A recent study from Finland, conducted by the University of Eastern Finland and Tampere University, measured particulate emissions from passenger cars preheating with an auxiliary heater in sub-zero conditions.
Image Credit: University of Eastern Finland
The preheating emissions were compared to calculated emissions produced by driving to identify the driving distance corresponding to the preheating emissions under current emissions standards.
Having reported their outcomes in the Atmospheric Environment: X journal, the scientists quantified auxiliary heater (AH) particulate emissions from the preheating of three gasoline and three diesel cars for nearly half an hour. Preheating was performed outdoors in sub-zero conditions, i.e., when preheating is suggested by the AH manufacturer.
Concerning particulate emissions, utilizing an auxiliary heater for nearly half an hour was comparable to a 97 km drive in a gasoline car or a 20 km drive in a diesel car under present emissions standards.
When driving short distances, vehicle preheating can produce significantly higher particulate emissions than the actual drive, especially when considering that the during-drive emissions of most cars are much lower than the limits set in the emissions standards.
Henri Oikarinen, Doctoral Researcher, University of Eastern Finland
Auxiliary heaters produce a considerable proportion of the preheating emissions on heater start-up and shut-down.
This is ideal for diesel-operated heaters, for which steady heating (not putting off the heater on and off) generates below one-third of the preheating emissions.
Additionally, a significant proportion of the particles produced by auxiliary heaters were in the smallest nanometric range: Over 50% of the particles produced by gasoline-operated heaters, and over 90% of the particles produced by diesel-operated heaters, were under 23 nm.
However, preheating extends the life cycle of the vehicle and also makes driving more comfortable. These findings do not suggest that people should stop preheating their cars; instead, we could reduce the emissions from preheating by using similar emissions reduction methods that are in place for engine emissions, also for fuel-operated auxiliary heaters. Fuel-operated heaters could also be switched for electric ones.
Panu Karjalainen, Study Senior Researcher, Tampere University
Current vehicle emissions standards are only applicable to particles that measure more than 23 nm; that is, the noted large quantity of particles under 23 nm in size is considerable and raises the question of whether the emissions of such smaller particles, too, must be controlled.
Fuel-operated auxiliary heaters are used for heating vehicles in cold conditions. Auxiliary heaters are generally called “Webasto” or “Eberspächer,” the biggest AH manufacturers.
Particulate emissions from auxiliary heaters are not controlled by legislation, and research into such emissions is rare. Consequently, the effect of AH emissions on air quality, health, and the global emissions budget, is yet to be identified. Studying AH emissions is an effective way to learn about the complete emissions obtained from vehicles.
In the past few years, vehicle engine emissions have decreased considerably after performing treatment methods such as carburetors and particulate filters by enhancing engine efficiency. However, auxiliary heaters currently available do not consist of similar after-treatment techniques that are in place for vehicle engine emissions.
The importance of AH emissions has been highlighted particularly for a few new vehicle models whose engine performance appears highly efficient and does not tend to produce sufficient heat during sub-zero conditions. In such cases, there is a need for an auxiliary heater for heating the vehicle also at the time of the drive.
Since AH emissions are currently not taken into account in vehicle emissions standards, it is possible to sub-optimize regulated vehicle engine emissions by using an auxiliary heater, even if this wouldn’t make sense in view of the total emissions.
Santtu Mikkonen, Study Research Manager, University of Eastern Finland
Oikarinen, H., et al. (2022) Particle number, mass, and black carbon emissions from fuel-operated auxiliary heaters in real vehicle use. Atmospheric Environment: X. doi.org/10.1016/j.aeaoa.2022.100189