Combustors
Heat input to the gas turbine Brayton cyc1e is provided by a combustor. The combustor accepts air from the compressor and de1ivers it at an e1evatedtemperature to the turbine (idea11y with no pressure 1oss). Thus， the com-bustor is a direct-fired air heater in which fue1 is burned a1most stoichio-metrica11y with one-third or 1ess of the compressor discharge air. Combustion products are then mixed with the remaining air to arrive at a suitab1e turbinein1et temperature. There are many types of combustors， but the three majortypes are tubu1ar， tubo-annu1ar， and annu1ar. Despite the many designdifferences， a11 gas turbine combustion chambers have three features: (1) arecircu1ation zone， (2) a burning zone (with a recircu1ation zone whichextends to the di1ution region)， and (3) a di1ution zone. The function of therecircu1ation zone is to evaporate， part1yburn， and prepare the fue1 for rapidcombustion within the remainder of the burning zone. ldea11y， at the end ofthe burning zone， a11 fue1 shou1d be burnt so that the function of the di1ution zone is so1e1y to mix the hot gas with the di1ution air. The mixture 1eaving the chamber shou1d have a temperature and ve1ocity distribution acceptab1e tothe guide vanes and turbine. Genera11y， the addition of di1ution air is soabrupt that if combustion is not comp1ete at the end of the burningzone，chi11ing occurs and prevents comp1etion. However， there is evidence withsome chambers that if the burning zone is run overrich， some combustion does occur within the di1ution region.
Combustor in1et temperature depends on engine pressureratio， 1oadand enginetype， and whether or not the turbine is regenerative or nonregen-erative especia11y at the 1ow-pressure ratios. The new industria1 turbinepressureratio'sarebetween17:1，and35:1，whichmeansthatthecombustor in1et temperatures range from 850 0F (454 0C) to 1200 0F (649 0C). Thenew aircraft engines have pressureratios， which are in excess of 40:1.
370
Regenerative gas turbines have combustor in1et temperatures， which range from 700 0F (371 0C) to 1100 0F (593 0C). Combustor pressures for a fu11-1oad operation vary from 45 psia (3.1 Bar) for sma11 engines to as much as588 psia (40.5 Bar) in comp1ex engines. Fue1 rates vary with1oad， and fue1atomizers may be required for f1ow ranges as great as 100:1. However， the variation in the fue1-to-air ratio between id1e and fu11-1oad conditions usua11ydoes not vary by more than a factor of three. During transient conditions，fue1-to-air ratios vary. At 1ightoff and during acce1eration， a much higher fue1-to-air ratio is needed because of the higher temperature rise. On dece1-eration， the conditions may be appreciab1y 1eaner.Thus， a combustor that can operate over a wide range of mixtures without the danger of b1owouts simp1ifies the contro1 system.
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本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 2(39)
