The E85 Discussion Thread

[45SET]

Noob question here.

But people say that they are getting worse fuel economy out of running E85. Now I know from previous posts that Pizzo is running 750cc injectors (Stock is 310cc?).

Now I'm no mechanic, and I'm not 100% sure, but Pizzo is running injectors that flow more then twice the capacity of the stock injectors. Wouldn't this be one of the main reasons for the increased fuel consumption? If you were to run 750cc injectors, and still using PUMP, wouldn't you expect similar fuel consumption?

[k20eg]

Noob question here.

But people say that they are getting worse fuel economy out of running E85. Now I know from previous posts that Pizzo is running 750cc injectors (Stock is 310cc?).

Now I'm no mechanic, and I'm not 100% sure, but Pizzo is running injectors that flow more then twice the capacity of the stock injectors. Wouldn't this be one of the main reasons for the increased fuel consumption? If you were to run 750cc injectors, and still using PUMP, wouldn't you expect similar fuel consumption?

Well youre only going to use as much fuel as your engine needs.. its not as if those 750's are going to be maxed out.

[45SET]

Well youre only going to use as much fuel as your engine needs.. its not as if those 750's are going to be maxed out.

That's true.

Wouldn't the amount of petrol (And the duty cycle of the injectors) be dependent on the tune? (ie running rich or lean) Also, I'm assuming that even though they won't max out, they would be pumping more petrol then the stock injectors.

[ChargeR]

That's true.

Wouldn't the amount of petrol (And the duty cycle of the injectors) be dependent on the tune? (ie running rich or lean) Also, I'm assuming that even though they won't max out, they would be pumping more petrol then the stock injectors.

Yes you are correct the amount of fuel used on a wide open throttle run will be heavily dependent on the tune, and for example the larger injectors fitted will be pumping more fuel in on E85 simply because the fuel requires a much more rich A/F ratio to be stoichiometric and is also oxygenated requiring further fuel compared to normal 98 octane pump fuel.

However the injector change itself doesn't require more fuel. Given no other fuel or engine changes a larger injector once tuned/compensated to the same A/F ratio should inject roughly the same amount of fuel, just at a lower duty cycle.

[45SET]

Yes you are correct the amount of fuel used on a wide open throttle run will be heavily dependent on the tune, and for example the larger injectors fitted will be pumping more fuel in on E85 simply because the fuel requires a much more rich A/F ratio to be stoichiometric and is also oxygenated requiring further fuel compared to normal 98 octane pump fuel.

However the injector change itself doesn't require more fuel. Given no other fuel or engine changes a larger injector once tuned/compensated to the same A/F ratio should inject roughly the same amount of fuel, just at a lower duty cycle.

ahh ok, that actually makes sense.

Thanks Tom.

[wpg81]

The air fuel ratio of the e85 fuel is totaly different to petrol!! This will be hard to explain and harder to understand but if u get it ,it will all come together! i will try my best to explain. i will use n/a air fuel numbers as thats what most of u will see/use.

Petrol's perfect air to fuel ratio is 14.7(air)to 1 (fuel). So 14.7 litre's to 1 litre of fuel. Cars are tuned to around low 13's at full trottle on a dyno(n/a).

E-85's perfect air to fuel ratio is around 8.5(air) to 1 (fuel). Therfore 8.5 litres of air to 1 litre of fuel. This is tuned to around 7.4 at full throttle on a dyno(n/a)

So if an engine uses 100 litres of air and fuel, at the prefect ratios you will use 6.4 litres of petrol or 10.5 litres of e-85. This works out to be 40% more fuel for the same amount of volume(air+fuel) through the engine.

Please note the numbers used might not be 100% correct but are very close and i am not a tuner!This information is to be used as a guide to explain the difference in fuel requirements and air to fuel ratios of the different fuels!

[tinkerbell]

, they would be pumping more petrol then the stock injectors.

as noted above the bold word is the key importance, if you were pumping methanol @ same pressure, you'd need ~2000cc ones! so the type of fuel determines the right size injectors for a given fuel pressure, but you gotta be able to re-map the ECU on a dyno...

fwiw - i run ID725cc injectors @ 70psi on 98 petrol - hardly any duty cycle though - i get easy 10L/100km...

[45SET]

The air fuel ratio of the e85 fuel is totaly different to petrol!! This will be hard to explain and harder to understand but if u get it ,it will all come together! i will try my best to explain. i will use n/a air fuel numbers as thats what most of u will see/use.

