Quote:
Originally Posted by Daox
What is the reasoning for using cold EGR for lean burn and hot for light/medium loads?
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For Cold EGR on my engine there are a few advantages I have found.
1) Knock Reduction.
I have found that when Cold EGR is enable I can maintain high load and decrease the air to fuel ratio (add fuel) and lower BSFC from increasing the timing advance while maintaining high load. A traditional HOT EGR would increase a tendency to knock and timing advance would have to be decreased.
OK now this is where it gets confusing. With my ability to run Ultra Lean Burn I have to increase timing advance a ton to make any power due to lean burn's slow burn rate. This helps a ton with pumping losses (running at 0 inch/hg to 2 psi). But there's a point of diminishing returns. Running this lean reduces pumping losses a ton, but at the same time increases BSFC due to a poorer efficiency due to running a higher timing advance. So by running mass amounts of cold EGR to keep from knocking I can now increase the fuel amounts for a more efficient BSFC with out losing high load due to less mass air. Where before if I were to add fuel the engine would increase its power due to the large amounts of air from the lean condition. This would in turn make me have to back off the throttle in which would increase pumping losses.
a) So I have kept my throttle angle and a high load (low pumping losses).
b) Increased fuel amounts for a improved BSFC.
c) Move my timing advance closer to TDC by a increase of the burn rate.
d) Increased efficiency by maintaining a correct ignition advance due to cold EGR.
OK back to (C) LOL
By getting closer to TDC for ignition I improve the likelihood of a misfire. This is due to a smaller quench area.
2) Lower Exhaust Back Pressure and Exhaust Temperature.
Lowering exhaust back pressure and temperature helps with knock and improves engine delta p. At low rpm high load there's a much higher risk of damaging exhaust valves due to high pressure and high temperature.
3) The ability to run higher amounts of EGR at a higher rpm and higher load.
This extends the mass air and high load without running extreme EGR temperatures. Cold EGR helps when running above traditional hot EGR mass flow.
Hot EGR advantages.
Hot EGR advantages in my case are just about normal controlling exhaust emissions.
My HOT EGR system will have one other job and that's working in conjunction with my new self contained waste solvent fuel system.
I'M adding a fuel system that will burn waste solvent from my local Auto Body shops. I'M going to run the waste solvent through my friends UNI Ram URS900solvent recycler just to make sure know one added any paint a other crap to the 5 gallon containers I pick up from the body shops.
This waste solvent system will only work while the engine is in vacuum. It will have a first stage preheater that runs off the engines coolant system then a second stage heater that is already installed ( hot air system) and the HOT EGR system. It has its own fuel tank, fuel pump and emulsifier jetting. The heating will be a must due to the Specific Gravity of the solvents themselves.
EDIT:
The waste solvent system will work along side of the normal fuel system and not by itself.