Applications of Air Compressors in Aircraft Air Start Unit.
The 3 ways of aircraft bleed air
Oil-free diesel air compressor is the core of the aircraft air start unit which provides pressurized air of a certain flow, pressure and temperature to the corresponding air-using system. Air-using systems in aircraft include air conditioning system, cabin pressurization control, wing anti-icing, engine inlet anti-icing, hydraulic oil tank pressurization, etc. There are three methods for aircraft bleed air.
Engine bleed air
The aircraft mainly bleeds air through the engine during flight. Typically, the left-wing engine supplies air to the left air conditioning system, while the right-wing engine supplies the right system. In special circumstances, the isolation valve can be opened to connect the engine bleed air systems on both sides. Engine bleed air is usually controlled by the following components.
The aircraft compressor in the engine bleed air passes through the pressure regulating shut-off valve (PRSOV), then through the precooler, to the air source main pipe. During this period, there are also temperature sensors, pressure sensors, etc. for detection to prevent over-temperature or over-pressure of bleed air.
APU bleed air
APU stands for Auxiliary Power Unit. It is located at the tail end of the aircraft. Its core is a small turbine engine. It is a power unit in addition to the main engine of the aircraft. Its function is to independently provide power and compressed air to the aircraft.
Some APUs can also provide additional thrust. Once an engine bleed air system fails, the APU can be used to bleed air at a certain flight altitude. Some aircraft can also bleed air from the APU to reduce engine power loss during takeoff. The APU bleed air is controlled by the APU bleed air valve.
As one of the power units of the aircraft on the ground, the APU will provide electricity and power after startup. Since the APU consumes fuel during operation, long-term use will cause increased carbon emissions and unnecessary fuel consumption.
Therefore, more and more airports have prepared ground bridge equipment (GPU) for aircraft to provide electricity and cooling to replace the APU, thereby reducing fuel consumption and carbon emissions.
At airports without GPUs, aircraft air start units and power supply units are often provided for aircraft to ensure air conditioning and electricity.
Aircraft air start unit
Aircraft air start unit is a special equipment that uses oil free dry air compressor to generate low-pressure, large-flow compressed air for aircraft, start aircraft engines, and provide auxiliary air supply and aircraft inspection for aircraft.
It is an indispensable support equipment for civil and military airports. If the aircraft APU fails or needs to be shut down for cooling, a large amount of air provided by the aircraft air start unit is needed to start the engine and assist the aircraft in taking off.
The aircraft air start unit, equipped with a truck-mounted diesel-powered dry oil-free screw compressor, generates robust compressed air to meet the ground air-start requirements for various large, medium, and small aircraft, as well as to power auxiliary equipment for aircraft ground inspection and maintenance.
Classification of air source pressure
Aircraft air source systems are utilized far more extensively than commonly assumed. Beyond supplying air for air conditioning and pressurization systems, they are critical for wing leading-edge anti-icing, engine starting, water tank pressurization, and fuel tank inerting.
Modern aircraft air source systems are categorized into high-pressure, medium-pressure, and low-pressure systems based on pressure levels, each differing in sourcing methods, system configurations, and applications:
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High-pressure air source
Typically sourced from engine bleed air, with pressures ranging between 40โ60 PSI.
Primary applications: Cabin pressurization, wing anti-icing, and engine inlet anti-icing.
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Medium-pressure air source
Usually derived from APU (Auxiliary Power Unit) bleed air, with pressures of 30โ40 PSI.
Key uses: Air conditioning, water tank pressurization, and hydraulic reservoir pressurization.
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Low-pressureair source
Generally supplied by ground air sources, with pressures of 10โ20 PSI.
Main applications: Ground air conditioning and engine starting.
As a ground support equipment (GSE) for aircraft line maintenance, ground air source units can start engines or supply air conditioning systems. These units typically operate in two modes: engine start mode and air conditioning mode. Compared to using APU, ground air sources offer a more economical solution by conserving onboard fuel.
Which type of air compressor is suitable for aircraft air start unit
Aircraft air start units are generally equipped with diesel oil-free air compressors as air sources to bleed air to aircraft engines.
