Michele Negri

Atomization of non-Newtonian fluids with an impinging jet injector: influence of viscoelasticity on hindering droplets formation

The formation of threads-like structures instead of droplets was observed in recent studies on the injection of non-Newtonian fluids through an impinging jet injector. In the present work different fluids, i.e. Boger fluids, linear and crosslinked polymer solutions,have been tested to determine which classes of fluids lead to the formation of such structures. Subsequently the correlation between the rheological and the spray behavior has been investigated. The influence of fluid elasticity in hindering droplet formation and leading to the formation of threads has been in particular analyzed in first experiments.

Combustion of Gelled Propellants Containing Microsized and Nanosized Aluminum Particles

The combustion behaviors of gel fuels containing micro- and nanosized aluminum particles were investigated in a pressurized chamber under typical ramjet conditions. Condensed combustion products were sampled in the jet plume behind the exit nozzles with two different rapid-insertion probes. The chemical composition of the samples was determined, and the structure of the sampled combustion products was studied with microscopic techniques. The formation of large aggregates of aluminum was observed, which left the combustion chamber with limited oxidation. The formation of such aggregates could explain why the substitution of micro-Al with nano-Al did not lead to the expected increase in combustion efficiency.

Recent Results on Thread Formation with an Impinging Jet Injector

The formation of thread-like structures instead of droplets was observed during the injection process of distinct gel fuels and non-Newtonian fluids with an impinging jet injector. The objective of the present paper is to contribute to a better understanding of the mechanisms leading to the formation of these structures. Tests with many different Boger fluids have been conducted. To analyze the obtained shadowgraph images of the sprays a graphical analysis method was implemented. This code determines the thread parameter, a number that is associated with an average dimension of the threads. A correlation can be observed between the fluid relaxation time and the thread parameter. On the other hand, shear viscosity and surface tension do not seem to have an influence on thread formation.

Development of ADN-based Thruster Technologies – An overview of the European Project Rheform

In the European project Rheform research activities aimed at improving ADN-based propulsion systems have been conducted. ADN-based propellants are extremely promising as hydrazine replacement. They have a lower overall life cycle cost due to simplified handling, higher specific impulse and higher density compared to hydrazine. In the paper an overview of the main results achieved during the project will be given.