Thread: turbo fitted and running

Originally Posted by Sparkie

Dougal,

Did you notice any change in power / egt running more advance?

Sparkie.

I noticed a small change in cruise EGT's (lower) which was expected, but it was also in the range of random variation caused by a million other factors (outside temp, wind etc).
There was a small amount more low end grunt, basically easier to light up tyres off the mark and a noisier idle.
I tried to use a glowplug as a cylinder head thermocouple, but the millivolt range was soo small that it was hard to make anything of it. A change from 4-5mv could be due to anything, but could also be a hotter cylinder head.

The real downside for me was boost related. In some situations the slightly cooler exhaust would mean not as much boost was available. This would result in the vehicle slowing enough on some hills that boost would drop further, EGT's would climb and I have to go down a gear.
This was the most frustrating part of it all. Doing 50km/h up a hill in 3rd instead of 80km/h in 4th.

Originally Posted by Sparkie

Thanks for the info everyone, certainly a complex issue, might have to see if a copy of the "diesel engine reference book" is available.

So what is the opinion on retarding the injection on a turbo'd N/A 4bd1 by 3' to bring in back in line with the standard 4bd1t timing? with it set static to 10' the advance curve would be fairly similar except for a a couple of degrees near the 3000rpm mark.

Should i have started this advance / retard question as a new thread? feels like i've thrown lambrovers a little off course.

Dougal,

Did you notice any change in power / egt running more advance?

Sparkie.

Sparkie mate it is all related so go ahead we can all learn from this

Originally Posted by clean32

...

Originally Posted by Bush65

...
The compressor has an operating region where it is most efficient, as the operating point moves to lower efficiency regions, it generates more heat in the compressed air for the particular air flow and the drive pressure at the turbine increases.

...

EH???

how so? pressure up = temp up this is a fixed given, i don't understand how temp can go up if the pressure isint going up?

...

Yes as boost pressure increases, charge air temp will increase.

I specifically referred to compressor efficiency.

The Ideal Gas Law is PV=nRT

where:
P is the absolute pressure
V is the volume
n is related to the number of air molecules, which is an indication of the mass
R is a constant number
T is the absolute temperature

From this equation relating the air pressure, temperature, volume, and mass of air, if you knowing any three, you can calculate the fourth.

The compressor efficiency provided in compressor maps is determined by comparing the temperature of the compressed air to the temperature determined from the ideal gas law.

Edit:

Originally Posted by Dougal

Just to clarify:

It's actually comparing it to the temps resulting from adiabatic compression.
But the ideal gas law is used to find the resulting pressures and temps from that adiabatic compression.

Adiabatic compression is perfectly insulated compression with no heat into or out of the gas. ...

Thanks for the correction Dougal - I shouldn't be so hasty with my posts.
End of edit.

If both temperatures were the same the efficiency would be 100%. But the actual efficiency of typical compressors (for turbos) is normally less than 75%

This means that the compressor is heating the air more than for ideal compression.

As the operating point moves to where the compressor is operating at still a lower efficiency, then the compressed air temperature will increase accordingly.

The compressor impeller has some slip in the air that flowing through it. Like a torque converter in an auto transmission, or you vehicle tyres spinning on a rock ledge, the slip creates heat and the work done is less than the input (i.e. lower efficiency).

The drive input to the compressor is provided by the turbine. The turbine has to provide more power to drive a compressor operating at lower efficiency.

This requires more drive pressure (pressure in exhaust manifold). As drive pressure increases, the engine volumetric efficiency reduces. Then the boost pressure has to be greater for the same air mass flow.

Originally Posted by Bush65

Yes as boost pressure increases, charge air temp will increase.

I specifically referred to compressor efficiency.

The Ideal Gas Law is PV=nRT

where:
P is the absolute pressure
V is the volume
n is related to the number of air molecules, which is an indication of the mass
R is a constant number
T is the absolute temperature

From this equation relating the air pressure, temperature, volume, and mass of air, if you knowing any three, you can calculate the fourth.

The compressor efficiency provided in compressor maps is determined by comparing the temperature of the compressed air to the temperature determined from the ideal gas law.

If both temperatures were the same the efficiency would be 100%. But the actual efficiency of typical compressors (for turbos) is normally less than 75%

This means that the compressor is heating the air more than for ideal compression.

As the operating point moves to where the compressor is operating at still a lower efficiency, then the compressed air temperature will increase accordingly.

The compressor impeller has some slip in the air that flowing through it. Like a torque converter in an auto transmission, or you vehicle tyres spinning on a rock ledge, the slip creates heat and the work done is less than the input (i.e. lower efficiency).

The drive input to the compressor is provided by the turbine. The turbine has to provide more power to drive a compressor operating at lower efficiency.

This requires more drive pressure (pressure in exhaust manifold). As drive pressure increases, the engine volumetric efficiency reduces. Then the boost pressure has to be greater for the same air mass flow.

