For more than a million years, humans have been using fire. Surprisingly, there are still things we don't know about flames. Scientists at DOE’s National Energy Technology Laboratory are using particle image velocimetry to understand why and how flames oscillate as their fuel-to-air consumption ratio is decreased. When new fuel-flexible gas turbines are designed run at these "lean-burn" conditions, they will produce electricity with less pollution. That's good. But flame oscillations could set up vibrations in the machinery -- vibrations strong enough to tear a $100 million engine apart. That's bad. Models incorporating NETL’s research results could help solve the problem.