Experimental Investigation of Hypergolic Ignition: Metal-Organic Framework as Green Fuel additives for Hybrid Rocket Propulsion

The rocket engine industry is dominated by liquid propellant rocket engines, in which both fuels and oxidizers in liquid form are used to produce thrust, usually fossil hydrocarbons or nitrogen-rich compounds. This approach is associated with safety risks, inherent complexity resulting in high costs and significant environmental impact. Hybrid rocket engines offer a simpler and safer alternative, with fuel typically in solid form within the combustion chamber, reacting with liquid oxidizer. To simplify these engines, complex ignition systems can be replaced with hypergolic additives. Our work explores the use of non-toxic hypergolic additives, specifically Metal Organic Frameworks (MOFs). This experimental investigation focuses on the ignition phase, using Sorbitol, which can be bio-sourced, and Paraffin as fuel, along with White Fuming Nitric Acid (WFNA) and High-Test Peroxide (HTP) as the oxidizers. To understand the ignition mechanism of hybrid fuels with MOFs, high-speed imaging techniques are employed in oxidizer droplet tests. Visible spectrum images determine the time delay between oxidizer contact and ignition. A Schlieren imaging system observes gas release before ignition, and a high-speed infrared camera measures the propellant temperature profile. Additionally, we introduce a novel approach to study the effect of oxidizer film thickness over the fuel tablet on the ignition delay and kinetics. The results will constitute a valuable database to improve our understanding of hypergolic ignition for hybrid propellant systems and support ongoing modelling efforts.