AF120
Air Fuel Ratio Control System, for shielded and non shielded applications
The AF120 Air/Fuel ratio control system provides cost effective emissions control for gaseous fuelled engines used in demanding applications such as Cogeneration, Water Pumping, Gas Compression and Power Generation, with a proven track record of reducing emissions, and more importantly holding emissions over a long term – without constant manual engine tuning.
The AF120 System is designed to accurately control the air/fuel ratio of stoichiometric engines fitted with a three way catalytic converter, and lean burn engines, with or without a cat. The system consists of the AF120 control module, a wide band oxygen sensor, wiring harness, control valve, software and documentation. For V-Type engines with two carburetors/pressure regulators, two AF120 air/fuel control systems can be used independently.
Most air/fuel control systems for gaseous fuelled engines in the market place currently use narrow band oxygen sensors (EGO or HEGO), that were originally designed for petrol/gasoline engines and provide an output voltage based on the O2 content of the exhaust, however these sensors only have a very narrow range of sensitivity, plus the area where stoichiometric (rich burn) gas engines operate, is an area that is proven to degrade over time (see below).
In the example (below), the air/fuel control system would be setup to control the engine to ensure the voltage output = V0 equates to stoichiometric air/fuel mixture. (Indicated “A” on the graph.)
However, over time the sensor output will drift and the air/fuel controller will have to add fuel to the air/fuel mixture, to ensure that the sensor output = V0. (Indicated “B” on the graph.)
This will lead to an engine producing very high Carbon Monoxide (CO) emission, putting the engine out of compliance, and producing more pollution than is necessary.
A = Stoichiometric (Lambda = 1) NOX and CO Emissions in Compliance
B = Lamdba < 1 - Engine Running Rich CO Emissions out of Compliance
The Gill AF120 system differs as it uses an off the shelf wide band oxygen sensor (UGEO), that provides a consistent, linear output in relation to percentage of Oxygen in an engines exhaust, and provides accurate measurement from very fuel rich air/fuel mixtures to up to 22% Oxygen concentration (Atmospheric concentration) – see graph below. This sensor can be used in both stoichiometric and lean burn configurations. And because of it’s linear characteristic allows the use of proportional control systems.
As the UEGO sensor provides such an accurate measurement of the oxygen concentration, when an engine experiences a change in load, the AF120 system is able to measure the change in O2 and make adjustments to the valve position accordingly leading to a faster and more accurate response to load steps. Engines using the Gill AF120 system have shown that the system is capable of keeping an engine’s emissions below strict requirements, such as those in California, for over 6 months, without the operator making changes to the engine, which is a major improvement over older narrow band systems.
AF120 Air Fuel Control Module
The AF120 control module can be used within a variety of control systems. In the carburetor bypass configuration the Gill AF120 fuel valve can be utilised. Alternatively the module can be used to control fuel pressure regulator systems and systems requiring turbo waste gate control.
Features include.
-Outputs to stepper or current controlled bypass valves.
-Fast start up due to heating of UEGO sensor.
-Programmable via easy to use Windows based GUI
-Controls Lambda value to set-point by means of proportional ,integral control loop
-Loop constants ,valve position offset and voltage filtering are programmable.
-The 4-20 mA output can drive pneumatic control valves on engines fitted with turbo waste gate.
Applications:
CHP Engines
Generator Set Engines
Compressor Engines
Commercial Vehicle Engines
Passenger Vehicle Engines
IDU10 Display
The optional display offers clear intuitive navigation through its menu screen, indicating the following:-
Lambda (mA), Setpoint (mA), Valve position (% open), Lambda heater resistance (Ohms) and status flags. Available in panel or surface mount variants.
AF120 Fuel Valve
The AF120 fuel valve has been designed to specifically operate with the AF120 control module for medium sized engines where a fuel bypass system can be utilised. Using a stepper motor with over two hundred steps provides absolute precision around the set point.
Oxygen Sensor
The wide band oxygen sensor is placed into the exhaust line just prior to the 3 way catalyst . This particular sensor is robust against gas poisoning and can be fitted through a M18 x 1.5 flange on the exhaust pipe.
Wiring Harness
A standard wiring harness is available enabling retrofit to existing engine configurations.The harness includes all necessary connectors to the electronics module, fuel valve and oxygen sensor. Alternatively a customised wiring harness can be provided for OEM applications.
Shielded Variant
EH12 Enclosure
For applications demanding a shielded enclosure, the AF120 control module is housed inside the EH12 enclosure. This allows for quick and easy termination of all cables from sensors mounted on the engine.
Shielded Valve
The AF120 fuel valve has been designed to specifically operate with the AF120 control module for medium sized engines where a fuel bypass system can be utilised. Using a stepper motor with over two hundred steps provides absolute precision around the set point.
SYSTEM SPECIFICATION
Power Supply
12 – 24V DC – Automatically sensed
Environmental
-40°C to + 90°C (-40°F to + 194°F), Sealed to IP67
MODULE SPECIFICATION
Inputs
Throttle position or MAP sensor for load mapping
Wideband UEGO sensor for exhaust oxygen measurements
Engine speed from engine position sensor
Additional sensor inputs for more rigorous applications
