detonation wave parameters in a variable cross section channel in gas mixture of methane with oxygen and nitrogen

Propagation of the detonation wave in gas mixtures of methane with oxygen in a channel of variable cross section was studied experimentally. To conduct these investigations a special detonation combustion chamber comprising sections of various diameters has been designed. In the section of detonation wave formation a combustible mixture was ignited. After that, a flame front accelerated till the formation of detonation. At the exit from the combustion chamber there was an outlet conical section. In conducted experiments the toe-in angle was equal to 3 °. The combustion chamber was open-ended. So an initial pressure inside the combustion chamber prior to each experiment was equal to the atmospheric pressure. The initial temperature was ambient one of 300 K. As a diagnostics, piezoelectric sensors of pressure and photo diodes were used.

Detonation initiation was accomplished by spark gap. For this pulse generator I-1 was used. Spark energy did not exceed 0.1 J and was much lower than the energy of the direct initiation of detonation.

Deflagration-to-detonation transition was occurred. A composition of the mixtures was selected in such a way that the detonation cell width was several times smaller than the diameter of the channel. The mixture was composed by the partial pressures of methane, oxygen, and nitrogen and was kept in the 40 l tank within 24 hours under 5-8 atm. pressure. Возникновение де- тонации возникало вследствие перехода горения в детонацию.

The aim of this study was to determine the parameters of a detonation wave in a channel of variable cross section in the methane-oxygen mixture. The influence of nitrogen impurities on the cell size and the speed and pressure of the detonation wave was investigated.

The waves velocities and peak pressures at the front of the detonation wave were measured depending on composition, including the presence of nitrogen. The sizes of the detonation cells were measured using smoked foil mounted inside the channel.

The effect of the interference of the shock waves in a conical section was studied.

Diagrams of the shock waves, flame fronts, and detonation waves in the combustion chamber depending on the mixture composition are presented. The paper gives data on some compositions of mixtures.