EXPERIMENTAL RESEARCH INTO THE INFLUENCE OF TWO­SPARK IGNITION ON THE DEFLAGRATION TO DETONATION TRANSITION PROCESS IN A DETONATION TUBE

The paper reports a study into the initiation of detonation in pulse detonation engines. The chosen direction to resolve this issue is the use of detonation tubes with multifocal ignition. We applied two spark discharges as a source of ignition, which ignited synchronously. The spark discharges were ignited at a distance, which provided for the intensive gas-dynamic interaction between the discharges. The interaction implied a collision between shock waves generated by the spark discharges. As a result, the growth in temperature of gas was ensured in the region between spark intervals, due to a collision between the oncoming shock waves. The influence of dual spark ignition on the time and length of the section where deflagration transfers into detonation along a detonation tube was studied by comparing the transition parameters for cases of single-spark and dual spark ignition all other conditions for research being equal. The study involved a detonation tube with a length of 2.3 m and an inner diameter of 22 mm. Spark plugs were located at the closed end of the tube. We applied a stoichiometric mixture of propane with oxygen, diluted with nitrogen by 50 % at the initial pressure in the mixture equal to 50 kPa. To register the time of propagation of the flame front and to measure the process rate, the tube was equipped with 22 ionization sensors. Distance between the sources of ignition was 6 mm. Length of the discharge interval at each source of ignition was 2.5 mm. Sources of ignition in the form of spark plugs were connected to high-voltage units with a total discharge energy of 3.3 J. The results of our study helped establish a reduction in the distance of deflagration to detonation transition by 1.6…2 times, and in the time of transition ‒ from 3.9 ms to 1.2 ms for the case of the transition from single-spark to dual spark ignition. The results obtained could be used when designing ignition systems for pulse detonation engines