Diesel air compressors used in aircraft air start units generally need to meet the following requirements:
Environmental requirements
The diesel air compressor of the aircraft air start unit should be able to work normally at an ambient temperature of -20โ~50โ and an altitude of less than 4000 meters.
Air capacity requirements
The diesel air compressor used for the aircraft air start unit should be able to meet the air supply requirements of different models under standard conditions (standard conditions refer to an intake temperature of 20โ and an intake pressure of 0.1MPa), and the exhaust temperature at the end of the aircraft compressor’s air pipe should not be higher than 200โ, and the continuous working time should not be less than 1h.
Air quality requirements
The air supply pressure and flow rate of the diesel oil-free air compressor of the aircraft air start unit should be adjustable to meet the requirements of different aircraft engines; the compressed air should meet the corresponding dryness and pollutant content standards.
Noise and emission requirements
Under the air supply state, the noise of the diesel air compressor unit of the aircraft air start unit should not exceed 100 dB(A). The exhaust pollutant emission limit of the oil-free air compressor should comply with the environmental protection regulations of the corresponding country.
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Contact your local Kotech dealer today and discover how an air compressor can increase your productivity and safety.
Kotech Diesel Oil-Free Air Compressor
Kotech’s specially designed oil-free air compressor for aircraft air start units is driven by a diesel engine and suitable for aircraft engine starting, auxiliary air supply, aircraft inspection, and air conditioning systems.
Its key features include:
- Oil-free dry air compressor: Delivers pure, oil-free compressed air, ensuring no contamination of aircraft engines or air conditioning systems by lubricants. ISO 8573-1 Class 0 certification for zero oil content and dew points below -40ยฐC to prevent icing in pneumatic lines.
- High efficiency and energy saving: Utilizes high-precision synchronized gears and high-temperature-resistant, anti-corrosion coatings to enhance compressor efficiency. Advanced models deliver adjustable airflows (typically 3,000โ6,000 CFM) and pressures (30โ50 PSI) to accommodate varying aircraft requirements.
- Low-temperature start: Equipped with an auxiliary heating system to ensure reliable diesel engine ignition in cold conditions.
- Safety and reliability: Incorporates multiple protection mechanisms, including high water temperature alarm/shutdown, overspeed alarm/shutdown, and low oil pressure alarm, ensuring operational safety. Scalable configuration, supporting mobile aircraft air start unit (ASU) carts and fixed ground stations, can be adapted to airport infrastructure.
- Noise control and emission compliance: The vehicle structure employs sound-absorbing materials to minimize noise exposure and protect operator health. Integrate noise suppression technologies to keep operational noise below 100 dB(A). Additionally, they comply with Tier 4 Final or equivalent emission standards, minimizing nitrogen oxides (NOx) and particulate matter.
- Intelligent monitoring: Integrated sensors track parameters such as air purity, pressure and temperature in real time, and automatically issue alarms when the bleed air is overheated or overpressured.
Configurations and applications of Kotech air start unit diesel air compressor
Kotech’s diesel-powered oil-free dry air compressor stably delivers high-pressure, high-temperature air at 42 PSI and 300 PPM.
It features user-friendly operation and an intelligent control system that automatically monitors and displays critical parameters such as exhaust pressure and temperature during aircraft startup.
Additionally, the Kotech aircraft air start unit compressor is housed in a weatherproof enclosure and equipped with an efficient cooling system. Powered by internationally renowned diesel engines (e.g., Cummins, Perkins, Yanmar, Caterpillar), it ensures high-performance operation in remote areas without grid power or water sources, during nighttime, and under complex weather conditions.
The Kotech aircraft air start unit compressor is widely applicable to large, medium, and small military and civilian aircraft, including the B737, B747, B757, B777, A300, A310, A320, A340, and A380 (excluding those equipped with GE90 engines).
Conclusion
While traditional air source systems simplify compressed air delivery to downstream systems, their drawbacks are evident: high-temperature, high-pressure pipelines permeate the aircraft, where leaks risk damaging adjacent equipment or compromising structural integrity.
Innovative air start unit air compressor air supply approaches reduce overall fuel consumption and, crucially, eliminate engine bleed air pipelines, mitigating risks of high-pressure gas leaks and significantly enhancing system reliability.
