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Mr. Carlos Agudelo, Link Engineering, UNITED STATES
Dr. Eng. Ravi Teja Vedula, Link Engineering., UNITED STATES
Mr. Quinn O'Hare, Link Engineering., UNITED STATES
Dr. Eng. Jaroslaw Grochowicz, Ford Werke GmbH, GERMANY
Dr. Theodoros Grigoratos, European Commission, Joint Research Centre, ITALY
The incoming air during brake emission measurements using inertia dynamometers has two primary purposes: providing a cooling regime that replicates within reason the vehicle brake temperatures and transporting the particles from the friction couple to the sampling plane. Each objective brings its challenges. The ideal cooling system on the inertia dynamometer would have to adjust for factors like a) amount of cooling as a function of vehicle speed and axle position – front or rear; b) wheel well design; c) relative cooling coefficients for the friction couple; d) temperature at the wheel well as function of temperature of the outside air, and the heat dissipation of the brake; and e) wheel and tire design, size, and airflow patterns. The ideal cooling regime to optimize the aerosol sampling would need to: a) have constant airflow during the entire test; b) ensure the air temperature and humidity remain constant at the sampling plane where the brake debris enters the sampling train; c) remain agnostic to the brake size, brake orientation, duty cycle, and potential interactions with the brake enclosure or brake fixture; and d) provide the proper balance of residence time, transport efficiency, and isokinetic sampling for large particles. Since the accomplishment of both sets of objectives conflict, the industry needs a set of compromises to allow the characterisation of brake emissions using laboratory methods, remain representative of the vehicle behaviour, and be practical for implementation during regular testing campaigns.
The laboratory methods to measure brake emissions need to be repeatable and reproducible. Task Force 1 within the Informal Working Group of the Particulate Measurement Program (within the UNECE/GRPE) developed a set of metrics to adjust brake cooling on the dynamometer. This paper presents the results of applying the proposed methodology and metrics to several vehicles from the California Air Resource Board program to update the EMFAC model. The vehicles were instrumented to measure brake activity on the proving ground and interact with the driver during the WLTP duty cycle; which was executed to remain within the target speed error bounds from GTR15. With this information and the brake hardware for each vehicle and axle, the work focused on determining the conditions for the dynamometer cooling air (temperature and airflow) to meet within reason the different PMP metrics.
The results of the experimental validation yielded valuable information to a) determine the cooling airflows for the subsequent inertia dynamometer tests, b) finetune the PMP brake cooling metrics and prepare a proposal for default settings, and c) verify the availability (or design) of isokinetic sampling nozzles for all instruments and sampling lines.
Task Force 1 of the PMP used these findings to complete the methodology for adjusting the cooling air, in cases where there are no direct measurements from vehicle testing or cooling rates applicable to the WLTP-Brake cycle.
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Dr. Theodoros Grigoratos
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16 July 2021
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16 July 2021