Multicyclic detonation initiation studies in valveless pulsed detonation combustors
Abstract
The present work investigates critical issues associated with a multicyclic operation of the valveless PDC. The first experimental investigation studied internal flow behavior associated with the fill and purge processes through combustion diagnostics outside of a detonation tube during a multicyclic PDC operation. Leakage of the combustible mixture was observed due to flow stratification created during the fill and purge processes. The flow stratification also has an impact on the local equivalence ratio leaving some combustion products from the previous cycle in the detonation tube which could affect the multicyclic operation of the PDC. The second experimental investigation was conducted to design and develop a PDC with the total absence of mechanical valves. The suggested configuration was based on a fluid-diode concept and flame stabilization analysis which provide an innovative scheme to operate in valveless mode. There are two critical waves generated initially to operate the PDC in valveless mode. After initiation of the spark plugs, there is a compression wave propagating towards the thrust surface which makes the inlet section pressurized while a deflagration wave propagates toward the detonation tube exit initiating the DDT process. The first reflected characteristic appears after the detonation wave front reaches the product-air interface which starts to depressurize the inlet section making the gasdynamic valve start to open. Operating frequency of valveless PDC is dependent on the size of combustor and the manifold configuration. In order to obtain a detailed understanding of flame the acceleration process leading to detonation initiation, flow visualization experiments were conducted in a rectangular detonation tube equipped with two dimensional obstacles. The flow visualizations were conducted via schlieren photography showing that the flame accelerator provides 1) production of various scale of turbulence, 2) enhancement of shock-flame interaction and 3) forced ignition by reflected shock over the obstacle and the detonation tube. These mechanisms of the flame acceleration process could provide how to optimize the flame accelerator minimizing pressure loss which deteriorates the overall performance of the PDC based system.
Degree
Ph.D.
Advisors
Heister, Purdue University.
Subject Area
Aerospace engineering
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