稀釋空氣孔
燃燒效率
27．大多數(shù)燃氣渦輪發(fā)動機在海平面起飛狀態(tài)下燃燒效率幾乎是100％，在高空巡航狀態(tài)降低98％。如圖4-10所示。
31．點火過程有貧油和富油極限，類似于圖4-1l中表示穩(wěn)定性的極限。然而，點火包線在穩(wěn)定包線以內(nèi)，因為在冷狀態(tài)下建立燃燒比保持正常燃燒要困難得多。
排放尾氣
32．在排氣中發(fā)現(xiàn)的不希望有的污染物是在燃燒室中產(chǎn)生的。有4種主要污染物是受法規(guī)控制的。它們是未燃燒的碳氫化合物(未燃燒的燃油)、煙(碳粒)、一氧化碳和氮的氧化物。影響污染物生成的主要條件是壓力、溫度和時間。
Combustion chambers
正常狀態(tài)
燃燒效率
Combustion stability
28.
Combustion stability means smooth burning and the ability of the flame to remain alight over a wide operating range.
29.
For any particular type of combustion chamber there is both a rich and weak limit to the air/fuel ratio, beyond which the flame is extinguished. An extinction is most likely to occur in flight during a glide or dive with the engine idling, when there is a high airflow and only a small fuel flow, i.e. a very weak mixture strength.
30.
The range of air/fuel ratio between the rich and weak limits is reduced with an increase of air velocity, and if the air mass flow is increased beyond a certain value, flame extinction occurs. A typical stability loop is illustrated in fig. 4-11. The operating range defined by the stability loop must obviously cover the air/fuel ratios and mass flow of the combustion chamber.
31. The ignition process has weak and rich limits similar to those shown for stability in fig. 4-11. The ignition loop, however, lies within the stability loop since it is more difficult to establish combustion under 'cold' conditions than to maintain normal burning. 33.在主燃燒區(qū)的富油區(qū)里，碳氫化合物轉(zhuǎn)化成一氧化碳和煙。新鮮的稀釋空氣可用于在稀釋區(qū)中將一氧化碳和煙氧化成無毒的二氧化碳。通過燃燒過程在稀釋區(qū)的繼續(xù)進行還能減少該區(qū)中未燃燒的碳氫化合物，以確保完全燃燒。
34．氮的氧化物是在和抑制其它污染物所要求的相同條件下形成的。因此，盡快地使火焰冷卻下來并減少燃燒可用的時間是符合愿望的。這些相互沖突
的條件要求進行折衷，但是，燃燒室設(shè)計與性能的連續(xù)改善已經(jīng)導(dǎo)致燃燒過程“清潔”得多了。
Emissions
32. The unwanted pollutants which are found in the exhaust gases are created within the combustion chamber. There are four main pollutants which are legislatively controlled; unburnt hydrocarbons (unburnt fuel), smoke (carbon particles), carbon monoxide and oxides of nitrogen. The principal conditions which affect the formation of pollutants are pressure, temperature and time. 材料
35．燃燒室包容壁及內(nèi)部零件必須能夠多承受主燃燒區(qū)中很高的燃氣溫度。實際上，通過采用現(xiàn)有的最好的耐熱材料、耐高溫涂層，以及用冷卻火焰筒的內(nèi)壁作為它與火焰的隔離層已經(jīng)實現(xiàn)了上述要求。
33.
In the fuel rich regions of the primary zone, the hydrocarbons are converted into carbon monoxide and smoke, Fresh dilution air can be used to oxidize the carbon monoxide and smoke into non-toxic carbon dioxide within the dilution zone. Unburnt hydrocarbons can also be reduced in this zone by continuing the combustion process to ensure complete combustion.
34.
Oxides of nitrogen are formed under the same conditions as those required for the suppression of the other pollutants, Therefore it is desirable to cool the flame as quickly as possible and to reduce the time available for combustion. This conflict of conditions requires a compromise to be made, but continuing improvements in combustor design and performance has led to a substantially 'cleaner' combustion process.
點火包線
圖4-10 燃燒效率隨空氣／燃油比的變化
ratio.
36．燃燒室還必須承受由燃燒產(chǎn)物造成的腐蝕、溫
度梯度產(chǎn)生的蠕變失效和由振動應(yīng)力產(chǎn)生的疲勞。
圖4-11 燃燒穩(wěn)定性極限
Fig. 4-11 Combustion stability limits.
MATERIALS
35.
The containing walls and internal parts of the combustion chamber must be capable of resisting the very high gas temperature in the primary zone. In practice, this is achieved by using the best heat-resisting materials available, the use of high heat resistant coatings and by cooling the inner wall of the flame tube as an insulation from the flame.
36.
The combustion chamber must also withstand corrosion due to the products of the combustion, creep failure due to temperature gradients and fatigue due to vibrational stresses.
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