Ammonia gas sensor for AdBlu® control system

29.01.2021

Environmental protection is one of the great challenges of the 21st century. Ensuring this while maintaining at least the same standard of living requires new innovative technological concepts. To reduce CO2 emissions in the area of individual transport, the trend is towards hybrid and electric drives. For large diesel engines, e.g. in cargo ships, the change to electric motors is not realistic due to the size of the batteries required. Here, at least a reduction of toxic NOx emissions must be achieved.

The current standard is exhaust gas aftertreatment, in which AdBlue® is injected into the exhaust tract. Up to now, AdBlue® injection has been electronically controlled according to engine speed, power and combustion temperature. Investigations by the Paul Scherrer Institute (PSI) have shown that too much ammonia in the system limits the functionality of the catalytic converter *. In reality, however, the values stored in the engine control system for the required AdBlue® admixture can lead to too much AdBlue® being injected, i.e. ammonia is contained in the exhaust gas; or too little is injected and NOx remains in the exhaust gas.

Both cases are not wanted, as ammonia is also a toxic gas. Constant monitoring and adjustment of the AdBlue® addition to the exhaust tract would therefore be advantageous. Ammonia sensors used so far work on the basis of metal-oxide sensors. These sensors have many cross-sensitivities to other gases present in the exhaust tract and thus make accurate measurement difficult. In fact, only spectroscopic sensor concepts provide the necessary sensitivity and selectivity to reliably determine the ammonia concentration in the exhaust tract of a diesel engine. However, conventional spectrometers are too large and too expensive for use in the engine. Therefore, a miniaturised non-dispersive ultra-violet (NDUV) spectrometer for exhaust gas analysis is being developed as part of the NH3Sens (NDUV Ammonia Gas Sensor) project.

Initial work focused on the optical simulation of the NDUV spectrometer and the selection and characterisation of the required components. Currently, a laboratory demonstrator is being set up with which the first ammonia measurements are possible. A sensor determines the absorption of UV light (~220nm) caused by ammonia in a gas cuvette. A reference channel enables the temperature and brightness of the LED to be monitored and the cross-influence of other gases in the absorption path to be determined.


* www.internationales-verkehrswesen.de/dieselabgase-ammoniak-menge/

AdBlue® is a registered trademark of the VDA (German Association of the Automotive Industry).



The research and development work described is funded by the Federal Ministry for Economic Affairs and Energy (BMWi) in the research project "NDUV Ammonia Gas Sensor" (NH3SENS).
FKZ: 49MF190821