Combustion of rocket-grade kerosene droplets loaded with graphene nanoplatelets-A search for reasons behind optimum mass loadings

Nanofluid-type fuels formulated by mixing minute quantities of graphene nanoplatelets (GNPs) with Isrosene, a refined form of kerosene utilized in semi-cryogenic engines by the Indian Space Research Organization ((SRO), were found to improve the convective heat transfer characteristics by 49% in a previous study. In this study, the combustion characteristics of such nanofluid-type fuels, such as initial mass burning rates, burning rate constants, and flame stand-off ratios, were determined for millimeter-sized droplets under ambient conditions. The impact of the specific surface area of the nanoplatelets and their relative mass loading in the nanofluid was determined. While the specific surface area did not have any impact on the combustion characteristics, the relative mass loading had a strong impact on the burning rate constants, with an increment of approximately 13.5% over Isrosene for a mass loading of 0.2%. There also existed an optimum value of mass loading, beyond which the burning rate constants. This anomalous behavior, which had earlier been conjectured to be due to various physico-chemical reasons, was attributed primarily to the gas phase conduction phenomenon, corroborated by the analysis of the temperature profiles in the gas phase, acquired using an infrared imaging camera. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.