HOW-TO-READ A COMPRESSOR MAP.

[task 0]

Here is some useful information I thought I would share with you guys.

 

HOW-TO-READ A COMPRESSOR MAP

 

 

using a map of a T04E 60 trim I will explain all the numbers on the map.

 

1-left side, PRESSURE RATIO

(14.7 + amount of boost) / 14.7 = PR

so to figure out the PR for 8 PSI

(14.7 + 8 ) / 14.7 = 1.54 PR

 

 

2-bottom side, AIRFLOW RATE UNDER BOOST (LB/MIN on this map)

Most methods of calculation your engine's airflow rate will give you the answer in cubic feet per minute (CFM). However most compressor maps measure airflow rate in pounds per minute (LB/MIN). As some of you may know the weight of air varies with the temperature. To convert CFM to LB/MIN use the following numbers.

@ 48 degrees F : (CFM * 0.078125) = LB/MIN

@112 degrees F : (CFM * 0.070318) = LB/MIN

@175 degrees F : (CFM * 0.06251) = LB/MIN

 

Say for example our airflow rate is 500 CFM , and the temperature is 112 degrees F.

(500 * 0.070318) = 35.16 LB/MIN

 

 

3-dotted line on far left side of "ovals", SURGE LIMIT

It is important to try and keep yourself on the right side of this dotted line whenever possible. If you fall to the left of this dotted line you will experience compressor surge. This type of compressor surge will occur when there is too much boost, but not enough airflow through the system, usually this is between idle and the point at which full boost is reached. The chirping sound that can be heard is a result of the oscillating air. This sound is often described as a "Snakelike" sound or a che-che-che sound.

 

*staying in the "surge limit" area for too long could possibly damage your turbo.

 

 

4-numbers on far right, 46,020, 69,640, 83,972 etc, COMPRESSOR RPM

This is RPM at which the compressor fans will be turning. an average RPM is between 90,000 and 130,000. The line that branches out from each of these numbers that goes towards the surge limit line shows you the RPM range of the compressor fan across the entire compressor map.

 

 

5-78%,75%, 74%, COMPRESSOR EFFICIENCY

This is related to the temp of air and how much it is being heated up as it is being compressed by the compressor. A low number (60%) means that the compressor is heating the air more a high number (78%) means the air is not heated as much when it is compressed.

 

 

6-"Ovals"

I you look closely you will see that the compressor efficiency numbers usually sit right on top of one of these Oval lines. These Ovals show you the boundaries of the compressor efficiency at the different percentiles. Think of it as a topography map that shows you different elevations or changes in elevations. The innermost Oval on the sample T04 E 60" is not labeleb but it is probably 79% or 80%, so any where inside that Oval and you would be operating in the 80% range of that compressor.

[HiAsAKite 0]

Its probably worth adding that this is typically covered (along with turbine maps) at 2nd year degree level.....

[trendy tramp 0]

a few things to add:

 

you should specify ADIABATIC efficiency in terms of efficiency - a perfect adiabatic system is one which can change pressure without a corresponding increase in temperature. teh efficiency is dependant upon the incident angle of the incoming air to the angle of the cmpressor blades which changes with speed.

 

the ovals you refer to are more commonly called efficiency islands

 

teh surge line is only approximate - most manufacturers are slightly optimistic of the surge characteristics of their compressors - some worse than others (naming no names :wink: ). when the constant speed line starts to decrease as you move left from peak efficiency is the true start of surge. so you may be in surge sometimes without realising it.

 

there are different types of surge. surge below a PR of about 2 is known as light surge and most OEMs will actually calibrate to move along the surge line, sometimes to the left of it as it is not damaging. moving further left or upwards or PR 2 will cause heavy surging which can damage the compressor wheel as supersonic pressure waves oscillate within the compressor wheel blades and splitter blades as it spins and flow breaks down. The ability to recover from surge is affected by the volume of the pre-compressor ducting - larger volume = longer surge period.

 

surge is actually a cyclic process and the compressor will go in and out of surge several times a second - hence the associated noise. although you may be measuring a mean PR and mass flow well within the non-surge region of the map, the compressor's locus of operation could actually be dipping into and out of surge.

 

most importantly, maps are gas stand tested and do not include the vehicle level intake pre/post compressor. The pre/post compressor geometrics can and will move the operating map away from it's measured map - 99% of the time for the worse. Usually the PR will reduce and/or the mass flow capability wil reduce - basically the map is squashed and hence performance is reduced.

 

and let's not forget axial swirl into the compressor which can have the same effect or have a beneficial effect - depending upon the direction of the swirl and the compressor wheel design.

 

the bottom left of the compressor map can also be extrapolated as this region can be entered under harsh tip-in (accel).

 

the constant speed lines can also be extrapolated to PR=1 to determine the choke characteristics of the compressor.

 

that's the basics on compressors - now how about turbines and matching :lol:

 

tt

[kongo127 0]

:shock: :shock: :shock: :shocked!: