Analysis of Ignition Process in Scramjet at Low and High Fueling Rates

Experimental Setup:Direct Connect Vitiated-Air Facility

A ramjet engine is a type of jet engine, in which there are no moving parts. Their design is simple, and the air drawn into the engine for combustion is compressed solely by the forward motion of the aircraft. Scramjets are another type of jet engine, very similar to ramjets, except for the air compressed in the engine of a scramjet is traveling at supersonic speeds, while the air inside a ramjet engine travels at subsonic speeds.

In the experiment, Schlieren flow visualization was used in order to capture images of the ignition process of the scramjet combustor, as well as images of the shock waves forming in the air intake. Schlieren visualization works by showing the density gradient through uneven light deflection. This flow visualization technique allows one to capture images of both normal and oblique shock waves, in order to study the movement and compression of supersonic flow.

Introduction:

Data:

In the experiment we used a Z-type Schlieren set-up as illustrated in the top left image. In the top right picture, the scramjet can be seen ignited. In the bottom two pictures, one can see our experimental set up, the scramjet engine chamber (bottom left), and the air compressor and intake (bottom right).

Two graphs: The top showing the time the fuel enters the engine, and the second showing the actual ignition time of the engine and how efficiently it burns. The Control Test is shown in blue, Test #1 is shown in red, and Test #2 is shown in green.

Test 2:

Test #2: one can see the change in the speed of flow, traveling through the engine chamber, as the igniter turns on and the engine begins to operate. In the top picture, one can see oblique shock waves. In the middle picture, taken after the first, one can see that the oblique shock waves are starting to compress as the engine starts to perform. And in the bottom picture one can see that at full operation, during a high fuel rate, the flow traveling through the chamber has slowed to a subsonic speed, as it experiences normal shock waves.

Control Test:

In the control experiment, Schlieren images of oblique shocks waves can be seen as engine remains off and supersonic gas flows through the chamber.

Test 1:

Test #1: one can see the before (top picture) and during (bottom picture) effects of the igniter while it “puffs” at a low fuel rate. Oblique shock waves are seen in both images as well, showing that the flow traveling through the chamber is super sonic.

Gareth Dunlap, Elias Fekadu, Ben Grove, Nick GabsaFaculty Members: Dr. Kenneth Yu, Dr. Camilo Munoz, Jason Burr

Use a Schlieren images to analyze the ignition process of a scramjet combustor.

Objective:

Conclusion: During a low fuel rate, a ramjet engine runs in ‘scramjet mode’ as the flow traveling through the engine travels at a supersonic speed, creating oblique shock waves, while at a high fuel rate, the flow traveling through the engine slows down to a subsonic speed, shown by normal shock waves.