In this 13-part series of articles, The Combustion Institute recognizes the 2021Distinguished Papers selected from among the scientific papers presented during the 38th International Symposium on Combustion. Congratulations to Robert E. Ferguson, Alan A. Esparza, and Evgeny Shafirovich for winning the DPA in the Spray, Droplet, and Supercritical Combustion colloquium. 

In their seminal paper, Combustion of aqueous HAN/methanol propellants at high pressures, Ferguson, Esparza, and Shafirovich provide new insights into the effects of pressure on the combustion of aqueous HAN/methanol propellants. Their research is most beneficial to rocket engine and spacecraft developers: Most satellites and spacecraft are equipped with propulsion systems that use extremely toxic hydrazine as a monopropellant. Due to environmental concerns and economic stimuli, “greener” monopropellants are being investigated; in particular, they researched hydroxylammonium nitrate (HAN)-based alternatives because of their potential safety and performance benefits. 

In the search for greener monopropellants, scientists have combined the fuel additive methanol with HAN solutions. However, the effects of pressure on the combustion of this propellant are poorly understood, especially regarding the fluctuation of burning rates as pressure increases. Ferguson, Esparza, and Shafirovich’s paper advances the understanding of this complex interplay between physical and chemical processes during the high-pressure combustion of HAN-based propellants. Specifically, they saw a sharp transition in burning rate at a specific pressure range, a crucial observation which must be accounted for in the design of rocket engines using this or similar propellants. After determining that pressure does not affect the chemistry of HAN decomposition, they were able to conclude that this observed transition was a result of the formation of a supercritical fluid at high pressures.  

These findings will facilitate the design and optimization of higher performance rocket engines that use safer monopropellants. Future spacecraft and rocket engines using green monopropellants will be safer and have lower operating costs during launch pad operations. Moreover, green monopropellants will also provide improved thrust for longer periods. 

This team’s research was conducted at The University of Texas at El Paso (UTEP). Experiments were conducted in the laboratories of UTEP’s Aerospace Center, both on campus and in Fabens, TX, just east of El Paso.  

Over 1,700 papers were submitted to the 38th International Symposium on Combustion. All papers were categorized into one of 13 colloquia, and then distributed to colloquium coordinators and co-chairs. Each paper was reviewed by at least three qualified individuals from a pool of over 1,000 peer scientific reviewers. Less than 50 percent of the papers submitted are accepted for presentation.  

Following the symposium, one paper presented in each colloquium is awarded the distinction of Distinguished Paper.  Visit hereto view the presentation. The 13 Distinguished Papers undergo committee review for consideration for the Silver Combustion MedalA paper selected for this honor exemplifies quality, achievement, and significance to advance a field of combustion science, and will be awarded during the 39th International Symposium in Vancouver, Canada.