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For example, if the static compression ratio is 10:1, and the dynamic compression ratio is 7.5:1, a useful value for cylinder pressure would be 7.5 1.3 × atmospheric pressure, or 13.7 bar (relative to atmospheric pressure). The two corrections for dynamic compression ratio affect cylinder pressure in opposite directions, but not in equal strength.
For example, 10–12% of all power generated in the UK is dedicated to the production of compressed air and a portion of this power is wasted energy. Large electrical cost savings can be achieved by installing a variable speed drive compressor in place of an existing rotary screw or piston machine.
Compressor characteristic is a mathematical curve that shows the behaviour of a fluid going through a dynamic compressor. It shows changes in fluid pressure , temperature , entropy , flow rate etc.) with the compressor operating at different speeds.
These effects are caused by the sluggish response of the spool (i.e. inertia effects) to rapid changes in engine fuel flow. Compressor surge is a particular problem during slam-accelerations and can be overcome by suitable adjustments to the fueling schedule and/or use of blow-off (bleeding air off the compressor, for handling purposes).
On civil turbofans, the first stage of the LP compressor is often a single-stage fan. If the HP compressor pressure ratio exceeds about 4.5:1, then the unit will probably have variable geometry (i.e. variable stators) on the first few stages, to make the surge line on the compressor map more shallow, to accommodate the shallow working line.
A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure. [ 1 ] [ 2 ] Pressures of up to 5,000 psig are commonly produced by multistage reciprocating compressors.
Compared to the CFM56, the LEAP makes greater use of composite materials, has a second-generation Twin Annular Pre-mixing Swirler (TAPS II) combustor, and a bypass ratio around 10–11:1. The high-pressure (HP) compressor operates at up to a 22:1 compression ratio, which is roughly double the corresponding value for the CFM56's HP compressor. [7]
As can be seen in the formula for maximum theoretical thermal efficiency in an ideal Brayton cycle engine, a high pressure ratio leads to higher thermal efficiency: = where PR is the pressure ratio and gamma the heat capacity ratio of the fluid, 1.4 for air. Keep in mind that pressure ratio scales exponentially with the number of compressor stages.
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