Elsevier

Combustion and Flame

Volume 227, May 2021, Pages 335-345
Combustion and Flame

Amines have lower sooting tendencies than analogous alkanes, alcohols, and ethers

https://doi.org/10.1016/j.combustflame.2021.01.016Get rights and content

Abstract

While the sooting tendencies of regular hydrocarbons, oxygenates, and complex fuel mixtures have been well-studied, far less research has been devoted to analyzing the influence of fuel-nitrogen on soot formation. The effect of nitrogen on soot formation becomes relevant for diesel fuels with nitrogen-containing additives, as well as biomass or biomass-derived fuels, which can contain up to 30% nitrogen-containing compounds by dry weight. To begin closing these gaps in the literature, the sooting tendencies of 14 C4 and C6 amines were measured. Sooting tendencies were quantified by re-scaling relative soot concentrations measured in fuel-doped methane flames into Yield Sooting Indices (YSI). The relative soot concentrations were measured with line-of-sight spectral radiance, and validation experiments confirmed that the presence of nitrogen in the test compounds did not interfere with this diagnostic. All of these amines had lower sooting tendencies than the structurally analogous hydrocarbons and oxygenates. The sooting tendencies of amine isomers with the same chemical formula varied significantly. Secondary amines with linear substituents were found to offer the lowest sooting propensity, while primary amines with branched substituents were observed to yield the largest sooting tendencies. The relationship between sooting propensity and chemical structure of the amines hints at the complex nature of soot formation, and highlights an interesting and unexplored area of combustion chemistry for further studies.

Section snippets

1. Introduction

Emissions of carbonaceous soot particles from combustion devices adversely impact human health and global warming. Ambient particulate matter, of which soot constitutes at least 10% [1,2], is one of the most important causes of reduced global life expectancy, leading to over 3 million deaths worldwide each year [3]. Recent calculations also conclude that soot is a major contributor to global warming, second only to CO2 [4]. As a result, many governments around the world have imposed particulate

2. Methods

In this work, the sooting tendencies of NHCs were quantified by doping a small amount of the test fuel into a nitrogen-diluted methane coflow flame, measuring the luminous signal due to soot, and linearly re-scaling the signal to YSI values [41,42].

3. Results

The aim of this study was to characterize the sooting tendencies of isomeric C4 and C6 amines. We begin by providing evidence that validates the YSI diagnostic in flames doped with NHCs, and then we present the measured YSIs for the amines.

4. Conclusion

In this work, the YSIs of 14 alkyl amines were determined. It was found that line-of-sight spectral radiance is a suitable technique for measuring sooting tendencies of nitrogen-containing hydrocarbons, with negligible error introduced due to the presence of nitrogen in the test compound. The YSIs of amines on the whole were found to be lower than structurally analogous hydrocarbons and oxygenates. Secondary amines with linear alkyl substituents were observed to have the lowest sooting

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Bioenergy Technologies Office (BETO) and Vehicle Technologies Office (VTO) Program Award Number DE-EE0007983. This work is also supported by the National Science Foundation (NSF) under Grant Number CBET 1604983. The XPS and XRF experiments were performed at the Yale West Campus Materials Characterization Core, using the PHI VersaProbe II X-ray

List of electronic supplemental information (ESI) materials

ESI A: A detailed diagram depicting the burner geometry used for the sooting tendency measurements

ESI B: Details on the compounds used in the soot blackness measurements.

ESI C: Details on amines and other nitrogen-containing hydrocarbons used in this study.

ESI D: Maximum LSSR Signal (relative to the undoped flame) from pyridine- and benzophenoneimine-doped flames versus concentration of dopant.

ESI E: LSSR Signal (relative to the average of the undoped flame) from undoped, toluene, and

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