Inside DRDO’s Actively Cooled Scramjet: Engineering India’s Path to Sustained Hypersonic Flight

India Defense

India’s Defence Research and Development Organisation (DRDO) is quietly advancing one of its most complex and strategically vital propulsion technologies—a scramjet engine with an active fuel-based cooling system, aimed at enabling sustained hypersonic flight. As India builds its Hypersonic Technology Demonstrator Vehicle (HSTDV) program, the scramjet propulsion system becomes central to long-range, ultra-fast strike platforms of the future.

The scramjet engine (Supersonic Combustion Ramjet) is designed to operate in the Mach 5+ regime, where air entering the combustion chamber does not slow down to subsonic speeds. But the incredible thermal and aerodynamic stresses at hypersonic speeds require advanced solutions. One of the biggest engineering challenges is thermal management, and this is where DRDO’s active cooling system comes into play.

 

The Problem: Hypersonic Heat

At hypersonic velocities (Mach 5 and above), the external surfaces and internal parts of a scramjet engine are subjected to temperatures exceeding 1000–2000°C. Conventional materials and passive cooling methods are insufficient, particularly in maintaining engine integrity and efficiency over prolonged flight durations.

Scramjets must also operate in extremely lean air conditions (due to high altitudes) and must ignite and sustain combustion in milliseconds—a task made more difficult when high temperatures risk component failure.

 

DRDO’s Solution: Active Fuel-Based Cooling

DRDO’s solution involves active cooling using the onboard fuel itself, a method drawn from advanced hypersonic propulsion research globally (including U.S. and Russian programs). Here's how it works:

1. Cooling Pipe Network Integration

   • A network of narrow cooling pipes is integrated around critical areas of the engine—particularly the combustor and intake. These act as heat exchangers.

2. Fuel as a Coolant

   • Instead of using a separate coolant, the fuel itself is circulated through these pipes before being injected into the combustion chamber. This dual role allows:

   • Extraction of heat from engine surfaces, keeping structural temperatures within safe limits.

   • Pre-heating or cracking (in some cases) of fuel, enhancing combustion efficiency and energy content.

   • This process is known as regenerative cooling, a technique also used in rocket engines like the Space Shuttle’s SSME and SpaceX’s Raptor.

3. Fuel Chemistry Consideration

   • At such high thermal loads, the chemical composition of the fuel may change. This phenomenon, called pyrolysis, can lead to the breakdown of hydrocarbons into lighter molecules or even deposition of carbon residues.

   • To counter this, DRDO is modifying the fuel formulation—possibly working with heavy hydrocarbons like JP-10 or kerosene variants—to ensure thermal stability, low coking, and high heat absorption capacity. Fuel chemistry is optimized to ensure that no carbon deposits clog cooling channels or reduce combustion efficiency.

4. Pressurization via Electrical Pump

• • To ensure controlled and pressurized flow through the cooling network, an electrically powered pump is employed. The pump regulates fuel pressure to maintain a balance between cooling efficiency and combustion needs.

  • Interestingly, this electrical pump is powered by a high-endurance battery developed by a private Indian company, a detail that reflects increasing public-private collaboration in strategic tech development.

 

Current Test Parameters and Flight Duration

Based on available test data (as of mid-2025), the HSTDV or scramjet platform has demonstrated:

• 15+ minutes in subsonic regime

• 15 minutes in supersonic regime

• 10 minutes in hypersonic regime (Mach 5+)

These durations are significant. Sustaining hypersonic flight for 10 minutes with controlled combustion and structural integrity places India in a narrow group of countries, including the U.S., Russia, and China, working on long-range hypersonic missiles and aircraft.

These figures are likely to evolve as more materials (including ceramic matrix composites, high-temp alloys) and control systems are validated.

 

Multi-Disciplinary Design Optimization (MDO): Faster, Smarter Execution

DRDO has chosen to carry out the scramjet project under a Multi-Disciplinary Design Optimization (MDO) framework. This modern engineering approach integrates:

• Material sciences

• Computational fluid dynamics

• Combustion chemistry

• Thermal and structural analysis

• Control systems and AI-based diagnostics

MDO allows multiple teams to co-design and iterate rapidly, enabling faster problem resolution and real-time optimization, especially important in hypersonic tech where traditional sequential development is too slow and inefficient.

 

Strategic Significance

Mastery over scramjet and active cooling tech paves the way for:

• Hypersonic cruise missiles with ranges exceeding 1000 km

• Reusable hypersonic vehicles

• Prompt global strike platforms

• Spaceplane propulsion systems

India’s program remains largely under wraps, but each milestone reflects a methodical and scientifically rigorous push toward indigenous mastery of next-gen propulsion systems.

In a domain where temperature, time, and speed redefine engineering limits, DRDO’s actively cooled scramjet is not just a propulsion system—it’s a statement of intent.