Visualization Research of Nonpremixed Biodiesel/Air Jet Flames Unstable Combustion Process

Based on the image processing technology and the largest Lyapunov exponent, this paper proposes a novel method for quantitative characterization of flame images to reflect flame instability in combustion chamber. The best threshold is obtained by an iterative method of red component to separation flame region. The combustion index is defined as the ratio of proportion of flame pixels to gray standard deviation of flame region for characterization spatial distribution of flame. Unsteady motions of the flames are characterized by the nonlinear time series of combustion index and largest Lyapunov exponent. Results show that the linear relation between combustion index and largest Lyapunov exponent are noticeable with a correlation coefficient of 0.7874 under same work condition. With quantitative research for the relationship between chaos and combustion state, The largest Lyapunov exponent not only can judge whether the flame is nonchaotic or chaotic, the value of it also reflected the combustion state, the chaometry.