In generator set applications, idle stability is critical for synchronization of the generator set with the electrical grid. Follow the chart for the Recommended Inlet Manifold Pressure, with no load on the engine.
| Recommended Inlet Manifold Pressure | |
| Engine RPM | Inlet Manifold Pressure (1) |
| 900 | 40 ± 5 kPaa (5.8 ± .7 psia) |
| 1000 | 50 ± 5 kPaa (7.3 ± .7 psia) |
| ( 1 ) | kPaa is kilopascal measured in absolute pressure. |
These recommended values are provided for reference only. Parasitic loads affect the required inlet manifold pressure. The engine choke trim can and should be adjusted to a manifold pressure level that provides the optimum engine stability and the load acceptance capability for the specific application of the engine.
Use the following guidelines for the proper adjustment of the choke trim.
- The choke trim should be adjusted in order to get an average exhaust port temperature of 500 to 550°C (932 to 1022°F) when the engine is operating below 40 percent load.
- If the wastegate is in the closed position, the engine may be over choked. The choke trim setting on the DDT needs to be made more negative in order to reduce the choking. This will permit the wastegate to help control the desired air fuel ratio.
- If the exhaust port temperatures are all lower than 500°C (932°F), then the engine is operating too lean. This can result in a high rate of cylinder misfires. The choke trim on the DDT needs to be made more positive in order to increase the choking.
- The maximum exhaust port temperature should not exceed 600°C (1112°F). If the exhaust port temperatures are higher than 600°C (1112°F), the engine is not getting enough air. This can result in detonation and/or component thermal degradation. The choke trim needs to be made more negative in order to reduce the amount of choking. If only one cylinder exhaust port temperature is exceeding 600°C (1112°F), then investigate for a mechanical problem with that cylinder.
Electronic Choke Trim Procedure
- Set the engine operating condition to the rated speed and no load (or minimum load possible).
- Connect the DDT to the Engine Supervisory System (ESS). Display the DDT screen "number 33" by pressing the "SELECT MODE" key in order to display the "CSP MENU" (customer selectable parameters) screen "number 03". Then press the "SELECT FUNC" key to display screen "number 33". Or simply enter the "number 33" and then press the "ENTER" key.
Screen "number 33" on the DDT will display the following:
"CHOKE TRIM"
"00 40/0900 33<"
The numbers on the second line of the display are: The choke trim "OFFSET" number which indicates the amount of offset that has been entered through the "ALT1" and the "ALT2" keys. The amount of the choke trim offset "00" represents the factory default setting. "40/0900" represents the Inlet Manifold Pressure (kPaa)/Engine speed (rpm).
Note: kPaa is kilopascal measured in absolute pressure.
- On the DDT screen "number 33", when the "ALT1" or "ALT2" keys are pressed, a command signal is sent to the choke actuator in order to change the position of the choke plate.
To raise the inlet manifold pressure, press the "ALT2" key. (The offset number on the DDT screen will decrease by one every time the "ALT2" key is pressed.)
To lower the inlet manifold pressure, press the "ALT1" key. (The offset number on the DDT screen will increase by one every time the "ALT1" key is pressed.)
This process should be done slowly. Pause after every adjustment in order to allow the engine to respond to the change in the inlet manifold pressure.
Monitor the following:
- inlet manifold pressure
- stability of the engine rpm
- position of choke actuator
- position of wastegate actuator
- individual cylinder combustion burn times
- individual cylinder exhaust port temperatures
To monitor individual cylinder misfire during the choke trim process, alternate between the choke trim mode and precombustion chamber calibration mode.
- Press "SELECT MODE" key in order to display "PC CAL MODE" .
- Press "SELECT FUNC" key in order to operate the engine in the precombustion chamber calibration mode.
- Press "ALT2" key in order to display combustion BT as a non-averaged number.
- Press "ENTER" key in order to monitor the individual cylinders.
A combustion BT of greater than 10 ms should be considered a misfire. The frequency of misfire will be reduced when the engine is properly choke trimmed.
Note: Do not over choke the engine. Load acceptance capability may be reduced.
