Klaus Madlener

Some Aspects of Rheological and Flow Characteristics of Gel Fuels with Regard to Propulsion Application

For the characterization of the flow and the spray behavior of fluids, non-dimensional numbers like Reynolds numbers are generally used. Gelled fuels are shear-thinning nonNewtonian fluids, whose rheological behavior concerning the shear viscosity - shear rate dependence can be described by an extended version of the Herschel-Bulkley equation in the propulsion relevant shear rate range. For the characterization process of this fluid type amongst others a generalized Reynolds number and a critical Reynolds number are presented.

Characteristic Flow and Spray Properties of Gelled Fuels with Regard to the Impinging Jet Injector Type

The flow and spray behavior of various gelled fuels, which are non-Newtonian shear-thinning fluids, is presented and compared. The present publication gives an overview about rheological properties, some aspects of the flow characteristics and of the atomization behavior of investigated gels with a doublet like-on-like impinging jet injector. Different breakup modes were observed in dependence of the jet exit velocity on the obtained shadowgraph images. Furthermore they are presented in a regime diagram with the generalized Reynolds number and the Weber number as parameters. Additionally a first attempt will be given to correlate both Newtonian and gelled fluids in a common regime diagram.

Characterization of Various Properties of Gel Fuels with Regard to Propulsion Application

Propulsion systems with gelled propellants combine the ability of thrust magnitude variation on demand with simple handling and storage capabilities. The present publication gives an overview about various properties of gelled propellants, which have been investigated in basic experimental setups and/or analytically. It includes rheological properties of selected gelled fuels with regard to shear strain, their flow behavior in tubes, their spray characteristics with regard to impinging jet injectors and combustion characteristics with a single injector in a pressurized chamber.

Breakup Characteristics of a Newtonian Liquid Sheet formed by a Doublet Impinging Jet Injector

The breakup characteristics of a plane fluid sheet flowing in a gaseous atmosphere is considered theoretically for Newtonian liquids. Several approximations belonging to hydrodynamic parameters are conducted to determine the influence of fluid properties on the breakup process. Experimental data is obtained by spray experiments with a like-on-like impinging jet injector setup and compared to the theoretical results concerning critical wave lengths and breakup lengths. The experiments show a good agreement to an introduced approximation method in the case of high viscous liquids.

Estimation of Flow Properties of Gelled Fuels with Regard to Propulsion Systems

Gelled fuels and propellants are shear-thinning non-Newtonian fluids. Their dependency of the shear viscosity nfrom the shear rate can be described with sufficient accuracy by an extended version of the Herschel-Bulkley nequation in the whole rocket and ramjet propulsion-relevant shear-rate range. Additionally to the analytically ndetermined generalized Reynolds number for fluids, which follow the extended Herschel-Bulkley equation, a method nfor the estimation of critical Reynolds numbers (as a phenomenological approach) is presented. Both dimensionless numbers are useful for the characterization of the flow and partially also of the spray processes of gel fluids. The results show furthermore that both the shear-thinning property and the yield stress tend to stabilize the laminar flow and thus shift the critical Reynolds number to higher values when compared to Newtonian liquids.

Experimental Investigation of Gelled Fuel with High Vapor Pressure Species and Metal Additives

§The addition of high vapor -pressure species into a gel fuel matrix can theoretically promote the combustion efficiency of the fuel. In the present study, the characteristics of various gel fuels with high vapor -pressure species and metal particles were investigated on the basis of their rheological, spray and combustion properties. Experiments were conducted using gelled Jet -A1 that contained hexane and cyclohexane at various concentrations, aluminum and magnesium. The results were compared to experimental results from the literature and the comparison indica tes that the addition of the volatile compounds has only a minor effect on the atomization and combustion.