RESUMO
Automobile friction brakes generate, in addition to coarse particles generated by mechanical processes, highly variable amount of nanoparticles from high temperature processes. The effects of braking conditions - speed, deceleration rate, brake rotor temperatures - on nanoparticle production were investigated here, aiming to provide practical guidance for reducing emissions through driving style and traffic management. Typical brake pads and a rotor from a common passenger car were subjected, on a brake dynamometer, to three runs of the WLTP brake cycle developed for brake wear particle measurements. Additionally, four sets of common brake pads were subjected to those parts of standardized brake performance tests believed to be reasonably realistic for common driving. Particle size distributions (5.6-560 nm electric mobility diameter, without removal of volatiles) show a dominant peak at 10 nm commensurate to the severity of braking and a non-linear increase of the total particle number at higher braking powers and higher total energy dissipated. The average emissions for three runs of the WLTP brake cycle were 3.3 × 1010 particles/km, while the harshest deceleration, 175-100 km/h at 5.28 m·s-2, has produced 8.4 to 38 × 1013 particles, corresponding to 2.5-11.5 thousands of km of WLTP-like driving. While previous studies have correlated higher PN production with higher average brake rotor temperature, a more complex relationship between nanoparticle emissions and a combination of initial rotor temperature, total energy dissipated and braking power has been observed here. From a driver behavior and regulatory perspective, it appears limiting harsh braking and braking from high speeds, possibly through improved driving practices, road design and traffic management, may potentially reduce brake wear nanoparticles. From the measurement perspective, it appears that "off-cycle" braking, even if relatively infrequent, may be associated with exponentially higher emissions and non-negligible share of the total emissions, and therefore should not be neglected.
RESUMO
Technological advances in heavy-duty vehicle engines, allowing them to reach NOx emissions comparable to European diesel passenger cars per km driven, are being compromised by aftermarket defeat devices such as selective catalytic reduction (SCR) emulators, many of which can be quickly deactivated by the driver. In a pilot study, the prevalence of trucks with excess NOx emissions on Czech motorways was evaluated using an ordinary Customs Administration patrol vehicle temporarily fitted with a portable fast-response Fourier Transform Infra Red (FTIR) analyzer, acting as an impromptu chase vehicle. The Euro emissions category of the truck was provided from the motorway toll collection transponders. A total of 222 unique trucks were measured during a one-week pilot project. Of these, 66% were Euro VI, 25% were Euro V, and 9% were older categories. NO/CO2 ratios were calculated as a ratio of numerical integrals of the peaks of measured concentrations, as a ratio of maximum measured concentrations, and by linear regression, with the regression approach yielding most realistic results and mean calculated error of 0.2 g/kWh NO. At assumed 85% NO in NOx and 634 g/kWh mean CO2 emissions, the mean emissions of the cleanest 83% of Euro V and cleanest 63% of Euro VI trucks were within the corresponding NOx limit (2 g/kWh for Euro V, 0.46 g/kWh for Euro VI) multiplied by a factor of 1.5. Providing for some allowance for legitimate occurrences of high NOx emissions, about 10-15% of Euro V and about 10-25% of Euro VI trucks are believed to be excess emitters, with no SCR functionality on about 10-15% of Euro VI trucks. The portable FTIR, temporarily mounted on a law enforcement vehicle, can be readily used as a screening tool, identifying vehicles to be stopped for additional inspection, but also during roadside emissions inspections.
