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How to use Real Driving Emission cycles in Simcenter Amesim?

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor

Summary

Why the automotive norm changed?

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.image.pngCycle operating ranges

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:

  1. A new cycle, more realistic, has been created: Worldwide harmonized Light vehicles Test Cycles (WLTC)

  2. Test in real life situation are added: Real Driving Emission (RDE)

  3. More pollutants will be measured: soot

  4. Any third party can proceed with measurements using Portable Emissions Measurement Systems (PEMS)

  5. Cold starts will be considered
  6. 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

 

 

How this norm will impact OEMs and suppliers?

The new RDE norm will allow more severe transient behaviors, cold starts, leading to more NOx emissions, especially for Diesel engines.

  • RDE cycle should be in favor of gasoline engines

 

At the same time, OEMs have to meet the Corporate Average Fuel Economy (CAFE) standards.

  • Reducing the CO2 footprint (95 g/km CO2 for 2020)
  • In favor of Diesel engines

The general trend to have Diesel engines for all usage is already going backward, even more after the Diesel gate.

  • Gasoline engine sales are increasing in Europe

image.png

 

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 :

  • Evaluate the emissions of the whole vehicle during the whole development cycle (Process)image.png
  • Get access to efficient modeling and simulation tools (Process)
  • Optimize the full engine map and transient behavior (Reduce emissions and fuel consumption)
  • Define cold start (-7°C) strategies (Post-treatment efficiency)
  • Test the engine calibration on many cycles and in a short period of time (Robustness)
  • Test all variants, on many cycles and in a short period of time (Robustness)
  • Get access to an exhaustive number of RDE cycles (Robustness)
  • Check if cycles are RDE compliant (Validity)
  • Improve the accuracy of pollutant measurement systems (Accuracy)

To cope with those issues, simulation tools can already provide solutions:

  • Numerical algorithms can find, efficiently, compliant RDE cycles,
  • Simulation software can handle such great number of use cases and capitalizes them,
  • Digital twins can keep the costs in range,
  • Predictive modeling can cover the full development cycle,
  • Adapted modeling solutions allow engineers to improve system and control development on all cases,
  • Machine learning can answer to the time constraint (100x faster than real time).

 

Is Simcenter Amesim the solution?

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.

image.png

 

Great improvements have been, continously, made to provide an easy and intuitive approach for the RDE cycles simulation.

 

IFP-Drive Library improvements

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.image.png

 

IFP-Exhaust improvements

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 100msimage.png

 

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:

  • accuracy
  • prediction
  • fast running models (DOC, on WLTC cycle (1750s), fixed time step 0.01s => simulation time 6s)image.png

     

    image.png

     

     

Dedicated RDE demonstrator

The demonstrator is available in the IFP-Drive library demo portail, in Simcenter Amesim.image.png

It is composed of three main steps:

  1. How to use cycles/recordings from different sources for the simulation?

  2. How to easily setup a vehicle model using IFP-Drive?

  3. How to estimate the fuel consumption and emissions on a given cycle?

 

  • Import RDE cycles

Currently, a clear process is defined for the following sources:

The following process is given for OSE Road files.

image.png

 

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

 

  • Setup IFP-Drive submodels

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.image.png

 

 

  • Estimate fuel consumption and emissions

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.image.png

 

Simcenter Amesim a complete solution!

  • Simcenter Amesim already provides solutions to simulate the whole vehicle
  • Dedicated solution for each subsystem
  • Different scalability levels to have the best compromise accuracy/simulation time
  • The whole development cycle can be covered thanks to predictive modeling
  • Most of solutions can cope with the Real Time constraint
  • Tools and workflows to assess RDE cycles are already available
  • Continuous improvement of existing solutions
  • Check out our website for more information

 

 

 

About the author

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.