Cheap DIY EFIE

[ShadeTreeMech]

If my college chemistry from close to 10 years ago is accurate, running leaner allows a higher o2 to fuel ratio, resulting in a hotter flame, regardless of heat transferrence.

This is part of the reason for hot rod diesels done by the DIY crowd tend to smoke a lot. Adding fuel to be burnt will absorb excess heat and lower EGTs, which is a good thing when you're running higher than spec PSI (I've heard of blokes shoving 60 psi into a 3.9 L Cummins 4 cyl. Talk about severe duty!)

Before fuel can be combusted, it must be brought up in temperature, so adding more fuel will cool the combustion cycle. More fuel to be warmed=more smoke, but cooler temps. As an example, think of why a nitrous system works. NO2 is injected into the intake, but in the higher versions, additional fuel is also injected to control the intake temps. Another example is the theory behind the EGR system, which injects a low O2 gas into the combustion process to lower EGTs. Anyone knowing anything about NOS injection knows too much will burn up the motor without injecting additional fuel.

[Phantom]

Wet NO2 systems are usually to help meet the fuel demands of the engine since you are effectively dumping O2 in the engine. If the car is at WOT with an AFR of 13 and then hit the NO2 say a 150 shot the AFR will jump to 20+ with no time to react and that is bad and the reason why they do wet systems not for the cooling effect.

[Olympiadis]

Originally Posted by ShadeTreeMech

If my college chemistry from close to 10 years ago is accurate, running leaner allows a higher o2 to fuel ratio, resulting in a hotter flame, regardless of heat transferrence.

Another example is the theory behind the EGR system, which injects a low O2 gas into the combustion process to lower EGTs.

All things being equal you are correct. In the varying conditions of actual engine operation there are a few more factors that affect burn speed in the chamber.

Being a combustion buffer, EGR will slow burn speed, the end result being a cooler combustion process and lower efficiency under most driving conditions, especially those requiring more engine power.

This EFIE trick can prove to be somewhat effective overall, but as has been said, a narrow-band O2 is not good at toggling at anything other than stoich, which would make this method problematic, and "touchy" to adjust.
Running this EFIE in combination with an active EGR system will also reduce its effectiveness at improving FE. A lean AFR combined with EGR flow will lower the AFR at which you reach the lean-misfire threshold, and thus limiting your fuel savings.

Burn speed will increase up to a point of enleanment, often around 15.8:1 (assuming no EGR) AFR or so, but will then start to decrease again. This (going leaner than 15.8:1 AFR) won't be an overall negative if it is only done during periods of low engine loading where little power is needed. This simple EFIE device doesn't operate based on engine load, so that is the key to making it work for you.
You could try to get fancy and make a circuit that would vary the output based on load, or you could use a 2-step system resistance that would switch between two settings based on a load threshold.

You will find that you can get away with 17.0:1 AFR or higher at very low engine load, like DECEL, or idling while coasting, and not kill the engine or worry about damaging anything.
At a higher load, like a steady cruise you'll probably find that you need to stick closer to the range around 15.8:1 AFR.

Using a WBO2 to monitor the AFR will be very helpful for getting your EFIE to perform.

[wagonman76]

I tried one once. It noticeably leaned out the engine. It also killed my mpg when using it because it didn't run so good. There was no happy medium, no point that mpg got better when using it. The best thing to do was to leave it alone.

[ShadeTreeMech]

Originally Posted by wagonman76

I tried one once. It noticeably leaned out the engine. It also killed my mpg when using it because it didn't run so good. There was no happy medium, no point that mpg got better when using it. The best thing to do was to leave it alone.

While I have no personal experience to back all this up, I do agree with wagonman. When the effects of getting it all wrong includes burning up the pistons and valves I'd say its a risky move at best with little net gain.