Petrol's perfect air to fuel ratio is 14.7(air)to 1 (fuel). So 14.7 litre's to 1 litre of fuel. Cars are tuned to around low 13's at full trottle on a dyno(n/a).

E-85's perfect air to fuel ratio is around 8.5(air) to 1 (fuel). Therfore 8.5 litres of air to 1 litre of fuel. This is tuned to around 7.4 at full throttle on a dyno(n/a)

So if an engine uses 100 litres of air and fuel, at the prefect ratios you will use 6.4 litres of petrol or 10.5 litres of e-85. This works out to be 40% more fuel for the same amount of volume(air+fuel) through the engine.

Please note the numbers used might not be 100% correct but are very close and i am not a tuner!This information is to be used as a guide to explain the difference in fuel requirements and air to fuel ratios of the different fuels!

I was reading through that, and I understood the air-fuel ratio stuff, as I've watched Adrian tune my car in the past, and noticed that he always gets the AFR to around the 13's.

But I'm getting confused about the parts were you've said:

Petrol's perfect air to fuel ratio is 14.7(air)to 1 (fuel). So 14.7 litre's to 1 litre of fuel. Cars are tuned to around low 13's at full trottle on a dyno(n/a).

E-85's perfect air to fuel ratio is around 8.5(air) to 1 (fuel). Therfore 8.5 litres of air to 1 litre of fuel. This is tuned to around 7.4 at full throttle on a dyno(n/a)

So if an engine uses 100 litres of air and fuel, at the prefect ratios you will use 6.4 litres of petrol or 10.5 litres of e-85

What I'm getting confused about I've bolded. With petrol you are using more parts petrol to air (14.7:1), then you would be with E85 (8.5:1), but you end up using more E85 in the long run. This just doesn't make sence to me, how can you require less of something, but use more?

This is just a question, not having a dig or anything.

[tinkerbell]

air to fuel ratio is a RATIO

so we are comparing 14 parts air to 1 part fuel (petrol)

to 8 parts air to 1 part fuel (e85)

so e85 is close to 16 parts air to 2 parts fuel

and it just to ram it home - it is a AIR to FUEL not a FUEL to AIR ratio...

intuitively - people think they use heaps of fuel - where as most of the substance that is ingested to make explosions is AIR...

[wpg81]

As tink said its always much more air than fuel! Like i said it takes a bit to get your head around but once you do it starts to all come together. The perfect air to fuel ratio is called stoicomteric(? spelling) and is the best comprimise between power and economy. This is a different ratio for different fuels, methanol, ethanol, lpg, petrol, deisel and this will require different amounts of fuel for each for a set amount of air.

[tinkerbell]

when the AFR of a given combustion process is @ 'stoich' it means there has been 'complete combustion of fuel'

here is an interesting graph showing the effects of tuning a petrol engine either side of 'stoich':

[45SET]

So...

For example, 14.7:1 doesn't mean 14.7L of fuel : 1L of air?

I think I'm starting to get my head around it...

[stevan]

Cool graph Dave, I didn't think Max power would be deviated to the "rich" side though, I thought it created a more powerful combustion on the lean side?

Other way around Robi

[ChargeR]

So...

For example, 14.7:1 doesn't mean 14.7L of fuel : 1L of air?

I think I'm starting to get my head around it...

14.7:1 means 14.7kg of air to 1kg of fuel. Remember that the ratios are mass based not volume.

Cool graph Dave, I didn't think Max power would be deviated to the "rich" side though, I thought it created a more powerful combustion on the lean side?

Other way around Robi

The chemical energy liberated in combustion per unit mass of fuel would be greater on the lean side, since you would get more complete combustion. However there is physically less mass of fuel in the cylinder being combusted, so less energy released and less resultant pressure on the piston and hence less power overall. We want to add fuel until combustion becomes so inefficient that power suffers, hence with all fuels the ratio for best power is always richer than stoichiometric.

[tinkerbell]

For example, 14.7:1 doesn't mean 14.7L of fuel : 1L of air?

you wont get get much further then, if you keep not reading what people post!

I didn't think Max power would be deviated to the "rich" side though, I thought it created a more powerful combustion on the lean side?

why would it create more 'powerful' combustion?

the most heat is created at stoich, and leaner also means slower burning...

(unless you are detonating, but that is not what you should be setting out to achieve)