Summary
As people may know, standards are in place to control the emissions of passenger cars worldwide since the 70's. Those standards use pre-determined speed profiles certified through laboratory procedures. For instance, in E.U., only the New European Driving Cycle (NEDC) is used.
As we can see on the graph, the NEDC covers a limited range of the engine map, leading to optimization strategies in this region only.
Vehicles were taken on real roads and emissions were measured. Euro6 Diesel cars emit, on average, 7 times their official limit for Nitrogen Oxides (NOx). On top of that, not all pollutants are considered like the soot emissions for gasoline engines.
The standards and cycles are obsolete. They do not represent a day to day usage of passenger cars. In the end, customers feel cheated on! They are not able to reach the Original Equipment Manufacturers (OEM) numbers for the fuel consumption and emissions.
To cope with all those issues, the E.U. commission decided to change the homologation procedure:
A new cycle, more realistic, has been created: Worldwide harmonized Light vehicles Test Cycles (WLTC)
Test in real life situation are added: Real Driving Emission (RDE)
More pollutants will be measured: soot
Any third party can proceed with measurements using Portable Emissions Measurement Systems (PEMS)
Post-treatment aging will be considered
RDE cycles are defined to represent real life scenario. They must take into account a variable environment, road slopes, wind, traffic and different driving behaviors. A list of criteria is defined to check if a cycle is "RDE" compatible. A simplified list is given below:
Urban |
Extra-urban |
Highway | |
Cycle repartition (+/- 10%) |
29% < ratio <= 34% |
33% |
33% |
Speed |
V < 60 km/h |
60 km/h <= V < 90 km/h |
V > 90 km/h |
Max. speed (+/- 15 km/h for less than 3% of driving time) |
- |
- |
145 km/h |
Average speed (stops included) |
15 km/h <= Vmoy <= 30 km/h |
- |
- |
Minimum travelled distance |
16 km |
16 km |
16 km |
Altitude difference (beginning/end) |
100m |
100m |
100m |
Maximum slope |
1200m/100km |
1200m/100km |
1200m/100km |
The new RDE norm will allow more severe transient behaviors, cold starts, leading to more NOx emissions, especially for Diesel engines.
At the same time, OEMs have to meet the Corporate Average Fuel Economy (CAFE) standards.
The general trend to have Diesel engines for all usage is already going backward, even more after the Diesel gate.
The norm change will impact drastically how OEMs and suppliers work and design their engines. In order to meet the norm targets with the new constraints, the number scenario and the complexity of new engines, they will need to :
To cope with those issues, simulation tools can already provide solutions:
Simcenter Amesim is a unique solution combining platform features (plot, dashboards, co-simulation interfaces) and a great number of dedicated solutions to model all the vehicle sub-systems, under one software.
Great improvements have been, continously, made to provide an easy and intuitive approach for the RDE cycles simulation.
A total libray rework has been done, allowing IFP-Drive to handle the complexity of RDE cycles. The environment (ambient air pressure, temperature, density, wind speed…) and road conditions (slope, grip…) can now vary during the driving cycle. It allows applying the environmental/road conditions changes from test acquisition.
A new generation of control oriented submodels is available. All after treatment systems (DOC, DPF, GPF, SCRF,...) and the generic monolith have been optimized to handle variable time steps and fixed time steps up to 100ms.
Those improvements allow the implementation of after-treatment system models on hardware-in-the-loop environments for Engine Control Unit (ECU) validation and adress the new challenges related to RDE:
The demonstrator is available in the IFP-Drive library demo portail, in Simcenter Amesim.
It is composed of three main steps:
How to use cycles/recordings from different sources for the simulation?
How to easily setup a vehicle model using IFP-Drive?
Currently, a clear process is defined for the following sources:
The following process is given for OSE Road files.
The pre-processing is done using a Python App, available only on this demonstrator. The tool will extract and generate the files necessary for IFP-Drive.
The vehicle definition (mass, SCx, tire dimension, gearbox ratios,...) and the engine definition are usually easy to obtain. Those parameters can be directly entered in the corresponding submodels.
On the other hand, the engine maps giving the torque, the fuel consumption and pollutant emissions are more difficult to get. To cope with this issue, an App is available on the IFP-Drive engine submodel, to ease the map generation from maccro parameters as the maximum torque/power at a given engine speed.
To complete the model setting, the cycle files, generated in previous section, need to setup in the driver submodel.
Now that the model is fully defined and the RDE cycle imported in Simcenter Amesim, the simulation can be launched. The plot configuration attached to the demonstrator will allow the visualization of the driver's outputs (acceleration, braking, gearbox management), the fuel consumption and the CO2 emisisons.
Thomas Sanguinetti is product manager in the Internal Combustion Engine team, since 2014. He focuses on turbocharged engines (IFP-Engine), hybrid vehicles (IFP-Drive) and real driving emissions (RDE). He is working on engine modelling since 2009, with different OEMs.