Case Study: HORIBA’s Solution for Emissions Testing

The MEXA-1400QL-NX analyzer delivers extremely precise and reproducible results

Since it has been introduced to the market in the last year, HORIBA’s MEXA-1400QL-NX exhaust gas analyzer has turned out to be an award-winning success. The state-of-the-art emission test system based on quantum cascade laser (QCL) technology exceeds expectations – measuring even more precisely than requested by legislation. After a first demonstration period, some major European OEMs and a number of suppliers already put the first analyzers into operation in 2011.

Due to its excellent measurement results, the QCL analyzer poses a convincing proposition with regards to emissions testing. Characterized especially by the wide dynamic range of measurement and the low detection limits, the analyzer delivers extremely precise and reproducible results. The QCL method is able to test both gasoline and diesel fuelled powertrains. Moreover, it has potential for testing some alternative fuelled powertrains too. A high number of orders proves that the QCL-based device is a forward-looking technology meeting customers’ demands.

The Principle Behind

Quantum Cascade Laser technology based analyzers utilize the principles of optical spectroscopy – just as conventional gas analyzers. A simplified explanation of that principle: A laser beam is passed through a cell with sample gas. The laser pulse is reflected by mirrors and then hits a detector. As exhaust components absorb energy in the form of electromagnetic waves, this influences the pulse shape of the laser beam.

However, conventional methods face difficulties in measuring components such as NO and NO2, NH3 and N2O. Proposed legislation as well as new after-treatment devices that comply with recent regulations lead to the need for further analysis capabilities especially in terms of these nitrogen exhaust components.

QCLs are able to produce light in the whole mid-infrared and potentially in the far-infrared spectrum. They can therefore emit high-resolution beams in regions in which the relevant nitrogen compounds exhibit high extinction coefficients, whereas the absorption tendency of coexisting gases is low in these regions.

Features of the Analyzer

Within HORIBA’s MEXA-1400QL-NX analyzer, four lasers work in parallel. This makes the emission test system capable of simultaneously measuring the four most relevant nitrogen compounds NO, NO2, N2O (nitrous oxide) and NH3 (ammonia). A short optical path length allows the use of small optical cells and leads to rapid responses and a very long path length enables very low detection limits. To resolve this trade-off, HORIBA developed an advanced design of the cell and the mirrors in particular. By creating two different path lengths within one compact gas cell, the MEXA-1400QL-NX gives way to the wide dynamic range measurement in one system configuration.

Thanks to the combination of a high-intensity, high-resolution light source and a sophisticated interference correction method, the MEXA-1400QL-NX is free of troublesome interference from CO, CO2, CH4, H2O and hydrocarbons. The response of NH3 measurement has also significantly accelerated.