Conventional emissions analyzers

The Chemi Luminescence Detection (CLD) measurement principle is the industry-standard method of measuring engine exhaust NO concentration. Conventional CLDs have response times of 1-2 seconds, and are typically used to measure "bag emissions" where the concentration changes very slowly.

A need for fast emissions analyzers

During the 1-2 seconds it takes a conventional CLD to respond, an engine will undergo many firing cycles. The conditions inside the combustion chamber can vary significantly between successive firing cycles- particularly when the engine conditions are changing rapidly such as during engine start or speed/load transients. The Cambustion CLD500 (sometimes known as an fnox or fast NOx analyzer) has a time response as low as 2ms T10-90%. This allows the CLD500 to distinguish between two adjacent firing cycles, and even offer information about the variation in NO concentration during a single exhaust stroke.

Benefits of fast emissions analyzers

Accurate measurement of exhaust emissions brings valuable insights into engine operation, and assists calibration engineers in reducing the engine out emissions. This can assist in emissions compliance while reducing after-treatment costs.

Optional Converter for NOx Measurement

CLD500 sample head with NO2 converter option

The CLD500 can also measure NO2 through the use of optional NOx converters (based on the stainless steel method of NO2 to NO conversion). With these converters the CLD measures total NOx. (There is a cross-sensitivity to ammonia and other reductants in the sample). When fitted with the NOx convertors, a 10ms T10-90% response time is achieved.

The ability to record NO emissions data on such a fast time scale has opened up a range of study areas.


The ability to measure cycle by cycle NO and NOx allows researchers and engineers to investigate and quantify features such as NOx breakthrough during lambda excursions on a gasoline engine.

Common to both Diesel and gasoline engines, EGR is a widely adopted technique for controlling NOx emissions. During transient operation, delays and imperfect control of EGR flow may lead to spikes in transient NOx emissions. Furthermore, distribution of recirculated exhaust gas between cylinders on a multi-cylinder engine is not always equal. This can lead to one cylinder receiving too little EGR, with a consequent increase in NOx emissions. The ability of the CLD500 to measure gas from a single cylinder (sampling in the port) as well as in the mixed exhaust provides crucial data to overcome such issues. Combined with fast CO2 measurement from Cambustion's NDIR500, the CLD500 allows the user to directly correlate NOx emissions and delivered EGR, even on a cycle-by-cycle basis.

A current major concern with urban air quality is the NOX emissions from diesel passenger vehicles.  Although legislated NOX limits for new vehicles have been steadily reduced over many years, a similar reduction in NOX air pollution hasn’t been achieved.  This has been attributed to the Real World Driving Emissions (RDE) of vehicles being only poorly represented by the standard European Drive Cycle.  Most OEMs are investigating “off-cycle” emissions by using on-board analyzers to measure directly from the vehicle’s tailpipe during urban and rural driving.  The CLD500 fast NOX analyzer can be configured to measure the fast transient [NO] emissions from any vehicle and some data showing the real time [NO] emissions during a real world driving can be seen here.

Selective Catalytic Reduction (SCR) is another method of reducing NOx emissions using ammonia or urea, and is increasingly used in heavy duty Diesel applications. SCR requires careful control of the conditions and reactant concentrations in the catalyst, and the CLD500 is used to monitor catalyst performance, both at cold start and during transient operation.

Lean NOx Trap (LNT) is another technology for reducing NOx emissions- using a NOx absorbing element which stores the NOx, and periodically purging the absorber while providing excess hydrocarbons which react with the NOx as it is released. The reactants then exit the tailpipe as H2O and N2. To perform well, the LNT and supply of reactants must be carefully matched to the exhaust conditions. The CLD500 is used to monitor LNT performance, even during transient conditions.

The CLD500 is available with support for AK protocol, allowing easy integration with the test bench for improved test reliability and reduced workload.

For more information see Applications and Sample data.

Download a brochure.

Please contact Cambustion for more information and prices.

Key Application Notes 
Title Data type Download File Size Last updated
Measurement of engine-out NOx for transient SCR urea dosing accuracy Application note PDF icon cld02v01.pdf 24.29 KB 24-Feb-2015
Heavy Duty Diesel NOx and EGR control Application note PDF icon cld03v01.pdf 19.27 KB 24-Feb-2015
Transient NOx emissions from a Euro 4 GDI vehicle during WLTP Application note PDF icon cld04v01.pdf 225.87 KB 08-Oct-2014
Mobile on-board NO measurement on a Diesel vehicle Application note PDF icon cld05v01.pdf 351.57 KB 16-Jun-2015
Flame Traverse Sampling Application note PDF icon CLD06v01 Fast gas analysis traversing a methane flame.pdf 607.88 KB 22-Sep-2015
Transient NO2:NOx ratio Application note PDF icon CLD07v01 Transient NO2 to NOx ratio.pdf 679.36 KB 17-Aug-2016
GDI vehicle NOx breakthrough due to scavenging (blow-through) Application note PDF icon CLD08v01 scavenging NOx breakthrough.pdf 319.08 KB 22-Aug-2016
Measurement of EGR delay and its effects on NOx emissions using the NDIR500 and CLD500 Application note PDF icon NDIR05v02 EGR delay.pdf 117.45 KB 24-Feb-2015