Effect of Hydrogen and Oxygen Equivalence Ratio on Deflagration-to-Detonation Transition in a Rocket Pre-Detonator

This paper presents optimized detonation through experimentation of varying equivalence ratios to find the most reliable fill fraction that results in detonation. This study aims to create a reliable pre-detonation system to further research in areas including, but not limited to rotating detonation engines and liquid rocket engines. In order to isolate equivalence ratio data set, regulated pressure of gaseous hydrogen (fuel) and oxygen (oxidizer) are set at a constant 140 psi throughout the study. Utilizing solenoid valves and Arduino controls mounted on a mobile test stand with a 0.25” outer diameter, 12” long tube, spark ignition delay, fill fraction, and equivalence ratios were tailored for optimization. Equivalence ratios ranging from 0.7 to 1.3 between fuel and oxidizer were utilized in order to create successful detonations at the lowest possible fill fraction. Acoustics were utilized in this study to confirm detonation success by measuring if the shockwave exceeded a decibel level of 170 dB. The results of the experimentation process determined that 0.3 fill fraction is the necessary length of tube required to reliably produce a detonation. Thus, reliable transition from deflagration-to-detonation can be achieved with 3.6” of tube length. To make this possible, an equivalence of 1.25 proved to be most successful, although there was little to no negative impact until a deviation of 10% from the ratio. Equivalence ratios higher than 1.5 were more reliable than 1 or lower, showing that it is better to increase the flow of fuel over oxidizer if the optimal ratio of 1.25 cannot be achieved. Observations from this study can be used to influence the integration of reliable pre-detonation systems for use in liquid and rotating detonation engines.