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Conventional CLD 1-2 second response time

Cambustion Fast CLD 1-10 millisecond response time

The Chemiluminescence Detector (CLD) is the industry-standard method of measuring engine exhaust nitric oxide concentrations. Conventional CLDs have response times of 1-2 seconds, and are typically used to measure “bag emissions” where the concentration changes very slowly. Cambustion's fast CLDs allow NO, total NOx and NO2 (via LIF) measurements at up to 1 kHz. This gives full resolution of short lived transients such as tip-ins or even individual firing cycle events.

Cambustion CLD sample head on tripod

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. Cambustion fast CLDs have a time response as low as 2 ms T10-90. This allows the analyzers to distinguish between two adjacent firing cycles, and even offer information about the variation in NO/NO₂ concentration during a single exhaust stroke.

In addition, increased awareness in local air quality has led to the need for fast and highly sensitive measurement of nitric oxides. To accurately determine the risk to human health it is critical these sometimes alarmingly high short-term exposures are quantified effectively. 

The recent changes in alternative fuel legislation has lead researchers to a new set of challenges. NO and NO2 production from Hydrogen combustion has been seen to be very sensitive to the fuel/air ratio, meaning cyclic variations in fuelling control can be easily quantified by analyzing cycle-by-cycle NOx concentrations. With careful lambda control, engine-out NOx concentrations can be minimised and savings can be made on aftertreatment system design.

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. The fast CLD is carefully designed and calibrated to be linear to well above expected engine-out levels (e.g. 0-10,000ppm range) while still retaining impressive sensitivity.

The CLD50 has allowed investigations into the real emissions exposure from vehicles allowing local and national health authorities to draw conclusions on road infrastructure and traffic flow changes, clean air zones, retrofit schemes and many more emission-reducing tools.

Cambustion NOx Analyzer Range

Fast CLD

New in 2021 is the CLD50, our fast CLD designed for both engine and non-engine single channel applications where a 15 ms T10-90 response time is sufficient. The CLD50 is capable of both [NO] and [NO₂] measurement directly (NO₂ via LIF) with only an oxygen and power supply needed.

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CLD500 two channel analyzer

Using a chemi-luminescence detector, Cambustion fast NOₓ analysers offer NO&NO₂ measurements at up to 500Hz. This is fast enough to observe NOₓ from individual firing cycles (which can vary substantially) and observe the consequent performance of NOₓ aftertreatment.

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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.

It is also important to quantify the contribution these emitters have to local and roadside air quality which can in-turn lead to high human exposure to nitric oxides. Due to recent improvements, the CLD50 can be configured for ambient monitoring with detection limits of 5ppb [NO] while retaining a 100ms response time. This allows local and national health authorities to draw conclusions on road infrastructure and traffic flow changes, clean air zones, retrofit schemes and many more emission reducing tools. Please refer to our air quality page for example videos.

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

TitleData TypeDownload FileSizeLast Updated
TitleTransient NOx measurements from motorcycle real world drivingData TypeApplication noteDownload Filecld10v02-motorcycle-rde-transient-nox-emissions.pdfSize1.63 MBLast Updated
TitleTransient NOx from in-service busesData TypeApplication noteDownload Filecld09v01-transient-nox-from-in-service-buses.pdfSize2.02 MBLast Updated

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