Particle Number Emissions During Regeneration of DPF-equipped Light Duty Diesel Vehicles - a Literature Survey

The study reviews published work on the particle emissions during regeneration of diesel particulate filters in an attempt to assess the PMP methodology under these operating conditions. During regeneration of the DPF a significant increase of the emitted number of particles is observed. Size spectra reveal a nucleation mode peaking at approximately 10 nm, at concentrations that can exceed the emission levels under non-regenerating conditions by more than three orders of magnitude. These nano-sized particles are found to be mostly volatile in nature with their concentrations correlating with the sulphate content of the emitted particulate matter. Particle number measurements following the PMP methodology are found to be little affected by this burst of nucleation mode particles, partly because of the large cut-off size of the CPC (23 nm) and partly because of the semi-volatile nature of the emitted nanoparticles, exhibiting more than 97% overall removal efficiency.JRC.DDG.F.9-Sustainable Transport (Ispra

Particle Measurement Programme. Volatile Particle Remover Calibration Round Robin

A dual ejector system with an intermediate Evaporating Tube was circulated at 11 laboratories to measure the Particle Concentration Reduction Factors (PCRF) at 30, 50 and 100 nm (as required by the legislation). In addition to this “Golden” Volatile Particle Remover (GVPR), a PALAS DNP 3000 graphite spark generator (Golden Aerosol Generator - GAG) and a TSI 3790 Condensation Particle Counter (Golden CPC – GCPC), were also circulated to compare the performance of the different aerosol generators (including CAST, sodium chloride and palladium) and CPCs employed at each laboratory. The study highlighted the importance of controlling and accounting for the pressures in the calibration setup. It also highlighted the difficulties associated with the measurement of the size distribution of the polydisperse aerosols produced by the generators that due to the high number concentrations are prone to significant coagulation. The study also provided evidence that the pre-treatment of sodium-chloride and CAST particles employed in most laboratories is not sufficient, and can lead to inaccuracies in the PCRF measurements at 30 nm if a CPC with a 50% counting efficiency at 23 nm is employed. No significant linearity issues were identified in the 15 in total CPCs that were cross-checked against the GCPC. However, a change of the operating temperature of TSI 3790 CPCs to reduce the cut-off size can lead to significant linearity issues for some units, and therefore such modifications must be accompanied by linearity checks.JRC.F.8-Sustainable Transpor

Feasibility of Introducing Particulate Filters on Gasoline Direct Injection Vehicles. A Cost Benefit Analysis

Starting from September 2011 a limit of 6×1011 #/km was introduced for the type approval of diesel passenger cars that will eventually apply to all new registered diesel passenger cars from September 2012. The same limit will also apply to diesel light duty vehicles but with a one year delay (09/2014 for type approvals and 09/2015 for all new registered vehicles). The regulation states that a Particle Number (PN) limit will also be introduced for the certification of Euro 6 technology gasoline-fuelled vehicles but the threshold value was not decided yet. While conventional Port Fuel Injection (PFI) gasoline vehicles can easily comply with the diesel limit, their Direct Injection (G-DI) counterparts are found to emit systematically above this threshold by up to 1 ½ orders of magnitude. It is therefore expected that application of the diesel particle number limit to G-DI vehicles may necessitate the installation of a particulate filter. At the same time, the penetration of G-DI vehicles is expected to rapidly grow in the near future in both the European and USA markets. This is due to their improved fuel efficiency compared to the conventional PFIs, that would potentially enable the target set in both EU and USA on the fleet-average carbon dioxide (CO2) emissions of future vehicles. It is foreseen that this vehicle category will dominate the gasoline market eventually replacing the conventional and less efficient PFI vehicles. There are concerns however, that their elevated particulate emissions may adversely affect the air quality in the future if no measure is taken to efficiently control them. In this direction the present study examined the feasibility of introducing Gasoline Particulate Filters in G-DI vehicles and investigated the associated implementation cost and environmental benefit.JRC.F.8-Sustainable Transpor

Assessment of particle number limits for petrol vehicles

The European Commission Regulations No 692/2008 and No 715/2007 set the regulatory framework for type-approval of motor vehicles with respect to emissions from light passenger and commercial vehicles (Euro 5/6). However, these regulations leave open some issues regarding the Euro 6 emission standards to be addressed and defined before the entry into force of these pieces of legislation. Among them, the Type I test particle number limit for vehicles equipped with Positive Ignition Direct Injection engines should be defined. The Joint Research Centre has carried out a study to support a possible implementation of such a limit for Euro 6 petrol vehicles. The first part of this report provides a review of the particle mass and number emissions of gasoline Port Fuel Injection (PFI) and Gasoline Direct Injection (G-DI) vehicles available in the literature. Over the second part, the particle mass and number emissions from a range of Euro 4 and Euro 5 gasoline vehicle/engine technology measured at JRC are synopsized. The vehicles have been tested over various driving cycles and ambient temperature conditions according to the Particle Measurement Programme (PMP) methodology.JRC.F.8-Sustainable Transpor

