Swirl and fuel composition effects on boron combustion in solid-fuelramjets

The objective of this experimental investigation was to determine the influence of swirl flow and fuel composition on boron combustion efficiency, combustion products, and specific thrust. A solid-fuel ramjet combustor that was directly connected with an air heater and an air supply was used. The experiments were conducted with and without inlet flow swirl. HTPB fuels containing up to 40% boron or boron carbide in varying compositions were applied. An exhaust particle sampling technique in connnection with a chemical analysis procedure was developed in order to measure the composition of the condensed combustion products. The principle of the sampling method was based on quenching the reaction products on a cold surface. The results show that boron combustion efficiency and specific thrust are strongly increased for swirl flow conditions. Boron combustion efficiency increases with increasing amounts of boron in the fuel until a maximum at about 20% boron is reached. Further addition of boron leads to a decrease in combustion efficiency. The observations also lead to a similar behavior of specific thrust. The results for boron carbide fuels were similar, but no maximum in combustion efficiency has been observed.