Then what the heck is this ottomind box doing for my diesel??!? j/k of coourse
Interesting. So with the same fuel you'd expect the HO truck to have lower egts, up to a certain point at least? And if the exhaust has greater volume and lower temps is this helping or hurting spool?

 

No apologies-- this is all on topic as far as I'm concerned (do I get OP discretion?)

Higher compression ratio would increase peak combustion temps, but average operating temp of the piston will actually go down because the peak temp exists for a split second, and the temp and pressure decay faster with higher compression-- giving an overall cooler running engine.

Another variable is RPM. If I take the exact same air/fuel ratio, the exact same engine timing and so forth and double the RPM, my EGTs will go up. This is simply because the TIME available to completely burn the charge is less, and you are more likely to be expelling hotter, still burning gasses.

That's why an engine needs more timing advance as RPM increases, and also why a 12V can't be optimized for a very broad range. You can either set it up for higher rpm, or low rpm, or midrange, but you'll give up one to get another. These guys running 22º timing aren't blowing people away with bottom end grunt. They are screamers running 4K rpm and then some.

jh

 

Yes, I would.

As for whether higher compression helps or hurts spoolup, I'd say it generally would hurt spoolup a bit. Here's my reasoning: thermo tells us that we can't create energy, just change forms. We also have to account for all the energy that goes in as coming out somewhere. So if the higher compression ratio results in more energy extracted from the charge (due to higher expansion ratio and a closer approach to theoretical Carnot values), then we MUST have less energy available in the exhaust stream to drive the turbocharger.

This is one way that turbochargers help to recover lost energy and increase efficiency. The "lost" power that we didn't extract from being forced to run a lower than desired CR can partially be recovered because that energy is contained in the exhaust, and hence partially converted to useful work by the turbine.

That's my official guess, anyway.

 

When we "correct" to atmospheric conditions, this 14.5 lb/min at 1000º becomes 23.8 lb/min! This is how the hotter drive temps show up as more energy to drive the turbine.

I am trying to put some additions onto my spread sheet. How did you get the 23.8 lbs/min number? By setting the PR = 1 and running the CMF equation?

PR = Drive Pressure / Back Pressure
T1 = Turbine Inlet Temp
Fin = Input Mass Flow in CFM
Fuel = Fuel flow rate in lbs/Min
Fcor = Corrected Mass Flow

Where:
PR = 1
Fin = 187
T1 = 1000
Fuel = .5
Then:
Fcor = 24.34 lbs/min (23.8 lbs/min)

Just trying to ensure I am accurate.

Thanks;
Jim

 

Yes, I just set PR to 1.

Your numbers look right to me and jive with my spreadsheet.

Results can vary depending on whether you correct to 70° (CGF equation) or 58° (std atmosphere).

I used 58, IIRC.



Justin

 

Based on this table

-and-

Assume:
500 HP
0.35 BSFC g/Hp-Hr
2750 RPM
70 Ambient
70 CE
76 IE
95 VE
28 AFR
1200 EGT

Fuel:
175.0 Lbs/Hr
2.9 Lbs/Min

24.3 Gal/Hr @ 7.2 Lbs/Gal Winter
25.4 Gal/Hr @ 6.9 Lbs/Gal Summer

AFR:
1097 CFM Required
82.1 Lbs/Min Required
53 Boost Required

CGF
151.3 Lbs/Min


Jiving with your spreadsheet Hohn?

Jim

 

I got to thinking about Hohn's thread related to an AFR Meter.

Could we calculate AFR backwarks using an exhaust pipe O2 sensor? I mean using real world attainable numbers to calculate the AFR.

Air: RPM and boost (calculated)
Fuel: Overhead Console (using a correction factor compared to MPG)

The first problem is to find a formula using fuel flow and excess O2 present in the exhaust (flue) gas stream to calculate air flow. Or conversely a formula that can calculate fuel flow using air flow and excess O2.

The second problem is finding a constant that can compare ideal stoichiometric AFR to the real world ISB best possible stoichiometric AFR. Or just maybe, the lowest possible excess O2 for the ISB running as close to stoichiometric as it possibly can.

Then maybe using the O2 sensor, that would likely be much less expensive than a AFR sensor, to find the actual AFR.

Not that any of this really matters one fart in a hill of beans, just curious mostly.

Anyone have any clues, or where I could look to do more research?

Jim

 

I wonder if one of AutoMeter's new A/F ratio meters would read closely enough for a diesel?

 

Dunno....

A diesel pulls allot of air. Need to check the scale I would think.

Jim

 

The problem with O2 sensors in diesels is that they get plugged by fine soot particles really quick. First you get a delayed response and then it's dead.

IMO we can use a combination of a mass air flow sensor from a gasser with at least 50% higher HP than the intended diesel and a fuel flow meter measuring the difference between fuel line and return. This should give us all the data needed.

Just my 2c

AlpineRAM

 

Yeah, I have given up on the excess O2 idea as well since I thougt about it some more. If it worked then I am pretty sure the newer diesel would have them equiped OEM. With the degree of adjustability in the CR, knowing the exact excess O2 could really help with tuning.

Are air flow sensors generally pressure temperature compensated?

Jim

 

VERY old thread, but was a great read.. THANKS!!!

 

Corrected turbine mass flow is based upon that the egt's are at a certain turbine inlet temperature. There is an ASME spec for both the compressor and turbine mass flow. The compressor mass flow is different than the turbine mass flow, there is a ratio of how much compressor mass flow to turbine flow is required. Basically with those turbine graph you can gauge when the turbine gets into its efficency area, so its fully spooled.

The compressor side is 59deg's F at sea level and inlet pressure is 14.7psiA

At pressure ratio of 5:1, you run the risk of breaking stuff. Higher the discharger pressure, more severe the surge condition becomes. Thrust bearings take a beating. Most compressor mid maps are around mid 70's for efficent.

Every manufacture rates compressor/turbine choke differently, so its hard to use the published maximum mass flow values at a glance.