Numerical simulations of the flowfield in a gaseous oxygen/hydroxyl-terminated polybutadiene hybrid rocket engine are carried out with a Reynolds-averaged Navier–Stokes solver including detailed gas/surface interaction modeling based on surface mass and energy balances. Fuel pyrolysis is modeled via finite-rate Arrhenius kinetics. A simplified two-step global reaction mechanism is considered for the gas-phase chemistry to model the combustion of 1,3-butadiene in oxygen. Results are compared with the firing test data obtained from a laboratory-scale hybrid rocket in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene cylindrical grains through an axial conical subsonic nozzle. With the oxidizer fed by this injector, which generates nonuniform conditions at the entrance of the fuel port, the fuel regression rate is shown to increase several times with respect to the case of homogeneous injection of the oxidizer through all the grain port area, in agreement with the experimental f...

Simulation of Gaseous Oxygen/Hydroxyl-Terminated Polybutadiene Hybrid Rocket Flowfields and Comparison with Experiments

A numerical rebuilding of a series of test data obtained with static firings of a lab-scale hybrid rocket is carried out with a Reynolds-averaged Navier–Stokes solver including detailed gas–surface interaction modeling based on surface mass and energy balances. Two experimental campaigns are considered in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene grains through an axial conical subsonic nozzle. A validation rebuilding of all of the firing tests has been performed first to highlight numerical prediction capabilities and modeling limits. Despite the several geometrical simplifications, which allows using a reduced number of cells in the computational domain and thus performing parametric analyses efficiently, the present computational fluid dynamics approach is able to capture the main features of the motor internal ballistics, fairly reproducing the average chamber pressure values and the fuel regression rate trends with oxidizer mass flux and port diameter. Computed f...

Hybrid Rockets with Axial Injector: Port Diameter Effect on Fuel Regression Rate

In this work, single-port, cylindrical grain laboratory-scale hybrid rocket motors are numerically simulated to study the effect of diaphragms. The effect of single and multiple diaphragms is investigated by varying diaphragm height, its axial location (for a single diaphragm), and spacing (for multiple diaphragms) at selected inlet GOX. A single diaphragm increases the local regression rate and its influence is prominent only in the region immediate downstream. Therefore, a tangible increment in average regression rate with a single diaphragm can only be realized for motors with small L/D( 10), use of multiple diaphragms are required to increase the regression rate and combustion effici...

Effect of Diaphragms on Regression Rate in Hybrid Rocket Motors

Regression rate behaviors of HTPB-based propellant combinations for hybrid rocket motor

Effect of swirl on the regression rate in hybrid rocket motors

In the present work, a numerical investigation is carried out for physics based identification of key parameters that govern scaling of single cylindrical port hybrid rocket motors. The grain port length to port diameter (or L/D) ratio was found to be a key scaling parameter along with maintaining oxidizer mass flux (G OX ) for near identical motor performance. Since L/D ratio dictates the overall oxidizer to fuel ratio (O/F), there exists an optimal L/D ratio (near stoichiometric overall O/F ratio) at which the characteristic exhaust velocity C * and combustion efficiency ηC are maximum. Thus the scope for tangible improvement in C * and ηC using a regression rate enhancement technique is only for motors with grain L/D ratio appreciably less than the optimal L/D ratio.

C. Palani Kumar

Papers

Effect of Diaphragms on Regression Rate in Hybrid Rocket Motors

Effect of swirl on the regression rate in hybrid rocket motors

A Computational Study on the Scale Effects of Hybrid Rocket Motors