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STAG AFR instead of exhaust gas analyser?

05.06.2017

STAG AFR instead of exhaust gas analyser?

STAG AFR is a wideband oxygen sensor controller that due to quick measurements of lambda coefficient allows the air-to-fuel ratio (AFR) to be controlled not only under steady-state but also transient conditions.

The STAG AFR unit enables the air-to-fuel ratio to be determined for engines fuelled with various fuels: petrol, diesel, methanol, ethanol or autogas (LPG, CNG).

In the vast majority of engines with indirect fuel injection working at high loads, the air-to-fuel ratio cannot be controlled. It means that if, for example, the autogas installation is not adjusted correctly, then the engine working at full load, e.g. during high speed drive on a highway, may be fuelled with an incorrect mixture. If the engine is fuelled with a rich mixture this may increase fuel consumption, while for a lean mixture the engine could not run at full power.  In extreme cases this could cause damage to the engine.

By using a wideband oxygen sensor controller, STAG AFR characterized by the fast measurement of excess air factor (lambda), it is possible to control fuel combustion under transient conditions and keep the AFR at appropriate level to enable the maximum engine power at normal fuel consumption.

STAG AFR (Air-Fuel Ratio) is a device that can be an alternative to stationary exhaust gas analysers, while being a mobile unit that can be used when driving.  This is a very important feature of this device, thus enabling the AFR to be monitored during transient engine operation (acceleration or running at full power).

By using the STAG AFR controller it is possible to adjust and diagnose fuelling systems (carburettor, injection), calibrate autogas systems, diagnose factory-mounted oxygen sensors and control the AFR to the engine during calibration of chip tuning systems.

I use the STAG AFR controller to calibrate the LPG installation and to verify operating parameters when the engine is running on petrol. Proper regulation of mixtures at high engine loads is the biggest problem of LPG system fitters. Most of vehicles enter then the so-called "open loop" mode when we decide on the amount of gas being injected. With a narrowband sensor installed in a car it is impossible to make such accurate system tuning due to its operating characteristics.  We may only find that a mixture is rich or lean, but without knowing to which extent. We have to get such data for accurate installation tuning.

The STAG AFR allows also to verify the injection system operation in the "closed loop". Most engines run then at excess air factor lambda close to 1. When driving a car with the OBD tester or other diagnostic tool connected we can view parameters that could seemingly indicate that the fuel injection system is working properly. We could not be more wrong, as the sensors wear over time and the controller makes inappropriate corrections based on their indications. At this moment we have an improper exhaust gas composition. Due to the STAG AFR we are able to verify it.

The STAG AFR controller manufactured by AC S.A. has been developed as a mobile device powered from a cigarette lighter receptacle (12 V). Communication with PC is enabled by USB, RS232 or Bluetooth interfaces, and a special, dedicated application ensures operation.

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