Compressor map: Difference between revisions

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An excellent source of more information can be found [http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html here].
An excellent source of more information can be found [http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html here].

==Pressure Ratio==

Expressed as <math>\frac{P_{outlet}}{P_{inlet}}</math> or, more commonly, <math>\frac{P_{MAP} - P_{ICdrop}}{P_{ambient} - P_{id}}</math>

Where <math>P_{MAP}</math> is manifold absolute pressure, <math>P_{ambient}</math> is ambient air pressure.

Note that <math>P_{ICdrop}</math> is intercooler pressure drop (pressure difference between <math>P_{outlet}</math> and [[MAP]]), and <math>P_{id}</math> is intake pressure drop (pressure difference between <math>P_{inlet}</math> and <math>P_{ambient}</math>).

Alternately, if boost is known, it is approximated by <math>\frac{P_{ambient} + P_{boost}}{P_{ambient} - P_{id}}</math>. Intercooler drop is ignored here for simplicity.

===Example===
==Mass Air Flow==
===Example===


[[Category:Compressor maps]]
[[Category:Compressor maps]]

Revision as of 02:38, 13 September 2006

Example compressor map.gif
Pressure ratio (y-axis)
The absolute inlet pressure divided by the absolute outlet pressure.
Mass air flow rate (x-axis)
The mass of air flowing through the intake/compressor over time. Usually lbs/min or CFM.
Surge line
The left hand boundary of the map, where the air flow is too low for the current pressure ratio. Blow off valves or Bypass valves are often used to relieve excess pressure to prevent sudden off throttle induced pressure surges.
Choke line
The right hand boundary of the map, where the turbo is approaching its flow limit
Overspeed line
The top boundary of the map, where the turbo is approaching its maximum shaft speed. Past this point, the turbo is liable to "overspin" and cause catastrophic bearing failure.
Turbo speed lines
The lines of constant turbo shaft speed.
Efficiency islands
The concentric regions on the map representing compressor efficiency. The smallest island in the center of the map is the "sweet spot", or where turbo is the most efficient.

An excellent source of more information can be found here.

Pressure Ratio

Expressed as or, more commonly,

Where is manifold absolute pressure, is ambient air pressure.

Note that is intercooler pressure drop (pressure difference between and MAP), and is intake pressure drop (pressure difference between and ).

Alternately, if boost is known, it is approximated by . Intercooler drop is ignored here for simplicity.

Example

Mass Air Flow

Example