Ramjet engines, How do they work?

At present, BrahMos is the fastest and only supersonic cruise missile on the planet. During its cruise, it breaks the sound barrier by traveling three times faster than a sound wave, and no known weapon system can intercept it due to its speed. In the first stage, solid boosters power this missile, and the second stage features the ramjet engines. We'll learn more about these intriguing engines in this video. We thank Brilliant.org for supporting this video. More about Lessick's brilliant collaboration towards the end of this video. To understand ramjet technology, we first need to understand the concept of shock waves. Everybody is familiar with the ripples that are created in water when an object is thrown into it. These ripples travel uniformly, right? Now, take a look at this interesting scenario. Suppose a boy is pulling a tennis ball towards him. The movement of the source produces ripples that are not concentric. Isn't that interesting? The same effect can happen with sound waves during aircraft movement. Here, the sound waves are taking the place of the water ripples, and the aircraft is taking the place of the tennis ball. In this scenario, the sound ripples will obviously travel at the speed of sound. But here is a brain teaser for you. What will happen if the aircraft moves at the speed of sound? Obviously, the sound waves won't be able to move forward. So, if you move along with the aircraft, it will look as if the sound waves are stuck at the front, forming a sound barrier. During World War II, the sound barrier was assumed to be an invisible wall due to the aircraft experiencing high drag. However, what if the aircraft moves faster than the sound waves? The concentrated waves at the front of the aircraft will suddenly form a distributed ripple pattern, as shown. The aircraft needs to apply more thrust during this transition. The distributed pattern has a conical shape. The interesting thing is that a very narrow volume with a thickness of 200 nanometers and high temperature and pressure is formed on this conical shape. The pressure in this narrow region is almost 29 times that of the atmospheric pressure. This region is known as a shock wave. Why is the shock wave formed when the airplane moves at a speed greater than the speed of sound? This result is because in fluid, the information travels at the speed of sound. When the airplane travels faster than sound, the air volume shaded in red color has absolutely no information about the disturbance the moving object is making. However, inside the green region, the disturbance in the fluid happened with prior information. When the disturbed fluids suddenly interact with fluid particles in the red region, which has no information about what is going on, a shock gets formed in the boundary. Shock waves can cause harm to a human body. However, even though these high pressure waves are disastrous, opportunity lies in the middle of difficulty. Using the concept of the shock wave, let's understand how a ramjet engine works. Ramjet engines have a very simple geometry. They have only three main stationary parts, a diffuser region at the entrance, a combustion chamber in the middle, and a nozzle at the exit. The duty of the diffuser is to increase pressure and temperature of the air. The ramjet engines will work only in supersonic conditions. Since the flow is supersonic, the scientists tweak the shock wave concept to increase the diffuser pressure. Let's see how. The shock waves get generated from many points of this cylindrical object. Remember, in a shock wave, the high pressure and temperature is there only in a narrow region. However, when many such shock waves club together, something interesting happens. You can see at the inlet, a conical region is formed with no effect of shock wave at all. This will be a low pressure region. It is also clear a high pressure conical wall is getting generated at the inlet region. What about the remaining volume? To understand the remaining volume condition, let's take a cross section of the cones at different lengths. You can see a flower-like shape. If you increase the number of cones, this flower will fill the entire area. Remember, the number of shock cones getting generated from a circle edge is infinite. This area filling is true for any length, which means after the initial void cone, a thick volume of high pressure and temperature air is formed inside the cylinder. In short, it forms automatic compression action with the help of shock waves. This is the ram effect. This high pressure and high temperature air can create effective combustion in the combustion chamber. Hydrogen is commonly used as fuel for ramjet engines. The combustion chamber further increases the gas temperature and also the fluid velocity. According to Newton's third law, the greater the exhaust jet speed, the more thrust the rocket derives. To increase the speed of the jet further, a converging-diverging nozzle is also added at the exit. Even though this simple diffuser arrangement achieves a very high pressure boost, if the combustion pressure exceeds limits, the shock front will be blown out, resulting in compressed air spilling out around the front of the tube. This spill limits the speed of the ramjet to 1.2 Mach. Scientists didn't stop here. They further improved the ram effect with the help of an aerodynamically designed inner body. In this new geometry, you can see that the area allocated for the air is actually decreasing along with the flow. For supersonic flow, when the area decreases, the pressure increases. In ramjets, the majority of the pressure rise happens due to the shock effect and because of a concept called oblique shock wave. When air hits the nose of the inner body, it deflects with some angle, forming an oblique shock wave. This oblique shock wave hits the outer tube, deflects multiple times, and is finally terminated by a normal shock wave. In this method, the air spillout does not happen, and scientists were able to achieve a high Mach number for the ramjet engine. Now, let's learn a little more about the combustion chamber design of ramjet engines. The airflow speed through the ramjet is so high that the mixing of fuel completes within 2 to 5 milliseconds. For complete mixing of fuel, an air flame holder is used, which helps to maintain continuous combustion. It also stops the flame from blowing out by sheltering it. Ramjets are the most efficient in the speed range of Mach 3 to Mach 6. When traveling at low speed, the thrust is insufficient to overcome the drag. As a result, the standalone ramjet engine is not feasible. It needs the solid booster to propel the missile towards supersonic speeds. The ramjet does not contain any moving parts, unlike jet engines. Before you leave, please make use of Brilliant.org-Lessig's collaboration and get a discount of 20%. Brilliant has recently upped the interactivity on their platform to a new level. Check out this interactive lesson on the center of mass, for example. This is an example of Brilliant's newly updated scientific thinking course. Follow the link given below and be a brilliant and creative engineer! We hope you enjoyed the amazing technology of the ramjet engines. See you next time!