Experimental Investigation of an Aluminized Gel Fuel Ramjet Combustor

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. Gel fuels combine the benefits of both liquid and solid fuels in terms of safety and performance and allow addition of metal particles without sedimentation. A lab-scale ramjet combustor was designed and built and a parametric investigation was conducted. The test facility included also an air heater to simulate flight conditions. More than 250 valid tests were conducted, varying the gel fuel type, motor length, air bypass ratio, and more. Paraffin wax and aluminum tristearate were used as gellants to create a stable gel and provide fine droplet atomization. Mass flow rates, pressure, and thrust were measured to calculate the experimental combustion temperature. 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 about 1400 s for non-aluminized fuels and 1200 s for 9 % aluminum gel fuel. Optimal aluminum loading was estimated at 9 % mass and a top combustion efficiency of 90 % was achieved.