PEMS (Portable Emission Measurement System) testing for RDE (Real Driving Emissions) measurements

In the context of Euro 6 approvals and future developments, a series of requirements must be satisfied, including measurements of pollutant emissions (gaseous pollutants and particles) based on laboratory measurements of exhaust emissions (using the WLTC cycle) supplemented by measurements of emissions under real driving conditions (RDE) carried out by a (PEMS).

Measurements in real-life driving conditions allow the correlation of pollutant emissions between the measurements made in the laboratory for the homologation cycle and the vehicle driven on the road every day.

The RDE tests are performed on open roads. These tests follow the different stages of the WLTC cycle. They must therefore begin with an urban section, followed by an out-of-town section and a freeway section. The tests in real driving conditions are carried out on roads with an altitude of less than 700 meters and temperatures between 0°C and 30°C.

All greenhouse gas and pollutant emissions are measured during an RDE test, but only NOx emissions are discriminating. Thus, for Euro 6d full, NOx emissions must not exceed 1.5 times the permissible emissions for a vehicle approved under this standard.

Note that in the context of Euro 6 homologation (and its future variations), RDE measurements are also required for ISC measurements.

This test is for vehicles already on the road that must also have remained compliant with emissions regulations. These tests are mandatory for all registrations as of January 1, 2019 and for all new registrations as of September 1, 2019.

The manufacturer must guarantee the conformity of the vehicle with the homologation data for a minimum of 5 years or 100,000 km, whichever comes first. In-service conformity refers to laboratory and real driving gas emission tests and evaporation tests.

Key stages of RDE measurements

The Joint Research Centre (JRC) the European Union's scientific and technical research laboratory, has published a Guidance note for light-duty vehicles on roadside testing using PEMS.

This guidance note provides best practice for the preparation, execution and monitoring of emissions tests that are carried out with PEMS on board light-duty vehicles (LDV) equipped with conventional combustion engines (petrol, diesel, CNG, LPG), in particular to test vehicles in accordance with the European RDE legislative requirements set out in Regulations (EU) 2017/1151, 2016/427, 2016/646, 2017/1154 and the latest RDE act4 package (Regulation 2018/1832 and corrigeum), collectively referred to in this document as the EU-RDE LDV Regulations.

RDE measurements using PEMS fall into 3 main categories:

The "official" EU-RDE tests carried out at the time of new vehicle approvals (EU-RDE-TA);
Official" EU-RDE tests performed on in-service vehicles with a certain mileage for in-service conformity testing (EU-RDE-ISC);
Other types of PEMS tests, not conforming to the EU-RDE LDV regulations, and performed for purposes other than the two mentioned above (e.g. vehicle development, development of emission factors, screening for defeat devices, etc.).

More specifically for the EU-RDE-TA and EU-RDE-ISC tests, the following vehicle selection criteria apply (non-exhaustive list):

For RDE-TA tests, the vehicle must be in good mechanical condition and must have been run-in and driven at least 3,000 km prior to the test. The running-in of the vehicle must use all available vehicle components.
For the RDE-ISC test, the vehicle must have been in service for at least 15 000 km and not more than 100 000 km. In addition, and since the date of its first registration, the vehicle must be between 6 months and 5 years old.
The vehicle must be registered in the EU.
The use of a trailer hitch to install the PEMS is permitted but the vehicle's power supply must not be connected to or used for the PEMS equipment. However, it is permissible to power any safety lighting of devices (such as number plate lamps and safety indicators) from the vehicle's battery, as set out in section 3.4.6 of Annex I of Regulation 2016/646.
Towing a trailer is not possible as it would have a significant impact on the test mass. However, lightweight trailers, such as a wheel speed sensor to measure vehicle speed, are permitted as long as the movement requirements of the RDE regulation can be met (speed, acceleration, payload, etc.) and are within the manufacturers' recommendations for trailer use. The maximum support load of the rear suspension must not be exceeded for safety reasons.
Tyre types and pressures must be in accordance with the vehicle manufacturer's recommendations. Tyres must have a tread depth in accordance with the recommendations of the customer safety associations (i.e. at least 3 mm tread depth for summer tyres and 4 mm for winter tyres).
In the case of a failed RDE test, samples of fuel, lubricant and reagent (if applicable) are taken and stored for at least one year under conditions that ensure sample integrity. Once analysed, the samples can be discarded.
For diesel vehicles: If the level of the urea tank does not ensure that the RDE test can be performed, the reagent must be refilled before testing. The warnings/dash reagent level should be checked before testing.
...

