University of Wisconsin -- Engine Research Center slide 1 Chemical characterization of particulate emissions from diesel engines: A review Author: M. Matti Maricq Reviewed by : Zongyu Yue

University of Wisconsin -- Engine Research Center slide 2Contents  Introduction  Sampling system and chemical analysis  Next generation diesels  Conclusion

University of Wisconsin -- Engine Research Center slide 3  Diesel PM:  Fractal-like agglomerates of primary particles, composed of carbon and traces of metallic ash, and coated with condensed heavier end organic compounds and sulfate;  Nucleation particles composed of condensed hydrocarbons and sulfate = soot = nucleation mode = condensed HC/SO4 = imbedded metallic ash Introduction

University of Wisconsin -- Engine Research Center slide 4 Introduction  Particulate matter (PM) is the only criteria pollutant regulated by US EPA that is NOT chemically defined. Chemical composition should be important in the potential environmental impacts of PM, including health effects, climate change, ecological effects, and visibility.  Diesel combustion is widely used in both stationary and mobile applications, and represents an important source of ambient particles. The rapid change in government air quality and emission regulations provides the primary motivation for the advance in diesel engine emission: to reduce tailpipe emissions and develop new methods to sample and characterize the emissions.  Exhaust aftertreatment is required to achieve new emission standard. For lowered PM emission, the regulatory method for PM mass measurement faces qualitatively new challenges as effects from temperature, humidity, electrostatic charge, and gas phase adsorption. Moreover, exhaust aftertreatment does not just lower emissions, but also alters the chemical composition of particle.

University of Wisconsin -- Engine Research Center slide 5 Sampling system and chemical analysis  Diesel PM sampling train:  Cyclone separator: remove large particles from the sample stream (typically > PM10)  XAD-Denuder: adsorb the gaseous material  Filter: particles and particle bound organic material pass through and are trapped by the quartz fiber filter or Teflon filter.  Polyurethane foam cartridge(PUF): collect the semi-volatile organics that blow off the filters  Replace filters with a cascade impactor, to provide size information regarding the collected PM.

University of Wisconsin -- Engine Research Center slide 6 Sampling system and chemical analysis  Chemical speciation methods:  Elemental analysis: X-ray fluorescence (XRF) or inductively coupled plasma mass spectrometry (ICP-MS). 44 chemical elements  Inorganic ions (SO 4 -2 ): Extracted with deionized-distilled water/alcohol mixture and analyzed using ion chromatography  Hydrocarbons: Extraction: Soxhlet, ultrasonic, and microwave-assisted Speciation: gas chromatography/mass spectrometry. Individual species are identified by the retention time and the mass spectrum, and quantified by the total ion count. Difficulties: complex structures, similar molecular weight, and trace species  Polar organic compounds: The retention time is too long. Thus, these compounds have to be converted to their methyl ester analogues by diazomethane derivitization.

University of Wisconsin -- Engine Research Center slide 7 Sampling system and chemical analysis  Emerging tools for PM chemical analysis:  Single particle Mass Spectrometer (MS)  Thermal desorption aerosol MS  Multiple laser approach  DMA/ICP-MS  Laser breakdown spectroscopy  Advanced X-ray methods: probe functional group structure (near-edge X-ray absorption fine structure)  Neutron scattering  Raman spectroscopy  Particle volatility

University of Wisconsin -- Engine Research Center slide 8 Sampling system and chemical analysis GC-MS ~35 % The primary emissions excluding the secondary formation of ammonium nitrate, van nuys tunnel, September 1993 ~83 % ~85 % ~72 %

University of Wisconsin -- Engine Research Center slide 9 Next generation diesels  Advances in diesel engine technology:  High pressure direct injection system, multiple injection: reduce both NOx and PM emissions, possibly alter the EC/OC ratio.  EGR: increase the PM level due to the oxygen dilution and lowered efficiency of soot oxidation.  Secondary effect: While particle number concentration and size depend on injection pressure, post injection fuel pulses, and EGR, the composition of the particles exiting the combustion cylinder should NOT be much affected. The principal effect will be the extent to which the fuel injection and EGR strategies alter gaseous hydrocarbon and sulfate emissions that subsequently condense onto the particles, or nucleate, as the exhaust cools.

University of Wisconsin -- Engine Research Center slide 10 Next generation diesels  Exhaust aftertreatment:  DPF: Substantially lowers PM mass emissions, but its effect on particle number is ambiguous, because the number can be dominated by nucleation particles formed downstream of the DPF.  Oxidation catalyst: Removes hydrocarbons that could otherwise condense on soot particles or nucleate as the exhaust cools Oxidizes SO2 to SO3, and yield sulfuric acid with the presence of water vapor, that promote nucleation or condense on soot  NOx aftertreatment: Lean NOx traps: low efficiency necessitate the use of EGR SCR: produce nitrate and nitro-organic compounds that contribute to PM.

University of Wisconsin -- Engine Research Center slide 11 Conclusion  An emphasis was placed on the chemical composition of PM emission, which is of central interest to the practical issues of health effects, climate change, source apportionment and aerosol modeling.  Traditional diesel exhaust PM characterization was reviewed with respect to sampling, speciation and result discussion. The emerging tools for chemical speciation were also discussed in details, pointing out the development and challenge in this area.  The impact of the new technique in diesel combustion on PM emissions were provided generally. It would be more interesting if this part was extended to the more advanced combustion model, such as LTC and RCCI.

University of Wisconsin -- Engine Research Center slide 12 Thank you for your attentions!

University of Wisconsin -- Engine Research Center slide 13 Sampling system and chemical analysis  EC/OC analysis:  Solvent extraction: determines the soluble organic fraction (SOF) of filter-collected PM  Thermal analysis: Firstly, the sample is heated in an inert atmosphere (>600 ºC), to volatilize organic material, which is subsequently oxidized and registered as OC; Secondly, the remaining sample is again heated, but this time in an oxygen environment, and the evolved CO2 is attributed to EC  For diesel exhaust PM (Japar et al, 1984), two methods have good agreement, but the EC/OC split is recognized to be operationally defined.

University of Wisconsin -- Engine Research Center slide 14 Next generation diesels  Fuel/lube oil modification:  Fuel: Low sulfur content: reduce PM emissions and enable the aftertreatment that vulnerable to sulfurate Change of the organic content : lower aromatic content lead to less PM emissions  Lube oil: Reduction in sulfur and ash