Custom Reduced Mechanisms for CFD
Scramjet engines, which likely will provide the next generation propulsion capability, operate at extremely high temperatures and air velocities, conditions that are very difficult to reach in a laboratory environment. Facilities capable of testing these engines are limited in number and very expensive to run. A much more efficient approach to engine design is to employ reacting flow Computational Fluid Dynamics (CFD) to carry out combustion modeling to predict engine performance. The combustion of hydrocarbon-based fuels is a complex process resulting in detailed kinetic mechanisms typically containing hundreds of species and thousands of reactions to obtain accurate results over wide ranges of conditions. It is impossible to employ these full hydrocarbon kinetic mechanisms directly in a reacting flow CFD code due to unacceptably long solution times. To reduce computer time, simplified global mechanisms using severely reduced species sets and non-integer concentration exponents are commonly used. Unfortunately, these mechanisms are not accurate and can also introduce significant numerical difficulties and instabilities into the reacting flow CFD solution process.
Reaction Systems has developed a unique approach that we call "Roadrunner Kinetics" to reduce complex kinetic mechanisms, allowing us to identify and retain only the most important species and reactions. Roadrunner Kinetics has delivered proven speed-up factors of up to 200 times or more with respect to the initial full detailed mechanism while also preserving good accuracy as shown in our website presentation. This methodology is also very flexible in that it also allows us to retain selected minor species of interest such as NO and NO2 to model NOx pollutant emissions, for example. Using this approach, we have developed reduced kinetic mechanisms for the combustion of fuels such as JP-7, methane, and ethylene with air as well as the hypergolic combination of monomethylhydrazine and red fuming nitric acid (MMH/RFNA). Moreover, "Roadrunner Kinetics" is automated to allow us to quickly develop custom mechanisms tailored for specific applications and conditions of interest at minimal cost to the customer.