XC90 AWD V8-4.4L VIN 85 B8444S (2005)
Fuel trim reduces exhaust emissions. Fuel trim reduces nitrous oxides (NOx), carbon monoxide (CO) and hydrocarbon (HC) emissions.
Theoretically, if the correct amount of oxygen is added during combustion, fuel can be converted to water (H2O) and carbon dioxide (CO2). Emissions
would then be completely safe.
In practice considerable amounts of hydro-carbons (HC) and varying amounts of carbon monoxide (CO) and carbon dioxide (CO2) remain.
Due to the high temperature and pressure, nitrous oxides such as NO and NO2 are also formed. The common designation for these gases is nitrous
By speeding up the reaction between the remaining reactive components using a catalytic converter, these can be converted to water (H2O), carbon
dioxide (CO2) and nitrogen (N2).
However this can only happen if the balance of hydro-carbons (HC), carbon monoxide (CO), oxygen (O2) and nitrous oxides (NOx) is exactly right in
the exhaust. This happens when the fuel air mixture before combustion is 14.7 kg of air per kg of fuel. The Lambda value is then said to be one,