טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGilad Gafni
SubjectExperimental Investigation of an Aluminized Gel Fuel
Ramjet Combustor
DepartmentDepartment of Aerospace Engineering
Supervisor Full Professor Natan Benveniste
Full Thesis textFull thesis text - English Version


Abstract

The goal of the present study is to investigate experimentally the performance of a ramjet combustor that uses a kerosene-based gel fuel combined with aluminum powder. Ramjet engines combined with gel fuel and metal additives can be used for tactical missiles that can, theoretically, reach strategic missile ranges. The potential of achieving such performance lays in the efficient combustion process and high utilization of the energy stored in metal/aluminum particles and the fact that ambient air serves as oxidizer.

Comparison of the theoretical predictions of a sea level ramjet operation to the experimental results of the current study demonstrates the potential in such propulsion system.

Gel fuels combine the benefits of both liquid and solid fuels in terms of safety and performance.  Moreover, they allow addition of metal particles without sedimentation, thus increasing the energetic performance.

 A lab-scale ramjet combustor was designed and built and a parametric investigation was conducted. The test facility included the combustor, an air heater that can simulate flight conditions and the fuel supplying system. More than 250 valid tests (150 included aluminum loadings) were conducted, varying the gel fuel type, motor length, air bypass ratio and more. Mass flow rates, pressure and thrust were measured in each experiment allowing the evaluation of combustion efficiency and potential performance. Two main types of gellants were investigated (paraffin wax and aluminum-tristearate) in order to create a stable gel, solid-like while at rest, and fine droplet dispersion when atomized. The experimental combustion temperature was calculated based on pressure and flow measurements. Theoretical temperatures and combustion efficiencies were calculated using NASA thermochemical program CEA.

   

The concept of the Gel Fuel Ramjet combustor has been proved to be feasible. Combustion temperatures varied in the range 1500-2000 K, depending on fuel type and fuel-to-air ratio, allowing the aluminum particles to ignite. Specific impulse was found to be high in comparison to rockets; with peaks over 1200 s. Good correlations to theoretical performance analysis were obtained.  Optimal aluminum loading was estimated at 9% wt. and a top combustion efficiency of 90% was achieved. The aluminum loading appears to have a significant effect on combustion efficiency. 

In order to achieve better utilization of the sprayed aluminum particles, inside the engine, structural modifications should be made to the experimental combustor to prevent ignited aluminum particles from extinguishment on the motor wall. Enlarging the motor inner diameter seems as feasible solution.