Experimental investigation of the axial oxidizer injectors geometry on a 1-kN paraffin-fueled hybrid rocket motor

The showerhead is the most common type of injector used in hybrid rocket motors due to its design and manufacture simplicity. The main drawback of the showerheads (SH) is the relatively low performance in terms of combustion efficiency because of the poor atomization of the liquid oxidizer. This study investigates the problem to enrich the technical literature by presenting detailed experimental data on showerhead injectors by a series of static firing tests using a 1-kN lab-scale hybrid rocket, applying four kinds of showerhead injectors, named SH1 (benchmark), SH2, SH3, and SH4. They differ from each other by the number, distribution, and dimension of the orifice elements. Main performance parameters such as fuel regression rate, specific impulse, and combustion efficiency are experimentally obtained.Two different series of tests were carried out. At first, the influence of SH injector geometries was studied. The injectors SH2, SH3, and SH4 were used under the same initial conditions, and the results were compared with SH1. In the second set of tests, the SH4 injector was chosen, and the effects of the fuel grain initial port diameter were investigated. Using the data obtained in the second battery of tests was possible to determine the influence of the fuel port diameter on the motor efficiency and establish the regression rate law of nitrous oxidizer/paraffin-based fuel for this specific configuration

Experimental investigation of injectors design and their effects on 1kN performance hybrid rocket motor

To investigate the effects of injection on the performance of hybrid rocket motors (HRMs), we have designed, manufactured and tested two types of injector: showerhead (SH) and pressure-swirl (PSW). This paper analyses the influence of the oxidizer injector design on the main performance parameters, such as the fuel regression rate, the specific impulse and the combustion efficiency. First, in order to observe the injector spray qualities, a series of cold tests using liquid water and liquid nitrous oxide are carried out, providing a good understanding of the spray profiles. Then, the motor performance data are obtained by a series of firing tests using N2O as oxidizer and paraffin as fuel. Due to its simplicity, large database and its easy manufacturing, the showerhead is used as a benchmark in this work. During this experimental analysis, the SH injector exhibits the highest regression rate. In terms of spray properties, the PSW has significant differences, generates the smallest Sauter Mean Diameter (SMD) in the formed spray and achieves good atomization. In spite of the fact that the PSW injector leads to the lowest regression rate, it results to a good specific impulse, increases the oxidizer-to-fuel ratio (/), and a uniform and smooth consumption of the paraffin fuel grain. Concerning the stability, SH injector exhibits lower oscillations in the chamber pressure. Some observations are made on exhaust plume intensity developed during combustion, and in firing tests with SH a blow-out phenomenon is strongly present.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Experimental regression rate profiles of stepped fuel grains in Hybrid Rocket Engines

In this work, we assess the impact of stepped hybrid rocket solid fuel grains on the performance of the engine. The influence of Forward Facing Steps (FFS) and Backward Facing Steps (BFS) on the regression rate is analysed on two different cylindrical motors and one slab burner with optical access. Accessible post-processing allows to quantify the local regression rate profiles induced by the steps for the cylindrical motors. For the slab burner, novel image processing approaches enable the authors to correlate the findings of the cylindrical motors precisely to the visual inspection of the slab burner. Using two different cylindrical motors with different fuel grain lengths stressed the importance of the total motor length on the effect of the steps. Shorter grains (118 mm) exhibit higher regression rates for FFS than for BFS (+41.3% versus +15.7%), whereas longer motors (500 mm) profit more from BFS than FFS (+26.3% versus ±0%). Moreover, using three different oxidizers (nitrous oxide, hydrogen peroxide and gaseous oxygen) and two different fuels (high density polyethylene and paraffin) at different O/F ratios, we showed that the beneficial properties of steps are valid for numerous configurations. This would allow the employment of stepped geometries to a variety of existing motors. Finally, the authors propose the possibility to approximate fuel grain designs by a set of multiple steps.Advancing Space Access Capabilities - Reusability and Multiple Satellite Injectio