SEAL 2835593 - Caterpillar

The control strategy for the air/fuel ratio is determined by these factors: setting for the fuel quality, the fuel flow and the combustion burn time. The setting for the fuel quality is the initial setting for the air/fuel ratio. The combustion burn time allows the control strategy to fine-tune the air/fuel ratio. The ratio is based on the quality of the fuel. Both of these adjustments are critical, and problems can arise if the adjustments are not properly set.Setting of the Fuel Quality
Note: Use the Caterpillar Electronic Technician (Cat ET) to adjust the setting for the fuel quality.The setting for the fuel quality is typically defined during the engine commissioning. The setting of the fuel quality does not require further adjustment unless the average lower heating value (LHV) of the fuel changes. To establish the setting for the fuel quality, a gas analysis and a measurement of the exhaust emissions are required.A current gas analysis is required before adjusting the value for the fuel quality. Obtain the analysis and enter the data into Caterpillar Software, LERW4485, "Gas Engine Rating Pro (GERP)". This program establishes the LHV through a calculation that weighs the effect of the various contents of the gas. This calculation is based on the percentage of the total gas. Set the fuel quality to this LHV.Note: Use the Caterpillar Software, LERW4485, "Gas Engine Rating Pro (GERP)". Use of only the data from the gas analysis can result in incorrect settings.A measurement of the exhaust emissions verifies that the engine is properly set. The emission levels for the fuel quality can be compared to the levels of these emissions that were recorded during the engine commissioning: NO, NOx, CO, CO2and O2.If the amount of NOx and CO in the exhaust are not within 10 ppm of the engine commissioning, the setting for the fuel quality may need adjustment. A leaner air/fuel ratio will reduce NOx and a leaner air/fuel ratio will increase CO. A richer air/fuel ratio will increase NOx and a richer air/fuel ratio will reduce CO. Two basic concepts of the control strategy must be understood before adjusting the fuel quality.Basic Engine Speed and Governing Control
The engine control strategy adjusts fuel flow. The fuel flow is based on the differential between the actual engine speed and the desired engine speed setting.If the actual engine speed is lower than the desired engine speed, the control will increase the amount of fuel flow. If the actual engine speed is higher than the desired engine speed, the control will decrease the amount of fuel flow. The application of load to the engine will result in a higher fuel flow to maintain the same desired speed.Basic Air/Fuel Ratio Control
The volume of fuel and the fuel heating value determine the amount of air that is required for maintaining the proper air/fuel ratio.The engine is tuned to a specific value for NOx. The value depends on the engine emissions rating. The value for tuning provides a cushion that is less