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Super hydrophobic and erosion resistant coating for turbine scroll and downstream pipe

Periodic Reporting for period 2 - ERICE (Super hydrophobic and erosion resistant coating for turbine scroll and downstream pipe)

Reporting period: 2020-04-01 to 2021-12-31

Deposition of ice on aircraft surfaces is a widespread problem causing high costs and impairing functionality and safety, as it leads to higher energy consumption, increased drag, lower energy output, but also risk of damage and accidents. Current solutions for the air cycle machine (ACM) use a heating system on the downstream pipe, thus requiring high energy. ERICE’s aim is to provide maturation of a low-energy, cost-effective and eco-compliant ice-mitigation system with equal or improved performance compared to the currently used active mitigation system and without a corresponding increase in weight and volume, as stated in the work-plan challenges of the SYSTEMS ITD within CleanSky2. ERICE´s solution aims to provide relevant energy savings with respect to current technologies without detriment in the ice protection performance and in surface robustness/durability.
ERICE’s development is an improved eco-friendly and cost-effective hydrophobic/ice-phobic surface solution (i.e. a passive ice protection solution) able to resist ice erosion conditions in a turbine scroll and downstream pipe of a representative ACM. The best results on the aluminium substrate have been achieved through a hybrid organic-inorganic coating (SiO2-ZrO2-methacrylate), thin (1-8 µm) and with low surface free energy. The coating is also very flexible, thus providing erosion resistance to the surface, and it presents very good adhesion to metal and plastic substrates (PEEK thermoplastic). ERICE coating has been also combined with texturing techniques (micropatterns transfer by hot embossing) on PEEK substrate, with excellent results.
The anti-icing properties of the treated surfaces have been evaluated in a classical ice tunnel as well as in a dedicated test set-up implemented at Cranfield University within ERICE project, to reproduce the conditions of ice formation, accretion and erosion phenomena inside the turbine and the pipe of a representative air cycle machine. Technological samples have been validated in ERICE test rig and further tests are also scheduled to be performed at the TM facilities on a complete Turbomachine.
Life Cycle Assessment and Life Cycle Costing have been performed to investigate and demonstrate the economic viability and ecological relevance of the studied ERICE solution for super hydrophobic and erosion-resistant coatings. ERICE coating showed better environmental and cost-effective performance than the reference solution currently in use.
Cranfield University implemented an ice test rig (Figure 1) capable of reproducing a range of conditions similar to the actual ACM, for which ice develops at the turbine exhaust pipe (Figure 2). Various types of ice can be formed depending on the inlet conditions. Two bespoke ice adhesion measurement devices have also been developed and manufactured.
Six commercial materials were screened at TECNALIA (Figure 3) to perform a benchmark reference for ERICE development.
TECNALIA implemented an innovative eco-friendly solution combining a sol-gel coating and surface texturing on AA2024 and PEEK. Surface treatments with hydrophobic behaviour have been formulated to fulfil the requirements for corrosion and erosion resistance with anti-icing performance. A hydrophobic sol-gel formulation with high viscosity has provided AA2024 with the best ice-phobic results, while a combination of texturing (through hot embossing) and hybrid sol-gel coating have been successfully applied on PEEK.
ERICE’s FSmooth and F75 (both developed by TECNALIA) are the best surfaces reducing the ice adhesion and are more prone to early shedding than the baseline TSAA solution. Further tests at Liebherr testing facility on a complete turbomachine are scheduled for summer 2022.
An economic and ecological analysis has been performed by QUANTIS: TSAA on AA2024 has been compared with ERICE sol-gel based coating and the results showed a better environmental performance of this last for all the assessed environmental indicators. From a cost perspective ERICE solution performs better and the potential economic benefits could be further increased when considering the operational costs, as it will allow reducing the energy consumption during flight.
The target groups of ERICE communication activities are industrial and scientific communities, policy makers, public and private investors, and the general public. The main ERICE actions include participation to conferences (although most were postponed due to COVID19); publication of project flyer; publication of a project video; regular feeding of ERICE updates through LinkedIn (TECNALIA team) and partners websites; paper submissions, etc. In addition, a patent for the sol-gel coating developed at Tecnalia has been granted (EP3842501).
The expansion of background studies of icing into condensing flow (mixtures of droplets, ice particles) and the consideration of the flow regime (combined ice deposition and erosion of the accreted ice) provides new opportunities and challenges in experimental science. An area of novelty is how a combination of droplet and solid particle erosion data are used to specify suitable impact conditions for erosion testing. ERICE´s approach, based on an close coupling of experiment and ice mechanical modelling, is novel in the development of a methodology for predicting the correct conditions for ice shedding. In addition, to the best of partners´ knowledge, it is the first fracture mechanics-based ice adhesion test on the inside of a pipe. The work is also novel in relation to the specific application.
New surface treatments have been developed based on the modification of hybrid sol-gel formulations and its combination with new processing methods such as nanoimprinting lithography. ERICE is a great opportunity for studying the combination of the mentioned technologies, with the aim of developing low surface free energy and super-hydrophobic surfaces and understanding the relationship to anti-icing and ice-phobicity properties. Thanks to the tailoring of an organic-inorganic material, which allows to balance mechanical properties such as hardness and flexibility, corrosion and erosion resistance in specific conditions have been demonstrated and a patent awarded.
ERICE novel technology has projection in more electrical aircraft configurations, as part of electrically driven environmental control systems and in bleed-less power configurations, thus contributing to the environmental, competitiveness and societal impacts. ERICE development is free of toxic materials with a detrimental impact on the environment and it meets REACH regulations. In addition, ERICE solution will substitute the active anti-icing systems currently used, based on heating systems and hence energy consuming. ERICE provides a passive anti-icing answer, which contributes to energy saving. The novel technology is also transferrable to other ice-sensitive turbine environments, ice-sensitive laminar-flow environments and even to ice-mitigation in other industry sectors, such as wind turbines or high-tension electrical cables.
In the medium/long term, the project will help strengthening the position of TECNALIA and CU (and associated business network) as leading technology providers for anti-icing application, contributing to European competitiveness targets. New scientific/technology knowledge is also generated, which will strengthen the position of the European scientific community in the field.
Full-scale rig front (left) and rear (right) assembly.
Example of ice accreted inside the AA2024 exhaust pipe.
Table with results of screening of commercial solutions.