1999/07/01 Caterpillar

3606 (8RB),
3608 (6MC),
3612 (9RC),
3616 (1PD) Engines In HFO Applications

Reference: Operation & Maintenance Manual; SEBU6966-02; "3600 Heavy Fuel Engines", Page 138, 'Fuel - Changeover'.

Reference: Engine News, August 1997, Page 22, "Procedures For Changing From Running On Heavy Fuel Oil (HFO) To Running On Distillate Fuel".

When performing fuel injector synchronization on HFO Engines, the following information must be kept in mind:

* Injector synchronization CANNOT be properly performed if heavy fuel oil is in the engine fuel system.

* Before shutting down these engines to perform injector synchronization, always change over to distillate fuel. Make sure that all the HFO has been removed from the engine before shutdown.

* If the engine has been shut down while operating on HFO (for example, emergency shutdown), the fuel system may be flushed with distillate fuel after shutdown.

NOTE: The section, 'Fuel - Changeover', in the Reference (Operation & Maintenance Manual) has been revised. The complete revised section, 'Fuel - Changeover', is as follows.

Fuel - Changeover - SMCS Code: 1280

Caterpillar 3600 Series Heavy Fuel Engines are designed to use heavy fuels for starting, operating, and stopping. These engines can also operate on distillate fuel. During the changeover between fuels, these engines can use a mixture of distillate fuel and heavy fuel.

Use caution not to change between heavy fuel and distillate fuel too quickly. Differences in the control of the fuel temperature can cause thermal shock and a lack of lubricity to the unit injector.

The following recommendations are based on having a system that meets Caterpillar recommendations and industry standards. The system design includes these features:

* A three-way valve for the selection of heavy fuel or distillate fuel

* A separate, isolated distillate fuel supply for the engine(s)

Circumstances for Changing the Fuel

Caterpillar 3600 Series Heavy Fuel Engines are designed to use heavy fuels for normal operation. However, it is preferable to operate with distillate fuel before stopping the engine for the following circumstances:

* Performance of service on fuel system components such as fuel filters and unit injectors

* When the engine is being shut down for an indefinite period of time and fuel circulation through the engine is stopped

Also, these engines may be operated on distillate fuel when the heavy fuel supply is restricted, reduced, or eliminated.

The following definitions will assist operators in determining the circumstances for changing the fuel:

General recommendation - Flush the engine fuel system with distillate fuel prior to performing any maintenance on the fuel system. Flush the fuel system with distillate fuel if the engine is shut down for more than 12 hours. If the jacket water heaters are not functional, flush the fuel system with distillate fuel at every shutdown.

Temporary shutdown - The engine is shut down for 12 hours or less. It is not necessary to change the fuel. The engine can be stopped and started with heavy fuel. Jacket water heaters must operate in order to maintain the temperature of the jacket water at a minimum of 65 C (149 F). Continue to circulate heavy fuel through the engine in order to maintain the temperatures of fuel system components for start-up. The fuel must have the correct viscosity and temperature at all times.

Extended shutdown - The engine is shut down for more than 12 hours or for an unknown length of time. Flush the engine fuel system with distillate fuel. Unless cold ambient conditions make the use of jacket water heaters necessary, use of jacket water heaters is not required. Shut off the circulation through the fuel system and the unit injector tip cooling module. Empty the air line to the starting motor. Lock the air valves to the starting motor in the OFF position. Space heaters for the generator must be operational.

Recommendations for Shutdown and Start-up

The use of proper operating practices is important. The following guidelines are recommended:

* For generator sets, operate the space heaters when the generator is not operating. This will help to prevent moisture damage to windings. The space heaters can be controlled with a thermostat or a relay.

* A lack of proper temperature control can lead to problems with the unit injectors or other fuel system components. Operate the jacket water heaters when the engine is shut down. This will help to maintain proper temperatures for start-up in the cylinder heads, cylinder liners, and fuel system components. Maintain a minimum jacket water temperature of 65 °C (149 °F).

* Follow the recommended procedures before starting any engine. Incomplete procedures can lead to system malfunctions that do not allow engine operation. See this Operation and Maintenance Manual, "Engine Starting" topic (Operation Section).

* Prior to starting any engine after an overhaul or after servicing the fuel system, ensure that all of the engine protective devices will function. Prepare to use the emergency stop button, if necessary.

* Test the engine with distillate fuel after an overhaul or after servicing the fuel system. Perform the test before changing to heavy fuel. Distillate fuel is much easier to clean up if, for example, a leak develops after starting.

