4.8 Article

Load-Dependent Emission Factors and Chemical Characteristics of IVOCs from a Medium-Duty Diesel Engine

Journal

ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 49, Issue 22, Pages 13483-13491

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.est.5b03954

Keywords

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Funding

  1. USEPA [RD834560]
  2. Camille and Henry Dreyfus Foundation
  3. MIT Consortium
  4. Caterpillar
  5. Chevron/Oronite
  6. Ciba Special Chemicals
  7. Cummins
  8. Detroit Diesel
  9. Infineum
  10. Komatsu
  11. Lutek
  12. NGK
  13. Sud-Chemie
  14. U.S. Department of Energy Office of Energy Efficiency and Renewable Energy: Oak Ridge National Laboratory
  15. Valvoline

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A detailed understanding of the climate and air quality impacts of mobile-source emissions requires the characterization of intermediate-volatility organic compounds (IVOCs), relatively-low-vapor-pressure gas-phase species that may generate secondary organic aerosol with high yields. Due to challenges associated with IVOC detection and quantification, IVOC emissions remain poorly understood at present. Here, we describe measurements of the magnitude and composition of IVOC emissions from a medium-duty diesel engine. Measurements are made on an engine dynamometer and utilize a new mass-spectrometric instrument to characterize the load dependence of the emissions in near-real-time. Results from steady-state engine operation indicate that IVOC emissions are highly dependent on engine power, with highest emissions at engine idle and low-load operation (<= 25% maximum rated power) with a chemical composition dominated by saturated hydrocarbon species. Results suggest that unburned fuel components are the dominant IVOCs emitted at low loads. As engine load increases, IVOC emissions decline rapidly and become increasingly characterized by unsaturated hydrocarbons and oxygenated organics, newly formed from incomplete combustion processes at elevated engine temperatures and pressures. Engine transients, including a cold-start ignition and engine acceleration, show IVOC emission profiles that are different in amount or composition compared to steady-state combustion, underscoring the utility of characterizing IVOC emissions with high time resolution across realistic engine operating conditions. We find possible evidence for IVOC losses on unheated dilution and sampling surfaces, which need to be carefully accounted for in IVOC emission studies.

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