Barouch Giechaskiel

Performance Evaluation of a Novel Sampling and Measurement System for Exhaust Particle Characterization

This paper presents a novel partial flow sampling system for the characterization of airborne exhaust particle emissions. The sampled aerosol is first conditioned in a porous dilutor and then subsequent ejector dilutors are used to decrease its concentration to the range of the instrumentation used. First we examine the sensitivity of aerosol properties to boundary sampling conditions. This information is then used to select suitable sampling parameters to distinguish both the nucleation and the accumulation mode. Selecting appropriate sampling parameters, it is demonstrated that a distinct nucleation mode can be formed and measured with different instruments. Using these parameters we examine the performance of the system over transient vehicle operation. Additionally, we performed calculations of particle losses in the various components of the system which are then used to correct signals from the instruments. Several quality characteristics are then discussed, such as the repeatability and reproducibility of the measurements and the potential to derive total emission rate with a partial flow sampling system. Comparisons in different laboratories show that repeatability (intra-laboratory variability) is in the order of 10% for accumulation mode particles and 50% for nucleation mode ones. Reproducibility (inter-laboratory variability) values are in the range of ±20-30%. Finally, we compared laboratory size distributions with ambient samples obtained chasing a vehicle. This demonstrated that the sampling system accurately reproduced the accumulation mode particles as well as the potential for nucleation mode formation. This sampling system has been used in the framework of a European project for measurement of emissions of a number of light duty vehicles and heavy duty engines.

Particle measurement programme (PMP) light-duty inter-laboratory exercise: comparison of different particle number measurement systems

The particle measurement programme (PMP) used a particle measurement system (reference system (RS)) to quantify the particle number emissions of several vehicles. The RS was circulated around several laboratories to represent an internal standard. During the exercise dilution factors, losses and volatile removal efficiencies of the RS were regularly checked. In parallel with the RS, some labs employed their own particle measurement systems (lab systems (LS)) to determine the emissions of the same test vehicles. Comparisons between results from the RS and the LS showed that several different instruments were capable of measuring particle number emissions to within ±15% across an emission range of four orders of magnitude. Real-time emission patterns also correlated well in most cases. However, larger differences were observed when dilution factors and losses were not accurately determined and subjected to correction. Equivalence between measurement systems can be achieved once calibration and validation procedures are standardized for both manufacturers and users.

Calibration and modelling of ejector dilutors for automotive exhaust sampling

Ejectors are widespread dilutors for automotive exhaust sampling. Their dilution ratio depends on their geometrical characteristics, the properties of the sample and the dilution gas, and the conditions at the ejector dilutor outlet. In this paper we present a detailed calibration of a typical ejector dilutor, and we model its operation under steady-state conditions. Experiments showed that the dilution ratio can shift by 10–20% when changing the sample or outlet pressure by only 5 kPa or the dilution gas pressure by 50 kPa. Increase of the sample temperature by 140 °C also leads to a dilution ratio increase of 20%. Diluting pure CO2 instead of ambient air may increase the DR by 20%, due to the different CO2 properties. These are typical changes in the operating conditions when sampling automotive exhaust. Hence, in order to predict and correct for these changes, we developed a model to calculate the actual value of the dilution ratio as a function of the ejector operating parameters. The model assumes compressible flow which reaches supersonic velocity at a variable cross-section duct. This terminates with a normal shock wave occurring at the mixing area. The model can be used with any calibrated ejector dilutor to predict changes in the dilution ratio in actual field measurements.

Future European emission standards for vehicles: the importance of the UN-ECE Particle Measurement Programme

Traffic-related emissions of fine particles represent one of the main sources of air pollution especially in urban areas. In particular, diesel engines are blamed as one of the main contributors for their inherent high particulate emissions. In order to reduce the impact on human health of particulate emissions from vehicles, new stricter emission standards were considered necessary for Europe. The introduction of very low particulate emission limits has required the development of an improved measurement procedure for particulate mass and a new measurement procedure for particle number. The Particle Measurement Programme (PMP) was established in 2001 on the initiative of some European states to achieve this target. The interlaboratory comparison exercise for light duty vehicles, co-managed by the Joint Research Centre (JRC) of the European Commission and the UK Department of Transport, was completed in 2007, and the results have provided the scientific basis for the new Euro 5/6 limits for particle number and particulate mass. The heavy-duty interlaboratory exercise was started in the second half of 2007 with an exploratory work carried out at the JRC and is still on-going.

