Statistical Assessment and Temperature Study from the Interlaboratory Application of the WLTP–Brake Cycle

Abstract

The relative contribution of brake emissions to traffic-induced ambient Particulate Matter (PM) concentrations has increased over the last decade. Nowadays, vehicles’ brakes are recognised as an important source of non-exhaust emissions. Up to now, no standardised method for measuring brake particle emissions exists. For that reason, the Particle Measurement Programme (PMP) group has been working on the development of a commonly accepted method for sampling and measuring brake particle emissions. The applied braking cycle is an integral part of the overall methodology. In this article, we present the results of an interlaboratory study exploring the capacity of existing dynamometer setups to accurately execute the novel Worldwide Harmonised Light-Duty Vehicles Test Procedure (WLTP)–brake cycle. The measurements took place at eight locations in Europe and the United States. Having several dynamometers available enabled the coordination and execution of the intended exercise, to determine the sources of variability and provide recommendations for the correct application of the WLTP–brake cycle on the dyno. A systematic testing schedule was applied, followed by a thorough statistical analysis of the essential parameters according to the ISO 5725 standards series. The application of different control programmes influenced the correct replication of the cycle. Speed control turned out to be more accurate and precise than deceleration control. A crucial output of this interlaboratory study was the quantification of standard deviations for repeatability (between repeats), sample effect (between tests), laboratory effect (between facilities), and total reproducibility. Three critical aspects of the statistical analysis were: (i) The use of methods for heterogeneous materials; (ii) robust algorithms to reduce the artificial increase in variability from values with significant deviation from the normal distribution; and (iii) the reliance on the graphical representation of results for ease of understanding. Even if the study of brake emissions remained out of the scope of the current exercise, useful conclusions are drawn from the analysis of the temperature profile of the WLTP–brake cycle. Urban braking events are generally correlated to lower disc temperature. Other parameters affecting the brake temperature profile include the correct application of soak times, the temperature measurement method, the proper conditioning of incoming cooling air and the adjustment of the cooling airspeed.

Unrecognized volatile and semi-volatile organic compounds from brake wear

“…Light braking (regime 1) is characteristic of urban driving, while heavy braking (regime 2) is characteristic of rural and highway driving. 51 The brake torque and rotor temperatures in the braking regimes adopted in the present study in general compare well with those reported as typical for some common make and model vehicles. 52 The maximum temperatures reached in each experiment are shown in Table S2 †.…”

“…Although some test cycles have been developed for brakes and tires, 36,51,53 there is no universally accepted protocol. There are a number of factors that impact emissions, including the velocity when the brakes are rst applied, the frequency and duration of braking, and the braking power and deceleration rate.…”

Vehicle Emission Models and Traffic Simulators: A Review

“…However, it was found that the NEDC test often did not reflect the conditions actually experienced when driving on public roads [50,51]. To improve the emissions and fuel consumption that occur when driving under road conditions, a new WLTP (World Harmonised Light Duty Procedure) driving test procedure was created [52]. With the new procedure, in addition to the determination of emissions during controlled driving tests with a chassis dynamometer, real driving emission (RDE) road tests are also carried out using mobile emission measurement systems -PEMS (Portable Emissions Measurement System) [53,54,55].…”

Tracer-Gas-Integrated Measurements of Brake-Wear Particulate Matter Emissions from Heavy-Duty Vehicles

“…Brake-wear PM emissions account for up to ∼50% of nonexhaust PM 10 emissions and ∼20% of the total traffic-related PM 10 emissions. ,, Brake-wear processes exhibit a particularly high level of PM emissions at an aerodynamic diameter ranging from 2 to 6 μm (i.e., mode diameter of mass-weighted particle size distributions). ,– At a range of friction material temperature (i.e., 100–400 °C), previous studies found a shift of the mode diameter of mass-weighted particle size distributions toward a smaller size when the temperature decreased. , The characteristics of brake-wear PM emissions also vary with the type of friction materials (e.g., nonasbestos organic, semimetallic, low metallic, etc.) and operational conditions (e.g., vehicle speed, deceleration rate, and brake power). ,– …”