Combustion instabilities in gas turbine engines often give rise to acoustic resonances. These resonances occur as manifestations of different acoustic modes, of which a single or multiple modes may be present. In this work, the acoustic behavior of a gas turbine model combustor, developed at DLR Stuttgart by W. Meier et al., was investigated using dimethyl ether (DME). The equivalence ratio and air mass flow rate were systematically varied. The results did not correspond to any one instability mechanism. It is concluded that, in the current burner configuration, integrated-acoustics occur that involve a combination of mechanisms, including a Helmholtz-type resonance from the plenum and convective-acoustic effects. To understand the instability, accurate measurements are needed of the correlation between heat release rate fluctuations and pressure fluctuations. Thus heat release rate must be recorded as a function of time and space. However conventional chemiluminescence offers only a line-of-sight measurement. High-speed formaldehyde planar laser-induced fluorescence was applied to study the motion of flame surfaces in response to the pressure oscillations of the instability. Flame shape has been correlated with instability strength and presence. The flame surface density and surface area fluctuated at the acoustic frequency and displayed motions correlated with the precessing vortex core (PVC) rotation. In nonresonating flames, the behavior of the formaldehyde structure and marked flame surfaces were dominated by the PVC motion, but the degree of surface area fluctuations was reduced compared to unstable flames. Results show that the frequency of the combustion instability varies with several operational conditions, including gas velocity, equivalence ratio, and convective time delays.

A multi-chamber model for the combustion instabilities manifested in a gas turbine model combustor was developed. The proposed model was used to explain the dependencies of instability frequency on burner geometry and other flow parameters, some of which could not be reconciled with previous models. The new model was built upon the Helmholtz analysis of two connected resonators. The instability frequency as well as the complex pressure ratio between two chambers were predicted by solving ordinary differential equations. To assess the assumptions and predictions of the proposed model, the spectra and magnitude of the oscillations of pressure, heat release rate, and velocity were measured for four different operating conditions: rich (R1), lean (L1), stoichiometric (S1), and reduced flow rate (R2) with a kilohertz laser diagnostic system. These measurements reconfirmed that the instability is of Helmholtz type. A global equivalence ratio that is consistently greater than unity was identified to be an enabling factor for combustion instability. This is also in agreement with the predictions made by the proposed model. Furthermore, the model was shown to be able to predict the right trend of instability frequency when multiple parameters were changed. It is concluded that the current model is an improvement over previous models, because the acoustic coupling between different chambers of the burner was considered.

Partially premixed combustion has the merits of lower NO x emission as well as higher efficiency. However practical applications of such technology have been hindered by acoustic instabilities generated in combustion chambers when gas turbine engines are operated in premixed mode. A thorough understanding of the physical processes which trigger and sustain this instability needs to be gained to aid the design of next generation low-emission high-efficiency gas turbine engines. In this work, acoustic instabilities manifested in the Gas Turbine Model Combustor (GTMC), which was developed at DLR Stuttgart by W. Meier and colleagues, were investigated. Specifically, the GTMC was operated with dimethyl ether (DME) in a fuel rich condition. Multi-point pressure measurements were carried out to characterize the dominant instability mode of the combustion chamber. Simultaneous Planar Laser-Induced Fluorescence (PLIF) of formaldehyde (CH 2 O) and pressure measurements were then made at a sustained frequency of 4 kHz. Flame surface densities, calculated from the flame edges detected in the PLIF images, were used as the indicator of flame heat release rate and determined both temporally and spatially. Finally a reduced order model was proposed to describe the observed combustion instability. Key predictions made by this model, such as instability frequency and pressure phase differences, agreed with experimental observations. Future work will focus on expanding present model to explore the effects of varying parameters on the combustion instability.

A new method of removing chlorpyrifos from contaminated water using molecularly imprinted polymeric microspheres for chlorpyrifos is described. Molecularly imprinted polymeric microspheres were prepared by the emulsifier-free polymerization method. The removal efficiency and selective recognition ability of the molecularly imprinted polymeric microspheres were studied. The highest removal efficiency was observed at pH=7. Moreover, molecularly imprinted polymeric microspheres can be re-used for at least 10 times without losing any removal efficiency. Molecularly imprinted polymeric microspheres provided a selective, simple, reliable and practicable solution to remove chlorpyrifos from contaminated water.

Horizontal drainage cushion plays a key role in vacuum preloading projects. The traditional horizontal drainage cushion is sand blanket which consumes large amount of sand and is not enviromentally friendly. Several improvements or modifications of horizontal drainage cushion were developed in engineer practices in recent years. Drainage net was used as horizontal drainage cushion in ultra-soft soil improving projects in order to solve the laying problem of sand blanket. Sand ditch was used to deduce the consumption of sand. Direct vacuum preloading method linked the PVDs and filer tubes together in order to improving the transfer efficiency of pressure and canceled the sand blanket at the same time. Low position vacuum preloading method set horizontal drainage cushion below the surface of the ground in order to cancel the sealing membrane.