Ok simple stuff, but i am still a bit confused about your original comment. I Know of the old Joule or work added heat, plus friction plus a bit of cavitations which would show as a jump in turbine revs but i am under the impression that with the exception of delaminating air flow the energy added is minuscule.

Air temperature (oF) Gauge Pressure (psi)
0 5 10 20 30 40 50 60 70 80 90 100
30 0.081 0.109 0.136 0.192 0.247 0.302 0.357 0.412 0.467 0.522 0.578 0.633
40 0.080 0.107 0.134 0.188 0.242 0.295 0.350 0.404 0.458 0.512 0.566 0.620
50 0.078 0.105 0.131 0.185 0.238 0.291 0.344 0.397 0.451 0.504 0.557 0.610
60 0.076 0.102 0.128 0.180 0.232 0.284 0.336 0.388 0.440 0.492 0.544 0.596
70 0.075 0.101 0.126 0.177 0.228 0.279 0.330 0.381 0.432 0.483 0.534 0.585
80 0.074 0.099 0.124 0.174 0.224 0.274 0.324 0.374 0.424 0.474 0.524 0.574
90 0.072 0.097 0.121 0.171 0.220 0.269 0.318 0.367 0.416 0.465 0.515 0.564
100 0.071 0.095 0.119 0.168 0.216 0.264 0.312 0.361 0.409 0.457 0.505 0.554
120 0.069 0.092 0.115 0.162 0.208 0.255 0.302 0.348 0.395 0.441 0.488 0.535
140 0.066 0.089 0.111 0.156 0.201 0.246 0.291 0.337 0.382 0.427 0.472 0.517
150 0.065 0.087 0.109 0.154 0.198 0.242 0.287 0.331 0.375 0.420 0.464 0.508
200 0.060 0.081 0.101 0.142 0.183 0.244 0.265 0.306 0.347 0.388 0.429 0.470

Originally Posted by clean32

Ok simple stuff, but i am still a bit confused about your original comment. I Know of the old Joule or work added heat, plus friction plus a bit of cavitations which would show as a jump in turbine revs but i am under the impression that with the exception of delaminating air flow the energy added is minuscule.

Perhaps you are trying to read too much into it!

My post was in response to another that I quoted so it would be clear what mine was about. That is:

Originally Posted by yt110

So is this why mine (non-wastegate intercooled)with a bit more fuel lowered the exh.temp then more fuel again up it goes,sort of fines a sweet spot of fuel,air temp and timing?

I offered an explanation considering compressor efficiency.

The effects of compressor efficiency are not minuscule. Unlike for example, a gas turbine, where the gas velocity is maintained, the air flow in the compressor used in the turbos we are discussing, is accelerated from the inlet to a high speed, and then reduced in the outlet (consider the transients not just average conditions).

The formula used to calculate the temperature using imperial measurement units is:

Tout = {Tin + Tin x [-1+(Pout/Pin)^0.263]}/efficiency

Example: the inlet temperature is 70 deg F, the suction pressure is -0.5 psig (a slight vacuum due to filter and inlet tract losses), the discharge pressure is 19 psig, and the compressor efficiency is 72%. What is the discharge temperature?

Tin= 70 deg F + 460 = 530 deg R
Pin= -0.5 psig + 14.7 = 14.2 psia
Pout= 19 psig + 14.7 = 33.7 psia
Pout/Pin = 33.7/14.2 = 2.373 (this is the compressor pressure ratio)

Tout = {530 + 530 x [-1+2.373^0.263]}/0.72 = 717.8 deg R

717.8 deg R - 460 = 257.8 deg F

Clearly, changing the compressor efficiency will change the outlet temperature.

Originally Posted by Bush65

The compressor efficiency provided in compressor maps is determined by comparing the temperature of the compressed air to the temperature determined from the ideal gas law.

Just to clarify:

It's actually comparing it to the temps resulting from adiabatic compression.
But the ideal gas law is used to find the resulting pressures and temps from that adiabatic compression.

Adiabatic compression is perfectly insulated compression with no heat into or out of the gas. The gas still heats as it's gaining energy from being compressed.
John's obviously using the right gas laws because his example came out right.

To back it up with some measurements.
I ran temp probes in my intake when I had a dust-eroded compressor wheel.
15psi on that damaged wheel resulted in 120C out of the compressor, which equated to 50% compressor efficiency.
Replacing it with new turbo (couldn't get a new wheel) gave me 105C at the same boost pressure with a noticable reduction in fuel use and better power. Calculations from that temp came out at 70% compressor efficiency.

Dr Alfred Buchi (the turbocharger inventor) has a law which basically states:
Turbine inlet pressure is a function of turbo efficiency (both compressor and turbine) and turbine inlet temp.

Which means the more efficient your turbo runs (both compressor and turbine), the less backpressure the turbo has. The hotter the exhaust gas, the less backpressure the turbo has.

Originally Posted by Bush65

(consider the transients not just average conditions).

AHHHH click, yes i was miss reading your original post, thanks