Interesting EGT observations.

**isuzurover** · 17th February 2012, 01:12 PM

As we don't yet have a dedicated research diesel engine for our engine dyno, the 4BD1T has been roped in from time to time for research.

I observed something interesting the other day when we loaded the engine up by restricting the air.

Case 1. Engine operating at ~3000 rpm with no load. A plate with a single 4 mm hole was placed over the intake of the air filter. The engine almost died, then revs picked up to a stable prm of ~1000. Huge quantities* of black smoke, but EGTs stable at only ~220oC (pre turbo). *=too high for any of the measuring equipment to measure.

Case 2. Engine operating at ~2000 rpm with no load. A plate with a 6x 4 mm holes was placed over the intake of the air filter. Engine rpm dropped to ~1500. EGTs stable at ~350oC (pre turbo), moderate amounts of grey-white smoke - as per a retarded diesel.

Just though some might be interested...

**Dougal** · 17th February 2012, 01:35 PM

Very interesting.

Did you get A/F readings for those two cases?

**roverrescue** · 17th February 2012, 01:47 PM

as a ratio I would imagine a 4mm hole would result in:

~0/alot

S

**isuzurover** · 17th February 2012, 02:00 PM

Originally Posted by Dougal

Very interesting.

Did you get A/F readings for those two cases?

We have a full exhaust gas composition (incl O2 and CO2) - not with me though. IRC O2 was 13-14% for case 2.

You can also calculate intake flow (at least in case 1) by assuming the restrictor is operating as a critical orifice (likely in case 2 as well). That would mean 1/2 an atmosphere pressure drop across the intake

**lambrover** · 17th February 2012, 08:26 PM

I don't think it is that strange. With less oxygen the unburnt fuel obviously creates black exhaust but is much cooler than burnt fuel. In the second test you have introduced more air/oxygen so more fuel is burnt creating the EGT difference.

I have heard when tuning on a dyno you can observe the point when you have turned the fuel up to much, at first you would get very high EGT's but buy adding more fuel it can't atomize and actually cools the temps down in the combustion chamber, but this washes the bore eventually.

**Dougal** · 18th February 2012, 07:10 AM

I believe the white smoke in the second test is due to the reduced compression ratio and therefore not enough heat to combust the fuel. Similar result to very retarded injection timing.

**uninformed** · 18th February 2012, 04:57 PM

Originally Posted by lambrover

I don't think it is that strange. With less oxygen the unburnt fuel obviously creates black exhaust but is much cooler than burnt fuel. In the second test you have introduced more air/oxygen so more fuel is burnt creating the EGT difference.

I have heard when tuning on a dyno you can observe the point when you have turned the fuel up to much, at first you would get very high EGT's but buy adding more fuel it can't atomize and actually cools the temps down in the combustion chamber, but this washes the bore eventually.

I think the drag and tractor pull Diesel guys turn their fuel WAY WAY WAY up for cooling....

**85 county** · 18th February 2012, 06:18 PM

rather standard stuff, would not expect any thing else

**uninformed** · 19th February 2012, 10:39 AM

Ben, was there a reason you didnt have the engine at the same rpm for both test cases?

**isuzurover** · 20th February 2012, 11:16 AM

Originally Posted by uninformed

Ben, was there a reason you didnt have the engine at the same rpm for both test cases?

Particulate levels were too high at case 1 conditions to measure.
We tried 3000 rpm with the 6-hole, however PM still too high to measure and didn't get EGT reading.

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