can an air/fuel ratio guage be mounted on a diesel? i have not seen any advertised by the big names when i look for a set for my 6-oh.

 

Diesel to not need an air fuel gauge. There is no octane rating on diesel you can dump as much fuel in as you want just as long as you have enough air to make the combustion happen. However when you get alot of black smoke (unburnt diesel) the engine can get hot really quick under heavy acceleration

 

I am sure it can be done but what will you gain. Diesels run lean almost all of the time. Stoichiometric (sp?) is around 15:1 on a diesel, so your gauge would most likely be off the chart on the lean side all of the time except when you are WOT. Would the sensor survive the bombardment of soot? That I dont know but I am sure its effective life would be short because of it.

 

A diesel engine can run at 100:1 at an idle. This is why there are concerns with wet stacking at extended long idles.

 

100:1 is lean, Wet stacking and lean don't go together in MY mind.
What is wet stacking in simple terms?

 

Wet stacking is a condition where all the fuel is not burnt after injection. It is usually a result of cold conditions in the combustion chamber. It can cause a host of problems on diesels new an old. The unburnt fuel ends up either in the crankcase where it dilutes your oil or in the exhaust system where it cokes up and deposits on everything. The term wet stacking or slobber (Detroits were famous for slobber) comes from the fact that after a long period of idling the inside of the exhaust pipe would be wet with unburnt/coked fuel and this residue would end up all over everything, the truck; the trailer; the stacks etc; it was a real PITA to clean up.

I hope this makes sense and clears things up for you.

 

Yup, 100:1 is very, very lean. Wet stacking aint happening with this number.

 

Actually wet stacking can occur in extremely lean conditions; the reason being, that unlike a gas engine where the fuel is usually well mixed with the air; a diesel injects the fuel during the compression stroke. This causes uneven distribution of fuel in the chamber and consequently regions which are very rich where the fuel doesn't burn perfectly and regions which are very lean where the fuel burns totally. The way the engine idles is it tries to control the fuel to sustain a commanded RPM; this is why the A/F ratios are absurdly high when looked at as an overall number; the swept volume of the cylinder does not change; you only alter the volume of fuel to maintain engine speed.

When a diesel engine is idling there is also dramatically reduced heat inside the cylinder; this reduced heat inhibits efficient combustion. and in the areas of combustion chamber where that A/F ratio is extremely rich all the fuel does not burn; creating a wet stacking condition.

There are other areas of engine dynamics which contribute to this effect:
Piston velocity is lower; therefore swirl effects are reduced; thus inhibiting fuel mixing.
The fuel flow through the injector nozzle is slower; reducing atomization; the larger droplets in the cylinder are correspondlingly harder to burn.
Due to the lower engine speed there is more time for the heat of combustion to be transferred to the engine coolant which results in a lower combustion chamber temperature; which again results in conditions which promote wet stacking.

 

OK, I had it straight. Got threw off by this statement.
Thanks for all the help.

 

I guess I should have taken a little more time to explain my thought process since I left for the weekend. But, 04Xcursion hit the nail on the head and conveyed what I should have included in my original response.

Evan