Developments in Emissions Testing Systems


Colin Pawsey
07/11/2016

Studies recently conducted by the Joint Research Centre (JRC) and some member states have shown that many light duty vehicles, particularly Euro 5 diesel vehicles, on the market today are not compliant with regulatory emission limits under real driving conditions. Previous results collected on Euro 3-5 vehicles indicate that real driving NOx emissions of light duty vehicles have barely changed over the last decade, despite increasingly stringent targets.

Real Driving Emissions

To develop a solution to this problem the Euro 5/6 Regulation 715/2007/EC [4] requires the European Commission to adapt type approval procedures to reflect the real driving emissions of regulated pollutants – CO, NOx, HC, PM/PN. In January 2011 the Commission established the Real Driving Emissions – Light Duty Vehicle (RDE-LDV) working group to assess the potential of two candidate testing procedures: Emission testing with random driving cycles in the laboratory, and on-road emissions testing with Portable Emissions Measuring Systems (PEMS).

The report published by the JRC after this research led to the decision late last year to primarily develop on-road testing with PEMS as the main real driving test procedure. In addition the JRC has been tasked with developing a PEMS-based test procedure by the end of 2013. When the new real-driving test procedure has been developed it could be introduced gradually along with more stringent Euro 6 regulatory standards in 2014, but is only likely to become effective from 2017 onwards.

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Random Driving Cycles and Portable Emission Measurement Systems

The report provided some interesting insights into the merits of both systems as vehicle manufacturers prepare for the changes in legislation.

Random driving cycle testing and simulation in the laboratory will remain vital tools for OEM’s as they design engine and exhaust systems to comply with on-road testing standards.

The principal conclusions of the report were:

  • That both test procedures are technically feasible.
  • That PEMS on-road emissions testing may cover a wider range of driving and ambient conditions than random cycle testing and is therefore potentially more effective in ensuring that the pollutant emissions of a wide range of light duty vehicles are properly limited during normal operation and use. But that the implementation of PEMS on-road emission testing faces several practical challenges, including the currently limited availability of PEMS equipment and knowledge, constraints on performing emissions tests due to the geographical locations of test sites, traffic conditions, and seasonal climate variations, as well as open safety concerns.
  • That random cycle testing is more effective than emissions testing with the NEDC, but may potentially cover a smaller range of driving conditions than on-road testing with PEMS. But also that random cycle testing in the laboratory presents an advantage over on-road testing as it allows the use of established, accurate analytical equipment, and enables the repetition and reproduction of individual emission tests under defined conditions. This may be particularly useful to OEM’s to help validate emissions results as compared with on-road test results.
  • That random cycle testing is more likely to be detected by vehicles, and may enable the use of defeat strategies to a larger extent than PEMS on-road testing does.

Emission Testing Systems

A further challenge for the EU is the development of a test protocol to measure particle number (PN) emissions of light duty vehicles under real driving conditions. Current laboratory test equipment is not suitable for use on-the-road, and last year the European Commission requested input from stakeholders, in particular manufacturers of instrumentation equipment, to communicate information about portable instrumentation that could be used for PN emission measurements.

The commission regulation implementing PN emission limits for Euro 6 positive ignition vehicles requires the European Commission to introduce a type approval test procedure to assess real-driving PN emissions by September 2017.

The development of efficient and viable testing systems will be required to fully implement these testing procedures and there are still challenges to overcome, including the integration of different testing devices and the collection and analysis of data.

AVL

The AVL M.O.V.E. System Control offers a solution with a robust and compact integration platform for in-vehicle measurement technologies that centrally collects all relevant measuring data, such as exhaust gas measuring values, indicating data, fuel consumption and driveability data, then processes them in an efficient data post processing and evaluation tool.

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Due to data consistency and the use of seamless methods the system enables the transition of real life data to the test bed, closing the gap between vehicle test and other test environments. The M.O.V.E. System Control includes sensors to gather environmental conditions such as pressure, temperature and relative humidity, as well as a GPS sensor. Further measuring devices can be connected via integrated Ethernet, CAN and USB interfaces.

