Research Projects

Common states of matter are solid liquid and gas. However, at very high pressures and sufficiently high temperatures matter behaves like a gas with liquid like densities, called ‘supercritical state’. This state offers characteristics of high thermal conductivity and high density of a liquid, while having lower viscosity and no surface tension like a gas. This eliminates two-phase flow and its associated losses. This is especially useful when one needs to have very high heat transfer rates and temperatures are quite high, like in heat exchangers in engines, where supercritical CO2 is used. Other applications (other than as solvents) include cooling of hot surfaces like in rocket nozzles, gas turbines, and other high speed propulsion devices like ramjets, scramjets, where fuel is used for regenerative cooling. Cooling of satellites that voyage towards the inner planets or the sun, or hydrothermal vents under the ocean also have supercritical fluid flows. Gas giants Jupiter and Saturn are known to have supercritical atmospheres. In engine applications where liquid fuel is injected into air for reaction, usually the fuel has to atomise, evaporate, mix and then react with air. Injection at supercritical state, which is highly diffusive, will directly mix fuel with air like a gas and react immediately. This lowers the time to heat release and offers higher heat release rates and thus higher engine power. Thus, the understanding of supercritical fluid injection into highspeed flows becomes essential for highspeed propulsion devices. While understanding of supercritical fuel injection is required universally in several fields, given the expertise of the PI, this work will focus on supercritical fuel injection into sub-and super-sonic crossflows, of sub- and super-critical air. Here, supercritical fluid (acetone or kerosene) will be created by passing pressurised hydrocarbons through heated tubes. This fluid will now be injected into a crossflow of air flowing at sub-/super-sonic speeds. The case of supercritical fluid injected into supercritical airflow will be attempted in a smaller rig considering flow rate requirements. High temperature supersonic airflow will be used to study non-condensing case of mixing studies. Pulsed injection of supercritical fluid into a crossflow will be attempted, as it gives higher penetration and mixing for gases. Study will be primarily based on schlieren imaging and PLIF based mixing studies with acetone and NO tracers. The lasers required for these studies are already available with the PI. Numerical simulations will also be performed to complement experimental measurements. Also, gas injection experiments will be performed for comparison. This research will pioneer advances in aerospace engines industry and generate experimental and computational knowhow in India on supercritical fluids. This will trigger new applications involving supercritical fluids, at least in heat exchanger, propulsion and combustion fields.