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Internal Combustion Engines

Real-Time Measurements of Engine-Out Trace Elements: Application of a Novel Soot Particle Aerosol Mass Spectrometer for Emissions Characterization

[+] Author and Article Information
E. S. Cross, J. F. Hunter

 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

A. Sappok

 Sloan Automotive Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139

E. C. Fortner, J. T. Jayne, W. A. Brooks, T. B. Onasch, D. R. Worsnop

 Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA 01821

V. W. Wong

 Sloan Automotive Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139

A. Trimborn

 Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA 01821; AeroMegt GmbH, Hilden 40723, Germany

J. H. Kroll

 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

J. Eng. Gas Turbines Power 134(7), 072801 (May 23, 2012) (10 pages) doi:10.1115/1.4005992 History: Received October 18, 2011; Revised October 22, 2011; Published May 23, 2012; Online May 23, 2012

Lubricant-derived trace element emissions are the largest contributors to the accumulation of incombustible ash in diesel particulate filters (DPF), eventually leading to filter plugging and an increase in engine fuel consumption. Particulate trace element emissions also pose adverse health effects and are the focus of increasingly stringent air quality regulations. To date, the rates and physical and chemical properties of lubricant-derived additive emissions are not well characterized, largely due to the difficulties associated with conducting the measurements. This work investigated the potential for conducting real-time measurements of lubricant-derived particle emissions. The experiment used the Soot Particle Aerosol Mass Spectrometer (SP-AMS) developed by Aerodyne Research to measure the size, mass and composition of submicron particles in the exhaust. Results confirm the ability of the SP-AMS to measure engine-out emissions of calcium, zinc, magnesium, phosphorous, and sulfur. Further, emissions of previously difficult to detect elements, such as boron, and low-level engine wear metals, such as lead, were also measured. This paper provides an overview of the results obtained with the SP-AMS, and demonstrates the utility of applying real-time techniques to engine-out and tailpipe-out trace element emissions. Application of the SP-AMS for engine exhaust characterization followed a two-part approach: (1) measurement validation, and (2) measurement of engine-out exhaust. Measurement validation utilized a diesel burner with precise control of lubricant consumption. Results showed a good correlation between CJ-4 oil consumption and measured levels of lubricant-derived trace elements in the particle phase. Following measurement validation, the SP-AMS measured engine-out emissions from a medium-duty diesel engine, operated over a standard speed/load matrix. This work demonstrates the utility of state-of-the-art online techniques (such as the SP-AMS) to measure engine-out emissions, including trace species derived from lubricant additives. Results help optimize the combined engine-lubricant-aftertreatment system and provide a real-time characterization of emissions. As regulations become more stringent and emission controls more complex, advanced measurement techniques with high sensitivity and fast time response will become an increasingly important part of engine characterization studies.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Ion signal intensities measured at nominal m/z = 68 showing a peak corresponding to the Zn68 + isotope at 67.9248 amu and a hydrocarbon fragment C5 H8 + at 68.0626 amu. The residual between the peak fit and raw data is also plotted in the figure.

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Figure 2

Empirical measurement of the isotopic abundance for each major isotope of zinc

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Figure 3

Empirical measurement of isotopic abundance for boron

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Figure 4

Specific lubricant-derived ash species ion signal intensities as a function of increasing CJ-4 oil injection rate. SMPS-measured size distribution is displayed as an image plot colored by the number concentration in the lower panel of the plot.

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Figure 5

SMPS volume distributions obtained by varying the sheath flow rate in the size-selecting DMA to systematically control the total mass concentration of particles sampled with the SP-AMS. The bi-modal distribution results from doubly charged particles (with equivalent mobility to singly charge 100 nm particles) being transmitted through the size-selecting DMA.

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Figure 6

Ion response for calcium, zinc, phosphorus and sulfate species as a function of total particle mass measured with the SMPS

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Figure 7

SP-AMS measured mass concentrations for zinc, calcium and phosphorus/phosphate as a function of calculated mass concentrations for each component based on elemental analysis of CJ-4

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Figure 8

(a) SP-AMS measured calcium and phosphorus/phosphate and (b) sulfate and magnesium as a function of zinc. All ion signals are normalized to the SMPS measured mass concentration. Marker color and size indicate engine speed and load, respectively.

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Figure 9

Average mass spectrum measured during high speed/high load engine operation. The upper panel (a) plots all ion signals and is dominated by hydrocarbon fragments (Cx Hy , green) and black carbon (Cx , black). The lower panel (b) displays ion fragments associated with trace elements from the CJ-4, fuel, and engine wear.

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Figure 10

SP-AMS measurements of potassium and sodium as a function of zinc across all engine speed and load conditions studied. All ion signals are normalized to the SMPS measured mass concentration. Marker color and size indicate engine speed and load respectively.

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Figure 11

SP-AMS measurements of lead and iron as a function of zinc across all engine speed and load conditions studied. All ion signals are normalized to the SMPS measured mass concentration. Marker color and size indicate engine speed and load respectively.

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Figure 12

SP-AMS measurements of hydrochloric acid and sulfuric acid as a function of zinc across all engine speed and load conditions studied. All ion signals are normalized to the SMPS measured mass concentration. Marker color and size indicate engine speed and load respectively.

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Figure 13

Configuration of accelerated ash loading system and Cummins ISB exhaust sampling apparatus. Measurements discussed in this work were all taken from sampling position ‘A’ located upstream of the DPF.

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