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Measuring automotive exhaust particles down to 10 nanometres

Periodic Reporting for period 1 - DownToTen (Measuring automotive exhaust particles down to 10 nanometres)

Reporting period: 2016-10-01 to 2018-03-31

Current evidence suggests that diesel and, more importantly, gasoline direct injection (GDI) vehicles emit solid particles smaller than 23 nm. This is precisely where DownToTen (DTT) aims at providing its scientific and technical contribution. DTT is developing a reliable and robust methodology that will enhance the regulatory approach in the assessment of particle number emissions down to at least 10nm. The size of approximately 10nm is selected to ensure that sub 23nm particles are regulated while avoiding measurement artefacts that may arise in the <10nm range. Focus is on particle number (PN) emissions of the new generations of internal combustion engines with direct injection – primarily gasoline but also diesel – under real world operation conditions. In parallel, the project aims at complementing the in-cylinder particle formation and particle filtration research being undertaken in linked technology development H2020 projects (uPGrAdE, PaREGEn, DiePeR).
Up to now, the DTT consortium work has focused on the following activities:
•Identify key particle properties, emission and measurement conditions. Specify available instruments and sampling set-ups. Assess the performance of sampling and instrumentation methods with laboratory aerosols (WP2) (Figure 1);
•Development of a synthetic aerosol test bench that was used to study different conditions of exhaust aerosol particles, including thermally treated exhaust aerosol, fresh untreated exhaust aerosol, and aged exhaust aerosol (WP2) (Figure 2);
•Evaluate the sampling and sample conditioning approaches and measurement configurations, to be employed for the measurement of particles >10nm using exhaust aerosols generated by various combustion engine types (WP3) (Figure 3);
•Determine the impacts of particle losses and dilution uncertainties on particle levels, in comparison to a potential limit value (WP3) (Figure 4);
•Perform characterisation studies of exhaust particles, including those <23nm, with a variety of instruments and measurement principles to establish ranges of exhaust concentrations, particle size distributions and volatile/non-volatile composition (WP3) (Figure 5);
•Utilisation of vehicles and engines from a range of technology types and operating conditions to generate challenging aerosol, abundant in <23nm particles (WP3) (Figure 6)
•Optimise and adapt the sampling and measurement approaches for use in RDE conditions (WP3);
•CFD simulation of the sampling system (WP3);
•Dissemination of the results so far (WP6)
Progress beyond the state of the art achieved so far can be summarized in the following points:
•Development of a prototype DTT sampling system, with proper dimensions and operation to suit on-board type of measurements of exhaust particles below 23 nm. The system offers decreased losses and improved PCRFs than commercial systems aiming at super 23 nm measurements.
•System versatility, offering the potential to measure thermally treated, fresh and aged (secondary) aerosol, utilizing the same principal components. This offers the possibility to characterize:
-non-volatile (aka ‘solid’) particles with the implementation either of a catalytic stripper or an evaporation tube
-delayed primary particles (i.e. freshly diluted exhaust aerosol)
-secondary (aged) exhaust aerosol.
•Computational fluid dynamics simulations that start providing detailed insights on the flow and particle interactions inside sampling systems.
•Collection of experimental and simulation evidence on the impacts of pressure waves (pulsations) in the exhaust gas on the dilution performance of sampling systems.
•Development of a synthetic exhaust aerosol test bench to enable testing of measurement systems, such as sampling set-ups, measurement instruments, or after-treatment systems with a range of synthetically produced exhaust-type of aerosols (soot, sulphate, organics). •Characterization of particle emissions and emissions events from a variety of latest diesel, gasoline and alternative fuel emission control systems, including Euro 6 SCR, and GPF type of sstems, including sub-23 nm particles.
•Identification of possible cases where exhaust emission particle artifacts continue to be present, by comparison of different commercial systems with the newly developed DTT sampling and measurement system.
•Production of new knowledge regarding the formation of particles in extremely low sulphate levels and the capacity of different thermal treatment devices to remove such particles, often reported as artifacts.
Work on emissions characterization conducted so far has demonstrated that
•The incremental levels of <23nm particles in the exhaust emissions of diesel and gasoline vehicles are on average ~40% and at most ~300%. These extra particles found below the current regulatory size range, are primarily generated by periodic, unstable events, such as diesel particle filter regenerations, hard accelerations, cold starts and urea reductant dosing.
•Only few drive cycle results produced particle number emissions (>10nm) higher than the current limit value, and observation of elevated levels of >10nm PN (in comparison with >23nm PN) does not necessarily mean that >10nm emissions exceed the limit value.
•From a regulatory perspective, and within DTT, it is important to determine the sources of <23nm PN, absolute particle emissions levels relative to the limit value, and if changes in <23nm PN emissions are observed, whether these are independent of the production of >23nm PN.
•There are other variables not yet studied that are considered for on-going evaluations (most severe RDE and other low temperature testing).

The societal impacts of the project to that phase can be summarized in the following bullet points:
•Contributions to securing clean and efficient energy use in transport by means of meticulously exploring emission control conditions and events that can challenge existing emission limits. The extension of the particle size limit below 23 nm goes into this direction.
•Assisting in identifying really green transport systems.
•Addressing topics within the climate action plans, in particular with regard to potential trade-offs between climate policies and potential impacts on air pollution.
•Increasing innovation by promoting understanding of pollutants formation and their transformation in the atmosphere, in particular for latest emission control systems, thus creating competitive advantages for the EU industry and science.
DTT prototype system
PN emissions before, during and after the DPF - Regeneration
Particle penetration of DTT system configurations. Comparison with AVL commercial system
Dilution ration analysis - Large eddy simulations (LES)
PN emissions from Standard Emissions Cycles
Synthetic exhaust aerosol flow bench (left) - connection with a typical set-up
Porous tube primary diluter (left) - ejector diluter (right)