User's Manual

Gas Analysis
69
Gas Analysis
OmiScan Gas Analysis of Results
CO -Carbon Monoxide - Carbon Monoxide is the product of incorrectly burned fuel,
so the obvious aim is to ensure that the CO level is as low as possible, the better the
combustion the lower the CO. However, due to unavoidable inefficiencies with
Internal Combustion Engine (ICE) there will always be an output of CO.
CO
2
- Carbon Dioxide - Carbon Dioxide is the result of correctly burned fuel so the
obvious aim is to ensure that the CO
2
level is as high as possible, typically 13% - 15%
for a catalytic converter vehicle. Non-cat would be typically 11% - 12.5%.
HC - Hydrocarbons - Hydrocarbons are basically unburnt fuel and so the obvious aim
is to have HC as low as possible but inefficiencies mean there is always an output of
HC.
O
2
Oxygen - Oxygen has to be present for combustion to take place so obviously the
aim is to have as little surplus oxygen as possible, typically up to 2%.
NOx - Nitrous Oxide is a gas generated by high combustion temperature and
pressure and this can be reduced by design of the exhaust and inlet valve overlap and
exhaust gas recirculation where the inert exhaust gas introduced into the inlet will
reduce the combustion temperature. NOx can only be measured when the engine is
under load.
AFR/Lambda - Air Fuel Ratio (AFR) or Lambda is the ratio of air to fuel and is
calculated from the amount of oxygen sensed in the exhaust gases.
From the exhaust gases the following relationships are formed:
• O
2
combines with CO to form CO
2
• CO is an indicator of air fuel mixture richness
• HC is an indicator of fuel mixture leanness or richness and misfires
• CO and O
2
are equal at the stoichiometric air/fuel ratio