Federico Moretto

Numerical Modeling of Paraffin-Based Fuels Behavior

In recent years paraffin wax has been introduced as a fuel for hybrid rocket motors. Its fundamental characteristic is a higher regression rate compared to classical polymeric fuels due to entrainment of liquid droplets from the fuel surface. For this reason paraffin wax is the main fuel used by CISAS in its research experiments. In order to study paraffin-based fuels behavior a 1D transient code of the fuel grain has been implemented. The first part of the paper describes the equations used by the numerical model and its validation. The second part of the papers deals with the phenomenology of supercritical entrainment. It is shown that above the critical pressure fluids behave in a different way respect to liquids. Three hypotheses have been done in order to describe supercritical entrainment. Finally the regression rate predictions of the model are compared with the experimental results. It is shown that the slope of the regression rate curve is strongly related to the entrainment law exponents because the vaporization regression rate is small compared to the entrainment part. The closure problem of droplet entrainment is described, highlighting the need for a physical based link between surface temperature, droplets temperature and vaporization temperature.

Optimization of a H2O2 Gas Generator for a Hybrid Rocket Engine

The EU FP7 SPARTAN project (SPAce exploration Research for Throttleable Advanced eNgine) aims at developing a highly throttleable propulsion system (10:1 thrust ratio), to perform soft and precise landing in planetary environments; the innovative technology relies on a hybrid engine burning HTPB and decomposed 87.5% H2O2 with vortex injection. In this framework the University of Padua (UPD) is responsible for developing a prompt and reliable CFD tool to support both design phases and internal ballistic analysis of the hybrid engine. To validate numerical results UPD has developed its own engine and ground testing are still ongoing to characterize hybrid performance in deep throttling. The issues related to handling and storing high concentration hydrogen peroxide have been overcome integrating the hybrid motor with a dedicated gas generator to reproduce 87.5% H2O2 in dissociated condition. The mixture produced inside the gas generator is then injected as oxidizer into the combustion chamber of the hybrid motor. This paper presents the main results of the optimization tests campaign performed on the integrated gas generator, to assess the injected hot mixture characteristics and ignition capability of the HTPB fuel.

SPONGE: a Sounding Rocket Experiment for PMDs

This paper describes the SPONGE experiment (Sounding rocket Propellant OrieNtation microGravity Experiment) developed at CISAS in collaboration with Thales Alenia Space Italy. The aim of this experiment is to provide the data for the validation of the CFD code created to study and design propellant management devices. SpongeCompressibleFoam is a code based on the OpenFOAM Platform, written at CISAS to simulate propellant management devices. The latter are passive static metal structures used in rocket tanks to control propellant behavior; they work using surface tension to ensure gas-free liquid delivery to the tank outlet. SPONGE flew on board the REXUS 9 ESA/SSC/DLR sounding rocket in February 2011, it is based on two counter rotating plates: (i) the experimental plate, on which the control equipment and a polycarbonate tank containing the sponge test-sample are placed and (ii) the balancing plate, rotating in the opposite direction with respect to the experimental plate and ensuring no momentum transfer to the rocket. The system rotates at four different angular velocities, allowing the study of the sponge and its retention capability under different centrifugal forces. The design and results are presented.