Dynalco AF-900PC Air/Fuel Ratio Controller - Manual (Page 4)

1. Introduction to the AF900PC
The AF-900PC is a state-of-the-art air/fuel ratio control system for single/dual bank,
spark-ignited, natural gas fueled carbureted engines. The AF-900PC incorporates
an extensive suite of advanced features that intelligently compensate for real-world
sensor and engine conditions.
This sophisticated system maintains the percentage of oxygen (O
2
) in the engine’s
exhaust gas stream by adjusting the amount of fuel to the carburetor(s). Fuel
valves mounted between the regulator and carburetor adjust the fuel pressure
applied to the carburetor to maintain the desired air/fuel ratio. The AF900PC is
designed to work with rich-burn engine systems using 3-way or NSCR type
catalytic converters.
In these applications it is very important to maintain air/fuel ratio to avoid damage
to the converter, prevent engine damage when fuel BTU content variations cause
the engine to run very rich or lean, and ultimately enable the engine to reduce
emissions.
2. Theory of Operation
Utilizing heated O2 sensor(s) in the exhaust stream (one per bank), the AF-900PC
provides PWM outputs to full-authority fuel valves in order to accurately control
air/fuel ratio over a wide load range. The O
2
sensor operates best slightly rich or
lean of a point called stoichiometric, which is an A/F ratio of 16.09:1 for natural gas.
Engines with catalytic converters should be run slightly rich of stoichiometric for
lowest emissions.
The AF900PC implements compensation through an intelligent closed-loop
algorithm which provides smooth control behavior that is adaptable to changing
engine load, speed, fuel quality, ambient temperature and catalytic converter
conditions.
In addition, the AF900PC offers optional intake manifold pressure sensor(s)
capability for further adjustment of the post-catalytic setpoints, allowing the catalytic
converter to maintain emissions over an even wider range of engine loads and
operating conditions.
The AF900PC system monitors the proper operation of all sensor inputs and
controller outputs, flagging errors and changing its operating mode when a fault is
detected.
Equipped with a powerful onboard data logging feature and real-time clock, the
AF900PC has the ability to log controller conditions at either pre-determined times
of day or on a time interval basis. This allows users to automatically capture and
store diagnostic errors and overall system performance internally over any given
period of time. It also aids in troubleshooting hard to catch intermittent system
problems.