Ecoboost engine question
With the Eco doing so well and loved by many and bragged about by Ford. Why is it not offered in the F250 ? I love mine but I'm curious.
Forum Discussion
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Turtle,
At this point, I think you are entirely correct about one thing for sure. Gasoline-DI(GDI) probably does not inject after TDC according to any info I found either. It seems a blatant enough mistake on my part, that I appreciate your very kind reply.
I don't know a lot about diesel, but I think they do inject more fuel after the initial charge during continued combustion. Apparently this won't work as well with gasoline, although I wouldn't entirely rule it out. The web info on GDI is kind of inconsistant and/or sketchy IMO.
On the other hand, I'm going to take the position of Devils Advocate to try to resolve some questions I still have, so if you will parden me for the sake of argument...
Definition:
Brake specific fuel consumption (BSFC) is a measure of the fuel efficiency of a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced.
First:
The 3.5L EB engine seems quite efficient under power, and comparable to NA offerings in the F-150. How can this be if excess fuel is wasted just for TC anti-detonation cooling?
One other glaring question is:
What happens to my assumed recovered energy contained in the greater loss of heat energy between a NA (naturally aspirated) engine and TC (turbo charged)? This is supposing that for identical fuel, the TC engine recovers some additional energy and therefore releases cooler exhaust than the NA engine which loses all remaining gaseous heat energy after the combustion stroke. It follows, and is my belief that the TC therefore either delivers just slightly more hp for same said fuel, or the same hp for slightly less fuel.
Wes
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I'm going to try to stay with my speculation that the TC BSFC does not necessarily specifically demand more fuel for high efficiency consumer use, and that there can be, and should be, a difference between relatively "crude" TC race engines and the latest, highly developed TC performance production vehicles.
I don't know exactly how Ford does it, but it appears to me that they have, by necessity, carefully tuned out detonation by other means rather than flooding the engine with excess rich fuel. A race TC engine owner often does not care if fuel is wasted (within reason) and the easiest pocket solution to intake charge cooling is normally chosen via excess fuel. I even ran my 2-stroke dirtbikes rich for similar reasons, but there was no easy safe alternative at the time. OTOH, modern 2-stroke DI outboards are extraordinarily fuel efficient in comparison.
I agree this is absolutely true for SC, the final exhaust, while under power, will reflect higher heat per-unit-hp delivered partly because more fuel must be burned to drive the compressor. No gaseous tail-pipe heat energy is recovered in SC after "thee standard recovery" from piston thrust pressure during combustion.
But I believe TC is different. The final "thow-away" exhaust is cooler, after passing through the turbo, designating that some heat energy has gone elsewhere besides tail-pipe waste or piston thrust. This drop in exhaust temp represents a large percent of the energy delivered to the impeller to compress the intake. It isn't really free energy... it's additional recovered energy from the same amount of fuel. There have even been uncommon cases where a turbo not only drives a compressor, but is also geared directly to the main propulsion shaft to take advantage of this principle. Ideally (not possible) the exhaust would exit at ambient surrounding air temp, and all burned fuel energy would be converted to rotational power ala 100% efficiency.
I agree, see above paragraph. I'm just saying more of the available, normally wasted energy from the fuel is put to work, as in TC can be more efficient than SC, and theoretically just as efficient, or rather more efficient, than NA. This hasn't been the case in the past but it is now the newest game in town.
I'm not absolutely sure the Wiki link is entirely correct or complete. It does strongly suggest that all stoic and power gasoline DI mixes must be accomplished by completed injection during the intake stroke to assure a homogenous mix. All other web sources seem to agree at this point. This homogenous mix requirement may be true of gasoline whereas diesel is more forgiving. But, logically, I doubt it.
Since ultra-lean gas mixes can be successfully ignited by using a stratified charge (rich near the sparkplug), I don't really see why some additional gasoline injection could not take place after TDC if it works in diesels. The ideal homogenous mix idea is that all fuel molecules are nearby all oxygen molecules, and that speedy combustion can therefore be completed during the short high speed power stroke. But I will guess, with carefully arranged "swirl" the molecular match is also quite good. I have to ask, why would diesel be that much more different than gasoline?
Ultra lean burn has oxygen left for the taking. All fuel is burned. Can after-TDC fueling take advantage of this "left-over oxygen" in a power type cycle?
