Optimum fuel consumption can be obtained by fine-tuning the air/fuel ratio and ignition timing. In order to make fine-tuning feasible, the engine must have stable operating parameters. The parameters must not exceed the following tolerances.
| Performance Parameters of the Engine | |
| Parameter | Tolerance |
| Jacket Water Coolant Temperature | |
| Inlet Manifold Air Temperature | |
| Temperature of the Gas | |
| Fuel Energy Content | |
| Load | ± 5% |
The correct air/fuel ratio is important for the following considerations:
- Margin of detonation
- Control of emissions
- Achieving optimum service life for the engine
If the air/fuel ratio is not appropriate for the fuel and the operating conditions, a failure of the engine may occur. The service life of the turbocharger, the valves, and other components may be reduced.
Changes in the temperature of the air supply affect the air/fuel ratio. In addition to seasonal changes, the air temperature changes overnight. Control of the temperature in the engine room will help to maintain the air/fuel ratio.
To optimize the inlet air temperature, use ducting and a heat exchanger. This use will help to avoid exposure to hot air from a generator. For more information, see Application and Installation Guide, LEKQ7250, "Air Intake". Consult your Caterpillar dealer for assistance.
Temperature of the Fuel Supply
Changes in the temperature of the fuel supply affect the air/fuel ratio. Warmer fuel is less dense than cold fuel. This results in a leaner mixture that causes a noticeable reduction of power. The recommended temperature differential of the air and the fuel is
The maximum fuel temperature depends on the temperature regulator (if equipped) of the aftercooler:
- For engines with a
32 °C (90 °F) aftercooler, the maximum temperature of the air/fuel mixture is43 °C (110 °F) . - For engines with a
54 °C (130 °F) aftercooler, the maximum temperature of the air/fuel mixture is65 °C (150 °F) .
For more information, see Application and Installation Guide, LEKQ7260, "Low BTU Engines". Consult your Caterpillar dealer for assistance.
Fluctuations of the fuel pressure can change the air/fuel ratio. For low-pressure gas fuel systems (
The gas pressure regulator maintains a pressure differential between the air and the fuel that is supplied to the carburetor. Set the pressure of the fuel supply according to the instructions in Systems Operation/Testing and Adjusting. The gas pressure regulator will maintain the pressure differential in response to changes in the air pressure.
A water manometer is used to measure the pressure differential. This measurement is taken when the engine is operating at high idle rpm with no load. When a load is applied, the fuel pressure will usually decrease by approximately
Throttle Angle and Exhaust Bypass (Wastegate)
A throttle angle of approximately 70 degrees is recommended for full load operation.
The following factors affect the angle of the throttle:
- LHV of the fuel
- Air/fuel ratio
- Setting of the exhaust bypass (wastegate)
- Altitude
- Ignition timing
After the desired exhaust emissions are achieved, the exhaust bypass is adjusted in order to achieve full load operation with the desired throttle angle. Excess boost generates back pressure in the exhaust manifold which raises pumping losses which increase fuel consumption.
Ensure that the angle of the throttle plate is properly set. This procedure will maintain the margin for detonation, also enabling the engine to accept load changes without lugging down and shutting off.