Cryogenic engines are widely used in the upper stages of launch vehicles due to their higher specific impulse, but they face challenges associated with liquid-vapour two-phase flows under extreme temperature conditions.
Understanding how vapour and liquid interact during rapid heat transfer processes is critical for ensuring reliable engine performance.
One of the key issues in semi-cryogenic engines arises when high-temperature gaseous oxygen comes into direct contact with liquid oxygen before entering the main pump.
For proper operation, the gas must condense completely; otherwise, residual gas can severely affect pump performance.
Conventional intrusive measurement methods disturb the flow and fail to capture the fast transients involved, making it difficult to study these phenomena in detail. This challenge has long hindered progress in cryogenic propulsion research.
To address this, ISRO funded a three-year research project at IIT-Bombay. Professors Atul Srivastava and Milind Atrey led the effort from IIT-Bombay, while Dr. Deepak Agrawal and Anant Singhal contributed from LPSC.
The team developed a novel optical method called Rainbow Schlieren Deflectometry (RSD), built from first principles, to directly measure thermal gradients around condensing vapour cavities in a pool of water.
Unlike intrusive probes, RSD allows researchers to capture the entire temperature gradient field around the vapour cavity and determine variations in heat transfer rates during vapour-liquid interactions.
This proof-of-concept demonstrated that the technique could successfully quantify heat transfer rates in liquid-vapour two-phase systems.
The technology was then applied in cryogenic environments, specifically to condensing gaseous nitrogen in flowing liquid nitrogen. Initial results confirmed the applicability of RSD for visualising spatio-temporally resolved thermal gradients in two-phase cryogenic flows. As part of the project, the know-how of the RSD technique was transferred to LPSC, enabling ISRO scientists to integrate the method into their ongoing propulsion research.
The knowledge gained from this study is expected to significantly improve understanding of two-phase heat transfer processes relevant to cryogenic propellants such as liquid hydrogen and liquid oxygen, which are essential for launch vehicles.
This deeper insight will support the design of more reliable and efficient cryogenic systems for ISRO’s future rockets. In particular, it complements ISRO’s ongoing semi-cryogenic engine development program, where the SE-2000 engine is being designed to replace the current L110 core stage of the LVM3.
The SE-2000, operating on liquid oxygen and kerosene, is expected to deliver a thrust of 2000 kN with a specific impulse of 335 seconds, enhancing payload capacity from 4 tons to 5 tons in geosynchronous transfer orbit.
The RSD technique thus represents a crucial advancement in experimental diagnostics for cryogenic propulsion. By enabling non-intrusive, high-resolution measurements of thermal gradients, it addresses a longstanding challenge in rocket engine research.
Its successful application in cryogenic conditions demonstrates its potential to accelerate the development of semi-cryogenic and cryogenic propulsion systems, ensuring India’s future launch vehicles are both more powerful and more reliable.
This breakthrough strengthens India’s position in advanced rocket technology, where only a handful of nations have mastered high-thrust semi-cryogenic engines.
IIT-Bombay
