Bulletin #D17 - English

Precautions for burning heavy fuel oil in DL-type enginesSK89-10

Heavy fuel oil (H.F.O.) burning in comparison to marine diesel oil (M.D.O.), poses some problems especially in low load condition situations. The main problems are due to the carbon deposits that form on engine parts giving rise to:

n reduced exhaust valve sealing ability, n reduced heat conduction (increased exhaust valve temperature), n valve blow by, n poor piston ring movement in ring grooves, n piston ring blow by, n L.O. contamination and deterioration, n increased L.O. consumption and n cylinder liner abnormal wear.

All of the above effects will be accentuated in the low load conditions when there is poor F.O. temperature, cooling water temperature and intake air temperature control.

1. Low load operation

Turbo charger blower and intake ports will be soiled by low load operation of the engine.

The following table shows the low load limit for each engine type in PS.

Engine model720 r.p.m. 900 r.p.m.

MDO IF 180 IF 380 IF 700 MDO IF 180 IF 380 IF 7006DL(B)-19 110 190 190 - 130 235 - -6DLB-20 140 235 235 - 170 295 - -6DL-20 140 235 235 260 170 295 - -6DL(B)-22 190 310 310 350 240 410 - -6DL-24 240 380 380 450 -6DL(B)-26 300 480 480 565 -6DL(B)-28 370 585 585 640 -8DL(B)-28 500 780 780 850 -6DL(B)-32 450 710 710 770 Note: DL-32 at 600 rpm

8DL(B)-32 600 945 945 1030 6DLM-40 1350 1575 1575 1575 Note: DL-40 at 480 - 515 rpm

When it is inevitable to operate the engine below the low load limit then strictly follow the guidelines below.

Maximum operating period under low load limit

After operating below the low load limit for periods as in the above table, then carry out a parts and cylinder cleaning operation by running the engine for at least 30 minutes with over 60% load.

a. About 10 minutes with zero load.b. More than 30 minutes using M.D.O. for cleaning operation.c. More than 30 minutes with over 60% load after operating under the low load limit.

Load Fuel oil type Max. operating period

Less than 20%M.D.O. less than 2 hoursH.F.O. do NOT operate

Between 20% and 35%M.D.O. less than 6 hoursH.F.O. less than 1 hour

2. Fuel oil pre-treatment

Vanadium and sodium which are included in heavy fuel oil, are responsible for the high temperature corrosion effect (Vanadium attack). Seawater, which is sometimes mixed with heavy fuel oil, helps Vanadium attack. Therefore, seawater must always be removed from the H.F.O. F.O. injection elements (F.O. plunger, nozzle etc.) will be corroded even after a short operating period when sea water levels are as low as 0.2%. Proper maintenance and continuous running of the F.O. purifier is recommended.

3. Properties of heavy fuel oil

It is very hard to know and identify all the properties of fuel when bunkering in different places around the world. Recent H.F.O. have negative influence on the engine parts due to its high viscosity, high density and impurities. This places increased load on the vessel equipment (separator, purifier, F.O. heating system) which must be maintained and operating properly.

However, the Calculation of Carbon and Aromatics Index (CCAI) table 1 (load time 45 secs) is an easy check on fuel quality.

The CCAI diagram shows that a low viscosity with high-density fuel has a poor

combustibility due to the many incombustible impurities in it.

In case of a CCAI of 850 - 870 fuel, it is necessary to increase intake air temperature. In addition, a 10% increase of the low load limit is necessary.

The CCAI table is included at the end of this bulletin for your reference.

4. Intake air temperature

An increase of the intake air temperature will support a better combustion. By opening the by-pass cock of the inter-cooler, the temperature can be increased. In cases where an inverse warming system is installed on the engine, check it is working properly.

The following must also be checked:

n Do not exceed 400oC exhaust gas temperature at normal load operation n Do not break out turbo charger surging at normal load operation

5. Maintenance tips

a. Keep a good F.O. injection and spray pattern by regular and careful maintenance of the F.O. nozzle.

b. Check F.O. injection timing. Generally too early an injection timing will spray atomized fuel on the cylinder liner thus destroying the oil film between liner and piston rings. This fuel enters the piston ring grooves and after combustion, it will be carbonized affecting ring movement and ring-sealing properties. Therefore, set the F.O. injection timing as follows:

c. Implement exhaust valve maintenance at an earlier stage. Initially carry out maintenance after 1000 to 1500 hours and reschedule next inspection depending on the condition of the valve at each inspection.

d. Decrease nozzle cooling oil temperature (for thermal oil). By decreasing nozzle-cooling oil temperature while engine is running to about 55oC, it prevents corrosion.

e. Control L.O. alkali value (pH value). When using L.O. with a high alkaline value (pH), carbon deposits on the exhaust valve include a high amount of calcium, which by its nature is very hard. The calcium scratches the valve seat

Engine DL-19 DL-20 DL-22 DL-24 DL-26 DL-28 DL-32 DL-40

Timing degrees B.T.D.C.

17-19 17-19 18-20 18-20 17-19 20-22 19-21 15-17

damaging the contact areas, which affects valve-sealing ability.

f. A minimum running-in period after replacing piston rings and/or cylinder liner is recommended. Running in period for piston rings is minimum 4 hours and for cylinder liner is minimum 7 hours. Set engine load in steps of 35%, 50%, and 75% during running in period. Thereafter, run the engine with M.D.O. for 200 hours.

Note: Always consult "OPERATION AND DAILY MAINTENANCE" and "USABLE LIMIT OF HEAVY FUEL AND ENGINE OPERATION CONTROL" in the Daihatsu engine Instruction Manual.

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