Modern 4-stroke gasoline engines are precision instruments compared to even models a few years ago. Today’s engines are designed to maximize power and gas mileage while minimizing harmful exhaust gases, especially carbon monoxide and sulfur oxides.
Therefore, it should come as no surprise that engine diagnosticians now use shop-grade gas analyzers to test the exhaust gases coming from a car. In fact, we have customers who are using meters like our 0-25% CO2 Sampling Data Logger with our extreme moisture filter to allow direct measurement.
The chemistry of internal combustion is simple: hydrocarbons (gasoline), oxygen and nitrogen (air) are burned to create water (gallons), carbon dioxide and nitrogen. It is the nitrogen that expands with heat to create the force needed to push the piston.
When every hydrocarbons are not completely “burned” carbon monoxide is the result. Therefore, you can think of carbon monoxide as the inverse of carbon dioxide: the higher CO2 and lower CO produced by an engine, the more efficient it is at burning fuel.
Diagnosticians have reported that measuring the CO2 levels in exhaust gases before and after the catalytic converter shows the efficiency of the unit under different loads and temperatures.
The ratio of air to fuel necessary to make the most efficient engine can be graphed. For example, about 12-15% of exhaust gases will be CO2 at idle. A great article titled “Understanding Exhaust Emissons” by Crypton Diagnostic Equipment details the entire process with even more information.