CAN interfaces enable the connection of vehicle Bus-systems such as ECU or vehicle CAN, while AVL devices are integrated by means of a generic device driver which is also used on AVL test beds. This approach provides easy and consistent device integration within different testing environments

Modelling and Simulation

From a manufacturing point of view, the virtual modelling of exhaust gas after-treatment systems has become a key technology. As OEM’s strive to design vehicles able to meet emission targets there is a need for more efficient systems, and simulation technologies have a significant part to play in their development.

IAV

IAV’s virtual exhaust system simulates the behaviour of the exhaust branch in real time. The model delivers conversion rates as well as temperatures along the exhaust system, while placing a focus on NOx emissions. The tool can be used by developers to calibrate parts of the control unit and to avoid complex and expensive bench testing. The model is capable of computing NOx conversion rates with extreme accuracy, whether the exhaust system has a NOx absorption catalyst or an SCR system.

All tests with the virtual exhaust gas after-treatment system are completely reproducible and can be repeated any number of times; an advantage over testing with real vehicles where conditions can never be absolutely identical. The data from simulations enables developers to optimise the interaction between the engine and the after-treatment system, to develop functions, and to provide the control unit with basic calibration. The technology has a very good consistency between computations and measurements in actual vehicles, with results in the standard cycles particularly good. IAV are in the process of developing their software, and intend to use their virtual exhaust gas after-treatment system in the advanced stages of calibration in the future.

Horiba

The Horiba Automotive Emissions Analyser – MEXA 7000 series, has been used by the automotive industry since its inception in 1995. It is an analyser system designed for the continuous measurement of a wide range of exhaust gas concentrations from all types of engine. The current version 3 of the series builds on the features of the original MEXA-7000, incorporating new analysers, new sample handling techniques, and extended controller functions.

The cabinet system measures raw and CVS diluted exhaust gases from all vehicle and engine types for basic research and development, model certification, quality testing and durability. It includes up to ten analysers to measure THC, CO, CO2, O2, NO/NOx, HC, N20, SO2, CH4 and EGR-CO2 over a wide dynamic range. The system is configurable for emissions from petrol, diesel and alternative fuel engines, and modular sampling and analysis components provide flexibility and expandability in system configuration. Low sample flow rates also help to minimise operational costs and allow the testing of engines with minimal exhaust gas output.

Accurate measurement and analysis of data will become ever more crucial as emission targets tighten. The MEXA-7000 version3 has a large selection of NOx analysers, including vacuum/atmospheric, hot/cold and wet/dry/switchable between wet and dry, to meet diverse testing requirements. Super-low emission (SLE) analysers provide 2% of point accuracy down to 0.1 ppm for HC, NOx, and CH4, and down to 1 ppm for CO.

Summary

As has been highlighted by recent research, light duty vehicles are not currently meeting emission targets under real driving conditions. A particular problem is the NOx emissions of diesel vehicles. To combat this issue and to adhere to European air quality targets, the European Commission has targeted the Joint Research Centre with developing a PEMS testing procedure before the end of 2013.

The report produced previously by the JRC assessed the potential of both PEMS on-road testing and random drive cycle laboratory testing, and concluded that PEMS testing should be the focus for a new type of emission testing to reflect real driving conditions. The procedures are likely to come into effect in 2017 and there are many challenges for manufacturers to consider as they try to develop engines and exhaust systems which will meet the requirements.

There are many different technologies and innovations in this sector and as the parameters of the regulations become clearer, so the technology will evolve. There is a requirement for development of PEMS systems to carry out the test procedures, and a need for systems which can integrate the various testing devices. For manufacturers the continued use of modelling and simulation technologies will be a crucial aid in the development of exhaust systems and exhaust gas after-treatment systems; while random cycle testing in the laboratory will continue to give OEM’s valuable data and insights into performance under real driving conditions.

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