Generally turbine engines are washed when the EGT trend is climbing towards its limits. During steady state cruise engine parameters are recorded and over time the figs will drift upwards as the engine gets older. Modern a/c will automatically d/load the data while on older a/c the F/E manually records the figures. On some a/c TO
data is automatically downloaded.
On the CF6-50 coke granules are used the clean the HPC. The bleeds are turned off engine power set at Flt idle and the granules are fed in over a period of 90 secs.
In addition to normal dirt the CF6 also has another reason for comp wash. The inner walls of the CF6 HP
Comp case is sprayed with aluminium during build and the comp blades will cut into this to minimise the tip clearance and thus improve efficiency. Naturally the 'ground off ally' passes down the compressor and it will attach itself to the blades as splatter. After a period of time a comp wash is carried out to remove this splatter.
JT9's & CFM56's are normally washed with warm water but if a deep clean is required a soap solution is used