China’s new Ram-Rotor Detonation engine pushes beyond Mach 5

As we see the UK’s attempts to develop new supersonic and hypersonic aircraft go into bankruptcy, and as US startups reach some measure of success, researchers in China have introduced what they call is a new hypersonic engine concept by integrating a ramjet with a rotary detonation engine – that is in fact loosely based on NASA technology.

A team at Tsinghua University in Beijing created a new design known as the Ram-Rotor Detonation Engine (RRDE) by combining a detonation engine and a rotor compressor based on ramjets, drawing inspiration from rotary engines.

The design aims to provide continuous thrust, operate at lower start-up speeds, and enhance overall performance. According to researchers, the approach could improve efficiency in hypersonic flight, potentially making high-speed travel more feasible.

The new study examines the new RRDE, which is intended to improve propulsion through effective detonation cycles. Rapid combustion, or detonation, increases pressure by compressing fuel and air with a shock wave and then releasing a lot of heat.

Despite the pressure advantages promised by detonation engines like the Pulsed Detonation Engine (PDE) and Rotating Detonation Engine (RDE), steady thrust and pressure are difficult to achieve under practical circumstances.

Building on prior research, scientists propose the RRDE, which uses rotating blades to compress, ignite, and expand gases in a single sequence. Inspired by the ram-rotor compressor concept, the RRDE is designed to manage shock waves and improve thrust by sustaining ideal pressure cycles.

The new research introduces RRDE’s structure, analyzes its performance, and demonstrates its potential through simulations, paving the way for advances in hypersonic and aerospace propulsion. The RRDE is designed to enable continuous detonation waves and steady engine operation, aiming for high pressure and efficiency.

Its core structure consists of a rotor with blades in a helical pattern within a stationary casing. As fuel and airflow through the channels between these blades, they are compressed, ignited, and expanded, all in one compact unit.

According to the team, the design minimizes disruptive shock waves, improving performance. The RRDE is adaptable since it can function at a variety of speeds by varying the rotor speed.

In contrast to existing detonation engines, the RRDE offers a more reliable and effective propulsion choice by addressing problems such as low start-up speeds in oblique detonation engines and discontinuous thrust in pulse detonation engines.

Test results showed that RRDE combines compression, combustion, and expansion in one rotor, using a detonation wave fixed relative to the rotor to improve pressure and efficiency.

The RRDE operates at various speeds by shortening the combustion path. The relative inlet velocity (V0), the absolute inlet velocity, and the fuel-to-air ratio (ϕ) are the three main determinants of its performance.

The team emphasizes that the study demonstrates that while higher absolute inlet speeds lower thrust and pressure gain, V0 increases both. The fuel ratio also influences efficiency; high efficiency is achieved within an ideal range.

Numerical simulations confirm the RRDE’s ability to stabilize the detonation wave and adapt to shifting inlet settings. Tests using a hydrogen-air fuel mix demonstrated the RRDE’s potential for effective propulsion, producing a pressure increase of 1.6.

Tests also confirmed a stable operation, achieving intake speeds up to Mach 4.2 to 4.5 times the speed of sound - and combustion gas temperatures near 2,100 Kelvin (1,827°C or 3,320°F).

Researchers claim that there are still engineering difficulties, such as maintaining steady detonation at lower speeds, protecting blades from heat, and rotor endurance at high speeds. Future research will focus on new materials, such as these exotic materials, and cooling techniques to advance the RRDE’s design and efficiency.

The details of the team’s research were published in the journal Science Direct.