When an engine anti-ice system required to provide protection against ice formation in the inlet. Engine service bleeds air extracted from the compressor of the diffuser of the engine anti-iced and routed to the inlet area through external piping and control valves.
Once an aircraft flies through the atmosphere with high humidity and a temperature around the freezing level. Moisture collects on the walls of this aircraft since ice.
In the atmosphere inlet of the turbofan engine are just two parts in which ice may collect over the surfaces. These are the inlet lip of the air inlet and the fan rotor.
To the fan rotor, the ice may accumulate on the fan blades and also on the surface of the spinner.
The ice onto a Top of This inlet and also the engine Elements Disturbs the airflow and also creates vortices.
In front of the breaker inlet, these vortices can cause shaky compressor operation and cause a stall and surge.
Ice over the fan blades additionally produces imbalance, which Leads to vibration.
Detached ice bits out of your inlet arrangement make a hazard for foreign object injury whenever they hit on the fan and the components on the other side of the fan.
To prevent ice accumulation on the fan blades, no special installations are necessary. At N 1 speeds above idle, the centrifugal force sheds the ice from the fan blade due to the glossy surface of the fan blades.
The Elements Positioned from the fan rotor are normally in warm surroundings because of the air temperature in these areas.
Here ice will accumulate only at low shaft speeds. This can be a problem in the primary airflow for the operation of the compressors due to the vortices generated by the ice.
As these components warm up during engine performance at higher shaft speeds. No steps are taken to prevent icing in these areas.
Many aircraft have air passages in the compressor inlet case, inlet guide vanes, nose dome, and nose cowling.
Hot compressor bleeds air flows through these passages to stop the formation of ice.
Ice can form when the engine operated at high speed on the ground when the temperature is as high as 10°C if the air is moist. The high velocity of the inlet air creates a pressure drop that lowers the temperature of the air enough for ice to form.
In flight, the anti-icing system is turned on before entering areas of visible moisture (rain or clouds) when the inlet temperature is between about 10°C and -15°C. Below -15°C, there is so little moisture in the air that ice is not likely to form.
If this should happen, direct a flow of warm air through the engine until all of the ice is melted and the rotating parts turn freely.
On the surface of an air inlet, the ice starts to build up around the stagnation point of the inlet lip.
To avoid this process it is sufficient to heat the inlet lip only. This can be done with warm air or electrically.
On turbofan engines, the usual principle is heating with warm air.
To minimize the extraction of energy from the engine and to prevent the overheating of the inlet structure. The supply of hot air can discontinue closing the shutoff valve of the system.
The pilot activates the system when he accepts that icing is imminent.
On some aircraft, ice warning systems installed to give the pilots a hint about the icing situation.
ENGINE ANTI-ICE AIR SYSTEM DESCRIPTION
The bled air also passes through a pressure-regulating anti-ice valve (Boeing: Thermal Anti Ice – TAI / Airbus: Engine Anti Ice) and a venturi restrictor.
Air is then sprayed through a piccolo tube into the nose cowl lip.
The ducting in multiple sections – engine mounted (upper, lower and FWD) and mounted in the fan cowl.
ENGINE ANTI-ICE VALVE DESCRIPTION
The engine anti-ice valve is of the butterfly type and usually electrically controlled and pneumatically actuated on modern civil aircraft.
When the valve operates, it regulates the maximum downstream air pressure to about 20 – 60 psi depending on the engine.
The engine anti-ice valve has:
- a butterfly valve sub-assembly
- an actuator sub-assembly
- a pilot regulator sub-assembly
- HP and LP pressure switches
- one filter
- an ON/OFF solenoid
The bleed air source is taken from the HP compressor.
When the engine operates and the ENG ANTI ICE push button switch selected ON:
The valve solenoid de-energized, the valve opens and regulates at about 60 psi depending on the engine.
The valve LP switch used to detect the open position of the valve when the pressure is more than 6 psi.
This information transmitted to the ECAM/EICAS and displayed as a green ENG ANTI ICE memo indication or EAI on the primary EICAS page.
The Engine Interface Unit on FADEC engines acquires the configuration of the ENG ANTI ICE push button switch and transmits it to the Full Authority Digital Engine Control (FADEC) system
The FADEC system then automatically selects continuous ignition to prevent a flameout caused by a stall/surge in the compressor caused by the ingestion of melted ice or flame out due to the ingestion of water.
The Zone Controller (ZC) or equivalent computer uses the position of the ENG ANTI ICE push button switch or the position of the engine anti-ice valve (provided by the LP switch) to calculate the bleed status coefficients and alter the bleed to the packs to prevent excessive bleeding off of air from the engine compressor, as well as informing the FADEC to increase the fuel flow for increase bleed scheduling.
When the ENG ANTI ICE push button switch selected off, the solenoid energized and the valve closes.
No indication then displayed on ECAM/EICAS.
On model civil aviation aircraft the appropriate aircraft computers inhibit the engine anti-ice system under the following conditions:
- Engine start – to prevent excessive bleed of hot air from the compressor during low RPM ranges
- Fan case overheat
- Engine anti-ice selector set to OFF
- Engine anti-ice selector set to AUTO with no ice detected.