There are many factors to consider, both mandatory and recommended

Parameters to be measured
Performance of the instrumentation
Test conditions
Test execution
Data evaluation

Test conditions for RDE - PEMS measurements

Regarding the test conditions, the following table presents the requirements (for requirements and recommendations for tests other than those defined in the EU-RDE-TA and EU-RDE-ISC, these can be found in the Guidance note for light-duty vehicles :

Condition	EU-RDE-TA & EU-RDE-ISC requirements
Test duration	90 to 120 minutes
Engine start	In order to assess the emissions during trips in hot start, a certain number of vehicles per PEMS test family shall be tested without conditioning but with a warm engine. An engine can be considered as warm when the engine coolant temperature and/or engine oil temperature is above 70 ºC.
Test route requirements - Urban, rural and motorway definitions and shares	- Urban, rural and motorway driving defined by speed: City: ≤ 60 km/h Rural: > 60 km/h and ≤ 90 km/h Highway: > 90 km/h For N2 vehicles with a device limiting speed to 90 km/h: Rural: > 60 km/h and ≤ 80 km/h Highway: >80 km/h - Urban, rural and motorway driving minimum distance: 16 km - Distance shares: City: ≥29% and ≤ 44 % Rural: ≥23% and ≤ 43 % Highway: ≥23% and ≤ 43 % The vehicle velocity shall normally not exceed 145 km/h. This maximum speed may be exceeded by a tolerance of 15 km/h for not more than 3 % of the time duration of the motorway driving. Local speed limits remain in force at a PEMS test, notwithstanding other legal consequences.
Test route requirements - Average speed and stop times	- Urban average speed: ≥15 km/h and ≤ 40 km/h - Cold start average speed including stops: ≥15 km/h and ≤ 40 km/h - Cold start maximum speed ≤ 60 km/h - Stop periods (when vehicle speed < 1km/h) shall account for 6 –30% of time duration of urban phase. No stop shall exceed 300 seconds or the trip will be voided. - Stop period during cold start ≤ 90 seconds
Ambient conditions – Temperature	- Moderate: ≥ 0°C and ≤ 30°C - Extended: (≥ -7°C and < 0°C) or (> 30°C and ≤ 35°C) Derogation limits(for new vehicles or types of véhicules depending of the different categories see more): - Moderate: 3°C to 30°C - Extended: -2°C to <3°C and >30°C to 35°C
Ambient conditions – Altitude	- Moderate: ≤ 700 m above sea level - Extended: >700 m and ≤ 1300m above sea level - Maximum altitude difference between start and end point: 100 m - Maximum cumulative altitude gain: 1200 m per 100km. Valid for both the urban and total trip.
Road conditions	EU-RDE-TA and EU-RDE-ISC cannot be performed on unpaved roads. In addition, even though the EU-RDE LDV regulations do not specify this point, common sense and safety recommend avoiding extreme weather conditions (mud, icy roads, and fresh snow).
Fuel lubricating oil, reagent	Vehicles must be run using market fuel, oil, and reagent, always following the recommendations of the vehicle's manufacturer. It is require d to collect a sample of the test fuel(s), oil and reagent(s) for EU-RDE tests whenever the emissions are above the NTE limit.
Driving Time	Tests should be conducted during normal working days (Monday to Friday). Recommended hours range from 7am to 8pm.
Vehicle payload	The vehicle's basic payload shall comprise the driver, a witness of the test (if applicable) and the test equipment, including the mounting and the power supply devices. The total shall not exceed 90% of the vehicle's permissible payload.
