Experimental Investigation On Working Characteristics Of Rotating Detonation Combustor And Its Combination With Turbine

The rotating detonation combustor(RDC),which can be used as the main combustion chamber of the turbine engine,has some advantages in terms of propulsion,structure and performance compared with the combustion chamber of the conventional engine.In this paper,the working characteristics of the RDC were experimentally studied with gaseous fuels and different air injection conditions,and it also established combined structures of an axial-flow turbine with an RDC and a radial-flow turbine with an RDC to study the working characteristics of combustors.Firstly,the working characteristics of the RDC fueled by the hydrogen,ethylene and hydrogen-ethylene-acetylene mixture were studied and the propagation characteristics of the detonation wave under three fuels were compared and analyzed.The results show that the hydrogen and hydrogen-ethylene-acetylene mixture can react with air in the combustion chamber to form a stable detonation wave,and the equivalence-ratio range of stable operation is relative wide.The hydrogen detonation wave can obtain a C-J velocity value of up to 94%,but the mixture fuel is only 67%.The stability of ethylene-air detonation wave in the RDC is less than that of other two fuels,and the combustion modes of acoustics combustion,flast deflagration,stable detonation and detonation to deflagration occur in the combustion chamber.Nextly,experiments were carried out to study on the working characteristics of a RDC under variable air injection conditions.The results show that the stability of detonation-wave pressure and velocity both initially increase and then decrease with the increase of slot width,and it could improve the stability of detonation-wave velocity via increasing the equivalence ratio.There is an optimal air-injection slot width to achieve better performance of the RDC under a same mass flow rate condition.For the structure of combining an RDC and an acentrifugal compressor,the detonation wave can stably propagate for a long time,and the detonation wave pressure increases with the increase of the air-injection area,but it is easy to form intermittence detonation with a larger injection area.The establishment time of detonation wave is related to the concentration of hydrogen and the air-injection aera.The effects of axial-flow turbine on the working characteristics of RDC were studied.Through comparing with the no guide vane tests,the results show there are pressure oscillations in the locations of the front side and back side of the guide vane,which have a same rotating frequency with detonation waves.The oscillation pressures are reduced by 64%after passing through the guide vane.For the guide vane tests,the scope of steady-operation state became narrower than that of the no guide vane,and is mainly affected by the reflected shock wave.For the study on effects of the axial-flow turbine on the working characteristics of the RDC,the detonation wave that can be successfully obtained via ignition methods of spark plug and pre-detonator,but there is an unstable establishment process,and the formation time for the pre-detonatore is shorter than that of the spark plug.The rotating detonation wave successively appears the two-wave state with a same direction,the two-peak wave state,and the state of strong-weak alternation during the formation process.Finally,only one stable detonation wave is formed in the combustor and propagates until the operation off.It also studied the effects of radial-flow turbine on the working characteristics of the RDC.Firstly,the effects of the guide vane on the propagation characteristics of the detonation wave were studied.The structure shows that the velocity of the detonation wave for the guide vane tests is higher than that of the no guide vane tests,the oscillation pressures are reduced by 63% after passing through the guide vane.There is a coupling relationship between velocity fluctuation and pressure fluctuation,and there is a phenomenon of low-frequency pressure fluctuation.For the no guide vane tests,only the two-wave collision mode is obtained for all the equivalence ratios,and the two-wave collision mode is able to propagate for a long duration,but the instability of the collision-point displacement will be formed after the double-wave collision.For the study on the effects of radial-flow turbine on the working characteristics of RDC,for the guide vane tests,the longitudinal pulsed detonation(LPD),single-wave(1-W),double-wave(2-W),three-wave(3-W)and four-wave(4-W)propagation modes of detonation wave appear in the combustor,and it is mainly related to the equivalent ratio.For the no guide vane tests,the combustor only has the 1-W and LPD modes.For the two conditions,the LPD appears with a high equivalence ratio.Based on the working characteristics of the RDC,it is experimentally demonstrated that the combined structure of an axial-flow turbine with an RDC is superior to the combined structure of a radial-flow turbine with an RDC.