AFRC Overview
AFRC Documents and Guides
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.
Setup
Video available for this topic: https://www.youtube.com/watch?v=PAmjcq7CPt0
ENGINE CONDITION
For proper AFRC operation, it is critical that the engine be in good operational status. Verify the following before running the AFRC:
- Valves are adjusted to factory specification
- Spark plugs are properly gapped and in good condition
- Cylinders have good compression
- Mixers are in good condition and regulator fuel pressure is set to factory specification
- Fuel connections are secure and leak-free
- Ignition system functioning correctly and timing set appropriately for fuel composition
CONTROLLER SETUP
While the engine is not running, perform the following steps to prepare the controller for operation:
- AFRC module is installed and wired
- Digital power valve(s) are installed
- Secure the front panel of the EIM to the enclosure by re-tightening the four (4) front panel screws
- Run signal source is properly connected
- Run signal source is properly selected on the Run Signal Trigger screen (Pg. 10)
- Fuel connections are secure and leak-free
- Load valve manual adjustments on external dynamic valves are fully open (full rich, or seven turns from fully closed) for startup only
- Enter Setup or Engineering mode on the controller by entering the appropriate password
- Set the “Control” toggle button on the AFRC Home screen (Lite Pg. 300, Adv. Pg. 200) to “Manual”
The engine can now be started.
VALVE SETUP
No valve setup required unless an External Dynamic or 600 Series valve is being used. For information on these valve types, their setup, and operation refer to “APPENDIX D. EXTERNAL DYNAMIC AND 600 SERIES VALVES”.
Sensor Setup
The AFRC Advanced has the following optional sensor inputs available for process monitoring, run signal, and mapping:
- Manifold Pressure Sensors (two available)
- "Manifold Press Left" and "Manifold Press Right"
- Single bank configurations utilize the "Manifold Press Left" input
- Sensors are pre-configured for the system and can only be enabled and disabled
- Analog (one available)
- "ANALOG"
- Configuration to 0-5V, 1-5V, or 4-20mA
- Oil Pressure Switch (one available)
- "Oil Pressure Switch"
- Pre-configured as normally open (N/O) and can only be enabled or disabled
- Thermistor (one available)
- "Ambient"
- Thermocouple (one available)
- "Manifold"
- Type-K thermocouple only
- Magnetic Pickup (one available)
- "RPM"
- 1-100 Volts
The AFRC Lite has the following optional sensor available for process monitoring and mapping:
- Manifold Pressure Sensor (one available)
- “Manifold Press”
- Sensor is pre-configured for the system and can only be enabled or disabled
The different sensor types are available for setup by selecting their respected buttons on the top of the screen.
Configuring the Analog and Discrete Inputs
To setup the manifold pressure sensors or the oil pressure switch, simply select the “Enable” toggle box next to the sensor label. Darker colored toggle buttons indicate the sensor is actively enabled.
For the general purpose “ANALOG” input, the following fields are required:
- Name – Label of the sensor that will be displayed within the AFRC’s user interface
- Enabled – Activates sensor input
- Output – 4-20mA, 0-5 Volt, or 1-5V sensor output type
- Low Scale – Lowest output value of the sensor
- Full Scale – Highest output value of the sensor
- Units – Units of the sensor
*Insert Image*
AI/DI Sensor Setup Screen
Configuring the Temperature Inputs
The thermocouple and thermistor inputs only require their respected “Enable” toggle buttons to be selected in order to be operational.
Configuring RPM
The RPM input is configured by providing the pulses per revolution and selecting the “Enable” toggle button. This option is only available on the AFRC Advanced.
RUN SIGNAL
By default, the run signal selection is set to “Auto-Detect”, which scans enabled sensors for each module. The AFRC Advanced has three applicable inputs:
- Pre-catalyst thermocouple (terminals 24 and 25)
- Oil pressure switch (terminals 39 and 40)
- RPM (terminals 17 and 18)
If an AFRC Lite is installed, the only available run signal trigger sensor available is the pre-catalyst thermocouple (terminals 21 and 22).
Additionally, the run signal can be generated from a connected EMD, if equipped, using the following inputs:
- Pre-catalyst thermocouple
- Oil pressure switch
Finally, the Ignition state can be used to determine run signal, if the ignition is in a running state the signal is set to Run.
*Insert Image*
Run Signal Trigger Screen
ALARM SETUP
Up to eight (8) custom alarms can be configured on the AFRC to display within the Alarms screen (Pg. 40) or to trigger an external alarm though the error relay (terminal 6).
