FR3145881A1 - CRYOGENIC CLEANING PROCESS - Google Patents

Abstract

CRYOGENIC CLEANING METHOD The method for cleaning an element of an aeronautical engine according to the invention, said element being polluted by deposits, said method is characterized in that it comprises the following steps: positioning a spray gun on an area to be cleaned, projection of pellets of dry ice under pressure on an area to be cleaned until the deposits are completely detached, evacuation of the deposits by dry ventilation or by a low-speed operation of the engine. Thus, this cryogenic cleaning uses carbon dioxide in solid form generally in the form of pellets of dry ice (solid carbon dioxide) which can, for example, have a diameter of 3 mm and a length of 15 mm. Figure to be published with the abstract: Figure 3

Description

CRYOGENIC CLEANING PROCESS TECHNICAL FIELD OF THE INVENTION

The technical field of the invention is that of aeronautical engines and more particularly a method of cleaning elements in these engines.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

An aeronautical engine is, for example, in the form of a turbojet comprising a compressor, a combustion chamber and a turbine. During operation, elements such as moving blades may have deposits in the form of particles or pieces. These particles or pieces may, during full throttle maneuvers and under the effect of the force generated by the gases, separate and impact the parts further downstream of the turbine. These impacts may be acceptable in some cases, but in other cases, they generate removal of the engine to repair these parts. Some of these parts are particularly fragile and can break. It is therefore necessary not only to clean but also to remove the particles and/or pieces to avoid having to change the damaged parts and remove the engine.

Today, a technique used to clean engines in situ is water washing, which aims to clean the entire engine with high-pressure water to improve its performance and which allows manual cleaning. The disadvantages of water washing are the presence of secondary waste, the risk of corroding the blades due to the presence of water and finally the fact that this technique is used globally on the entire engine but does not allow for local cleaning and therefore more precise cleaning of a part. As for manual cleaning, it takes time and is abrasive, which leads to a risk of losing material on the part.

Other cleaning techniques exist such as sandblasting and chemical bath: the main disadvantage of these techniques is that they cannot be applied in situ but only when the part is removed from the engine.

Sandblasting also has the disadvantage of being abrasive and the chemical bath is also toxic and polluting.

All these techniques are therefore not satisfactory because they all have a defect.

The invention provides a solution to the problems mentioned above, by making it possible to clean engine elements in a targeted manner and to eliminate debris, without risk to other engine elements located downstream, thanks to a non-polluting and non-abrasive process.

• positionnement d’un pistolet de pulvérisation sur une zone à nettoyer,
• projection de pellets de glace carbonique sous pression sur la zone à nettoyer jusqu’à détachement complet des dépôts,
• évacuation des dépôts par ventilation sèche ou par une manœuvre à bas régime du moteur.

The cleaning method according to the invention consists of cleaning an element of an aeronautical engine, the element being polluted by deposits, said method is characterized in that it comprises the following steps:

• positioning a spray gun on an area to be cleaned,
• projection of dry ice pellets under pressure onto the area to be cleaned until the deposits are completely detached,
• evacuation of deposits by dry ventilation or by operating the engine at low speed.

This cryogenic cleaning uses carbon dioxide in solid form, generally in the form of dry ice pellets (solid carbon dioxide) which can, for example, have a diameter of 3 mm and a length of 15 mm.

These pellets are projected onto the surfaces to be treated by a flow of compressed air sent by a spray gun connected to a shooting machine. The combination of intense cold and mechanical shock causes the detachment of the polluting deposit, leaving only pure waste that is easy to treat.

Since dry ice is as hard as chalk, this process cleans surfaces gently and is therefore non-abrasive.

The evacuation of deposits is done by dry ventilation for example by running the engine at low speed in order to evacuate the deposits at low speed and thus avoid their impact energy being too high for the other parts of the engine located downstream.

