Correct me if I'm wrong , but according to a few dyno runs I have seen and what I have read you actually would see a slight drop in power (About 5%) when running a high octane gasoline compared to E85. So basicly on E85 you should be able to pick up about 5% power. From what I understand this is due to alcohol being oxygenated and carring extra oxygen into the combustion.

I would assume this would hold true with high octane racing fuel as well.

 

Ever hear of VP's Q16?

 

Nope. If that's the case, the gas tune is probably less than ideal. E85 has a lower energy density than gasoline which measn more is needed to get the same energy delivery, one of the reasons your E85 equipped injectors are twice the size of gas injectors for the same engine. Essientially you're burning pre-oxygenated fuel... to get the same hp you need to up the volume. If you're able to squeeze out every last pony from upping the CR you could get say 1% more, but no more than you could with any other race gas at that octane rating... the catch of course is the increased fuel required to do this so E85 will require a "wetter" charge which makes all those internal swirl thingys less effective. The up side is your fuel will vaporize easier on the valves/piston, but likewise, droplets will be smaller or even missing depending on delivery. This idea of droplet size and charge density ("wetness" of air/fuel mix entering cylinder) is the stuff of NASCAR and top builders... way more than I could tell you about. Chemicly though, there is no way E85 gets you anywhere NEAR 5% gain if both are tuned well. Chemically, it's a NEGATIVE impact on the energy density. This is why winter gas (with less/no ethanol) can get a touch more hp than summer blends (besides the ambient temp differences).

Actually that's the reason it has a lower energy density... ethanol is already partially oxidized by having an oxygen bond. If you ran Ethane and oxygen separate you'd get that energy bond back for combustion, but as ethanol it's reduced the potency of the fuel... it's like throwing a half-burnt log into the fireplace... sure it'll burn, but it doesn't have the same energy content as a similar non-charred log.

Nope... high octane race gas is not from pre-oxygenating the fuel, instead the gasoline is doped with aeromatic compounds like toluene or other high-carbon molecules. The energy density for premium vs regular gas is non-existant... same goes for most race gasolines. Aviation fuel has high octane (usually leaded) fuel as well but due to the density difference between Av fuel and gas you'll get different hp curves unless you adjust the injectors to deliver more fuel.

Without getting into some more detailed O-chem jargon that's about as far as I can explain it... for use in gas engines, octane rating has nothing to do with energy density, which is related to hp. Pre-oxygenating the gasoline is basicly like adding a EGR leak that's always flowing.

 

Well then, let us take the thermodynamics approach.

After a quick search the specific energy of each fuel are as listed below.

Gasoline
47,300 kj/kg

E85
32,340 kj/kg

Now to be easy for everyone to follow let us do our analysis on 1kg of air to be combusted. Let us also use maximum power rich mixture. The values for these are as listed below.

Gasoline
12.5

E85
6.975

Now lets figure out due to the mixtures exactly how many kj's are being released to the air if a complete burn occurs.

Air fuel ratio is defined as mass of air / mass of fuel. We have 1kg of air.

So 1kg air / max power air fuel ratio will give us the mass of the fuel.

Gasoline = 1kga/12.5 kga/kgf = 0.08 kgf

E85 = 1kga / 6.975 kga/kgf = 0.143369176 kgf

Now back to those specific energies which are in kj per kg and we just learned how many kg it takes to do the job so we can solve for how much energy is released for each fuel on 1kg.

E85 = 32,340 kj/kg (0.143369176 kg) = 4637 kj

Gasoline = 47,300 kj/kg (0.08 kg) = 3784 kj

Uh oh, the E85 just slapped down gasoline hard in terms of energy released when given the correct air fuel ratio. Not by a little but by 22%....... in theory only.

In reality you can only move so much volume of fluid at a certain rate Through your engine. If your fuel vaporizes before your get it to the cylinder, your ve goes down and with it your power. Now you also have to pump all the water and spent gasses out as well as the fuel on the intake, this also costs you power. Phase changes pumping losses, heat losses etc etc etc all sorts of things chip away at that margin until there is just a little bit left. It may be as much as 5% by the time you get to the tire or as little as nothing.

Also in my own testing, e85 preffered a much leaner ratio for best power approximately 8:1. Then again I dont run gasoline at 12.5:1 either, more like 12.8-.9, compare your real numbers to your real numbers . Its gonna be different for everybody.

I will be back later to post about compression and why not to go insane with it and give reason to match it to the engine.

 

1) You're assuming complete combustion... not likely, but good enough for our model.

