A high speed camera investigation is presented into the behavior of CO 2 dry-ice particles in an application of dry-ice blasting to the defouling of commercial aircraft engine compressors. An image acquisition system is deployed in the compressor section of an aircraft engine and is used to determine the evolution of dry-ice particle size and velocity from the nozzle exit to the entrance to the engine's high pressure compressor as the engine is cranked. A comparison study between CO 2 dry-ice particle laden flows and airflows with single Polyoxymethylene (POM) particles of various diameters is also presented. Measurements are made using a range of blasting system pressures and using sonic and supersonic blasting nozzles. The behavior of large CO 2 dry-ice particles (d P ≥ 1 mm) in this discontinuously and inhomogenously laden flow is compared to that of single POM particles under similar flow conditions and is found to behave similarly. The experiments presented turn out to be useful for supporting development of special purpose dry-ice blasting systems.

A dynamic indentation experiment is presented for assessment of the adhesive behavior of a range of coatings in erosive defouling of commercial aircraft engines using CO 2 dry-ice. A series of experiments is presented in which particles made from a reference material (polyoxymethylene-POM) and from CO 2 dry-ice are made to impact compressor airfoils under a range of impact angle and velocity conditions. The airfoils investigated are coated with an indicator material (PTFE), which is typically used to visualise the defouling effect in large scale compressor defouling experiments. In addition, fouled compressor airfoils taken from service and coated with a fouling typically found in low-pressure compressor stages are investigated. The energy required for the reference particles (POM) to create a defouling effect for the different coatings is determined by an experimental evaluation of their coefficient of restitution. This energy requirement is assumed to be fouling specific. Empirical defouling functions are presented. They correlate the defouling effect for both particle materials under various impact conditions. The empirical correlations are developed into a simulation procedure to predict particle impact erosion and energy dissipation of coated surfaces in numerical indentation simulations.

On-wing cleaning of engine compressors for commercial aircraft is a required maintenance task which results in greater operating efficiency and lower emission rates. It is typically carried out by injection of water and detergents into the intake of an engine while the engine is being cranked by the starter (i.e. dry-cranked). The dry-ice blasting process, a cleaning system which uses an air-flow and CO 2 dry-ice particles as cleaning agent, has been proposed as an alternative method which is potentially capable of efficient cleaning. In this context, an experimental and numerical investigation of the dry-ice defouling process is presented. A prototype of the new cleaning-system is used to defoul the compressors of a GE CF6-50 engine in a test-rig. The injected dry-ice particles disintegrate into smaller fragments and defoul the airfoils upon collision inside the dry-cranked engine. The study addresses an insight into the dry-ice particle behavior during the process and the numerical assessment of the defouling efficiency. Air-flow measurements, particle-tracking experiments utilizing a high-speed camera (HSC) and airfoil surface-mapping experiments are presented. The particle recordings are made at three positions inside of the engine and these are two-dimensionally postprocessed. The airfoil surface-mapping utilizes photographies and image post-processing to compare the airfoil surfaces before and after cleaning. The airfoils investigated are coated with polyexymethylene, which is used to visualize the defouling effect in large scale engine experiments. The process is simulated in steady state with Ansys CFX and the implementations of the newly developed particle breakup-and erosion models for dry-ice are used in an Euler-Lagrangian formulation. Rotational periodicity is assumed, and the airfoil domains are linked with a mixing-plane approach. Predicted air flow properties of the dry-cranked engine, particle size and particle velocity data, and defouling patterns of the blading are compared using experimental data where possible. Cleaning efficiency is assessed at various instants of time using various parameters of the particle breakup model and of the particle injection formulation. The overall agreement of predicted and experimental data is found to be satisfactory for engineering purposes. The mean deviations encountered range from 9.7 to 22.4%. Possible improvements of the numerical strategy presented are identified and discussed.

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