Electromagnetic radiation in a jet engine: nature, mitigation, application

Jet engines are widely used in aviation and astronautics. Their operation is based on the ejection of a high-speed gas jet that creates thrust. In addition to mechanical and thermal processes, various electromagnetic phenomena arise in a jet engine. Electromagnetic radiation accompanies combustion processes, the motion of charged particles, and the operation of the engine's electronic systems.

The nature of electromagnetic radiation emitted by jet engines

Electromagnetic radiation — is the propagation of energy in the form of electromagnetic waves. It arises from the accelerated motion of electric charges. In a jet engine such conditions occur constantly:

• during fuel combustion,
• during gas ionization,
• during turbulent plasma motion,
• during the operation of electrical equipment.

Below are shown the locations where electromagnetic waves arise in various jet engine designs

1. turboshaft engine
2. turboprop engine
3. turbofan engine
4. Turbojet engine
5. Ramjet engine
6. Rocket engine

Sources of electromagnetic radiation in a jet engine

1. The fuel combustion process

During combustion of the fuel-air mixture, high temperatures are produced (up to 2000–2500 K). Under such conditions:

• molecules become excited,
• atoms emit photons,
• thermal (infrared) radiation arises.

This radiation belongs to the infrared range and is the main type of electromagnetic radiation of the engine.

2. Gas ionization

At high temperatures part of the gas becomes ionized — free electrons and ions appear. Their motion:

• creates currents,
• causes radio-frequency radiation,
• forms plasma effects.

This is especially pronounced in afterburner chambers and rocket engines.

3. Turbulence and shock waves

In the jet stream there arise:

• vortices,
• shock waves,
• rapid pressure changes.

These processes cause fluctuations in the density of charged particles, which also leads to the emission of electromagnetic waves.

4. The engine's electronic systems

Modern jet engines are equipped with:

• control systems,
• sensors,
• generators,
• cable lines.

The operation of these devices is accompanied by electromagnetic radiation in the radio range.

Radiation ranges

Different ranges of electromagnetic radiation are observed in a jet engine:

• infrared (thermal radiation of the jet),
• visible (flame glow),
• ultraviolet (excited atoms),
• radio-frequency (plasma processes and electronics).

Practical significance

1. Aircraft detection

The engine's infrared radiation is used by:

• heat-seeking homing heads,
• detection systems.

2. Engine diagnostics

From the radiation spectrum one can determine:

• temperature,
• gas composition,
• engine operating mode.

3. Electromagnetic compatibility

It is important to take radiation into account for:

• preventing interference,
• protecting onboard electronics,
• ensuring the reliability of control systems.

Power distribution graph of a jet engine's electromagnetic radiation

Below is an approximate graph of the power distribution of a jet engine's electromagnetic radiation (a typical turbojet engine running on Jet-A kerosene). The X axis is frequency, the Y axis is relative radiation power.

Main peaks:

• radio range — weak noise from the plasma and electronics
• infrared range — main maximum (thermal radiation of the jet)
• visible/UV — a small peak from the flame

Physical meaning of the electromagnetic wave power distribution

Low frequencies (radio)

• noise from the jet plasma
• operation of generators
• cables acting as antennas
  → power is small

Microwave range

• fluctuations of the ionized flow
• jet turbulence
  → medium level

Infrared range — maximum

• thermal radiation of hot gases
• temperature 800–1800 K
  → main contribution of energy

Visible and ultraviolet

• flame glow
• excited atoms
  → small peak

Mitigating interference caused by jet engines

Electromagnetic interference from jet engines can affect radio communication, navigation systems, and onboard electronics. Therefore, special methods have been developed to reduce and suppress it.

Main causes of interference

Interference arises due to:

• ionization of gases in the engine jet
• spark discharges in the ignition system
• operation of generators and electrical equipment
• turbulence and plasma processes
• long cable lines acting as antennas

Methods of mitigating interference from jet engines

1. Shielding

Metal shields are used for:

• cables
• electronic units
• sensors

Shielding prevents electromagnetic waves from radiating outward and protects sensitive equipment.

Examples:

• braided shielding of shielded cables
• metal housings of instruments
• shielding partitions in the engine

2. Signal filtering

Used are:

• LC filters
• ferrite rings
• impulse noise suppressors

They reduce high-frequency noise entering the power supply and control circuits.

3. Grounding and potential equalization

Proper grounding:

• reduces parasitic currents
• lowers the level of radio interference
• prevents charge accumulation

It is important to use a single grounding point and avoid "ground loops".

4. Optimal cable routing

To reduce interference:

• power and signal lines are separated
• cables are twisted (twisted pair)
• conductor length is reduced
• they are routed away from the engine

5. Use of interference-resistant electronics

Used are:

• differential inputs
• digital filters
• robust data transmission protocols

This reduces sensitivity to external interference.

6. Plasma and thermal methods

For the jet stream:

• optimizing fuel composition
• stabilizing combustion
• reducing ionization

This reduces the engine's radio-frequency radiation.

7. Shielding the ignition system

This is especially important for:

• spark plugs
• ignition wires
• high-voltage units

Used are:

• resistive spark plugs
• shielded wires
• metal housings

Practical significance

Mitigating interference makes it possible to:

• improve the aircraft's radio communication
• increase navigation accuracy
• protect the autopilot
• ensure flight safety

Use of the various wave ranges of a jet engine

A jet engine emits electromagnetic waves across different ranges. Each range has its own practical application in aviation, diagnostics, and safety systems.

1. Infrared range

The main source — is the engine's hot jet and heated structural parts. This radiation belongs to
Infrared radiation.

Use:

• thermal imaging observation systems
• aircraft detection systems
• engine temperature monitoring
• overheating detection of parts

Example: thermal imagers capture the temperature of the nozzle and the jet.

2. Visible range

The flame glow in the combustion chamber belongs to
Visible light.

Use:

• visual monitoring of combustion
• mixture quality diagnostics
• afterburner mode monitoring

From the flame color one can determine:

• rich mixture — yellow glow
• normal — blue
• overheating — bright white

3. Ultraviolet range

Excited atoms emit
Ultraviolet radiation.

Use:

• flame sensors
• combustion presence monitoring
• automatic engine start systems
• onboard energy accumulation

Such sensors react quickly to the appearance of a flame.

4. Radio-frequency range

The ionized jet and electrical equipment create
Radio waves.

Use:

• jet plasma analysis
• engine mode monitoring
• turbulence research
• fault diagnostics

Sometimes the engine's radio noise is used to monitor its condition.

5. Microwave range

The plasma jet can interact with
Microwave radiation.

Use:

• radar studies of the jet
• flow velocity measurement
• plasma density monitoring

This is applied in scientific research and engine testing.

Summary table of applications of a jet engine's electromagnetic waves

Conclusion

Electromagnetic radiation in a jet engine is a natural consequence of high-temperature and plasma processes. It arises from fuel combustion, the motion of ionized particles, and the operation of electrical equipment. Studying this radiation is important for engine diagnostics, improving efficiency, and developing detection and protection systems.