Physical Characterization of Exhaust Particle Emissions from Late Technology Gasoline Vehicles

The study assesses the feasibility of introducing the regulated particle number measurement procedure for the regulation of gasoline vehicles, focusing on the established cut-off size of 23 nm. A range of late technology gasoline vehicles were tested under regulated and unregulated test conditions. The results indicated a distinct emission behavior of Direct Injection Gasolines (G-DI), Port Fuel Injection gasolines (PFI) and Diesels equipped with Particulate Filters (DPF), that differed both in terms of the absolute levels but also with respect to the fraction of undetected nano-sized non-volatile particles. The latter was found to be around 20% (based on comparisons with a Condensation Particle Counter (CPC) having a 50% cut-off size at 4.5 nm) for three G-DI vehicles tested, but ranged between 40 and 70% for the two PFIs measured. Interestingly, a relatively large fraction of undetected nanosized was also observed for two late technology DPFs, ranging between 30 and 50%. To a large extent these differences originate from differences in the size distributions and the relatively blunt shape of the counting efficiency curve of PMP compliant CPCs. Under conditions favouring nucleation mode formation in the dilution tunnel, excessive particle concentrations were detected by the low cut-off size CPCs, and especially the one with a d50 at 4.5 nm, that could exceed those of the PMP compliant CPC by up to one order of magnitude. However, the concentration of these nano-sized particles was found to decrease with increasing the dilution ratio in the first stage of the Volatile Particle Remover (VPR), indicating that this is rather a volatile artifact possibly originating from re-nucleation of evaporated material downstream of the VPR. The study also investigated the potential offered by a range of available approaches to effectively control particle emissions from G-DIs. These included the use of a Gasoline Particulate Filter (GPF), the introduction of ethanol in the fuel but also an advanced engine concept combining port and direct fuel injection. The GPF system was found to very efficient in controlling particle number emissions under all driving conditions, having no visible impact on carbon dioxide emissions. The use of fuel with hi-ethanol content (75-85%) was also found to be beneficial especially at high engine loads (up to 97% reduction of non-volatile particle numbers ) and during cold start operation (up to 70% reduction). The tests with the “hybrid” G-DI-PFI vehicle indicated that there exists the potential for significant reduction of PM formation through engine measures. The non-volatile particle number emissions of this vehicle remained below the diesel limit over all hot start tests.JRC.F.8-Sustainable Transpor

EU-PEMS PM Evaluation Program - Second Report - Study on Post DPF PM/PN Emissions

This study evaluated the performance of five in total candidate PEMS-PM systems at diesel exhaust PM levels spanning from 20 mg/kWh (Euro V) to post CRT. The different emission levels were simulated by means of a CRT/bypass configuration. The PEMS-PM systems evaluated included Horiba's On Board System with Transient PM measurement (OBS-TRPM), AVL's Micro Soot Sensor (MSS) and Gravimetric Filter Box (GFB), Control Sistem's micro Particulate Sampling System (m-PSS), Sensors Portable Particulate Measurement Device (PPMD) and Dekati's Mass Monitor (DMM). The correlation between the PM results determined with the PEMS instrumentation and that measured with the laboratory sampling systems was found to depend on the filter media employed. This was attributed to adsorption artefacts that become more important as the PM levels decrease. Teflo filters were found to be less susceptible to gas adsorption artefacts, but were difficult to handle yielding some times even negative masses. Even with Teflo filters, however, more than 99% of the PM at CRT out levels was OC which could not be detected by the real time aerosol instrumentation and therefore is expected to be adsorbed material. Furthermore, background PM levels at all candidate systems utilizing laboratory conditioned dilution air averaged at a level equivalent to 3 mg/kWh which is almost 1/3 of the Euro VI level. The background was even higher (equivalent to ~5 mg/kWh) for the PEMS system that employed ambient air (internally conditioned) for the dilution. The study also evaluated the performance of the real time sensors employed in the different candidate systems using both engine exhaust aerosol and Poly(Alpha)-Olephin spherical particles. The results of these experiments revealed a number of issues related to the calibration of the instruments and cross sensitivities to non PM sources. These findings need to be addressed by the manufacturers as they are expected to significantly affect the accuracy of the measurements in PEMS applications.JRC.DDG.F.9-Sustainable Transport (Ispra