Stoichiometric mode. I agree this should best take place as homogenous, and perhaps swirled for the most consistant flame front. There appears no reason to do it otherwise.
Full power mode. Rather than excessively enrichen the mix to prevent detonation ala "firehose", the fuel is very briefly increased just barely to the point that all oxygen molecules "can find" a fuel companion, even if just a few raw fuel molecules are left. At this time the maximum possible combustion takes place for all available air. My guess is that this is seldom done nowadays with any unburned fuel being anti-EPA. I think the term, "Full Power Mode" is becoming obsolete, or nearly so.
I think premium simply allows the engine to produce more power. The high compression caused by boost lets the EB efficiently take advantage of higher octane fuel. I don't think it has to burn premium, but it is a case where it pays off in performance. FWIW, my old 5.0L Mustang also suggested premium for better performance, but I never used it. The DWs Corvette demanded premium, and that is what it got.
I think the Ford ecoboost has a detonation sensor because it could detonate if the computer had no way to know it was starting. But with the sensor, the fast computer can reliably compensate and the EB can precariously run at max just under the detonation threshold.
==================================================================
I think the 3.5L Ford EB lives on the edge and Ford thinks it can reliably keep doing it and survive. This latest technology is amazing and I have much to learn about it yet.
Wes
...
Turtle,
At this point, I think you are entirely correct about one thing for sure. Gasoline-DI(GDI) probably does not inject after TDC according to any info I found either. It seems a blatant enough mistake on my part, that I appreciate your very kind reply.
I don't know a lot about diesel, but I think they do inject more fuel after the initial charge during continued combustion. Apparently this won't work as well with gasoline, although I wouldn't entirely rule it out. The web info on GDI is kind of inconsistant and/or sketchy IMO.
On the other hand, I'm going to take the position of Devils Advocate to try to resolve some questions I still have, so if you will parden me for the sake of argument...
Definition:
Brake specific fuel consumption (BSFC) is a measure of the fuel efficiency of a shaft reciprocating engine. It is the rate of fuel consumption divided by the power produced.
First:
The 3.5L EB engine seems quite efficient under power, and comparable to NA offerings in the F-150. How can this be if excess fuel is wasted just for TC anti-detonation cooling?
One other glaring question is:
What happens to my assumed recovered energy contained in the greater loss of heat energy between a NA (naturally aspirated) engine and TC (turbo charged)? This is supposing that for identical fuel, the TC engine recovers some additional energy and therefore releases cooler exhaust than the NA engine which loses all remaining gaseous heat energy after the combustion stroke. It follows, and is my belief that the TC therefore either delivers just slightly more hp for same said fuel, or the same hp for slightly less fuel.
Wes
====================================================================
Turtle n Peeps wrote:
Wes is does not matter if it's a race engine or street engine or carb or DI. A turbo/supercharged engine will always have a higher BSFC figure than a N/A engine.
I'm going to try to stay with my speculation that the TC BSFC does not necessarily specifically demand more fuel for high efficiency consumer use, and that there can be, and should be, a difference between relatively "crude" TC race engines and the latest, highly developed TC performance production vehicles.
I don't know exactly how Ford does it, but it appears to me that they have, by necessity, carefully tuned out detonation by other means rather than flooding the engine with excess rich fuel. A race TC engine owner often does not care if fuel is wasted (within reason) and the easiest pocket solution to intake charge cooling is normally chosen via excess fuel. I even ran my 2-stroke dirtbikes rich for similar reasons, but there was no easy safe alternative at the time. OTOH, modern 2-stroke DI outboards are extraordinarily fuel efficient in comparison.
Turtle n Peeps wrote:
The turbo, or belt drive supercharger (pump) needs power to turn the compressor blades or rotors. That power just does not come out of thin air. It comes from fuel burnt and this is why a supercharged engine will have a higher BSFC.
I agree this is absolutely true for SC, the final exhaust, while under power, will reflect higher heat per-unit-hp delivered partly because more fuel must be burned to drive the compressor. No gaseous tail-pipe heat energy is recovered in SC after "thee standard recovery" from piston thrust pressure during combustion.
But I believe TC is different. The final "thow-away" exhaust is cooler, after passing through the turbo, designating that some heat energy has gone elsewhere besides tail-pipe waste or piston thrust. This drop in exhaust temp represents a large percent of the energy delivered to the impeller to compress the intake. It isn't really free energy... it's additional recovered energy from the same amount of fuel. There have even been uncommon cases where a turbo not only drives a compressor, but is also geared directly to the main propulsion shaft to take advantage of this principle. Ideally (not possible) the exhaust would exit at ambient surrounding air temp, and all burned fuel energy would be converted to rotational power ala 100% efficiency.
