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Combustion characteristics in a non-premixed cool-flame regime of n-heptane in microgravity
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Takahashi, Fumiaki Hicks, Michael C. Katta, Viswanath R. |
| Copyright Year | 2015 |
| Description | A series of distinct phenomena have recently been observed in single-fuel-droplet combustion tests performed on the International Space Station (ISS). This study attempts to simulate the observed flame behavior numerically using a gaseous n-heptane fuel source in zero gravity and a time-dependent axisymmetric (2D) code, which includes a detailed reaction mechanism (127 species and 1130 reactions), diffusive transport, and a radiation model (for CH4, CO, CO2, H2O, and soot). The calculated combustion characteristics depend strongly on the air velocity around the fuel source. In a near-quiescent air environment (< or = 2 mm/s), with a sufficiently large fuel injection velocity (1 cm/s), a growing spherical diffusion flame extinguishes at â1200 K due to radiative heat losses. This is typically followed by a transition to the low-temperature (cool-flame) regime with a reaction zone (at â700 K) in close proximity to the fuel source. The 'cool flame' regime is formed due to the negative temperature coefficient in the low-temperature chemistry. After a relatively long period (â18 s) of the cool flame regime, a flash re-ignition occurs, associated with flame-edge propagation and subsequent extinction of the re-ignited flame. In a low-speed (â3 mm/s) airstream (which simulates the slight droplet movement), the diffusion flame is enhanced upstream and experiences a local extinction downstream at â1200 K, followed by steady flame pulsations (â0.4 Hz). At higher air velocities (4-10 mm/s), the locally extinguished flame becomes steady state. The present axisymmetric computational approach helps in revealing the non-premixed 'cool flame' structure and 2D flame-flow interactions observed in recent microgravity droplet combustion experiments. |
| File Size | 1542185 |
| Page Count | 10 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_20150018397 |
| Archival Resource Key | ark:/13960/t3jx3ck9j |
| Language | English |
| Publisher Date | 2015-05-17 |
| Access Restriction | Open |
| Subject Keyword | Diffusion Flame Negative Temperature Coefficient Pulsating Flames Fuel Combustion Diffusion Flames Heptanes Chemical Reactions Flame Propagation Drops Liquids Air Flow International Space Station Gaseous Fuels Gravitational Effects Combustion Temperature Extinguishing Microgravity Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
