Simpler direct water injection cycles

In the search for higher plant thermal efficiency, the simplicity of the two basic STIG and EGT cycles, as described by Frutschi and Plancherel, has to some extent been lost in the substantial modifications described above. But there have been other less complex proposals for water injection into the simple unrecuperated open cycle gas turbine one simply involves water injection at entry to the compressor, and is usually known as inlet fog boosting (IFB) the other involves the front part of an RWI cycle, i.e. water injection in an evaporative intercooler, usually in a high pressure ratio aero-derivative gas turbine plant. 

For the IFB plant the main advantage lies in the reduction of the inlet temperature, mainly by saturating the air with a very fine spray of water droplets [13]. This, in itself, results in an increased power output, but it is evident that the water may continue to evaporate within the compressor, resulting in a lowering of the compressor delivery temperature. A remarkable result observed by Utamura is an increase of some 8% in power output for only a small water mass flow (about 1% of air mass flow). However, the compressor performance may be adversely affected as the stages become mismatched [14], even for the small water quantities injected. 

In the second development, the emphasis is on taking advantage of the increa.sed specific work associated with evaporative intercooling and of the increased mass flow and work output of the turbine. Any gain on the dry efficiency is likely to be marginal, depending on the split in pressure ratio. 

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