- inlet manifold pressure
- If engine stability is unacceptable after properly completing the choke trim procedure, refer to the Testing and Adjusting, "Governor Adjustment Procedure" of this manual.
Note: The position of the choke plate can be returned to the factory setting that is programmed into the personality module by pressing the "0" key while the DDT screen "number 33" is displayed.
Pressing the "ENTER" key, while DDT screen "number 33" is displayed will change the choke trim screen to display the following:
"CHOKE TRIM"
"00 00/00 kPa 33<"
The numbers on the second line are: Choke trim offset, Actual Inlet Manifold Pressure (kPaa)/Desired Inlet Manifold Pressure (kPaa).
Note: A change in the fuel consumption due to a change in the engine stability (misfire), will change the DESIRED manifold pressure.
As described above, the actual inlet manifold pressure can be changed from this screen by the use of the "ALT1" and the "ALT2" keys in order to adjust the position of the choke plate.
Pressing the "ENTER" key while the DDT screen "number 33" is displayed will return the choke trim screen to display the Actual Inlet Manifold Pressure and the Engine rpm.
Note: To prevent zeroing out any adjustments that have been made, always use the "SELECT MODE" key in order to exit the screen "number 33" .
Mechanical Choke Trim Procedure
The inlet manifold pressure can be adjusted by changing the length of the connecting rod linkage between the choke actuator and the choke plate. Refer to the Specifications Manual for the choke linkage setting specifications.
- Set engine operating condition to the rated speed and no load (or minimum load possible).
- Loosen the jam nuts on the linkage rod that connects the choke actuator to the choke plate. This connecting rod has LH and RH threads on the opposite ends.
- To change the inlet manifold pressure, adjust the length of the linkage rod.
Note: Increasing the length of the connection may disengage the connecting rod from the rod end assembly.
This process should be done slowly. Pause after every adjustment in order to allow the engine to respond to the change in the inlet manifold pressure.
Monitor the following:
- inlet manifold pressure
- stability of the engine rpm
- position of choke actuator
- position of wastegate actuator
- individual cylinder combustion burn times
- individual cylinder exhaust port temperatures
- inlet manifold pressure
- After completion of the choke trim process, tighten the jam nuts on the linkage rod.
- Confirm that all the cylinders are firing by checking the combustion burn times for the cylinders (screen "number 14" on the DDT). A combustion burn time greater than 10 ms will indicate that the cylinder is misfiring. Also, check the cylinders for low exhaust port temperatures. If engine stability is unacceptable after properly completing the choke trim procedure, refer to the Testing and Adjusting, "Governor Adjustment Procedure" of this manual.
Air Lines (Choke)
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| Illustration 1 | g00481262 |
Air Lines (Choke) Adjustment (1) Actuator lever and shaft. (2) Actuator indicator. (3) Adjustable rod and ends. (4) Air inlet from turbocharger. (5) Aftercooler. (6) Choke plate. | |
Use the following procedure in order to assemble and adjust the linkage for the air lines (choke).
- Remove rod and rod ends.
- With the choke in the fully closed position, assemble the actuator lever on the actuator shaft at an angle of 3 degrees from vertical.
- Assemble the rod ends onto the adjustable rod in order to provide equal thread engagement.
- Install the adjustable rod and adjust the rod length so that the choke plate in is fully closed position and the actuator indicator is just at the closed (100 percent) position.
Note: The actuator indicator is calibrated to show the percentage not the angle that the choke plate is open or closed. 3 degrees is equal to approximately 5 percent.
- Tighten stop nuts on the rod ends.
Torque for the stop nuts on the rod ends ... 25 ± 6 N·m (18 ± 4 lb ft)
Correct adjustment and lubrication of the mechanical actuator linkage should result in good engine operation over the entire speed/load range of the engine. If no load instability is encountered, and the mechanical linkage is adjusted correctly, the Digital Diagnostic Tool can be used to electronically fine tune the actuator in order to improve the engine operation at no load conditions. Use the "TRIM" mode and the instructions that are included with the DDT in order to make the adjustments.