Unsteady Nozzle Design for Pulse Detonation Engines

A quasi-one-dimensional, Euler model with detailed finite-rate chemistry is used to conduct a parametric assessment of area ratio effects on the performance of unsteady nozzles in a pulse detonation engine (PDE). Using results from the parametric study, design criteria are suggested for evaluating optimal contraction and expansion nozzle area ratios. In particular, a method using simple isentropic analysis is revealed for identifying optimal expansion area ratio for a given tube configuration. To validate the parametric analysis, three nozzle sections are tested in the Stanford experimental PDE facility. Time resolved thrust and specific impulse (Isp) measurements are made for each nozzle and compared to simulated results. Additionally, Schlieren imaging is used to investigate the blowdown gasdynamics in each of the three nozzles. Comparisons between simulated and measured impulse data are addressed using insights gathered from the flow visualization. Resulting analysis indicates that multi-dimension wave phenomena are important for nozzles with converging sections. Over-prediction of Isp by the model is attributed to an inability to accurately capture the pressure in the plateau region, as well as the inability to accurately model the DDT process. The relative contribution of each of these effects is quantified. Experimental measurements validate trends observed in the parametric study and reveal that an appropriately optimized diverging nozzle produces the largest single-cycle Isp augmentation. The applicability of single-pulse results to realistic multi-cycle engines is discussed, with emphasis on the importance of maintaining high reactant fill pressure between multi-pulse cycles. To this effect, the inclusion of a minimal throat section is addressed as a plausible solution despite its deleterious impact on single-cycle performance.