Configuring alarms is done on the Alarm Setup screen (Lite Pg. 305, Adv. Pg. 206) through the following parameters:
- Sensor – Input or condition to be monitored
- Only enabled sensors are available for selection
- Min – Minimum trigger value (optional)
- Max – Maximum trigger value (optional)
- Duration – Time, in seconds, for the sensor reading to either be below the minimum trigger value or above the maximum trigger value to become active
- Action – Action to take when alarm becomes active
- Warning – Displays the alarm within the Alarms screen (Pg. 40) and flashes the “Alarms” button on the footer of the display
- Shutdown – Closes the error relay (terminal 6), displays the alarm within the Alarms screen (Pg. 40), and flashes the “Alarms” button on the footer of the display
It is optional to select both “Min” and “Max” values, but at least one must be selected for sensor monitoring alarms. Selecting both values is available for monitoring a condition within a window, if desired.
*Insert Image*
Alarm Setup Screen
Upon selecting the necessary information, the alarm is enabled by toggling the “Enable” toggle box next to the sensor’s name.
Note: Modifying an existing alarm requires the “Enable” toggle box to be toggled off and back on to take effect.
Note: A sensor can be placed in two alarm rows. For example, a PostCat TC alarm could be configured to shutdown at 1250, and generate a warning at 1000.
AutoControl Range Alarm
If AutoControl is used on the AFRC Advanced, the final alarm in the Alarms Setup screen (Pg. 206) is the “AutoControl Range” alarm. This alarm can be used to fall back from “AutoControl” to “Setpoint” mode in the event the Post Catalyst O2 sensor milliVolt reading is pushed outside the set range, which can indicate the sensor is failing.
On a trigger of the alarm condition, the AFRC will go into “Setpoint” mode with a target setpoint valve defined by the alarm. The default is “777”. To change the fallback setpoint value, select the “Setpoint: 777” button within the alarm row.
This event will trigger an alarm, AFR062 (min trigger) or AFR063 (max trigger), on the Alarms screen (Pg. 40). This alarm must be reset in order to switch back from “Setpoint” mode to “AutoControl” mode. A security access level of Setup or Engineering is required to reset the alarm.
Controlling The Engine
Detecting the Run Signal
With the engine running, the AFRC will detect the engine operation through the sensor trigger defined within the Run Signal Trigger screen (Pg. 10). If a valid run signal is recognized, the black text in the header next to the “Home” button will display “Eng: Run”.
Sensor Warm Up
Upon detecting the system run signal, the bank status within the control box will display “Heater Warmup” indicating the sensors have been started. After the sensor heaters are warmed, the AFRC will be ready to control. When the AFRC is ready, and in “Manual” control mode, the bank status will display “Ready” and will wait until the control mode is transitioned from “Manual” to “Auto”. A security level of Setup or Engineering is required to toggle the control mode.
If the AFRC is already in “Auto” mode, it will start the process for initializing control.
Load Delay
Once the sensor is warm and in “Auto” mode, the AFRC will go into a load delay. By default, the load delay waits 30 seconds before the controller starts to move the valve.
If an AFRC Advanced is used and “Auto Control” is enabled, the controller not transition to delay mode until the pre-catalyst or post-catalyst thermocouple read a light off temperature of 550 degrees F.
Starting Control
When starting control, the bank status will update to “Attempting To Control”. The valve will automatically adjust to try and match the actual O2 reading with the desired target setpoint. As the valve finds the position that’s meets the target and is stable, the status will update to “Controlling”.
Optimizing The Target Setpoint
The oxygen target setpoint “Target” should be set to optimize catalyst performance. This should be conducted while the engine is at a normal operating temperature and under normal loading. An exhaust gas analyzer should be used to reach optimum performance.
If an AFRC Advanced is used and “Auto Control” is enabled, no target setpoint adjustment is necessary.
External Dynamic and “600” Series Manual Valve Adjustment
If an external dynamic or 600 series valve is in use and the desired oxygen sensor target setpoint cannot be reached, then the valve will need manual adjustments. These valves contain an external “load” screw, which must be rotated to make adjustments (for more information, refer to “APPENDIX D. EXTERNAL DYNAMIC AND 600 SERIES VALVES”).
