Conventional CLD 1-2 second response time
Cambustion Fast CLD 2ms second response time
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
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.
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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.
Key Application Notes
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|Title||Transient NOx measurements from motorcycle real world driving||Data Type||Application note||Download File||cld10v02-motorcycle-rde-transient-nox-emissions.pdf||Size||424.03 KB||Last Updated|
|Title||Transient NOx from in-service buses||Data Type||Application note||Download File||cld09v01-transient-nox-from-in-service-buses.pdf||Size||1.18 MB||Last Updated|