Learn how a ramjet engine works, its pros and cons, and how it differs from other jet engines. A ramjet engine is a fast and simple jet engine that uses air compression.

A ramjet engine operates on the principle of air compression through the forward motion of an aircraft. As the aircraft moves, the intake system compresses incoming air. This compressed air is mixed with fuel in the combustion chamber and ignited, producing high-pressure, high-temperature gases. The expanding gases are then exhausted through a nozzle, generating thrust according to Newton's third law of motion. Ramjets have no moving parts for air compression, making them simpler than turbojets. They are most efficient at high speeds, typically supersonic, and are often used in conjunction with other propulsion systems for takeoff and acceleration, as they require a certain minimum speed to function effectively.

The engine takes in air at high speed from the forward motion of the vehicle. This air enters the engine through an inlet where it is compressed. The incoming air is compressed due to the forward motion of the vehicle and the shape of the engine's inlet. Fuel is injected into the compressed air and ignited. Unlike traditional jet engines, ramjets do not have moving parts to compress the air, so compression and combustion occur simultaneously at supersonic speeds. The ignited fuel-air mixture expands rapidly, generating high-speed exhaust gases that exit the engine at the rear. This creates thrust according to Newton's third law of motion (action and reaction), propelling the vehicle forward.

How does a ramjet engine work?

Ramjet engines are a type of jet engine that can achieve very high speeds by using the air compression caused by the vehicle's motion. They are simpler and lighter than other jet engines, but they also have some limitations and challenges. In this article, you will learn how a ramjet engine works, what are its advantages and disadvantages, and how it differs from other types of jet engines.

1 Basic principle

A ramjet engine consists of three main parts: an inlet, a combustion chamber, and a nozzle. The inlet captures the air that flows into the engine due to the vehicle's speed and compresses it by slowing it down. The compressed air then enters the combustion chamber, where fuel is injected and ignited. The hot and expanding gases then exit the nozzle, creating thrust. The thrust depends on the difference between the pressure at the inlet and the pressure at the nozzle.

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Suvankar Majumder

Founder & CEO of Agnirath Aerospace and Defence Research Private Limited
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A ramjet engine operates on the principle of air compression through the forward motion of an aircraft. As the aircraft moves, the intake system compresses incoming air. This compressed air is mixed with fuel in the combustion chamber and ignited, producing high-pressure, high-temperature gases. The expanding gases are then exhausted through a nozzle, generating thrust according to Newton's third law of motion. Ramjets have no moving parts for air compression, making them simpler than turbojets. They are most efficient at high speeds, typically supersonic, and are often used in conjunction with other propulsion systems for takeoff and acceleration, as they require a certain minimum speed to function effectively.

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Pooja Sawant

Mechanical Systems Service Engineer at Boeing with expertise in Technical Support and Aeronautics.
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The engine takes in air at high speed from the forward motion of the vehicle. This air enters the engine through an inlet where it is compressed. The incoming air is compressed due to the forward motion of the vehicle and the shape of the engine's inlet. Fuel is injected into the compressed air and ignited. Unlike traditional jet engines, ramjets do not have moving parts to compress the air, so compression and combustion occur simultaneously at supersonic speeds. The ignited fuel-air mixture expands rapidly, generating high-speed exhaust gases that exit the engine at the rear. This creates thrust according to Newton's third law of motion (action and reaction), propelling the vehicle forward.

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Muhammad Umair Naeem

MTO at Atlas Honda | xResearch Intern at NEDUET | xIntern at Hino-Pak Motors | xIntern at Key-Stone Enterprise | xIntern at Atlas Honda | NEDUET
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To put it simply, the ramjet has no moving parts at all. The primary components of a ramjet include an Inlet, a diffuser, a combustor and a nozzle. The supersonic free stream Mach number strikes the inlet center body generating an oblique shock wave. The static temp and pressure is increased downstream. The inlet compression system terminates in a Normal shock wave which decelerates the flow to subsonic. The flow enters the diffuser where it's Mach no is further decreased and the fuel is added in the 3rd stage (combustor). The A/F mixture is burned which in turn increases the Mach number and static temp thus causing the subsonic flow to accelerates in the convergent part of the nozzle. In the divergent section, flow expands up to Mach 5.

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2 Advantages and disadvantages

One of the main advantages of a ramjet engine is its simplicity. It has no moving parts, such as compressors or turbines, which reduces its weight, complexity, and maintenance. It also has a high thrust-to-weight ratio, which means it can produce a lot of thrust with a relatively small engine. Another advantage is its efficiency at high speeds. A ramjet engine can operate at supersonic or even hypersonic speeds, where other jet engines become less effective.

However, a ramjet engine also has some disadvantages. One of them is its inability to start from rest. A ramjet engine needs a minimum speed to compress the air enough for combustion. This means that a ramjet engine needs another propulsion system, such as a rocket or a turbojet, to accelerate to its operating speed. Another disadvantage is its limited range of speeds. A ramjet engine works best at a specific speed, depending on its design and geometry. If the speed is too low or too high, the engine may lose thrust or overheat.

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3 Comparison with other jet engines

A ramjet engine is a type of air-breathing jet engine, which means it uses the oxygen in the air for combustion. Other types of air-breathing jet engines include turbojets, turbofans, and turboprops. These engines use compressors and turbines to compress and expand the air, and they can operate at a wider range of speeds than a ramjet engine. However, they are also heavier, more complex, and less efficient at very high speeds.

Another type of jet engine that can achieve very high speeds is a scramjet engine. A scramjet engine is a variation of a ramjet engine that can operate at hypersonic speeds, where the air flow is supersonic throughout the engine. A scramjet engine has a more complex inlet and combustion chamber design, and it requires more advanced materials and technologies. A scramjet engine can potentially reach speeds of Mach 10 or higher, but it also faces many technical and engineering challenges.

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4 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How does a ramjet engine work?

1

2

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4

1 Basic principle

2 Advantages and disadvantages

3 Comparison with other jet engines

4 Here’s what else to consider

Aerospace Engineering

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How does a ramjet engine work?

1

2

3

4

1 Basic principle

2 Advantages and disadvantages

3 Comparison with other jet engines

4 Here’s what else to consider

Aerospace Engineering

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