stumbled upon this, havent really thought about it in that sense:
"Regarding the tuning of a gasoline engine with the use of a wideband O2 sensor, in the presence of methanol. I'd like to have a learned opinion on whether my thinking is clear in this matter.
The question has arisen more than once as to the effect that injecting methanol, or a mixture of methanol and water, has on AFR.
Now, a wideband O2 sensor really measures lambda. Through the use of a scaling factor or a lookup table, the controller then converts this to AFR format, and that's what most folks are accustomed to looking at on their gauge.
With gasoline, we know that 1λ = 14.7:1 AFR. So if the engine is running at precisely stioch (1λ actual), the display gauge reads 14.7.
Now, for methanol, the ratio for stoichiometric combustion is somewhere in the neighborhood of 6.5:1. So if we were running an engine on pure methanol, we'd have calibrated our wideband controller such that 1λ produces a display of 6.5. Hypothetically, if we were to take that same engine and run it on gasoline, then a stoichiometric mixture of gasoline and air (again, 1λ), despite being 14.7:1 in reality, would still produce a display of 6.5.
Agreed so far?
Getting back to practical matters, let's say that we're tuning a turbocharged engine. Ignoring detonation, conventional wisdom tells us that we want to shoot for an AFR of about 12.5:1 for best torque, assuming optimum ignition timing. By my math, 12.5:1 for gasoline is 0.85λ (12.5 / 14.7 = 0.85). So we do that, and now we have a fuel table that achieves 12.5:1 on gasoline.
Now, let's say we're going to introduce some methanol into the engine. First off, I'm going to assume that the presence of water has no effect upon AFR, so the exact concentration of water to methanol is unimportant. And second, I'm going to assume that the quantity of water/methanol being introduced is significant enough to affect the engine's AFR in a measurable way- we'll say a ratio of 25% meth/water mixture to fuel (by volume).
So we start injecting the mixture and, assuming we do not reduce our fuel trim, the mixture starts going richer than 12.5:1. So we obviously start decreasing fuel to bring the mixture back towards our target. And this is where the big question arises.
The only data I've been able to find suggests that peak torque on meth is achieved at about 5.5:1. By my calculations, this comes out to 0.85λ, which is exactly the same number we came up with for the peak-torque lambda for gasoline.
So the question becomes: Assuming our WBO2 system is calibrated for gasoline, is it safe to assume that when the display on it reads 12.5 (equating to 0.85λ) that regardless of the ratio of gasoline to methanol going into the engine, the overall ratio of the combined mixture of fuels to air is ideal?
thoughts?
original post:
http://www.alcohol-injection.com/fo...e-methanol-afr-lambda-stoichiometry-2158.html
"Regarding the tuning of a gasoline engine with the use of a wideband O2 sensor, in the presence of methanol. I'd like to have a learned opinion on whether my thinking is clear in this matter.
The question has arisen more than once as to the effect that injecting methanol, or a mixture of methanol and water, has on AFR.
Now, a wideband O2 sensor really measures lambda. Through the use of a scaling factor or a lookup table, the controller then converts this to AFR format, and that's what most folks are accustomed to looking at on their gauge.
With gasoline, we know that 1λ = 14.7:1 AFR. So if the engine is running at precisely stioch (1λ actual), the display gauge reads 14.7.
Now, for methanol, the ratio for stoichiometric combustion is somewhere in the neighborhood of 6.5:1. So if we were running an engine on pure methanol, we'd have calibrated our wideband controller such that 1λ produces a display of 6.5. Hypothetically, if we were to take that same engine and run it on gasoline, then a stoichiometric mixture of gasoline and air (again, 1λ), despite being 14.7:1 in reality, would still produce a display of 6.5.
Agreed so far?
Getting back to practical matters, let's say that we're tuning a turbocharged engine. Ignoring detonation, conventional wisdom tells us that we want to shoot for an AFR of about 12.5:1 for best torque, assuming optimum ignition timing. By my math, 12.5:1 for gasoline is 0.85λ (12.5 / 14.7 = 0.85). So we do that, and now we have a fuel table that achieves 12.5:1 on gasoline.
Now, let's say we're going to introduce some methanol into the engine. First off, I'm going to assume that the presence of water has no effect upon AFR, so the exact concentration of water to methanol is unimportant. And second, I'm going to assume that the quantity of water/methanol being introduced is significant enough to affect the engine's AFR in a measurable way- we'll say a ratio of 25% meth/water mixture to fuel (by volume).
So we start injecting the mixture and, assuming we do not reduce our fuel trim, the mixture starts going richer than 12.5:1. So we obviously start decreasing fuel to bring the mixture back towards our target. And this is where the big question arises.
The only data I've been able to find suggests that peak torque on meth is achieved at about 5.5:1. By my calculations, this comes out to 0.85λ, which is exactly the same number we came up with for the peak-torque lambda for gasoline.
So the question becomes: Assuming our WBO2 system is calibrated for gasoline, is it safe to assume that when the display on it reads 12.5 (equating to 0.85λ) that regardless of the ratio of gasoline to methanol going into the engine, the overall ratio of the combined mixture of fuels to air is ideal?
thoughts?
original post:
http://www.alcohol-injection.com/fo...e-methanol-afr-lambda-stoichiometry-2158.html
