Design of an improved linear aerospike engine

 

Fisica  |  Tecnica

 

Stefano Hauswirth, 2004 | Lugano , TI

 

Aerospike engines are a unique type of rocket propulsion system with a design and working principle that diverges from the industry standard bell nozzle engine. Instead of expanding the exhaust created within the engine combustion chamber through a closed geometrical shape, aerospikes instead rely on a specially sloped ramp, on which the gasses glide over. The external engine wall is composed of the ambient atmospheric pressure that compresses the exhaust along the ramp. Due to this, aerospikes are theoretically the most efficient rocket engines to ever be conceived, as it allows them to be altitude compensating, meaning that they do not suffer from over or under expansion when they leave the atmosphere towards the vacuum of space. But the nature of the aerospikes design also carries several hurdles, mainly related to its weight and cooling difficulties.

Introduction

This project is centered on designing an optimized linear aerospike engine, based partly on already existing experimentation done with them in the past, but creating it using modern computerized design tools and software. The engine concept will focus on reducing the aerospikes thermodynamic problems while increasing its performance and efficiency using modern advances in manufacturing and computer design.

Methods

My research is divided in 3 main sections: the first was understanding the basics of rocket propulsion, the concept of over and under-expansion with the principle behind an aerospike engine, its advantages, problems, and the different types of aerospikes. The second is dedicated to the design of the engine, starting from an already existing prototype. For the design, I choose 2 main aspects to improve: 1. the optimization of the main component of any aerospike, which is the isentropic ramp. I calculated its geometry using the method of characteristics, which describes the flow of the exhaust at supersonic speeds. This is inefficient to solve manually, so to make the accurate contour of the nozzle, I used a Python script. 2. Design improvement of a regenerative cooling system for the newly created aerospike ramp. The cooling system created is a series of channels that run below the surface of the ramp, where the liquid methane fuel flows through, cooling the engine. The final part is an assessment of different manufacturing methods that could be used to build the newly designed engine, and possibly scale up production to mass scale.

Results

Through the comparison of different prototypes, created based on different values taken from the SpaceX Raptor engine, and by obtaining needed data through calculations made by rocket propulsion analysis, I substantially improved the theoretical performance of my new aerospike engine. The final engine contour has an expected efficiency of 405 seconds of Isp (at 57kPa) and can theoretically produce around 3.6 mil. N of thrust. Compared to the Raptor engine, my aerospike has 15% more specific impulse and generates 63% more thrust. The use of liquid methane instead of hydrogen has led to a decrease in weight compared to the original prototype, as the plumbing system requires less insulation and is simpler.

Discussion

The model is an improvement over the engine that is originally considered. The refining of the ramp geometry and the addition of a cooling system aided in reducing the originally abysmal thermodynamic performance of the engine. However, to truly determine the thrust output and efficiency of this new engine, it would need to be physically tested by building a scaled-up prototype. Even if this is an improvement, it is still the start, as other aspects of an aerospike engine can be taken in consideration, such as a redesign of the engine’s combustion chamber or its turbopumps. Regarding the engine’s production, the right manufacturing method depends on the number of engines needed. This may change depending on the scale of production, if just for prototype testing or larger mass production.

Conclusions

The aspects analyzed in this research are only a part of what can be obtained by studying the aerospike design concept. The real-world physics and aerodynamics are still not fully understood, mainly since no full-scale prototype has ever flown on a spacecraft. In order to obtain reliable data to improve the designs further, the engine would have to be replicated to be tested. From a design point of view, the research done here relating to the linear aerospike nozzle has obtained concrete improvements in engine performance and is perhaps the first in years, and hopefully could be used as a base for further attention given to these unique rocket engines.

 

 

Valutazione del lavoro espressa dall’esperto

Maximilian Kirchhoff

Stefano hat mit seiner Arbeit zu der Aerospike Engine ein für die Luft- und Raumfahrt zukunftsträchtiges Thema aufgegriffen und durch seine einfach verständliche Zusammenfassung ein komplexes physikalisches Thema zugänglich gemacht. Mit seinen Optimierungen und grundlegenden Hinweisen für die Herstellung hat er einen ersten Schritt für die Realisation geschaffen. Happy lift-off and godspeed!

Menzione:

molto buono

Sonderpreis «European Space Camp (ESC)» gestiftet von der SJf-Trägerschaft

 

 

 

Liceo cantonale di Lugano 2, Lugano-Savosa
Docente: Jérémie Aebischer