2) Calculating the amount of fuel needed for the combustion of 1 kg air is novel if you had an unlimited air supply (please, no The One That You Love jokes ), however as shown by the very low a/f ratio needed for EtOH to combust efficiently you see the need for twice as much fuel, meaning you're decreasing the amount of air that can fit into the cylinder with the fuel used. Considering the vaporization of EtOH under normal conditions I'd be shocked if it wasn't fully vaporized by entry. What's this mean? It means that instead of a very small amount of gasoline droplets in suspension, the EtOH vaporizes, becomes gaseous and literally becomes part of the air. This "displacing air" is known to me minor in gasoline due to the high A/F ratios used and the fact that most gasoline enters as fuel (much more condensed than gaseous vapor). This is the same "displacing air" effect used by Nitrous to increase the amount of oxidizer by replacing air (20% O2) with Nitrous (100% N2O... worth about the same as 50% O2), but in the case of alcohol, it REDUCES the amount of O2 available (1 OH group on an alcohol is worth about 50% that of O2) meaning any air displaced by EtOH reduces the oxidative power by half.

So how much air IS removed from vaporized EtOH?

1.000 kg EtOH * (1000 mole EtOH / 46.06 kg EtOH) = 21.7 moles EtOH
6.975 kg air * (1000 mole air / 14.2 kg air) = 491 moles air

(21.7 moles EtOH) / (491 moles air + 21.7 moles EtOH) = ~5% of the mixture.

Hence... there is a 5% drop in oxidizing power of the charge when using EtOH... assuming you haven’t found a way to make the cylinder larger to compensate (ie. using forced induction).

Personally I wouldn't consider a 12.5:1 gas ratio ideal... I've found 11.5:1 to 12 is probably a better solution... which raises your calculated fuel weight per kg air to about 8.6, and hence the kj/kg air to about 4100... almost the same as EtOH once you reject the 5% loss EtOH has due to vaporization.



3) I'd like to point out here that the max kJ/kg is simply not more than about 30% due to technical losses. The reason we can harness this energy is due to thermo-baric expansion and careful valve timing. With comparable gas and E85 set ups generating similar kJ per combustion, the differences in hp and MPG is due primarily due to harnessing this expansion differently. It's known that max-cylinder pressure near ~12.5 to 15 degrees past TDC leads to ideal conversion between combustion and kinetic energy. Turbos and forced induction can lengthen this push a bit, but changing chemistry (such as using propane or Nitrous) changes the flame front speed and the pressure curve per cycle. E85 has a faster flame speed than gasoline and pulls the curve closer to a pulse than a longer "thump"... which means less advance timing is needed to get ideal timing for hp... but that also means it falls off faster after that point than gasoline. On the upside any compression during the advance timing of gas or EtOH is stored and released due to the spring effect of a sealed cylinder, but the loss of a longer expansion can't be made up for. The effect of this is probably minimal, but I suspect it adds to the loss of hp/mpg seen in E85 vehicles.

At full air flow they will likely be similar and you'd hope that not all the E85 would vaporize at high flow rates (less time to vaporize before getting to the chamber), though at higher vacuum near-idle driving the differences are undeniable... EtOH gets lower MPG due to lower energy density and flex vehicles using both are known to get between 6% and 25% less mileage with E85. The proof is there for mileage. HP seems to be a toss up and more a tuning game, but to claim it gets even a 10% gain in hp is umm... "unlikely".

 

And that's the catch isn't it? at stoich ratios... trying to get max mpg, e85 loses miserably (see any Flex fuel vehicle), and as you said, leaning to 8:1 will help power (much like going from 14.7:1 stoich for gas at idle to 12:1 for power will as well).

Here's the crux of the issue:

8:1 means you have only have 0.125 kg f to 1kg air... reducing the amount of air/O2 the vaporized E85 will displace (cutting your losses to probably only 4%). This of course affects the total kj available at max power... dropping it to 0.125 * 32340 = 4040 kj without ANY O2 displacement. With only a 3% loss you'll get 3921 kj. Even closer to gasoline; less than a engine with peak hp at 12:1 a/f which starts with 3941 kj.

The harnessing differences due to flame front and thermal expansion differences make up the most of the differences seen, but at ideal tuning, it's pretty much a toss up. Definitely not a gain worth chasing for $1000's of dollars to convert and suck up the heavy MPG losses (the government won't subsidize E85 forever... when they cut the handouts prices will spike HARD).



From an "environmental" view, E85 doesn't make much sense for now... using a corn source is inefficient and leads to food shortages/price hikes, but even worse, Ethanol easily vaporizes. Evaporative emissions from gas pumps pumping E85 is MUCH higher than gasoline pumps... the differences are even apparent in E10 verses straight gasoline, it's a matter of chemistry, no dodging it.

As switch grass and other options to make EtOH become feasible E85 will cease to be a burden on tax payers through subsidies and allow corn and other agricultural prices to drop for consumers, but the pump emissions will continue to rise.

