where:
ηcomb二 efficiency
的的α二 mass f1ow of gas
的的f二 mass f1ow of fue1
h3二 entha1py of gas 1eaving combustor
h2二 entha1py of gas entering combustor
LHV二 fue1 heating va1ue
The 1oss of pressure in a combustor is a major prob1em， since it affects both the fue1 consumption and power output. Tota1 pressure 1oss is usua11y in the range of 2-8% of static pressure. This 1oss is the same as a decrease in compressor efficiency. The resu1t is increased fue1 consumption and 1ower power output that affects the size and weight of the engine.
The uniformity of the combustor out1et profi1e affects the usefu1 1eve1 ofturbine in1et temperature， since the average gas temperature is 1imited by thepeak gas temperature. This uniformity assures adequate nozz1e1ife， which depends on operating temperature. The average in1et temperature to the turbine affects both fue1 consumption and power output. A 1arge combustor out1et gradient wi11 work to reduce average gas temperature and conse-quent1y reduce power output and efficiency.Thus， the traverse number must have a 1ower va1ue-between 0.05 and 0.15 in the nozz1e.
Equa11y important are the factors that affect satisfactory operation and 1ifeof the combustor. To achieve satisfactory operation， the f1ame must be se1f-sustaining， and combustion must be stab1e over a range of fue1-to-air ratios to avoid ignition 1oss during transient operation. Moderate meta1 temperaturesare necessary to assure 1ong 1ife. A1so， steep temperature gradients， whichcause warps andcracks， must be avoided. Carbon deposits can distort the 1iner and a1ter the f1ow patterns to cause pressure 1osses. Smoke is environ-menta11y objectionab1e as we11 as a fou1er of heat exchangers. Minimum carbon deposits and smoke emissions a1so he1p assure satisfactory operation.
Combustion Terms
Before proceeding with combustordesign， a definition of some terms is necessary:
1. Reference velocity. The theoretica1 ve1ocity for f1ow of combustor-in1et air through an area equa1 to the maximum cross section of the combustor casing (25fps (8mps) in a reverse-f1ow combustor; 80-135 fps (24-41 mps) in a straight-through f1ow turbojet combustor).
2. Profile fαctor. The ratio between the maximum exit temperature and the average exit temperature.
3.
Trαversenu的ber (te的perαture fαctor ). (a) The peak gas temperature minus mean gas temperature divided by mean temperature rise in nozz1e design. (b) The difference between the highest and the average radia1 temperature.
4.
Stoichio的etric proportions . Constituent proportions of the reactants are such that there are exact1y enough oxidizer mo1ecu1es to bring about a comp1ete reaction to stab1e mo1ecu1ar forms in the products.
5. Equivαlence rαtio. The ratio of the oxygen content at stoichiometric conditions and actua1 conditions:
o二 (Oxygenjfue1 at stoichiometric)
(Oxygenjfue1 at actua1 condition)
6. Pressure drop. A pressure 1oss occurs in a combustor becauseofdiffusion， friction， and momentum. The pressure drop va1ue is 2-10% of the static pressure (compressor out1et pressure). The efficiency of the engine wi11 be reduced by an equa1 percent.
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本文鏈接地址：燃氣渦輪工程手冊 Gas Turbine Engineering Handbook 2(40)
