Non-compliance risk analysis

Since the entry into force in 2015 of the Euro 6 standard, the approval of thermal vehicles has been carried out in real traffic conditions, on driving cycles called RDE cycles (from the English acronym “Real Driving Emissions”). The great diversity of these cycles (due to the weather, topography, road network and local legislation or driving style) represents a real challenge for car manufacturers who must control the risk of non-compliance of their vehicles in the multitude of cases that it is possible to encounter.

The evaluation of a vehicle over an RDE cycle is done by calculating a compliance factor, which is based in particular on the mass of pollutants emitted per kilometer travelled. To comply with the standard, this conformity factor must be less than 1. It is crucial for a manufacturer to assess the risk (i.e. the probability) that his vehicle will obtain a conformity factor exceeding the standard, over an RDE cycle drawn randomly.

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OSE has designed a method for statistical analysis of the risk of non-compliance, based on a representative database of RDE cycles and on a control of the confidence interval of the emission models provided by the manufacturers (or designed by OSE).

Risk analysis: from the global indicator to the finest granulometry

The developed method makes it possible to generate the probability distributions of the conformity factors of each of the pollutants. The results are presented in the form of a dashboard allowing dynamic filtering on the different driving styles, cycle phases (start, city, road, motorway), weather conditions, weight on board the vehicle, etc. and thus to evaluate the performance of the vehicle in different situations.

This dashboard also makes it possible to sort the cycles according to their severity and level of pollutant emissions, to identify in an ergonomic way the most demanding cycles among the database of thousands of cycles and to display their characteristics in detail: GPS track, speed profile, altitude profile, temporal evolution of emissions during the cycle, etc. The tool offers turnkey all the information necessary for manufacturers to run these cycles on site with their vehicle.

Risk analysis : probabilistic methods and physical simulations

The risk analysis method for non-compliance with pollutant emission standards developed by OSE is based on 3 pillars:

– The generation of hundreds of thousands of RDE cycles, reproducing the geographical, topographical, meteorological, legislative and driving style diversity that it is possible to encounter, thanks to the OSEroad tool. This database is then reduced to ten thousand cycles, using discriminating physical variables and advanced clustering techniques, in order to be able to use it in numerical simulations in a reasonable time.
– The design of pollutant emission models (or the use of models provided by the manufacturers), calibrated using bench measurements or PEMS (Portable Emissions Measurement System), in order to be able to simulate vehicle emissions on all cycles of the database. We have developed an uncertainty model to control the errors of the measurements and of the emissions model.
– The post-processing of the results, by calculating the probability distribution of the compliance factor, as well as all the relevant characteristics to sort and filter the cycles, in order to offer global risk indicators while allowing access to the smallest details the most demanding cycles.

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In 6 months