Evaluation of Regression Rate Enhancing Concepts and Techniques for Hybrid Rocket Engines

Abstract

The low regression rate of Hybrid Rocket Engines (HREs) is one prominent characteristic that is addressed in most abstracts concerning hybrid propulsion. Over the years, researchers developed and investigated numerous ways to tackle the low regression rate problem of HREs. This article is a collection and assessment of these diverse methods and designs. It allows for a quick overview of the different mechanisms that are being employed and can serve both as information and inspiration. The enhancement ideas are grouped together as (a) adjustments to the solid fuel chemical properties, (b) advanced injection methods and concepts and (c) improving the combustion chamber design. These different techniques are discussed and their individual impact on the regression rate is assessed both qualitatively and quantitatively. All methods that are presented come with a different set of advantages and disadvantages, making the regression rate enhancement a trade-off problem. In our view, the most promising designs and methods are those that only call for minor adjustments to the HRE design, as they can be also added to already existing engines. Above all, it is to be said that regression rate enhancing techniques that change the unique features of HREs (namely safety, simplicity and low cost) are to be employed with caution. Only if the achievable regression rate increase is justifying the implications for the HRE in the envisioned use-case, these concepts represent promising alternatives to the status quo.

Numerical Study on Post-Combustion Chamber Impact on Hybrid Rocket Performance

“…Thermal energy usable for kinetic expansion Chemical energy stored within the propellants (6) In terms of the combustion temperature, the efficiency may be defined as the ratio of actual to ideal combustion temperature. This expression is normally derived from thermodynamic cycle processes, assuming ideal gas behavior.…”

“…Besides the used solid fuel, especially the fuel geometry is of key importance, since complex geometries can enhance turbulence and therefore heat transfer. Different helical or segmented geometries have been investigated, showing significantly increased fuel regression rates [5,6]. Since mixing of the reactants within the flow is important to ensure complete combustion, there is a need for detailed analysis of combustion evolution along the engine axis.…”

Bridging the Technology Gap: Strategies for Hybrid Rocket Engines

“…Nozzle erosion of the ablatively cooled graphite nozzles in HREs poses a significant problem. When the material of the nozzle throat erodes, the pressure and the I sp of the engine [5,92,93] changes as well. Generally speaking, the nozzle erosion limits the burn duration.…”

Regression Rate and Combustion Efficiency of Composite Hybrid Rocket Grains Based on Modular Fuel Units

“…At a constant oxygen mass flow rate, there is an antagonism between the rise rate of regression and enhancement of flux enhancement, which often involves employing multiport structures to augment the burning surface. This carries certain risks, such as the collapse of adjacent ports caused by the increased volumetric load [12,21]. For this reason, it is more attractive to use a modified single port to improve the fuel grains and resulting Aerospace 2024, 11, 262 2 of 18 turbulence to increase the regression rate [22].…”