Comparisons of Laboratory and On-Road Type-Approval Cycles with Idling Emissions. Implications for Periodical Technical Inspection (PTI) Sensors

Abstract

For the type approval of compression ignition (diesel) and gasoline direct injection vehicles, a particle number (PN) limit of 6 × 1011 p/km is applicable. Diesel vehicles in circulation need to pass a periodical technical inspection (PTI) test, typically every two years, after the first four years of circulation. However, often the applicable smoke tests or on-board diagnostic (OBD) fault checks cannot identify malfunctions of the diesel particulate filters (DPFs). There are also serious concerns that a few high emitters are responsible for the majority of the emissions. For these reasons, a new PTI procedure at idle run with PN systems is under investigation. The correlations between type approval cycles and idle emissions are limited, especially for positive (spark) ignition vehicles. In this study the type approval PN emissions of 32 compression ignition and 56 spark ignition vehicles were compared to their idle PN concentrations from laboratory and on-road tests. The results confirmed that the idle test is applicable for diesel vehicles. The scatter for the spark ignition vehicles was much larger. Nevertheless, the proposed limit for diesel vehicles was also shown to be applicable for these vehicles. The technical specifications of the PTI sensors based on these findings were also discussed.

Evaluation of Measurement Procedures for Solid Particle Number (SPN) Measurements during the Periodic Technical Inspection (PTI) of Vehicles

“…The slope only for tests performed in this study was very similar and equal to 8.3 × 10 6 cm 3 /km. The correlation factor determined in this study was very near to the value of 10 7 cm 3 /km reported in a previous study [17]. Thus, a vehicle that fails the typeapproval test is expected to emit hot low idling PTI23 concentrations greater than 7 × 10 4 #/cm 3 .…”

“…The same vehicle complied with Euro 6 SPN 23 limits during type-approval testing. At other studies [17,37], after DPF regenerations vehicles emitted high SPN 23 concentrations (also at idling) and needed 10-15 min of driving to reduce their SPN 23 emissions. Herein, we investigated a possible accelerated methodology for avoiding vehicle fails due to normal DPF efficiency reduction after a regeneration and not having to drive or idle the car for 20-30 min.…”

“…In addition, it has similarities with the current SPN methodology during Type 1 type-approval testing, as will be discussed below. The new particle number concentration measurement at low idle was shown to have a quite good correlation with the SPN emissions during type-approval cycles for diesel vehicles [16,17]. The correlation coefficient between the two tests was found to be approximately 10 7 cm 3 /km [17] meaning that a diesel vehicle with 1 × 10 5 #/cm 3 low idling emissions would approximately emit 10 12 #/km at the regulatory cycle.…”

“…The new particle number concentration measurement at low idle was shown to have a quite good correlation with the SPN emissions during type-approval cycles for diesel vehicles [16,17]. The correlation coefficient between the two tests was found to be approximately 10 7 cm 3 /km [17] meaning that a diesel vehicle with 1 × 10 5 #/cm 3 low idling emissions would approximately emit 10 12 #/km at the regulatory cycle. Note that the regulatory limit is 6 × 10 11 #/km (also for particles larger than 23 nm).…”

Overview of Vehicle Exhaust Particle Number Regulations

“…The JRC of the European Commission is also working on the topic to prepare common recommendations for particle number instrumentation and procedures for PTI purposes. Details about the simplified methodology and the specifications can be found elsewhere [91].…”