Abstract
Research or engineering questions
The progress in passenger car emissions legislation has spurred new and effective emission control technologies that comply with Euro 5 and most lately Euro 6 targets. However, the efficacy of many of these technologies is linked to operating temperatures and ambient conditions do have an effect on those. Furthermore, the cold-start/cold-ambient temperature at -7 °C test (the Type VI test) has been part of the type approval validation portfolio since 2002. However, limit values have been set on carbon monoxide (CO) and unburned hydrocarbons (THC) only, and there has not been any revision ever since. Moreover, this test is imposed only on petrol-fuelled cars. Assessment of the emissions from diesel-powered vehicles and emissions of NOx are therefore of interest, as well as to evaluate how the latest-generation of emission control systems targeted to EU5 type approval cope with the low ambient temperature.
Methodology
VTT has evaluated and reported cold-start performance of new cars since 1993, addressing also durability of the technology in Nordic conditions [1],[2], [3], [4]. This work has been continued, and each year a batch of some 10 to 20 cars representing that particular model year has been tested. The objective of this work has been to make an assessment of the cold-start performance, and evaluate how it has been developing. Furthermore, the aim is to provide first-hand results for the motoring press of those cars for their annual evaluation tests. Therefore, measuring fuel consumption and CO2 has been part of our test, even if it is not part of the legislative procedure. Moreover, we have also measured NOx, even if that is not part of the type approval test procedure.
As of today, our database includes some 250 petrol-fuelled cars as well as some 70 diesel-powered models, and in total well over 300 cars with different level of emissions control has been measured with almost the same procedure.
Results
The paper shall assess the emissions of CO, HC, NOx and fuel consumption (and CO2). We report both cold-start and warm start performance in order to assess the efficacy of the emission control, as well as excess fuel consumption in low ambient temperatures, as well as give some indications of the trend that the EU5 emission type approval level may present, when portrayed against the older-generations (EU2, EU3 EU4).
Limitations of this study
Even if the total number of tested vehicles is fairly high, the selection of each year’s fleet is quite arbitrary. Thus, averages may be biased, and may not give a balanced view of the technology at large.
What does the paper offer that is new in the field in comparison to other works of the author
This is an update of more EU4 cars (35) and some 100 cars with EU5 emissions level not present in the previous analysis.
Conclusions
The progress in lowering the type approval values for regulated emissions from EU2 to EU5 level is not necessarily seen, if we use cold-start emissions as a benchmark. Furthermore, the assumed supremacy of the diesel technology regarding cold-start emissions that was the basis for waiving it from the low temperature cold-start test may not be so clear anymore, as the results of the worst diesels are mixed with the figures from the best petrol-fuelled cars. Also, what regards to NOx, low temperature test gives also quite high emissions, especially for diesel-powered cars. Furthermore, the absolute level of fuel consumption (and CO2 emissions) has been lowering, but in relative figures the excess fuel consumption is still notable.
Key words: petrol, diesel, passenger cars, cold-start, low ambient temperatures, emissions fuel consumption