Cool Flames Investigation

The objectives of this investigation are to: 1) Examine the combustion behavior of n-dodecane and mixtures of n-dodecane/iso-dodecane at pressures ranging from 0.25 atm to 5 atm. 2) Analyze the effects of helium dilution on cool flame behavior. 3) Examine the behavior of combustion characteristics. 4) Investigate the relationship between droplet size, pressure, and flame extinction, and (5) understand the consequence of soot formation during cool flame combustion.

The Combustion Integrated Rack (CIR) contains the Multi-User Droplet Combustion Apparatus (MDCA) which facilitates the controlled combustion of fuel droplets. A system of gas bottles and fuel syringes delivers the desired gas mixture to the combustion chamber ranging from 0.25 to 0.5 atm. Droplets of fuel are dispensed and suspended between hypodermic needles or tethered using silicon-carbide fibers. A hot-wire igniter is positioned near the droplet for ignition. After ignition the wire is retracted. Fuels observed include n-dodecane, farnesane, and mixtures of n-dodecane/iso-dodecane. Fuels diluted with molecular oxygen, atomic nitrogen, and helium to study the influence on flame extinction and dynamics. Flames were observed with a black-and-white camera for droplet size measurements. A UV camera was used for capturing the OH* radical emissions and flame size. Other high resolution cameras were used for monitoring and documentation. Narrow-band and wide-band radiometers for analyzed flame radiation.

Flame combustion of liquid hydrocarbon fuels such as n-dodecane, n-dodecane/iso-dodecane mixtures, and faresane in microgravity can provide insights into low-temperature chemical kinetics, revealing critical parameters like droplet extinction diameters and flame dynamics that are not observable on Earth.

A basic understanding of cool flames is important for understanding ignition phenomena of practical fuels and fuel additives. Cool flames play a key role in the development and selection of new fuels and the design of advanced engines such as clean, high-efficiency Homogeneous Charge Compression Ignition (HCCI) engines. The research will also help combustion chemists to develop new computational models to compute combustion performance in for many practical applications on earth, including an understanding of how cool flame reactivity determines octane and cetane number for fuels in spark ignition and diesel engines. Cool Flames Investigation (CFI) will provide critical validation for complex chemical kinetic mechanisms, advance the understanding of flame dynamics and instabilities in low-temperature combustion, and support the design of safer spacecraft systems by refining knowledge of combustion in microgravity environments.