Experimental study on end-gas autoignition and detonation under different flame velocities of n-heptane in confined chamber

Abstract

<p indent="0mm">Detonation is a special type of combustion phenomenon in engineering under extreme conditions and is the main bottleneck that restricts further improvement in the thermal efficiency, emission, and fuel consumption of an engine in an engine-downsizing process. To best understand the detonation phenomenon, an experiment that investigates the influence of flame velocity on end-gas autoignition and detonation is carried out in a constant-volume combustion chamber equipped with different perforated plates, which uses n-heptane fuel. First, different flame velocities are induced under the same oxygen concentration by installing perforated plates with different porosities. The results show that all normal combustion modes occur under low oxygen concentration. Meanwhile, under high oxygen concentration, the intensity of the shock waves is enhanced with the increase in the flame velocity, which promotes the transition of the combustion modes from normal combustion to end-wall and two-point autoignition. Then, double-perforated plates are used to further accelerate the flame to investigate the difference in the autoignition conditions under different acceleration conditions. We find that a higher flame velocity can induce end-gas autoignition under a low oxygen concentration. Finally, a comparison of the combustion modes under different conditions using the same flame velocity reveals that the reactivity of the mixture also significantly influences autoignition.