The Problem of Fuel-oil Ash Deposition in Open-cycle Gas Turbines

The loss of power due to the deposition of fuel-oil ash on the turbine blades at present limits the use of boiler fuels in open-cycle gas turbines, and therefore prevents the more widespread application of this form of prime mover in the marine and industrial fields. The nature and occurrence of the ash-forming constituents are discussed, followed by consideration of the possibilities of removal of these from the oil. There appears to be no solution along these lines nor by removal of the ash from the gas stream. The basic factors controlling deposition of ash are still not fully understood and therefore further experimental work is required. However, a method which gives a considerable reduction in deposition has been discovered. In this, combustion of the fuel droplets is controlled so that each droplet burns down and leaves the combustion chamber as a hard, dry, carbon particle containing an appreciable proportion of the ash. The combustion loss due to this unburnt carbon is less than 1 per cent. Long-term engine tests are now required to assess the practical use of the method. Another means of reducing deposition which appears to offer considerable promise is the use of various additives to the fuel or gas stream. Of those tested the oxides of silicon, zinc, and magnesium were the most effective.