Published online by Cambridge University Press: 04 July 2016
It is understandable for fundamental cycle efficiency reasons that the technology level claimed by manufacturers in the development of gas turbines has tended to be judged by the declared maximum TET, but this is not any longer an adequate criterion. A better criterion would be the maximum TET at which it is possible to operate a turbine for a given value of the net turbine shaft efficiency after allowing for all the cooling losses without a penalty in the operating life of the turbine in service.
Figure 1 shows how the specific fuel consumption of turbofan engines varies with turbine entry temperature and overall pressure ratio for different levels of polytropic efficiency of all the components of −2%, +2%, +4% relative to datum. The importance of obtaining the highest possible component efficiencies rather than by further increasing TET and overall pressure ratio (which increase engine complexity and cost), is clearly brought out.