Stag AFR - About the Program Window; 6 Guidelines for Use of the STAG AFR Controller; Adjustment of LPG;CNG Systems in Gasoline Engines

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5.8 "About the program" window
Rysunek 11. "About the program" window
This window shows the contact data of the company AC S.A. – the manufacturer of the controller and
software.
6. Guidelines for use of the STAG AFR controller
In gasoline engine, the optimum air-fuel mixture composition (AFR - Air/Fuel Ratio) is one gram of fuel
per 14.7 grams of air. For this ratio, all oxygen available in supplied air is theoretically used to completely
burn all of the fuel. This is so called "stoichiometric" air-fuel ratio and differs for various fuels:
 unleaded gasoline – 14.7
 diesel oil – 14.6
 LPG – 15.5
 CNG – 17.2
The lambda parameter is the ratio of the current mixture content to the stoichiometric one. For example,
for a gasoline engine when the mass ratio of fuel to air is 14.7, the lambda parameter is 1. When an engine
is running on a rich mixture, the value of lambda parameter drops below 1. For lean mixtures the lambda
value is greater than 1. Generally, spark-ignition engines equipped with a narrowband oxygen sensor at
low and medium loads, automatically maintain the lambda parameter close to 1. They reach its maximum
power at slightly enriched mixture (lambda between 0.8 and 0.9 in intake low engines; between 0.75 and
0.85 in turbocharged engines).
6.1 Adjustment of LPG/CNG systems in gasoline engines
To adjust autogas installation properly in an engine equipped with a narrowband oxygen sensor (usually
of voltage-control type) the mixture content should be checked at full load. The value of lambda
parameters on gasoline and gas under the same conditions (identical gear and rpm) should be identical.
If a car has not been factory equipped with a oxygen sensor, the full range of loads and rpm should be
set so that the lambda parameter remains almost unchanged after fuel conversion.