Tham khảo tài liệu 'gas turbine engineering handbook 2 episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | An Overview of Gas Turbines 35 orate partly burn and prepare the fuel for rapid combustion within the remainder of the burning zone. Ideally at the end of the burning zone all fuel should be burnt so that the function of the dilution zone is solely to mix the hot gas with the dilution air. The mixture leaving the chamber should have a temperature and velocity distribution acceptable to the guide vanes and turbine. Generally the addition of dilution air is so abrupt that if combustion is not complete at the end of the burning zone chilling occurs which prevents completion. However there is evidence with some chambers that if the burning zone is run over-rich some combustion does occur within the dilution region. Figure 1-24 shows the distribution of the air in the various regions of the combustor. The Theoretical or Reference Velocity is the flow of combustor-inlet air through an area equal to the maximum cross section of the combustor casing. The flow velocity is 25 fps mps in a reverse-flow combustor and between 80 fps mps and 135 fps mps in a straight-through flow turbojet combustor. Combustor inlet temperature depends on engine pressure ratio load and engine type and whether or not the turbine is regenerative or nonregen-erative especially at the low-pressure ratios. The new industrial turbine pressure ratio s are between 17 1 and 35 1 which means that the combustor inlet temperatures range from 850oF 454oC to 1200oF 649oC . The new aircraft engines have pressure ratios which are in excess of 40 1. Combustor performance is measured by efficiency the pressure decrease encountered in the combustor and the evenness of the outlet temperature profile. Combustion efficiency is a measure of combustion completeness. Combustion completeness affects fuel consumption directly since the heating value of any unburned fuel is not used to increase the turbine inlet Figure 1-24. Air distribution in a typical combustor. 36 Gas Turbine Engineering Handbook .
