JET FUELS DEVELOPMENT AND ALTERNATIVES

The jet engine group comprises aero turbines, ramjets and rockets, the ir level of performance increasing in that order, with fuel requiremen ts showing both similarities and differences. The conventional fuel fo r aero turbine engines,for example, is aviation kerosine, several vari ants of which exist for specific applications. Aviation fuel specifica tions are invariably stringent, and variations with density are shown for typical properties. The dwindling availability of optimal crudes o ver the last 25 years has resulted in a general degradation in the qua lity of aviation kerosine, with adverse effects on combustion performa nce, emissions and engine life except where hardware solutions emerged in parallel. In fact, the reduction of emissions is seen to be more a matter of engine design than fuel technology. In the near term, suppl ies of kerosine may be supplemented from sources other than crude oil, whereas in the longer term, kerosine may be substituted by liquid met hane and/or liquid hydrogen. In comparison with kerosine, liquid hydro gen produces more nitrogen in its combustion products on a fuel mass b asis, but less on an energy basis, although the flame temperature is h igher giving possibilities of more NO,. The fuel requirements of high energy content and storage stability apply across the board, but addit ional parameters of concern are heat capacity in the case of ramjets, and combustion-product chemistry with rockets, which demand a range of candidate high-performance fuels.