Fuel unsaturation effects on NOx and PAH formation in spray flames. (15th November 2015)

• Record Type: Journal Article
• Authors: Fu, Xiao; Aggarwal, Suresh K.
• Is Part Of: Fuel. Volume 160(2015)
• Page Start: 1
• Page End: 15
• Publication Date: 2015-11-15
• Subjects: Fuel unsaturation -- NOx and PAH emissions -- N-heptane and 1-heptene spray flames -- 3D simulations; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2015.07.075
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: 3-D, transient, turbulent spray flame simulations performed. Reduced mechanism developed and validated for the ignition and combustion of n-heptane and 1-heptene. Spray vaporization and combustion models validated using Sandia data. Effect of fuel unsaturation on NO x and PAH emissions examined. Reaction path analysis performed to examine the increased PAH formation in 1-heptene flames. Abstract: The effect of fuel unsaturation on NO x and PAH formation in spray flames is investigated at diesel engine conditions. The directed relation graph methodology is used to develop a reduced mechanism starting from the detailed CRECK mechanism (http://creckmodeling.chem.polimi.it/index.php/current-version-kinetic-mechanisms/low-and-high-temperature-complete-mechanism ). The reduced mechanism and spray models are validated against the shock tube ignition data and high-fidelity, non-reacting and reacting spray data from the Engine Combustion Network (ECN). 3-D simulations are performed using the CONVERGE software to examine the structure and emission characteristics of n-heptane and 1-heptene spray flames in a constant-volume combustion vessel. Results indicate that the combustion under diesel engine conditions is characterized by a double-flame structure with a rich premixed reaction zone (RPZ) near the flame stabilization region and a non-premixed reaction zone (NPZ) further downstream. Most of NO x is formed via thermal NO route in the NPZ, while PAH species are mainly formed in the RPZ. A small amount of NO is also formed via prompt route in the RPZ, and via N2 O intermediate route in the region outside NPZ, and via NNH intermediate route in the region between RPZ and NPZ. The presence of a double bond leads to higher flame temperature and thus higher NO in 1-heptene flame than that in n-heptane flame. It also leads to the increased formation of PAH species, implying increased soot emission in 1-heptene flame than that in n-heptane flame. Reaction path analysis indicate that the increased formation of PAH species can be attributed to the significantly higher amounts of 1, 3-butadiene and allene formed due to β scission reactions resulting from the presence of double bond in 1-heptene.