5 Main Gases That Exhaust Gas Analyzers Measure

An exhaust gas analyzer is a device that is used to indicate the fuel-air ratio of an engine’s fuel mixture, such as in automobiles. Modern shops that offer cars or car parts consider gas analyzers as essential and affordable tools to verify a vehicle’s functionality. There are 5 main gases that analyzers commonly measure. Continue reading to learn about them.


Filtered ambient air mostly enters an engine and forms a part of the fuel mixture. 20.9% of oxygen or O2 is in ambient air. In most engine types, this O2 is consumed when the fuel is burned. Oxygen levels in analyzers indicate the unburned air and represent a lean fuel mixture. Lean conditions refer to an excess of O2.

Carbon Monoxide

Fuels that are burned to some degree often result in carbon monoxide or CO. It can be measured in percent or parts per million (PPM). High levels of CO denote a rich mixture of fuel. It’s referred to as a rich condition if the fuel mixture contains excess fuel. Perfect fuel mixtures are metered in enough fuel to consume all of the oxygen that enters the engine.

Carbon Dioxide

The level of carbon dioxide or CO2 is produced by combustion and represents the level of fuels that are fully burned. With this given, if a CO2 exhaust gas analyzer shows a higher level of CO2, it means higher efficiency for the engine. Fuel injection engines mostly show an approximate 15% of CO2.


The hydrocarbon or HC’s channel is calibrated as propane or hexane depending on the style or type of engine the analyzer will be used on. The measurement will come out in PPM and will represent the level of unburned fuel. A good running, modern automobile typically shows 10PPM or less while forklifts or trucks may show higher levels of PPM because of the type of fuel and style of the engine.


NOx refers to NO and NO2 or nitric oxide and nitrogen oxide. The measurement of this gas is in PPM which corresponds to the combustion products of burning nitrogen. This usually occurs in higher engine temperatures related to being under load or a lean fuel mixture. Engines fueled with diesel are normally associated with particulate emissions and a higher NOx.

A gas analyzer, like a CO2 exhaust gas analyzer, measures these gases and effectively gives operators a completed reading about the measurement of the various gases present in the sample. It provides feedback about the engine’s status which then allows mechanics to quickly troubleshoot if there are problems.


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