A Most Reactive Mixture Analysis of Ozone- and Temperature-Enhanced n-Heptane Droplet Autoignition and Cool Flame Burning in Microgravity

ABSTRACT

Numerical simulations are used to study effects of ozone (O₃) and thermal enhancement on autoignition and subsequent burning characteristics of isolated n-heptane droplets in microgravity conditions. Particular focus is given to effects of O₃ on low temperature combustion, or cool flames. Levels of ambient O₃ mole fraction and ambient temperature are varied from 0 to 0.03 and 400 K to 750 K, respectively. A comparison between two low temperature chemistry enhancement strategies – O₃ addition and temperature increase – are investigated on an equivalent energy addition basis to evaluate relative effects on combustion characteristics. Results of this study are analyzed using physical and mixture fraction approaches because of unique insights offered by these frameworks. Ignition and ensuing flame propagation are investigated via a most reactive mixture analysis, evaluated using homogeneous reactor simulations of mixture compositions and temperatures surrounding the droplet. Lastly, a Damköhler number analysis is performed to explore oscillatory ignition dynamics.

KEYWORDS:

• Microgravity
• droplet combustion
• cool flame
• ozone enhancement
• thermal enhancement
• n-Heptane

Disclosure statement

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.

Additional information

Funding

This research is supported by the U.S. National Aeronautics and Space Administration (NASA) under award No. NNX16AQ95A.