevent seizure due to heat generation and ensure effective cooling.

6. Once engine is stopped, and if it is safe to do so, engage turning gear and keep engine turning over. Effective cooling, indicate seizure.

7. After a minimum period of 30 minutes, a per SMS and OEM instructions. The engine maybe isolated and crankcase doors opened.

8. The OMD and alarm system should be checked for correct operation and a full crankcase inspection including deflections should be carried out.

Front 7

With reference to exhaust gas economisers/waste heat boilers:Explain the possible consequences of not maintaining the gas side heat transfer surfaces in a clean condition;

Back 7

1. soot build up, reduction in heat transfer efficiency

2. soot build up, cause an uptake fire

Front 8

With reference to exhaust gas economisers/waste heat boilers: describe how the gas side heat transfer surfaces are maintained in a clean condition during operation of the unit;

Back 8

1. soot blow/ultrasonic

2. liase with bridge, change course

3. increase load, exh gas velocity to blow off

4. check feed tank, air receiver

5. monitor inlet/outlet temp, monitor exh.

Front 9

With reference to exhaust gas economisers/waste heat boilers: describe a gas side out-of-service cleaning method, explaining why out-of-service cleaning is necessary even though in-service cleaning is carried out.

Back 9

soot blowing cannot remove all deposits, especially at joints of tubes and headers

good chance to inspect internal condition

1. allow engine to sufficiently cool down and isolate.

2. open drain and prove clear

3. open access doors and take note and record condition / photos for PMS

4. water wash. check condition of drains, stop when no soot flow.

5. prove drain clear and close

6. allow sufficient time to cool down and close access doors

Front 10

State THREE other indications of overheating or existence of conditions that might result in a crankcase explosion;

Back 10

1. High bearing temperature 2. Metallic particles in lub oil sample would indicate worn bearings3. Excessive lub oil temperature

Front 11

describe the operating of an oil mis detector

Back 11

There are various designs of OMD, a popular one working on the scattered light principle. Crankcase sample is drawn in using an extraction fan ion the individual detector units. The units consist of a light source, compensating receiver and measuring receiver. The compensating receiver ensures the correct intensity of light by providing feedback to the source transmitter. Any oil mist will scatter the light source, which is detected by the measuring receiver, producing an analogue signal which is compared to a desired value and an error output, alarm presented.

Front 12

Describe, with the aid of a sketch, a crankcase explosion relief valve:

Back 12

Conical Alluminium alloy spring for low inertia

Deflector shield to deflect any release downwards and out of harms way.

Dome shaped Flame gauze to cool and dissipate any flame. The free area > valve open area

Non Return valve and temperature resistant, nonstick seal to allow positive opening and prevention against back flow

Front 13

explain how a crankcase explosion door functions in the event of an explosion; state a reason for the crankcase explosion relief doors opening, other than because of an explosion.

Back 13

When a crankcase explosion occurs, the flame front generated can reach massive speeds and generate sufficient pressure that will blow of ordinary crankcase doors, allowing the explosion to escape into the E/R, injuring personnel, damaging equipment, but also allowing an inrush of air that will lead to a bigger explosion. The relief door lifts at 0.2 bar and maintains the crankcase pressure below 1.3 bar (typically). The flame is dissipated through the gauze and the non return valve prevents this inrush of air.

Piston blow by or faulty stuffing box may allow pressurised air to enter the crankcase and inadvertently open the relief valve.