Fuel Bypass Valve

During normal operation, the valves for the fuel supply lines and the fuel return lines are open. The bypass valve between the supply lines and return lines is closed. When the fuel supply lines and the fuel return lines are closed, fuel does not flow to the fuel filters. The filters will cool. Hours may be required for heating the fuel filters before starting the engine. When the fuel to an engine is changed, the bypass valve must be adjusted in order to maintain the correct fuel system pressure. Adjustment of the bypass valve also maintains the circulation of fuel through the fuel system when the fuel supply and return lines are closed.

For sites with more than one engine sharing one fuel oil conditioning module, the fuel pressure to any operating engine will increase when another engine is shut down. When the fuel to an engine is changed, the bypass valve must be adjusted in order to maintain the correct fuel system pressure to any operating engine. Normal supply pressure from the fuel oil conditioning module is 6.5 to 7 bars. This pressure is needed in order to maintain a pressure of 550 to 620 kPa (80 to 90 psi) to any operating engine.

Changing the Fuel

The method that is used for changing the fuel depends on the equipment that is used. Different sites may have different equipment. The following methods are possible:

1. The fuel system can be flushed, using an auxiliary fuel pump, a separate fuel tank, and separate fuel lines.

2. The fuel supply can be switched, using a dual source of fuel at the fuel oil conditioning module.

A motorized, three-way valve with a clock timer is recommended for the fuel changeover procedure. This valve can be used with a single engine and with sites that have more than one engine sharing one fuel oil conditioning module. The fuel can be changed during engine operation or after stopping.

Changeover from HFO to Distillate Fuel During Engine Operation

1. Operate the engine at reduced load.

2. Set the changeover valve time control for 45 to 50 minutes.

3. Make sure that all valves from the distillate fuel line to the booster module are OPEN.

4. Change the fuel selector switch on the booster module control box from heavy fuel to distillate fuel.

5. Monitor fuel temperature and viscosity during the changeover period. Adjust the bypass valve in the fuel lines to balance the fuel supply pressure to each engine at 550 to 620 kPa (80 to 90 psi).

6. When the fuel viscosity is reduced to ten (10) cSt, the valve which allows fuel flow through the fuel cooler should be opened slowly, until there is a maximum flow of fuel to the fuel cooler.

7. When the fuel viscosity reaches eight (8) cSt, the steam feed to the Vokes filter should be slowly closed.

8. When the full fuel flow is directed through the fuel cooler, the viscosity will continue to reduce to a final level of four to five (4 to 5) cSt. After the final viscosity level of four to five cSt is reached, operate the engine at constant load for 15 minutes. This step will ensure that all of the heavy fuel has been cleared from the engine prior to reducing the load or increasing the load.

9. If reducing the load to stop the engine, unload the engine and allow an appropriate cool-down period before shutting the engine off.

10. After the engine has stopped, close the fuel supply and fuel return lines at the engine. Close the injector tip cooling supply and return lines.

Changeover from Distillate Fuel to HFO During Engine Operation

NOTE: Depending on the load conditions and the volume of fuel in the system, complete fuel changeover may require up to one hour.

1. With the engine(s) operating at reduced load, move the fuel selector switch on the booster module from distillate fuel to heavy fuel.

2. Monitor fuel temperature and viscosity during the changeover to heavy fuel. Maintain the fuel supply pressure to each engine at 550 to 620 kPa (80 to 90 psi). If necessary, adjust the fuel bypass valve. Be careful to avoid sudden changes in either fuel temperature or fuel viscosity during the changeover. Check the fuel valve routing. Sufficient fuel should be routed through the fuel cooler before returning to the booster module. Make sure fuel viscosity stabilizes at approximately 15 to 20 cSt at the unit injector.

3. When the fuel temperature and viscosity have stabilized (after the changeover is complete), close the distillate fuel supply line valve to the booster module.

Changeover from HFO to Distillate Fuel After Engine Shutdown

This procedure is based on the following conditions: the engine was previously stopped while operating on heavy fuel, and the jacket water heater is operating.

1. Adjust the engine's fuel supply line from HFO to distillate fuel. The clean distillate fuel will become contaminated with heavy fuel oil while the engine's fuel system is being flushed. Adjust the fuel return line to return the fuel to the HFO day tank.

2. Adjust the fuel bypass valve to maintain 550 to 620 kPa (80 to 90 psi) fuel pressure to any operating engine(s).

3. Start the distillate fuel supply pump and monitor fuel pressure to the engine being flushed.

4. Monitor the fuel returned to the heavy fuel day tank. When the returned fuel is not contaminated with HFO, switch the fuel return line to return the fuel to the distillate day tank.

5. Stop the distillate fuel supply pump.

6. Close the fuel supply valve and the fuel return valve at the engine. Check that the injector tip cooling supply valve and return valve are closed.

7. Proceed with the planned maintenance activity.