Using NCSA's SGI Origin2000 supercomputer, Madnia's work at the Computational Fluid Dynamics Laboratory at SUNY-Buffalo focuses on understanding flame-vortex interaction. This interaction causes pockets of reactants and products to swirl around flames in tornadoes of current and heat. These tornadoes, called vortical structures, are thought to be the dominant force driving turbulence in combustion.

"In most combustion systems, like aerospace propulsion, industrial furnaces, and power plants," Madnia says, "turbulence plays a key role in the mixing and reactions within the flames." Modeling vortical structures gives Madnia a better understanding of the ways turbulence influences the chemistry of burning fuels. This knowledge will help him, and other researchers, strike a very exacting balance in designing combustion systems. They will be able to find the most efficient flow of fuel for a given system.

Vortical structures are often affected by the method used to introduce fuel into a combustion chamber. For instance, when fuel is injected from a circular orifice, a donutlike shape develops in the fuel. This shape is called a vortex ring, and Madnia studies how a vortex ring forms when a hydrocarbon-based fuel combusts in air.

Using a model consisting of 49 chemical species and 277 reversible elementary reactions, his simulations predict the different ways the flame is created and how it interacts with the vortex ring of fuel. The result is a library of flames.

Some simulations are flames that are rich in methane, others are lean. Some flames create large amounts of polluting nitrogen oxide and soot, others produce very little. For example, one variation models a flame that ignites in the wake of a fully formed vortex ring of fuel. As this flame burns, the heat it releases significantly distorts the vortex ring. By the end of the burn, the ring itself is almost destroyed. (See Figure 1.)

In another variation, the temperature of the entire system is increased, significantly altering its ignition dynamics. This time, the ring catches fire as it's being formed, so less heat is released and the vortex ring of fuel is less distorted. (See Figure 2.)

Simulations like these, Madnia says, show how to alter a flame's characteristics to create more or less heat and less pollution. They let scientists tinker with ways to create cleaner flames.