I am simulating unsteady combustion with coupled solver. At the begining, I set Courant as 0.1 and time step as 0.01. The solution converged slowly. To accelarate the convergence, I change Courant as 2. But the time becomes 0.02s. And if I change Courant as 10, the flame will extinguish. How do I change the Courant and ensure the flame not to extinguish.

i HAD SIMILAR PROBLEM WITH MY MODEL TOO, I GUESS ITS LIKE THIS.

BY DEFINITION COURANT NUMBER IS DIRECTLY PROPORTIONAL TO TIME STEP DT, SO IF YOU REDUCE COURANT NUMBER TIME STEP REDUCES AND VICE VERSA, WHICH MEANS THAT AT HIGH COURANT NUMBERS, THE SOLUTIONS PROCEEDS AT A FASTER RATE AND THIS IS WHY YOU SEE YOUR FLAME GETTING EXTINGUISHED, I AM SURE IF YOU REDUCE COURANT NUMBER TO 0.001, YOU WONT SEE ANY COMBUSTION EITHER. I GUESS YOU SHOULD OPTIMIZE COURANT NUMBER WITH TIME STEP TO AN INSTANT WHEN YOU GET THE RESULTS MATCHING WITH ACTUAL EXPERIMENTAL PHENOMENA, I AM NOT SURE IF THIS OF ANY HELP OR NOT, BUT THIS IS ALL I COULD KNOW SO FAR. WISH YOU GOOD LUCK