Comparative Assessment of Two Different Sampling Systems for Particle Emission Type-Approval Measurements

The Particle Measurement Programme (PMP), initiated from different Member States, aims at developing a method and sampling recommendations for a particle number-based emission standard, to support future emission regulation in Europe. In this paper we applied two different commercially available dilution systems (an FPS from Dekati Ltd and an MD19-2E from Matter Engineering AG) to record the particle emissions of a Euro II and a Euro III diesel passenger car. The latter was also fitted with a diesel particle filter (DPF) to simulate future emission levels. At their present development stage, both dilution systems failed to totally comply with all requirements of the PMP protocol. The main problems appeared to be the lack of accurate determination of the dilution ratio and the inability to reach the desired dilution temperature. However, they were able to eliminate nucleation mode particles and the results demonstrated that particle number concentration measurement is equally repeatable to the gravimetric method for the Euro III vehicle and even more so for the DPF one. Over the type-approval cycle, the Euro III vehicle was found to consistently emit below 10 14 km -1 particles without a DPF and 10 11 km -1 particles with the DPF. The exact level could only be determined with external dilution ratio determination. These results suggest that it is possible to repeatably measure the particle number emissions but some additional refinements are still needed to todays technical solutions to meet the demanding requirements of type-approval measurements.

Effect of ejector dilutors on measurements of automotive exhaust gas aerosol size distributions

Ejector dilutors have long been used for automotive exhaust particle sampling, as they can offer a low-cost option for stable dilution. In an ejector dilutor, pressurized air expanding in the periphery of a nozzle draws in and mixes with an exhaust sample which is then led to analytical equipment. The combination of processes involved may lead to particle losses which can affect the measurement. This study examines the losses of diesel exhaust particles of different characteristics (nucleation mode, non-volatile accumulation mode, internally and externally mixed accumulation mode) when these are sampled through an ejector dilutor. A scanning mobility particle sizer (SMPS), an electrical low-pressure impactor and a diffusion charger were used as analytical equipment to characterize losses with different instruments. Particle losses were found negligible for all practical applications of diesel exhaust aerosol sampling. Also, the sampling outlet and the operating pressure of the ejector dilutor were found to have a non-measurable effect on the distribution shape. Some variation of the labile nucleation mode particles was attributed to evaporation within the SMPS rather than an ejector effect, and this was confirmed by sampling solid NaCl particles in the same size range. The study further confirms the usability of ejector dilutors for exhaust particle sampling and dilution.

Impact of selective catalytic reduction on exhaust particle formation over excess ammonia events.

The introduction of selective catalytic reduction (SCR) aftertreatment to meet stringent diesel NOx emission standards around the world increases exhaust ammonia. Further to the direct air quality and health implications of ammonia, this may also lead to particle formation in the exhaust. In this study, an ammonia SCR system was examined with respect to its impact on both solid and total exhaust particle number and size distribution, downstream of a diesel particulate filter (DPF). Fuel post-injection was conducted in some tests to investigate the effect of ammonia during active DPF regeneration. On average, the post-DPF solid >23 nm and total <23 nm particle number emissions were increased by 129% (range 80-193%) and by 67% (range 26-136%), respectively, when 100 ppm ammonia level was induced downstream of the SCR catalyst. This is a typical level during ammonia overdosing, often practiced for efficient NOx control. Ammonia did not have a significant additional effect on the high particle concentrations measured during DPF regeneration. Based on species availability and formation conditions, sulfate, nitrate, and chloride salts with ammonium are possible sources of the new particles formed. Ammonia-induced particle formation corresponds to an environmental problem which is not adequately addressed by current regulations.

Particle emissions characteristics of different on-road vehicles

Due to the stringent emission standards set worldwide, particulate matter (PM) emissions from diesel vehicles have been significantly curtailed in the last decade, and are expected to be reduced even further in the future. This evolution has brought forward two main issues: whether PM emissions should only be regulated for diesel vehicles and whether gasoline powered vehicles can be further neglected from PM emission inventories. This paper addresses these issues comparing the characteristics of particle emissions from a current diesel passenger car, a gasoline one and two small two-wheelers. It is shown that the gasoline car is a negligible source of particle emissions while the two-wheelers may be even more significant particle sources than the diesel car.

A Note on the Comparison of Particle Number Counters

Comparison between two systems (methods) of measurement is predominantly performed by linear regression, which in some cases can be misleading. In this note, we employ the example of comparing two particle number counters to show how the limits of agreement statistical approach, used extensively in clinical research, can be an alternative and more reliable way to compare methods.

Implementation of Portable Emissions Measurement Systems (PEMS) for the Real-driving Emissions (RDE) Regulation in Europe

Vehicles are tested in controlled and relatively narrow laboratory conditions to determine their official emission values and reference fuel consumption. However, on the road, ambient and driving conditions can vary over a wide range, sometimes causing emissions to be higher than those measured in the laboratory. For this reason, the European Commission has developed a complementary Real-Driving Emissions (RDE) test procedure using the Portable Emissions Measurement Systems (PEMS) to verify gaseous pollutant and particle number emissions during a wide range of normal operating conditions on the road. This paper presents the newly-adopted RDE test procedure, differentiating six steps: 1) vehicle selection, 2) vehicle preparation, 3) trip design, 4) trip execution, 5) trip verification, and 6) calculation of emissions. Of these steps, vehicle preparation and trip execution are described in greater detail. Examples of trip verification and the calculations of emissions are given.