AFRC 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.

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