Ever since the Wright brothers flew the first airplane on a cold December afternoon over a century ago, humans have dreamed of flying higher (and faster).

According to classical physics, the faster a body moves, the more friction it experiences with the medium in which it moves, requiring more power to increase or even maintain its speed. The increased demand for power translates into a greater demand for fuel, which represents more weight and requires more power to be moved. This vicious circle is a technical issue that plagues aeronautical engineers, and the possible solutions are far from cost-effective.

Most recently, a team of Chinese researchers has pushed the envelope by successfully testing a hypersonic detonation engine that could propel aircraft up to Mach 9, or nine times the speed of sound, the South China Morning Post reports. The novel engine runs on aviation kerosene, which is much cheaper and safer than hydrogen solutions.

The background of hypersonic engines

To better comprehend the importance of this advancement, let’s first learn about the history of hypersonic engines. The first jet engine for flight was made in the 1930s and consisted of a device with compressed air and fuel. When the mixture was ignited, hot gas was produced, capable of being transformed into the mechanical energy necessary to move the aircraft.

Later, in the 1940s, the ramjet engine was developed: an internal combustion engine that burns fuel and generates higher pressures within the engine, resulting in higher exhaust velocities and, thus, more reaction. Planes had to be accelerated well before the engine could generate the final explosion that accelerates the plane above the speed of sound in the air to reach that speed.

In 2004, an aircraft developed by NASA with this type of engine reached a speed of Mach 7, which is seven times greater than the speed of sound.

Supersonic flights

Supersonic flight occurs when an aircraft’s speed exceeds the speed of sound in the air (343 m/s or 1125 ft/s). In aeronautics Mach is used as a reference measurement. The supersonic speed is Mach 1.

The characteristic gray cone of smoke billowing from the tail of supersonic aircraft is hot static air left behind by the aircraft as it accelerates. As you fly at hypersonic speeds, the surrounding air heats up and “sticks” to the plane’s surface. The air particles in which the spacecraft flies have to glide over this stagnant air, which forms the characteristic cone of supersonic flight.

The new Chinese engine

Hypersonic flights have been a reality for a long time. But so far, all its applications and development are related to military activity. As previously stated, the team of Chinese researchers says they can build a cheap and safe hypersonic engine for commercial use.

Commercial engines use kerosene combustion, which is more stable and cheaper than the hydrogen used in hypersonic engines. The team claims to have found a way to use kerosene in the combustion of the hypersonic engine. These engines, they argue, could propel planes at speeds 9 times the speed of sound. That would mean getting anywhere in the world in just a few hours.

The research team led by Liu Yunfeng published their results in the Journal of Experiments in Fluid Mechanics. In their article, they propose an engine that runs on kerosene fuel, instead of hydrogen-like standard supersonic aircraft, which means it carries neither the cost nor risk of explosion that hydrogen solutions do. Another particularity of this new engine is that it works from a detonation, which is especially useful at speeds greater than Mach 8.

The engine’s objective

As reported in the South China Morning Post, the oblique detonation engine underwent a series of successful ground tests in Beijing’s JF-12 hypersonic shock tunnel. Although its applications are clearly oriented toward military defense, the Chinese government hopes to discover civil applications in this type of technology, allowing a revolution in the transportation of Chinese passengers inside and outside its vast territory.

Because of the novelty of this type of technology, experts believe that much work remains to be done before bringing a hypersonic detonation engine to the industrial market, as manufacturing costs are currently exorbitant.