A NIST Kinetic Data Base for PAH Reactions and Soot Particle Inception During Combustion

Dr. Wing Tsang | National Institute of Standards and Technology (NIST)

WP-1198

Objective

Federal and state environmental agencies have been authorized to regulate particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) emitted from local sources. Military bases and local airports are increasingly being identified as point sources of these pollutants and are being held accountable for their PM and PAH emissions. In addition, government personnel are exposed to soot particles and PAH emitted from military diesel and gas turbine engines. This is a concern because fine particles are a health hazard, and certain PAHs are carcinogenic. Motivated by these factors, the military and their engine manufacturers are working to reduce PM and PAH formation in existing and future engines.

The objectives of this project were to develop a National Institute of Standards and Technology (NIST)-quality, gas-phase chemical kinetic data base that describes the transformation of fuel molecules to their desired end products of carbon dioxide and water, as well as to undesired PAH compounds, and to develop the first quantitative soot particle inception model based on experiments.

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Technical Approach

Existing data was compiled, evaluated, and updated using NIST CHEMRATE, a user-friendly reaction rate theory program, to determine which kinetic rates would potentially be measured. Rates were further identified for fuel cracking and reactions involving PAHs with three or fewer rings using a shock tube and for reactions involving early soot or PAHs with three or more rings using a well stirred reactor. A particle inception model was developed based on experiments performed in diffusion flames and in a well-stirred reactor. Both atmospheric pressure work involving gaseous fuels and high pressure work involving liquid fuels were completed. The data base and model developed under this project were tested in the Air Force Research Laboratory UNICORN (Unsteady Ignition and Combustion with Reactions) computer code.

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Results

Refer to http://kinetics.nist.gov/CKMech/ for a listing of reactions in the data base and a listing of other data bases that are useful for making comparisons. The data base developed in this project is important for the description of PAH and soot formation, given that such phenomena can only be formed as the combustion mixture becomes richer. Fifty-one unimolecular decomposition and five isomerization reactions and 24 species processes were integrated into a heptane combustion data base consisting of 347 species and 1745 reactions. In addition, the reactions leading to PAH formation from small unsaturated compounds were captured in the new data base. This database permits the simulation of combustion phenomena across the entire range of stoichiometries.

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Benefits

The PAH/particle inception model developed in this study will allow the military to streamline PM mitigation strategies using computer-based engine design and fuel additive development.

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Points of Contact

Principal Investigator

Dr. Wing Tsang

National Institute of Standards and Technology (NIST)

Phone: 301-975-2507

Fax: 301-975-3670

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