STOPPING THE ENGINE
The engine may be stopped at any time. The AFRC will detect the engine has stopped based on the trigger selected on the Run Signal Trigger screen (Pg. 10). When using thermocouples as the run indicator (“AFRC Pre-Cat TC” or “EMD Pre-Cat TC”), the controller will detect the engine has stopped after the pre-catalyst thermocouple drops below the trigger point (450°F by default). When using an oil pressure switch (“AFRC Oil Pressure” or “EMD Oil Pressure”), AFRC RPM, or Ignition State, the controller will immediately detect the engine has been shut down.
After the controller detects a shutdown, the digital power valve will fully open and then move to the startup position. This digital power valve cycle is repeated once after each engine shutdown to maintain calibration of the digital power valve position.
Engineering Adjustments
While in Engineering security mode, the Engineering Setup screen (Lite Pg. 304, Adv. Pg. 207) is available through the Setup screen (Lite Pg. 301, Adv. Pg. 201). This screen provides access to gain adjustment and other engine configuration settings.
*Insert Image*
AFRC Engineering Setup Screen
GAIN ADJUSTMENT
The AFRC operates on a PID control loop to automatically adjust the valve to match the actual sensor reading to the target setpoint. By default, the control loop has been pre-tuned to find the target setpoint quickly while maintaining stability. If the condition exists where the valve needs to be either more or less responsive, the PID control loop can be adjusted by selecting the “Faster” or “Slower” buttons around the “Response Time” label. Slowing the valve response will decrease the sensitivity of the control loop, and increasing the valve response will increase the sensitivity of the control loop. The individual PID values are automatically adjusted based on the single “Response Time” value. The default “Response Time” value is 50 and is adjustable between 0 and 100.
CONTROL TYPE
The AFRC Advanced has the ability to switch between control types “Setpoint” and “Auto Control”. The AFRC Lite is fixed for “Setpoint” type control.
Auto Control
“Auto Control” is a patented control algorithm that uses both a pre-catalyst and post-catalyst O2 sensor to find the most appropriate target setpoint and maintains that setpoint through a variety of conditions. The target setpoint is not user adjustable and is managed by the AFRC Advanced without the need for any user input. “Auto Control” is only available for single bank and dual bank rich burn engine configurations. Multi-setpoint mapping is disabled while in this mode.
If “Auto Control” is selected as the control type, options will be made available to adjust the software to target either for a richer or leaner setting using the “Lean” and “Rich” buttons on the Engineering Setup screen (Pg. 207). By default, this setting is configured for equal CO and NOx reduction with a rich/lean setting value of 50. Due to varying site conditions, including fuel gas and ignition timing, this value may require an initial adjustment after installation. If lower CO emissions are desired at the expense of higher NOx, the rich/lean setting can be reduced by selecting the “Lean” button to adjust rich/lean value less than 50. Similarly, if lower NOx emissions are desired at the expense of higher CO, the rich/lean setting can be increased by selecting the “Rich” button to adjust rich/lean value greater than 50. The rich/lean value’s range is 0 to 100, where 0 is the maximum lean value and 100 is the maximum rich value.
When “Auto Control” is selected, an alarm is automatically generated on the Alarm Setup screen (Pg. 206) to switch to “Setpoint” control if the “Auto Control” setpoint drifts below 600 or above 800. If the alarm is triggered, it must be reset on the Alarms screen (Pg. 40) before “Auto Control” can be re-enabled. Typical cause of the drift outside of this range is an expired or ineffective Post-Cat O2 sensor.
Setpoint Control
“Setpoint” control mode controls off of a user, or mapping table, defined setpoint that corresponds with the desired emissions reduction. If desired, multiple setpoints can be used to automatically change the target setpoint based on sensor readings through the AFRC’s mapping feature.
LOAD DELAY
The load delay setting adjusts the amount of time to delay the AFRC from taking control of the valve after it has detected a valid run signal and the sensors are warm. The intention of this configuration is to allow the engine to fully warm up and load before taking control.
The default value is set to 30 seconds, but the delay can optionally be configured to 1 minute, 5 minutes, 10 minutes, or 20 minutes.
COMBUSTION TYPE
The AFRC can be configured to control either a rich-burn or lean-burn engine. Adjusting this parameter sets various displays elements within the user interface.
O2 TYPE
The AFRC allows the O2 sensor type to be selected while the combustion type is configured as “Rich Burn”. The two O2 sensor types supported are narrowband and wideband. The narrowband sensor is a 4-wire heated sensor that can only read within a very narrow window around stoichiometric combustion and is suitable for rich burn combustion. The wideband sensor is a 6-wire that can read a much wider range and is suitable for both rich and lean burn combustion types.