Advantageously, the projection of the pellets is directed using an endoscope connected to the spray gun. The shooting machine will give a certain speed to the pellets which will thus be charged with kinetic energy, be projected onto the part by the spray gun and, upon impact, generate a localized shock wave which facilitates the decohesion of the deposit on the treated surface. The endoscope allows precise positioning of the spray gun shot on the deposit thanks to a vision of the treated part.

Advantageously, the method comprises a step of introducing the endoscope and the spray gun into the engine. The endoscope makes it possible to see into the internal parts of the engine and thus reach and target polluted areas not visible from the outside.

Advantageously, the pellets are projected by a flow of compressed air.

Advantageously, the dry ice pellets are at a temperature between -78.2°C and -78.5°C. The temperature difference between the pellets and the engine element causes sublimation due to the physical characteristics of CO ₂ . Sublimation is a change in the state of CO ₂ from −78.2°C to 20°C (average normal temperature) from solid to gaseous without passing through the liquid phase. The CO ₂ then takes up to 500 times its volume and expels the pollution, already weakened, from its support.

Advantageously, the cleaned element is a rotor blade.

Advantageously, the blade belongs to a low pressure turbine.

A second aspect of the invention relates to a cleaning device implemented by a cleaning method having at least one of the preceding characteristics, said device is characterized in that it comprises a compressor, a shooting machine, a spray gun and an endoscope attached to the spray gun.

BRIEF DESCRIPTION OF THE FIGURES

The figures are presented as examples and in no way limit the invention.

is a sectional view of an aeronautical turbojet;

is a perspective view of a turbine blade with a deposit;

is shown the action of dry ice pellets on a deposit;

is shown different stages of the process;

is an example of a cryogenic cleaning device;

is a perspective view of a spray gun with an endoscope;

illustrates the different possible movements of the spray gun.

DETAILED DESCRIPTION

Unless otherwise specified, the same element appearing in different figures has a single reference.

Throughout the description, the part first in contact with an air flow in the direction of its flow will be called "upstream", and the part located behind in the direction of the air flow will be called "downstream".

There shows an example of an aeronautical engine 1 such as an aeronautical turbojet which comprises a fan S, a low pressure compressor C1, a high pressure compressor C2, a combustion chamber D, a high pressure turbine T1, a low pressure turbine T2 and a nozzle E. The air flow is illustrated by the arrows F, and is from the fan S, upstream, to the nozzle E, downstream.

As can be seen in the , during operation of the engine 1, the moving blades 10 may have deposits 2, incrustations, particles or debris brought by the air. These particles or debris, come to be deposited at different places on the different parts (here at the foot of the blade), then can, during full throttle type maneuvers (under the effect of the force generated by the gases) separate and impact the parts located further downstream of the engine.

The cleaning device 4 illustrated comprises a power supply, dry ice 40, a compressor 41, a blasting machine 42 and a spray gun 43. The dry ice 40 is poured into the blasting machine 42 and then sprayed by the spray gun 43.

The 43 spray gun can be oriented in all directions as can be seen , which allows you to reach all parts of the elements you want to clean.

In the example of the , the spray gun 43 is coupled to an endoscope 44 which will make it possible to see the areas to be cleaned even if these are inside the engine 1. The endoscope 44 includes lighting and an optical system which conveys the image from one end of the device to the other in order to be able to correctly position the spray gun 43. It is thus possible to reach non-visible parts without having to dismantle the engine 1.

