Multifunctional Graphene-Based Additives for Enhanced Combustion of Cracked Hydrocarbon Fuels under Supercritical Conditions

As a particulate fuel additive, functionalized graphene sheets (FGS), with and without the decoration of nanoparticles, provide a means to form stable colloids with liquid hydrocarbons, act as in situ catalysts, and prevent attached nanoparticles from agglomerating or sintering during heating. Recent pyrolysis experiments and simulations have shown the synergetic effect of Pt and FGS structures accelerating fuel conversion and hydrogen formation. In this paper, the role of graphene-based additives (with and without platinum (Pt) nanoparticles) on enhancing the ignition and combustion characteristics of cracked n-dodecane hydrocarbon fuels under supercritical conditions is examined. Supercritical ignition and combustion experiments were conducted using a high pressure and high temperature windowed combustion chamber coupled to a supercritical fuel pyrolysis reactor. The combustion experiments indicated that the presence of small amounts of particulate additives (100 ppmw) to the fuel can reduce ignition times and increase subsequent combustion rates. In particular, the addition of FGS-supported Pt nanoparticles reduced ignition delay times by nearly a factor of 3 (12.4 to 4.2 ms), increased spray spreading angles by approximately 32.0% (15.4 to 20.3 degrees), reduced the flame liftoff length by 54.0% (1.74 to 0.8 mm), and demonstrated an increase in fuel conversion for a fixed reaction time of 35.0% relative to the pure fuel baseline. These results support the notion that nanostructured fuel additives have the potential to enhance both the heat sink capacity and combustion performance of liquid hydrocarbon fuels for their use in advanced high speed propulsion systems.