Abstract
Current particle number (PN) emission limits set by regulation, involve counted particles with a dimension >23 nm. The measurement procedure is specified and involves the dilution of the exhaust gas in a so-called constant volume sampling (CVS) device. Research efforts are concentrating in the further development of existing measurement techniques in order to capture smaller particles down to 10 nm, given their higher health threatening potential.In the present study, six state of art, Euro 6, gasoline vehicles and in addition, one compressed natural gas (CNG) light duty vehicle, have been measured on the chassis dynamometer during different test cycles. Three particle sampling lines have been used, two in parallel at the CVS, counting particles >23 nm and 10 nm, and a third one directly at the tailpipe of the vehicle. The results allow a detailed evaluation of the emitted PNs. In addition, differences in the emissions patterns of the direct fuel injection (DI) and multi point port injection (MPI) gasoline vehicles could be identified. During cold starts, particles have been separated in distinctive size classes in order to obtain relevant number-size distributions.Counting particles >10 nm resulted in roughly doubling the PN emissions in respect to those when counting particles >23 nm. This relation holds for all examined driving cycles. PNs measured at the CVS where significantly higher than at the tailpipe, especially when capturing also the smaller particles. The CVS could be identified contributing to the increase of the registered particle numbers during cycle parts with no or very low engine particle emissions.Lowest PN emissions have been measured in combination with the CNG vehicle. The differences between DI and MPI gasoline vehicles have been significantly lower than expected from previous studies. While the MPI gasoline vehicles have been identified to emit more PN during cold start, the DI vehicles emit larger numbers during high engine loads. During cold starts, higher emissions of smallest particles have been evident.The increased rated power to displacement ratio of modern engines, based on the current “downsizing” trend, shows a good correlation with the PN emissions.
Highlights
In recent years, legislation introduced particle number (PN) emission limits for diesel vehicles
This raises the question whether the higher PNs downstream the constant volume sampling (CVS) are emitted by the engine or whether they have been in the CVS from previous measurements
The particle number (PN) emissions of six typical gas oline and one compressed natural gas (CNG) powered vehicles, all homologated according to the Euro 6b emissions limits, have been studied in detail
Summary
Legislation introduced particle number (PN) emission limits for diesel vehicles (light duty vehicles since 2011, heavy duty vehicles since 2014). The major effect, was the wide implementation of diesel particle filters (DPFs) in practically all new diesel vehicles. Several research investigations [1,2,3,4] reported high PN emissions of gasoline vehicles, in particular those utilizing direct injec tion (DI) for the fuel introduction in the combustion chamber. The more conventional multi point port injection (MPI) engines had been reported to have significantly lower PN emissions. A limit for the PN emissions of DI gasolines was introduced, effective from 2014. The PN limit though was higher than for diesel vehicles and only after September 2017, diesels and DI gasolines have to respect identical limits
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