Content/ topic 4 Check exhaust gas composition
The compositions of engine exhaust gas
The toxic gases emitted by the car engine are:
- Carbon dioxide
The level of CO2 is a product of combustion and represents the amount of fully burned fuel. Therefore, a higher CO2 level indicates a higher engine efficiency. Many fuel injection engines will show approximately 15% CO2.
- Carbon monoxide
Partially burned fuel results in CO. High CO levels indicate a 'rich' fuel mixture. A perfect fuel mixture meters in exactly enough fuel to consume all of the O2 entering the engine. A perfect ratio is not sustainable in real-life operation. A fuel mixture that contains excess fuel is usually referred to as a 'rich' condition. A 'lean' condition refers to an excess of O2.
- Nitric oxide and nitrogen dioxide NOx
NOx generally refers to NO and NO2 (nitric oxide and nitrogen dioxide). This measurement is in ppm and represents the combustion products of burning nitrogen. This occurs at the higher engine temperatures associated with a lean fuel mixture or being under load. Of the NOx output of a typical engine, the NO component will usually make up the highest proportion. Diesel engines are generally associated with higher NOx and particulate emissions.