Vehicle pre-conditioning	Before an EU-RDE-TA or EU-RDE-ISC test, the vehicle has to be driven for at least 30 minutes, parked with doors and bonnet closed and kept in engine-off status between 6 and 56 hours within moderate or extended altitude and temperatures conditions. Soaking temperature 3 hours prior to the test must be recorded. It is recommended to drive in normal roads and at least 20 to 25 minutes on the motorway to limit the risk of regeneration of the DPF during the actual test. In general terms, the recommendations regarding the use of vehicle air-conditioning, auxiliary devices, payload, road condition, gear shifting, tyre conditions and the driver behaviour apply to the pre-conditioning drive. When several EU-RDE tests are conducted in consecutive days, the previous day EU-RDE test can be used as pre-conditioning drive for the current day test. Problems identified during the pre-conditioning and the total soaking time should be reported. It is not necessary to make use of the PEMS instruments during the pre-conditioning drive. However, its use is encouraged to identify potential problems with the instrumentation performance or in the recording that may prevent/delay the actual EU-RDE test. During the parking in low temperatures it might be wise to heat the PEMS equipment using an external source in order to avoid issues of condensation. For a hot EU-RDE test, the vehicle shall be driven to reach an engine oil or engine coolant temperature above 70C. Then the engine shall be stopped, and the pre-test shall be performed (calibration of PEMS system).
Vehicle air-conditioning and auxiliary devices	The air conditioning system or other auxiliary devices can be operated in a way which corresponds to their possible use by a consumer at real driving on the road. Any misuse of the air-conditioning system should be avoided, such as for instance using it with open windows, if not needed for the measuring equipment. The recommended temperature for the comfort of the passenger(s) is in the range of 20 to 24°C. All original auxiliary devices available to the user are allowed (i.e. only original devices from the Manufacturer). Any use shall be documented. Electrical auxiliaries that are automatically shut-down when their goal is achieved (i.e. rear window heating, mirror heating, etc.) should only be re-started again if actually needed for a safe driving.
Vehicle gear shift and operating modes	When several gear shift and/or vehicle operating modes are available the vehicle can be tested under any mode: eco, standard, sport, etc. with the exception of the off-road modes (for non-paved roads). It is however recommended to use the predominant mode, including the D (drive) mode for automatic transmissions. OVC-HEVs vehicles may be tested in any selectable mode (charge depleting, charge sustaining), including battery charge mode. In case a vehicle has a "race" mode, to be used only on test tracks, this mode shall not be used for EU-RDE testing, as safety features might be disabled. It is strongly recommended not to disable safety related vehicle modes (e.g. ABS, DSC, ADM, ESP, etc.) in case the test is carried by non-professional drivers.
Vehicle battery	Vehicles should not be tested with an empty battery. In case the vehicle has problems starting, the battery may be replaced following the recommendations of the vehicle's manufacturer. The vehicle shall then be pre-conditioned as indicated above and tested. It is possible to charge the battery prior to the pre-conditioning but not before the start of an EU-RDE-TA or EU-RDE-ISC tests.
Vehicle tyres	The tyre types and pressure shall be according to the vehicle's manufacturer recommendations. The tyre pressure shall be checked prior to the pre-conditioning and adjusted to the recommended values if needed. The tyre profile depth should be verified according to the recommendations of customer safety associations (e.g. ADAC), but should have at least 3mm of tread depth for summer tyres and 4 mm for winter tyres. The use of chains is not permitted since the EU-RDE trip speed requirements cannot be fulfilled and it is not recommended to drive on snow during EU-RDE tests and it is not recommended to drive under extreme weather conditions during EU-RDE tests.

Route selection for RDE measurements

Any mapping device can be used to define a route that can comply with the requirements of the EU-RDE test, including the required urban/rural/highway distance shares, the altitude difference between the start and end point and the cumulative altitude gain.