• on positionne le pistolet de pulvérisation 43 à proximité du dépôt 2 de la zone à nettoyer de l’élément du moteur 3 pour y projeter des pellets 5,voir la première image,
• par effet mécanique, l’impact des pellets 5 de glace carbonique chargés d’énergie cinétique (EC = ½ mv²) va fragilise le dépôt 2, voir la deuxième image. Cette énergie dépend de la vitesse de projection qui est choisie pour s’adapter au besoin selon le type et la taille du débris à enlever ou de la pièce en fonction de la zone à nettoyer ou du matériau de la pièce à nettoyer, elle est comprise entre 60 à 120m/s, et si on utilise une buse de sortie à profil venturi, la vitesse peut aller jusqu’à 290m/s,
• sous l’effet de la basse température (entre -78,2°C et -78,5°C voire -80°C pour la glace sèche carbonique), le dépôt 2 se fragilise, se contracte en se fissurant et se détache du support. Le différentiel thermique, différence de température entre le dépôt 2 (induite par la glace carbonique) et le support, facilite le décollement du dépôt 2, et au moment de l’impact, la glace carbonique se sublime, c'est-à-dire passe de l’état solide à l’état gazeux en prenant jusqu’à 700 fois son volume, ce qui a pour effet de provoquer le soulèvement du dépôt de la zone à nettoyer, voir la troisième image,
• évacuation des dépôts par une ventilation sèche F0 avec une faible vitesse pour éviter que les dépôts détachés n’impactent les pièces situées en aval de façon trop violente et sans risque de dégradation. Cette ventilation sèche pourra être obtenue en faisant tourner le moteur à bas régime soit environ 15 à 20% de son fonctionnement maximal. La ventilation va créer une poussée qui va évacuer les dépôts. Ceci est fait en général quand le moteur est au ralentit sol, ou « ground idle » en anglais. Celui-ci est différent selon la taille du moteur et donc l’avion qu’il motorise.

There illustrates steps of the method according to the invention:

• the spray gun 43 is positioned near the deposit 2 of the area to be cleaned of the engine element 3 to spray pellets 5 there, see the first image,
• by mechanical effect, the impact of the pellets 5 of dry ice loaded with kinetic energy (EC = ½ mv²) will weaken the deposit 2, see the second image. This energy depends on the projection speed which is chosen to adapt to the need according to the type and size of the debris to be removed or of the part depending on the area to be cleaned or the material of the part to be cleaned, it is between 60 to 120m/s, and if a venturi profile outlet nozzle is used, the speed can go up to 290m/s,
• under the effect of the low temperature (between -78.2°C and -78.5°C or even -80°C for dry carbon dioxide ice), deposit 2 becomes fragile, contracts, cracks and detaches from the support. The thermal differential, the temperature difference between deposit 2 (induced by the dry carbon dioxide ice) and the support, facilitates the detachment of deposit 2, and at the time of impact, the dry carbon dioxide ice sublimates, i.e. passes from the solid state to the gaseous state, taking up to 700 times its volume, which has the effect of causing the deposit to lift from the area to be cleaned, see the third image,
• evacuation of deposits by dry ventilation F0 with a low speed to prevent the detached deposits from impacting the parts located downstream too violently and without risk of degradation. This dry ventilation can be obtained by running the engine at low speed, i.e. approximately 15 to 20% of its maximum operation. The ventilation will create a thrust which will evacuate the deposits. This is generally done when the engine is at ground idle. This is different depending on the size of the engine and therefore the aircraft it powers.

Claims (7)

Method for cleaning an element (3) of an aeronautical engine (1), said element (3) being polluted by deposits (2), characterized in that it comprises the following steps:

• positioning a spray gun (43) on an area to be cleaned,
• projection of pellets (5) of dry ice under pressure onto the area to be cleaned until the deposits (2) are completely detached,
• evacuation of deposits (2) by dry ventilation or by operating the engine at low speed (1).

Cleaning method according to claim 1, characterized in that the projection of the pellets (5) is directed by means of an endoscope (44) connected to the spray gun (43). Cleaning method according to the preceding claim, characterized in that it comprises a step of introducing the endoscope (44) and the spray gun (43) into the engine (1). Cleaning method according to one of the preceding claims, characterized in that the pellets (5) are projected by a flow of compressed air. Cleaning method according to one of the preceding claims, characterized in that the pellets (5) are at a temperature between -78.2°C and -78.5°C. Cleaning method according to one of the preceding claims, characterized in that the cleaned element (3) is a rotor blade. Cleaning method according to the preceding claim, characterized in that the blade belongs to a low pressure turbine.