AFRC Overview
AFRC Documents and Guides
Run Signal Trigger and System Temperature Units
Overview
The EMIT air/fuel ratio controller (AFRC) is available in two offerings: the AFRC Advanced and AFRC Lite. Both controllers are designed to control turbocharged or naturally aspirated carbureted stationary natural gas or propane engines for either rich-burn or lean-burn applications. The AFRC Advanced is equipped to control a dual or single-bank engine with multiple options available for sensory monitoring, multi-setpoint control, and an optional control algorithm, Auto Control. The AFRC Lite offers the same setpoint and multi-setpoint control as the AFRC Advanced but has been optimized for single-bank engines. Unless otherwise noted, both controllers will be referred to simply as “AFRC” through the remainder of the manual.
Use of the AFRC controller with an appropriate catalytic converter can result in dramatic reductions in exhaust gas pollutants, particularly Oxides of Nitrogen (NOx), Carbon Monoxide (CO), and Hydrocarbons (HC). Rich-burn NSCR catalytic converters require a constant oxygen content of less than 0.5% from the engine in order to work effectively – the AFRC provides the control needed to maintain that constant oxygen concentration. In lean burn applications, the use of the AFRC with an oxidation catalyst can result in dramatic reductions in exhaust gas pollutants of Carbon Monoxide (CO), Hydrocarbons (HC) and Volatile Organic Compounds (VOC).
The air fuel ratio of the engine is maintained by setting the appropriate oxygen sensor target setpoint that corresponds with the desired emissions reduction. The controller automatically targets and maintains the setpoint by adjusting the valve position which allows or restricts the amount gas streamed into the mixer which then richens or leans the engine. The valve is moved and stabilized using a finely-tuned Proportional Integral Derivative (PID) control loop that automatically adjusts the correct valve position quickly with little overshoot or error. If desired, multiple setpoints can be used to automatically change the target setpoint based on sensor readings through the AFRC’s mapping feature. In addition to this “Setpoint” control type, the AFRC Advanced offers optional “Auto Control” configuration for single bank or dual bank rich burn engines that can efficiently find and maintain the optimum target setpoint automatically for maximum emissions reduction. No setpoint adjustment or multi-setpoint mapping is required.
Run Signal Trigger and System Temperature Units
The run signal trigger and system temperature units are configured on the Run Signal Trigger screen (Pg. 10) of the EIM, which can be accessed under the AFRC Setup page (Pg. 201).
The AFRC uses one of seven possible methods to recognize if an engine is running. The available sensors to trigger the run signal are below.
- Auto-Detect (Default)
- Scans all other run-signal sources for conditions indicating the engine is running
- AFRC Pre-Catalyst Thermocouple
- AFRC Advanced terminals 48 and 49
- AFRC Lite terminals 21 and 22
- AFRC Oil Pressure Switch
- AFRC Advanced terminals 15 and 16
- Oil Pressure Switch must be enabled on Sensor Setup – AI/DI (Pg. 202) screen of the AFRC Advanced
- AFRC RPM
- AFRC Advanced terminals 17 and 18
- RPM must be enabled and pulses per revolution must be defined on Sensor Setup – RPM (Pg. 205) screen of the AFRC Advanced
- EMD Pre-Catalyst Thermocouple
- EMD terminals 24 and 25
- EMD Oil Pressure Switch
- EMD terminals 39 and 40
- Oil Pressure Switch must be enabled on Sensor Setup – AI/DI (Pg. 104) screen of the EMD
- Ignition State
- Uses the current ignition state to determine run signal, if the ignition is in the “Engine Running” or “Engine Running With Warnings” state the run signal is set to running.
“Auto-Detect” will scan the other enabled “Trigger Sensor” inputs of the AFRC Advanced, AFRC Lite, EMD, and Ignition and toggle the engine run signal to “Run” if any of them indicate the engine is running.
If “Auto-Detect”, “AFRC Pre-Cat TC”, or “EMD Pre-Cat TC” is selected, a trigger temperature must also be configured. The trigger temperature defines the temperature at which the run signal will toggle. Any temperatures above the trigger will indicate the engine is running, and any temperatures below the trigger will indicate the engine is off. The default trigger temperature is 450°F.
Regardless of the selection on this screen, the ETS system will use “Auto-Detect” for the “Eng. Run” text on the top of pages, engine runtime hours, and alarm activation. The selection on the Run Signal Trigger page only effects when the AFRC considers the engine running. Note that if the AFRC pre-cat TC is the only sensor available, it will take time for the sensor to warm up enough for the EIM to display “Eng. Run”.
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