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A drag coefficient for application to the WLTP driving cycle

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journal contribution
posted on 01.09.2017 by Jeff Howell, David C. Forbes, Martin Passmore
The aerodynamic drag characteristics of a passenger car have, typically, been defined by a single parameter: the drag coefficient at a yaw angle of 0°. Although this has been acceptable in the past, it does not provide an accurate measure of the effect of aerodynamic drag on fuel consumption because the important influence of the wind has been excluded. The result of using drag coefficients at a yaw angle of 0° produces an underprediction of the aerodynamic component of fuel consumption that does not reflect the on-road conditions. An alternative measure of the aerodynamic drag should take into account the effect of non-zero yaw angles, and a variant of wind-averaged drag is suggested as the best option. A wind-averaged drag coefficient is usually derived for a particular vehicle speed using a representative wind speed distribution. In the particular case where the road speed distribution is specified, such as for a driving cycle to determine fuel economy, a relevant drag coefficient can be derived by using a weighted road speed. An effective drag coefficient is determined with this approach for a range of cars using the proposed test cycle for the Worldwide Harmonised Light Vehicle Test Procedure, WLTP. The wind input acting on the car has been updated for this paper using recent meteorological data and an understanding of the effect of a shear flow on the drag loading obtained from a computational fluid dynamics study. In order to determine the different mean wind velocities acting on the car, a terrain-related wind profile has also been applied to the various phases of the driving cycle. An overall drag coefficient is derived from the work done over the full cycle. This cycle-averaged drag coefficient is shown to be significantly higher than the nominal drag coefficient at a yaw angle of 0°.

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering

Volume

231

Issue

9

Pages

1274 - 1286

Citation

HOWELL, J., FORBES, D.C. and PASSMORE, M.A., 2017. A drag coefficient for application to the WLTP driving cycle. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 231 (9), pp. 1274-1286.

Publisher

SAGE © IMechE

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Acceptance date

22/02/2017

Publication date

2017-08-09

Notes

This paper was accepted for publication in the journal Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering and the definitive published version is available at http://dx.doi.org/10.1177/0954407017704784.

ISSN

0954-4070

eISSN

2041-2991

Language

en

Exports