NUMBER OF BANKS
The AFRC Advanced allows for the number of banks to be selected as one (1) or two (2). The AFRC Lite does not include this configuration as it is intended for single bank configurations only.
“ERROR” DISPLAY
When making ‘Control Type’, ‘O2 Type’, or ‘Banks’ adjustments on the Engineering Setup screen (Lite Pg. 304, Adv. Pg. 207), it is normal for text in red to present itself next to the ‘Engine Configuration’ label for a short period of time. The purpose of this text is to declare that the EIM and the AFRC configuration are out of synchronization. Once the synchronization is successfully completed (typically 2 seconds), the error message will be removed indicating the requested change was made.
Mapping Setup
The AFRC features the ability for the target setpoint to automatically adjust based on changes to environmental conditions or sensor readings. This is accomplished by building a table, or map, that associates multiple target setpoints to a set of sensor conditions. As the sensor readings change, an offset can be applied to the target setpoint so that it changes autonomously. This feature can be used to account for environmental factors or load swings that may affect the engine’s performance or emissions.
A map can contain as little as two, or as many as five, points. Each point includes an offset to the target setpoint and a sensor reading associated with that offset. The offset is a value that is applied to the original, or base, target setpoint displayed on the AFRC Home screen (Lite Pg. 300, Adv. Pg. 200). The sensor value can come from any of the available sensors that are mappable, but all points in the table must be associated with a single sensor.
The generated target setpoint is calculated based on the two to five points entered within the table. If the sensor reading is between any two of the configured points within the table, the offset will be interpolated. If the sensor reading is less than the lowest value in the table, the corresponding lowest offset will be used. If the sensor reading is greater than the highest value in the table, the corresponding highest offset will be used.
*Insert Image*
Multi-Setpoint Graph Example
MAPPING SENSORS
While in “Setpoint” control mode, the AFRC Advanced provides the following sensor options for mapping while, if properly equipped:
- Manifold Pressure
- Ambient Temperature
- Manifold Temperature
- RPM
- Post-Catalyst O2
The AFRC Lite provides the following option for mapping, if properly equipped:
- Manifold Pressure
ADDING MAPPING POINTS
While in Engineering security mode, the Mapping Setup screen (Lite Pg. 330, Adv. Pg. 230) is available through the Setup screen (Lite Pg. 301, Adv. Pg. 201). This screen provides access to generating mapping points and enabling the mapping feature.
Before adding points to the mapping table, a sensor must be selected from the “Sensor” drop down box in the top center of the screen. The drop down box is populated based on sensors that are connected and enabled through any of the sensor setup screens. For the AFRC Lite, no drop down box is available as the only supported sensor is the manifold pressure sensor.
Upon selecting a sensor from the drop down box, the current sensor reading will be displayed within the “Create New Point” box on the mapping screen along with an offset of zero. If the engine emissions are currently satisfactory at current conditions, this condition can be added to the table by selecting any of the “Add” buttons within the “Mapping Table” box. The sensor value and associated offset of 0 will be added to the table.
Alternatively, the sensor value can be adjusted by selecting the “Increase” or “Decrease” buttons around the value. The offset associated with the selected sensor value can similarly be adjusted by pressing the “Rich” or “Lean” buttons around the displayed offset. When both the sensor and offset values are configured, select the “Add” button of the slot within the “Mapping Table” where the point is to be added.
The table is capable of accepting up to five (5) points but is valid with as few as two (2). Mapping points can be cleared out by selecting the associated “Delete” button next to the entry. The order of the points within the “Mapping Table” does not matter as the system will automatically sort the points based on the sensor value when the map is enabled. Points can only be added or deleted when the mapping feature is disabled.
*Insert Image* Mapping Setup Screen with Mapping Enabled
RUNNING THE MAP
The toggle button in the upper left corner of the mapping screen must be selected to engage the mapping table. Enabling mapping will change the text to the right of the toggle button from “Mapping Off” to “Mapping On” and remove the buttons from the mapping table to make changes.
Below the toggle button is the status of the AFRC. Possible status messages include:
- “Attempting to Engage Mapping” – Mapping feature is being initialized
- “Mapping Active” – Mapping is currently operational
- “Mapping Not Enabled” – Mapping is off
- “AFRC Not Detected” – No AFRC was found when mapping attempting to initialize
- “Error – Check Setup” – An error occurred attempting to initialize mapping
- Not enough mapping points available
- Duplicate mapping points were present
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”.
*Insert Image*
