Fuel System (Air/Fuel Ratio Control)
The fuel system includes these components:
- Engine control module (ECM)
- Fuel metering valve
- Nitrogen oxide sensor
- Inlet manifold pressure sensor
- Inlet manifold temperature sensor
The fuel metering valve controls the amount of fuel that flows to the turbocharger compressor. The inlet air that is needed for compression also enters the turbocharger compressor. The ECM determines the requirement for the mixture of air and fuel. The ECM sends a signal to the fuel metering valve. The fuel metering valve controls the volume of the gas flow to the engine. The air/fuel mixture is cooled in the aftercooler. The mixture enters the cylinders through a throttle valve.
If equipped, a sensor for nitrogen oxide measures the amount of nitrogen oxide in the exhaust gas. The inlet manifold pressure and temperature are monitored. This information is provided to the ECM. The ECM uses this information to adjust the flow of fuel in order to meet emissions requirements. This is a continuous process during engine operation.
If the engine is not equipped with an sensor for nitrogen oxide, the ECM will calculate the actual charge density. The actual charge density is compared to the desired charge density. To achieve the desired condition, the ECM sends a command signal to the fuel metering valve. This is a continuous process during operation with loads that are greater than 25 percent.
The ECM sends a signal to the throttle valve. The throttle controls the flow of the air/fuel mixture to the cylinders.
The engine is equipped with an electronic ignition system. The system provides dependable firing and low maintenance. The system provides precise control of the spark and the ignition timing for each cylinder.
The system also provides diagnostic capability that enhances troubleshooting. The primary ignition wiring is routed internally through the engine.
The engines are equipped with protection from detonation. A detonation sensor is located between every two cylinders. The ignition timing is retarded for a cylinder when excessive detonation is sensed in that cylinder. If the maximum retarded position is attained and detonation continues to occur, the ECM shuts down the engine.
The engines are equipped with flame arresters. The flame arresters are located at the entrance of each inlet port. If the engine backfires, the flame arresters prevent the fire from entering the air/fuel mixture.
The engine lubrication oil is circulated by a gear-driven pump. The oil is cooled and filtered. A bypass valve provides unrestricted flow of lubrication oil to the engine parts if the oil filter elements become plugged.
The engine also has a turbocharger oil accumulator. This accumulator provides oil to the turbocharger during hot shutdowns and during start-up.
The standard cooling system has a gear-driven centrifugal pump. For applications that combine heating and power, the pump for circulating the jacket water is supplied by the customer. The cooling system has temperature regulators that regulate the temperature of the coolant. The temperature depends on the application.
The turbocharged engine has a Separate Circuit Aftercooler (SCAC). The SCAC is required to operate at one of the following two inlet temperatures. The temperature depends on the engine rating and the application.
- 32 °C (90 °F)
- 54 °C (130 °F)
If the inlet temperature to the SCAC exceeds these temperatures, consult your Caterpillar dealer.
The oil cooler will not be in the jacket water circuit if the jacket water system operates at a temperature that is greater than 99 °C (210 °F). The circuit for the oil cooler and the circuit for the aftercooler may be separate systems or the circuits may be combined into one system. In the combined system, a pump circulates water through both the aftercooler and oil cooler cores. The combined system uses a thermostatic control to regulate the oil temperature. This prevents overcooling.
Jacket water for high temperature cooling can be supplied at temperatures up to 127 °C (260 °F). The customer must supply a pump for circulating the jacket water.
Engine efficiency and maximum utilization of engine performance depend on adherence to proper operation and maintenance recommendations. This includes the use of recommended lubricants, fuels, and coolants.
For the engine maintenance that is required, refer to this Operation and Maintenance Manual, "Maintenance Interval Schedule".