Exhaust Gas Analysis


In 2019, road traffic accounted for around 40% of nitrogen oxide emissions. 30 years earlier, it was over 50%. This is all the more surprising, if we consider the fact that the number of registered cars has increased massively.

The decrease of emissions is made possible primarily by improved technology in the vehicles that reduces pollutants and by better combustion in the engine compartment. In order to really solve this issue, detailed understanding of it is key. This is where the measurement of exhaust gases plays a very important role. Only if we can quantify them, we can fully understand how they emerge and reduce them.

Exhaust Gases from Combustion Process

One liter of fuel produces up to 10,000 liters of exhaust gases when burned in the engine. This increase occurs during the combustion process. Fuel consists of many different hydrocarbon compounds. During combustion, the lighter hydrogen is replaced by the heavier oxygen from the air, producing carbon dioxide and carbon monoxide. The nitrogen in the air reacts with the oxygen to form various nitrogen oxides. The exact composition differs depending on the type of engine. Diesel engines, for example, emit many times more nitrogen oxides than gasoline engines.

Testing Methods Become more Stringent with Improved Technology

Non-dispersive infrared spectroscopy (NDIR) uses a broadband infrared source. The source covers the entire wavelength spectrum required for the measurement of a wide range of gases, especially CO₂.


Vehicles of all kinds must be regularly tested for their exhaust gas quantity and composition. The maximum emission values differ depending on the standard in which they are approved. Particularly in the case of diesel engines, exhaust gas purification must be used to reduce the large quantity of nitrogen oxides. With the injection of urea and an SCR catalytic converter (Selective Catalytic Reduction), the nitrogen oxides react to form harmless nitrogen. Ever since the emissions scandal in 2015, exhaust gas tests must also be carried out under real driving conditions.

Sturdy Testing Equipment is an Advantage

Optical gas measurement technology in NDIR (non-dispersive infrared) has long been a proven technique for measuring carbon compounds and nitrogen oxides.


However, the new test methods that are employed while driving place higher demands on the measurement equipment. Strong vibrations and shocks must be tolerated. Axetris Infrared Sources can perform in difficult conditions and withstand vibrations and shocks without a loss of performance or characteristic changes. In addition, the IR Source promises high modulation frequencies up to 100Hz, which enables extremely high-resolution real-time measurements. With their compact design, measurement devices can be realized in very small sizes; making the Axetris IR Source particularly suitable for mobile measurement methods.