Modeling the effects of hydrogen and nitrogen addition on soot formation in laminar ethylene jet diffusion flames May Yen a,⇑ , Vinicio Magi b , John Abraham a,c a School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, United States b School of Engineering, University of Basilicata, Potenza 85100, Italy c Department of Mechanical Engineering, San Diego State University, San Diego, CA 92182, United States highlights  Sooting ethylene/hydrogen/nitrogen flames are simulated with a semi-empirical model.  Predicted results are qualitatively in agreement with experimental results.  Addition of hydrogen/nitrogen to ethylene flames reduces soot mass.  Substitution of hydrogen/nitrogen results in even greater reduction in soot mass. article info Article history: Received 30 April 2018 Received in revised form 25 July 2018 Accepted 28 July 2018 Available online xxxx Keywords: Soot modeling Semi-empirical models Laminar sooting flames Ethylene/hydrogen/nitrogen diffusion flames abstract The effects of adding hydrogen and nitrogen on soot concentration in atmospheric laminar ethylene jet flames are studied computationally and computed results are compared with experimental ones. Two sets of flames are studied: one in which the total volumetric injected flow rate is kept fixed and ethylene is substituted with either hydrogen or nitrogen and the other in which the ethylene volumetric flow rate is fixed but varying amounts of hydrogen and nitrogen are added. A two-equation semi-empirical model is employed to model soot. The model is able to qualitatively predict the measured trends of reducing soot concentration as hydrogen or nitrogen is added to ethylene or substituted. Quantitative agreement is within an order of magnitude and the results are found to depend strongly on the coupling between radiation and soot. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Soot is an important constituent of particulate emissions from combustion devices. Reducing particulate emissions into the atmo- sphere is an imperative as it has been shown to have negative effects on climate change and human health (Melillo et al., 2014; WHO, 2014). For this reason, particulate emissions are regulated by government agencies (EPA, 2016). Soot is primarily a byproduct of fossil fuel combustion. The burning of fossil fuels generates power for transportation, electricity generation, and industrial applications. While there are successful efforts to transition from fossil fuel combustion as a source of energy to renewable non- carbon sources of energy, the combustion of fossil fuels is likely to be the primary source of energy for transportation and electric power generation for the foreseeable future (Coram and Katzner, 2018). Hence, there is a need to understand the mechanisms of soot formation in order to identify ways to reduce its emissions. It is important to recognize that the formation of soot is desired in some combustion applications, e.g. boilers, where efficient radiative heat exchange is critical. Even in such applications, the prevention of the emission of the soot to the environment is criti- cal. Improved understanding of soot formation mechanisms can lead to the development of models for soot formation which can then be employed to develop combustion systems that are more efficient and cleaner. The details of soot formation during gaseous combustion are still the subject of inquiry. It is believed that soot is formed in the fuel-rich regions of hydrocarbon diffusion flames where poly- cyclic aromatic hydrocarbons (PAH) form and grow into increas- ingly larger species through hydrogen abstraction and carbon addition (HACA) until they are large enough to be considered a nascent soot particles (Howard, 1991; Kennedy, 1997). Once a nas- cent soot particle is formed, it continues to grow via the HACA mechanism. Furthermore, soot particles collide and combine to https://doi.org/10.1016/j.ces.2018.07.061 0009-2509/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: myen@purdue.edu (M. Yen). Chemical Engineering Science xxx (2018) xxx–xxx Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces Please cite this article in press as: Yen, M., et al. Modeling the effects of hydrogen and nitrogen addition on soot formation in laminar ethylene jet diffusion flames. Chem. Eng. Sci. (2018), https://doi.org/10.1016/j.ces.2018.07.061