Abstract
Vehicular evaporative emissions have been recognized as an important source of volatile organic compounds to the environment and are of high environmental concern since these compounds have been associated to the formation of surface ozone and secondary organic aerosols. Evaporative emissions occur during any vehicle operation. In Europe, a revised legislative test procedure has been recently introduced to better control evaporative emissions during parking. However, emissions related to normal driving conditions—the so-called running losses—have received less attention compared with the other categories. The current study aims at giving some insights to the prevailing temperature conditions in fuel tanks of typical European vehicles during normal driving operation. The effects of ambient air temperature, trip duration, vehicle speed, and fuel tank level on the temperature reached by the fuel inside the tank under different real-world operating conditions were studied. Tank temperature can exceed 40 °C depending on ambient and driving conditions. Ambient temperature was found to be the most important parameter affecting the tank temperature. Trip duration and driving pattern may also have an influence on the tank temperature particularly when long trips combined with high vehicle speed are examined. Additionally, the difference between tank and ambient temperature was examined during the individual trips and was found to vary between 1 and 10 °C depending on the testing conditions. The most important parameters affecting the delta temperature were found to be the trip duration and the maximum vehicle speed. Finally, the purging strategy of two of the test vehicles was monitored, and the parameters affecting the purging flow rate were investigated. No strong correlation between the canister flow rate with ambient temperature, vehicle speed, or fuel level was observed in either of the tested vehicles. Substantially different canister flow rate levels between the two vehicles point to different purging strategies.
Highlights
Evaporative emissions from vehicles consist of volatile organic compound (VOC) emissions not linked to the combustion process of the fuel inside thermal engines
US EPA categorizes evaporative emissions based on the evaporative mechanism with the following processes: permeation, tank vapor venting (TVV—vapor generated in fuel system lost to the atmosphere when not contained by evaporative emissions control system), liquid leaks, and refueling emissions
The objective of this study is to investigate the temperatures that can be reached by the fuel inside the tank for different vehicles tested in real world under different operating conditions
Summary
Evaporative emissions from vehicles consist of volatile organic compound (VOC) emissions not linked to the combustion process of the fuel inside thermal engines. US EPA has provided a list of compounds considered relevant for evaporative. In the USA, as well as some developed East Asian countries, the vast majority of the passenger vehicles are composed of gasoline engine; the topic of evaporative emissions is completely relevant. In Europe, the European Automobile Manufacturers Association (ACEA) recently announced a 5-year tendency for increase of the petrol vehicle share with 49.4% of total passenger car registrations in 2017 (EU-15) being composed of gasoline engine (ACEA 2018). One out of two newly registered passenger cars is a petrol vehicle highlighting the need for considering evaporative emissions. Other sources of VOCs are the so-called background emissions and are direct emissions from the vehicles’ paint, tires, plastic components, interior trims, or other fluids and tend to be very small compared with evaporation and permeation emissions (Hata et al 2018)
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