Turtle n Peeps wrote:
It has been erroneously stated many times, and sometimes in big publications that turbo's are "Free Horsepower." Nothing could be further from the truth. Pumps need energy to work and that energy comes from fuel.
It takes a lot of HP to turn pumps. Whether it's a water pump or an oil pump or an air pump. In the case of an ICE that power comes from fuel.
I agree, see above paragraph. I'm just saying more of the available, normally wasted energy from the fuel is put to work, as in TC can be more efficient than SC, and theoretically just as efficient, or rather more efficient, than NA. This hasn't been the case in the past but it is now the newest game in town.
Turtle n Peeps wrote:
Now let me talk about DI engines and the way they function. There is a wide misconception that DI engines can't pre-ignite because they inject the fuel after TDC. This is just not the case for several reasons.
Without writing a big book about the subject this article explains it better than I can.
I'm not absolutely sure the Wiki link is entirely correct or complete. It does strongly suggest that all stoic and power gasoline DI mixes must be accomplished by completed injection during the intake stroke to assure a homogenous mix. All other web sources seem to agree at this point. This homogenous mix requirement may be true of gasoline whereas diesel is more forgiving. But, logically, I doubt it.
Since ultra-lean gas mixes can be successfully ignited by using a stratified charge (rich near the sparkplug), I don't really see why some additional gasoline injection could not take place after TDC if it works in diesels. The ideal homogenous mix idea is that all fuel molecules are nearby all oxygen molecules, and that speedy combustion can therefore be completed during the short high speed power stroke. But I will guess, with carefully arranged "swirl" the molecular match is also quite good. I have to ask, why would diesel be that much more different than gasoline?
Turtle n Peeps wrote:
In short, a DI engine has 3 main modes:
#1. Ultra lean burn. (The DI engines see this mode VERY, VERY seldom. Going down a slight hill or during a medium to low speed at a steady speed are some times that an engine might this mode. The fuel is injected during the latter parts of the compression stroke)
#2. Stoichiometric mode. (In this mode the engine injects the fuel exactly the same "time" as an old bank to bank system; during the intake stroke. Nothing new here, same ol, same ol of yesteryear.)
#2. Full power mode. (Fuel is again injected during the intake stroke. The fuel curve goes to full rich mixture to prevent detonation.
Ultra lean burn has oxygen left for the taking. All fuel is burned. Can after-TDC fueling take advantage of this "left-over oxygen" in a power type cycle?
Stoichiometric mode. I agree this should best take place as homogenous, and perhaps swirled for the most consistant flame front. There appears no reason to do it otherwise.
Full power mode. Rather than excessively enrichen the mix to prevent detonation ala "firehose", the fuel is very briefly increased just barely to the point that all oxygen molecules "can find" a fuel companion, even if just a few raw fuel molecules are left. At this time the maximum possible combustion takes place for all available air. My guess is that this is seldom done nowadays with any unburned fuel being anti-EPA. I think the term, "Full Power Mode" is becoming obsolete, or nearly so.
Turtle n Peeps wrote:
For those that still want to debate the facts please answer this question. Why does Ford recommend premium fuel for the Ecoboost when towing? Why would they do that? After all, if the Ecoboost can't detonate why do we need premium fuel for it during heavy load and HP? The only reason to cut back timing or use premium is to prevent detonation.
Or this question: Why does Ford ecoboost have a detonation sensor if it can't detonate?
I think premium simply allows the engine to produce more power. The high compression caused by boost lets the EB efficiently take advantage of higher octane fuel. I don't think it has to burn premium, but it is a case where it pays off in performance. FWIW, my old 5.0L Mustang also suggested premium for better performance, but I never used it. The DWs Corvette demanded premium, and that is what it got.
I think the Ford ecoboost has a detonation sensor because it could detonate if the computer had no way to know it was starting. But with the sensor, the fast computer can reliably compensate and the EB can precariously run at max just under the detonation threshold.
==================================================================
I think the 3.5L Ford EB lives on the edge and Ford thinks it can reliably keep doing it and survive. This latest technology is amazing and I have much to learn about it yet.
Wes
...