For EU-RDE-TA and EU-RDE-ISC tests:

The journey must always start with the urban part, which must be carried out on urban roads with a speed limit of 60 km/h or less. If the urban part of the journey is to be carried out for a limited period of time on roads with a speed limit of more than 60 km/h, the vehicle must be driven at speeds up to 60 km/h. The journey must start with urban driving, followed by rural driving and motorway driving;
The journey must be made in the order urban-rural-motorway, however, rural driving may be interrupted by urban driving, and motorway driving may be interrupted by urban and/or rural driving;
The journey may start and end at the same place;
The vehicle speed must be above 100 km/h for at least 5 minutes;
For vehicles of categories M2 and N2 which are equipped, in accordance with Directive 92/6/EEC, with a device limiting the speed of the vehicle to 100 km/h and 90 km/h, the speed of the vehicle on the motorway must be greater than 90 km/h and 80 km/h respectively for at least 5 minutes.

Once the route(s) have been defined, it is recommended that they be "tested", using a data logger to record vehicle speed and altitude. It is recommended to perform these tests at the times of day scheduled for the full EU-RDE test with the PEMS. Depending on the local traffic situation and potential traffic jams, it is also advisable to design alternative routes and/or local detours. It is also recommended to avoid using the same street more than twice in a specific route.
It is suggested not to always choose the same route for each EU-RDE test, but to vary them. It is also recommended that the hot EU-RDE test is performed on the same route as the equivalent cold tests.

Items to check before installing the PEMS instruments

Tyre pressure - Tyre tread depth - OBD check - Are there any warning lights activated on the dashboard? - Vehicle fluids - Aerodynamic modifications - Mileage (EU-RDE-TA: 3,000 - 15,000, EU-RDE-ISC: 15,000 - 100,000 km) - Age of the vehicle - Country of registration and use - Is the vehicle subject to a recall or maintenance campaign - Has the vehicle been used for racing/motor sport - Has the vehicle carried heavy loads beyond the manufacturer's specifications? - Check for signs of tuning - Has any part of the emission after-treatment system been replaced - Service and repair history

Key steps for RDE measurements using PEMS

Instrument Installation (detailed by PEMS component)

Step 1 - Installation of the PEMS main unit
Step 2 - Exhaust Flow Meter Range Selection
Step 3 - Installation of the exhaust gas flow meter
Step 4 - Mounting the GNSS antenna
Step 5 - Preparing the ECU communication cables
Step 6 - Connecting and installing the ECU communication cable
Step 7 - Installation of the power supply
Step 8 - Installation of the weather station
Step 9 - Connecting the heating sensor(s)
Step 10 - Connecting the other tubes and cables

Pre-test procedures

Step 11 - Checking connections and wiring
Step 12. Check the charge level of the PEMS power batteries
Step 13. Power up the main software
Step 14. Start up and stabilise the main unit
Step 15. Checking the zero level of the analysers
Step 16. Calibration of the analysers' range
Step 17. Archive zero and span calibration data
Step 18. Cleaning the exhaust flow meters
Step 19. Checking the gas analyser system for leaks
Step 20. Checking the flow meter
Step 21. Check that the data acquisition storage media and backup have sufficient space
Step 22. Spot check
Step 23. Check GNSS
Step 24. Check weather station
Step 25. Check that all temperature controllers are set to the correct operating values
Step 26. Switch to battery power
Step 27. Start the engine

Perform the test

Step 28. Check ECU communication, if applicable
Pre-test including a validation test (recommended)
Verify pre-test or validation test data (recommended)
Step 29. Normal test execution

Post-test

Step 30. Conclusion of a test
Step 31. Checking the zero and sensitivity of gas analysers
Step 32. Zeroing the exhaust gas flow meter
Step 33. OBD post-test check
Step 34. Saving the test data
Step 35. Checking the test data
Step 36. Switch off the emission sampling system and all measuring equipment
Step 37. Switch off the power to the instruments

Conclude the test run (dismantle the PEMS)

Step 38. Dismantle the PEMS equipment and return the vehicle/machine to its initial configuration.
Step 39. Weight of installed PEMS equipment (including batteries)

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