EU-PEMS PM Evaluation Program - Third Report – Further Study on Post DPF PM/PN Emissions

This study evaluated the performance of five in total candidate PEMS-PM systems at diesel exhaust PM levels spanning from 20 mg/kWh (Euro V) to post DPF. The different emission levels were simulated by means of a DPF/bypass configuration. The PEMS-PM systems evaluated included Horiba’s On Board System with Transient PM measurement (OBS-TRPM), AVL’s Micro Soot Sensor (MSS) and Gravimetric Filter Box (GFB), Control Sistem’s micro Particulate Sampling System (m-PSS), Sensors Portable Particulate Measurement Device (PPMD) and Dekati’s Mass Monitor (DMM). The work focused on the effect of sampling time on the performance of the PEMS-PM instrumentation. To this end, repeated WHTC tests were performed with PM samples taken over a single WHTC but also over three consecutive test cycles. Teflon filters exhibited superior performance from TX40 and Quartz filters, showing little dependence on the sampling time and at the same time resulting in better agreement between the reference instrumentation and the candidate PEMS-PM systems. The study also evaluated the performance of the real time sensors following some revisions and modifications considered by the manufacturers in response to the findings of the previous (phase 2) campaign. The experimental results verified the improved performance of the revised instrumentation but also revealed some areas for further improvements.JRC.DDG.F.9-Sustainable Transport (Ispra

Particle Emissions from a Euro 5a Certified Diesel Passenger Car

The particle emissions of a Euro 5 technology DPF-equipped diesel passenger car were characterized under regulated and unregulated conditions. More specifically, the vehicle was tested under the New European Driving Cycle but also under the Common Artemis Driving Cycles. Measurements were conducted at 22°C and -7°C test cell temperatures. The particle characteristics investigated included PM mass emissions as well as “non-volatile” particle number emissions. The PMP compliant particle number measurement system was supplemented with two additional CPCs allowing for the quantification of unregulated sub-23 nm particles in the size bins of 4.5 to 10 nm and 10 nm to 23 nm. The DPF regenerated actively thrice during the measurement campaign providing some information on the emission performance of the vehicle under these conditions.JRC.DDG.F.9-Sustainable Transport (Ispra

Measuring soot particles from automotive exhaust emissions

The European Metrology Research Programme participating countries and the European Union jointly fund a three year project to address the need of the automotive industry for a metrological sound base for exhaust measurements. The collaborative work on particle emissions involves five European National Metrology Institutes, the Tampere University of Technology, the Joint Research Centre for Energy and Transport and the Leibniz Institute for Tropospheric Research. On one hand, a particle number and size standard for soot particles is aimed for. Eventually this will allow the partners to provide accurate and comparable calibrations of measurement instruments for the type approval of Euro 5b and Euro 6 vehicles. Calibration aerosols of combustion particles, silver and graphite proof partially suitable. Yet, a consensus choice together with instrument manufactures is pending as the aerosol choice considerably affects the number concentration measurement. Furthermore, the consortium issued consistent requirements for novel measuring instruments foreseen to replace today’s opacimeters in regulatory periodic emission controls of soot and compared them with European legislative requirements. Four partners are conducting a metrological validation of prototype measurement instruments. The novel instruments base on light scattering, electrical, ionisation chamber and diffusion charging sensors and will be tested at low and high particle concentrations. Results shall allow manufacturers to further improve their instruments to comply with legal requirements

Physical Characterization of Brake-Wear Particles in a PM10 Dilution Tunnel

A dilution tunnel was designed for the characterization of brake-wear particle emissions up to 10 μm on a brake dyno. The particulate matter emission levels from a single front brake were found to be 4.5 mg/km (1.5 mg/km being smaller than 2.5 μm) over a novel real-world brake cycle, for a commercial Economic Commission for Europe (ECE) pad. Particle Number (PN) emissions as defined in exhaust regulations were in the order of 1.5 to 6 × 109 particles per km per brake (#/km/brake). Concentration levels could exceed the linearity range of full-flow Condensation Particle Counters (CPCs) over specific braking events, but remained at background levels for 60% of the cycle. Similar concentrations measured with condensation and optical counters suggesting that the majority of emitted particles were larger the 300 nm. Application of higher braking pressures resulted in elevated PN emissions and the systematic formation of nano-sized particles that were thermally stable at 350 °C. Volatile particles were observed only during successive harsh braking events leading to elevated temperatures. The onset depended on the type of brakes and their prehistory, but always at relatively high disc temperatures (280 to 490 °C)