IIT Bombay–ISRO Research Breakthrough Helps Visualise Heat Flow Inside Cryogenic Rocket Engines

Indian rocket-engine research has taken an important step forward with IIT Bombay scientists, working with ISRO’s Liquid Propulsion Systems Centre in Thiruvananthapuram, developing a non-intrusive optical method to study thermal gradients in cryogenic engine flows. The project, recently concluded at IIT Bombay’s Department of Mechanical Engineering, focuses on one of the most difficult areas of advanced propulsion: understanding how vapour and liquid behave during rapid heat-transfer processes inside extremely cold rocket systems.

The work is significant because cryogenic and semi-cryogenic engines operate under demanding thermal conditions. In such systems, fluids are handled at very low temperatures, and even small disturbances in heat transfer or phase change can affect engine stability, pump performance and overall reliability. IIT Bombay’s post noted that liquid-vapour two-phase flow remains a major concern in cryogenic engines because of extreme temperature limits, and efficient engine operation depends on a clear understanding of how vapour and liquid interact during rapid heat transfer.

The specific challenge studied by the researchers is highly relevant to semi-cryogenic propulsion. In such engines, high-temperature gaseous oxygen can come into direct contact with liquid oxygen and must condense before entering the main pump. If the condensation remains incomplete, residual gas can disturb the pump’s performance and affect the smooth feeding of propellants into the engine. This is not a small laboratory curiosity; it is the kind of hidden internal behaviour that can determine whether a high-performance rocket engine runs efficiently and safely.

Traditional heat-transfer measurements in such flows are difficult because inserting probes into the fluid can disturb the very flow being measured. These intrusive methods may also fail to capture fast transient changes, especially when liquid and vapour are interacting rapidly. To address this, ISRO funded a three-year research project at IIT Bombay. The IIT Bombay team included Prof. Atul Srivastava and Prof. Milind Atrey, while Dr. Deepak Agrawal and Anant Singhal were associated with the work from LPSC.

The researchers developed an optical method known as Rainbow Schlieren Deflectometry. Instead of placing instruments inside the fluid, the method uses light to visualise temperature gradients around vapour cavities. In the proof-of-concept stage, the technique was applied to directly measure thermal gradients around a condensing steam cavity in a pool of water. This allowed scientists to observe the full temperature-gradient field around the vapour cavity and estimate how heat-transfer rates changed during the liquid-vapour interaction.

In simpler terms, the method gives researchers a way to “see” heat-flow patterns that would otherwise remain invisible. When temperature changes occur inside a fluid, they alter optical behaviour. By studying how light is deflected through the fluid, scientists can map where thermal gradients are forming and how they evolve over time. This is especially useful in rocket propulsion, where fast-changing flows cannot always be captured by conventional sensors.

After validating the method in a steam-water system, the technology was applied in a cryogenic environment involving condensing gaseous nitrogen in flowing liquid nitrogen. IIT Bombay said the initial results demonstrated the applicability of Rainbow Schlieren Deflectometry for visualising spatially and temporally resolved thermal gradients in two-phase cryogenic flows. The know-how developed under the project has also been transferred to LPSC.

The larger importance of this research becomes clearer when placed alongside ISRO’s semi-cryogenic engine programme. ISRO has been developing a 2000 kN-class semi-cryogenic engine using liquid oxygen and kerosene, intended to power the semi-cryogenic booster stage of LVM3 and future launch vehicles. ISRO has stated that induction of semi-cryogenic propulsion, along with an uprated cryogenic stage, can enhance LVM3’s payload capability to geostationary transfer orbit from 4 tonnes to 5 tonnes.

This means better thermal understanding is not merely an academic achievement. It can support more reliable engine design, better pump performance, safer start-up sequences and more efficient management of propellant flow. In high-thrust engines, where turbo-pumps, pre-burners, control components and combustion chambers must work under severe pressure and temperature conditions, small improvements in understanding can translate into major improvements in reliability. ISRO has described the SE2000 semi-cryogenic engine as a complex oxidiser-rich staged-combustion system with high chamber pressure and demanding material requirements.

For India’s space programme, the IIT Bombay–LPSC work adds another layer of indigenous capability. India is not only building engines and test facilities but also developing the diagnostic science needed to understand what happens inside those engines. Such experimental techniques can help engineers refine designs, validate simulations and reduce uncertainty before full-scale engine operations.

The positive outlook is clear. As ISRO moves toward heavier launch vehicles, reusable systems, next-generation propulsion and higher payload capacity, advanced ground research will become increasingly important. Technologies like Rainbow Schlieren Deflectometry can help India study complex cryogenic and semi-cryogenic flow behaviour without disturbing the system being observed. That makes it a valuable tool for future propulsion research.

The breakthrough shows how India’s space ecosystem is maturing: ISRO provides mission-driven engineering challenges, IITs contribute deep scientific research, and the outcome strengthens national capability. By making hidden heat-transfer processes visible, IIT Bombay and LPSC have opened a sharper window into the internal physics of rocket engines — a window that can help India build more efficient, reliable and powerful launch vehicles in the years ahead.