Shock Tube Experimental Studies on CH/Visible Light/Pressure as Ignition Delay Criteria

Ignition delay time is a key parameter in evaluating the ignition processes of fuel mixtures. By using shock tube experiments, this paper compares three ignition criteria, namely, CH*, visible light, and pressure under high and low diluent conditions, respectively. Main comparison principles include signal-to-noise ratio, readability of signal curves, and model validation. Different types of CH* and visible light response curves are displayed. Experimental results indicate that CH* is the most appropriate ignition criterion under high diluent conditions. Visible light is the second most suitable choice, whereas pressure is unsuitable as the ignition criterion. Under low diluent conditions relevantly, CH*, visible light, and pressure can all be used as the ignition criteria. Moreover, visible light signals generally occur later than CH*, and the visible-light reading results are correspondingly larger, whereas an overlarge gain factor can result in smaller visible-light reading results than those of CH*. In summary, the optimum sequence of three ignition criteria decreases in the order of CH*>visible light>pressure under different diluent conditions.