542 Engine Operating Conditions

One obvious way to raise system efficiency is to operate gas turbines with more aggressive operating conditions, i.e., higher pressure ratios and/or greater TITs. For example, the designer can choose to operate at higher TITs or to increase pressure ratios in the system. As Figure 5.15 illustrates, substantial system efficiency improvements are possible with either of these approaches for a typical simple-cycle engine in the MT size range.

However, the strict cost constraints require use of metal components without advanced features found in more expensive gas turbine engines (e.g., air-cooled blading). As a result, rising pressures and temperatures quickly reach limits that exact a steep price in engine component life. High temperatures are especially problematic due to the creep-life and stress constraints of the materials used in MTs. As a point of reference, TITs in current MT designs vary between 1600 and 1850°F [870 and 1000°C]). At this temperature level, the strengths of the high-temperature materials typically used in MTs are very sensitive to temperature and quickly lose strength (and, thus, reduce engine life) with higher temperature.

Increasing system pressure ratio, of course, raises stresses in the system. When coupled with the relatively high temperatures mentioned earlier, it is easy to see why these two aggressive conditions can so dramatically shorten engine life. One of the more important advantages of the two-shaft MT

Pressure Ratio

Pressure Ratio

FIGURE 5.15

Pressure ratio and TIT effects for nonrecuperated MTs.

design is that these life-limiting stresses are essentially split between the two turbines. The effect is so favorable that the designer can even use somewhat higher TITs and still preserve long engine life. One other disadvantage of operating at higher pressure ratios is the resulting need for higher fuel delivery pressures because higher output pressures from the fuel gas booster (required in at least half of the U.S. natural gas service area) are required, thereby consuming more parasitic power.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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