Droplet combustion studies on novel cage hydrocarbons using color-ratio pyrometry

The temperature, luminosity, and relative soot volume fraction profiles of three novel energetic cage hydrocarbons-bis(nitratomethyl)-1-3-bishomocubane (DNMBHC), diazido-dimethyl-bishomocubane (DADMBHC), 1,3 bishomocubane dimer (BHCD), an RP-1 surrogate fuel (RP-1-s), and its constituents were estimated using color-ratio pyrometry (CRP) with a consumer-grade DSLR camera. For temperature measurements, data acquisition rates of 50 fps were obtained by enabling the RAW video recording feature in the camera. In combination with the temperature profiles of the combusting droplets, luminosity measurements allowed the estimation of the relative soot volume fractions, and thus sooting propensities of various fuels were established. Additional temperature measurements were also made using calibrated bare wire B-Type thermocouples, which were found to corroborate well with CRP results for RP-1-s and its constituent fuels. However, in scenarios where the sooting tendencies of the fuel were high, as was the case for the novel energetic fuels, soot deposition over the thermocouple bead was a problem, and thermocouples were found to be ineffective in predicting the maximum flame temperatures. Though the novel energetic fuels generated more soot than RP-1-s, CRP results revealed that their maximum flame temperatures were also higher than RP-1-s, which is advantageous from a combustion standpoint. The secondary atomization as a result of the microexplosions in the novel fuels was also found to be beneficial in increasing the combustion temperatures. Overall, the BHC compounds were assessed to hold considerable promise as liquid propellants, with DNMBHC emerging as the most promising.