Research On Operational Characteristics Of A Valveless Self Excited Pulse Combustor Of The Helmholtz-type

Pulse combustion as an advanced combustion has many advantages over conventional combustion, such as high combustion efficiency, low pollution emissions. However, pulse combustion mechanism is very complex, the major bottleneck for popularization and application of conventional pulse combustors of the Helmholtz-type with mechanical or aerodynamic valves is the self-priming mode of gas supply, which results in low power operation and low load regulation. In this paper, the idea of a valveless self-excited pulse combustor of the Helmholtz-type, using continuously forced air and fuel supply, which makes use of the combustion chamber acoustic structure directly, was presented. The advantages of this pulse combustor are self-adjusted for the equilibrium pressure, operation reliability, high volumetric heat load, wide range of heat load regulation which may realize in large scale pulse combustors. The main objective of the paper is to experimentally and theoretically study the operational characteristics of the valveless self-excited pulse combustor of the Helmholtz-type, such as frequency, pressure, heat transfer, operation stabilization and adjusting methods. The main results are as follows:(1) The experimental system of a valveless self-excited pulse combustor of the Helmholtz-type which can produce pulse combustion with continuously air and fuel supply and directly making use of the Helmholtz resonant acoustic structure of the combustor was developed. Self-adjusted for the heat load of the combustor can be achieved by this method of air and fuel supply. Experimental results show that the pulse combustor designed in this paper can produce stable pulse combustion, and the pressure amplitude of pulse combustion is higher than that of conventional pulse combustor at the same conditions.(2) The operational characteristics of the valveless self-excited pulse combustor of the Helmholtz-type, such as frequency, pressure and heat transfer were theoretically and experimentally investigated. The relations of the structure of the combustor, excess air coefficient, heat release with pressure and frequency were obtained. The validity of the theoretical analysis was confirmed by experimental investigation on the operational characteristics of the pulse combustor with single tailpipe and multiple tailpipes. The heat transfer coefficient of pulsating flow is about 2-5 times of that of stable flow according to the quantitative comparison of pulsating flow and stable flow in single tailpipe and multiple tailpipes at the same Re number. The pulsating flow characteristics in tailpipe were described and the reason of the enhancement in heat transfer was explained by the simulation results of pulsating flow in tailpipe based on the experimental working condition.(3) A mathematical model for the stability of the valveless self-excited pulse combustor of the Helmholtz-type was established. The model considered the influences of the mode of reactants supply, the chemical reaction in the combustion chamber, radiation and convection heat loss of the combustion chamber wall, as well as fluid density changes in the tailpipe on stable operation of pulse combustion. The calculation results of the model within the range of experimental condition were compared with the experimental data and the conditions for stable operation of the valveless self-excited pulse combustor of the Helmholtz-type were obtained(4) Adjusting methods for pulse combustion without changing the structure of the combustor were presented. A decoupling chamber pressure adjusting system was set up at the end of the self-excited pulse combustor tailpipe. The effects of the decoupling chamber pressure variation on the operational characteristics of the pulse combustor were experimental studied. The regulations between each parameter were analyzed by acoustic theory. The method for enhancing heat transfer of the pulse combustor was proposed. Frequency hopping phenomena that may occur during the operation in the self-excited pulse combustor was experimentally studied. The regulation of operating frequency with power and equivalence ratio was measured; the mechanism of the phenomenon was explained by Rayleigh criteria. The effective methods for adjusting the pulse frequency hopping were presented.