I'm convinced heavier fuels like diesel are WAY more responsible from a pollution stand point, though every engine in existence will need to have a turbo system and pricey injectors which will raise car prices for sure.

Best option? Electric motors, Li-Ion or more advanced batteries, and a clean-power-grid (nuke, hydro, wind). Battery and motors are a great place to invest IMO.

 

BTW, a quick search online shows most E85 users treat it jsut like ~100 octane fuel from a boost/DCR stand.

One forum says Saab changes it's boost from "5.8 PSI for pure gasoline to 13.8 PSI for E85" meaning the extra 10 octane points is good for about 8 psi of boost, which sounds about right (maybe a psi or two more than 100 octane gas but that's again, likely just a tuning variance).

If you run SOLELY E85 in the engine (i.e. not a NA flex fuel vehicle) your best bet is to run a turbo/supercharger and play with the boost to an appropriate level... but you could go for NA with high DCR and make fine adjustments with cam swaps... but unless you run a DOHC/OHC cam design or have adjustable valve timing, that's probably more effort than most will invest in.

Pump gas is good for about 8.5 to 9 DCR... 100 octane gas is good for about 2 more SCR over pump gas... so a DCR of 9.5 shouldn't be out of range with E85... but that's a LOT of assumptions (such as VE being similar regardless of the e85 vaporizing effect).

Personally if I was going to try a E85 engine without boost, I'd go for a safe SCR like 12:1 or so and then bump the DCR to about 9.5 using a moderate cam (extreme, high-rpm targeted cams will typically drop your DCR... which is how my 396 with 12.5 SCR runs around 8.9:1 DCR). This allows you to swap cams for future gasoline use, and still gets your E85 octane gains allowing you to increase hp numbers a touch (probably about 1% compared to DCR that you'd used for pump gas).

Lots of variables, and lots of new ground to forge through... is it worth it?

 

I am going to be honest here, I am not going to read all of those novellas you wrote in any detail in the very near future. I have too much other stuff to do right now, and my retort and addition of information would take me a day to dumb down and make concise.

Yes my model is very simple and straight forward however unlikely. That is very much on purpose. The user base here is not capable of basic physics much less more advanced thermodynamics and 3-4 phases of heat transfer and fluid mechanics all rolled into the same model. If you will notice I said the gain could be from 0-5% I also spoke of the ve reduction due to phase change of the ethanol etc etc etc. I did not take into account gasoline is 10% ethanol either which makes them closer and throws off the max best power ratios and the stoich ratios. I also avoided talking about the wiebe equation for the different parts of a combustion event, its easier to just say you only get 30%.

I am not here to teach anybody upper level energy processes or engineering fundamentals. But, I will nudge them in a direction of correct thinking.

I will try to make a post this weekend regaurding compression ratio. Best just simple straight forward advice is just to match it to the camshaft just as you would with gasoline. Mid to low 9's for dcr is not out of the question. What e85 will enable you do to is to run a nice big racey camshaft and have the compression to make it livable on the street with fuel you can get at the corner and it is cheap (well sort of).

Steve whats your day job, chemist?

 

Biochemist actually... but I suffered through P-Chem for a minor. :-/

Like I said above, the E95 is really a wash except for small gains by being able to run higher DCR... but the fuel itself is less efficient, vaporizes more and may approach gasoline at max hp a/f... but at stoich and less than WOT conditions it's a serious loser. Flex fuel may be useful in future-proofing your car if gasoline ever get bans... but I have a feeling that's not gonna happen any time soon.

As for CR vs hp gains, David Vizard did a great couple articles on that many years ago that's still floating around the net. Diminishing returns is a known issue, as is the issue that detonation doesn't rely just on DCR, but the cam ramp profiles, the VE of the engine (which varries with rpm), and any changes to the chamber/piston top/spark plug over time. What really matters here is chamber pressure (PSI) near TDC and outside of a basic compression test or an ultra-expensive piezo sensor in the chamber you have to go with what works in gthe pastg and hold your breath when fordging ahead (computers can sim all you want, but the sim is only as accuate and the data put in).

 

I know your case is that e85 and gasoline will be very close. However you do have to consider that in a fuel injected enginethe droplets are very fine and they are not subject to heat from the manifold really. Also if they are, your manifold temp is going to drop pretty rapidly and achieve somewhat of a steady state. Heat transfer is most generally related to a temperature differential in at least 2 of its modes. So as manifold temp goes down vaporization will be reduced. An 11 second jump down the racetrack is more than enough to do the job of cooling down an intake on an alcohol engine (go put your hand on a methanol cars intake after a run it is quite cold). I do consistantly see a power gain on e85 which I run in the summer, and make it myself inbulk. It has to be denatured to avoid a visit from excited guys in atf jackets though, gasoline works for that. My personal car goes from about 118mph on gas to 121mph on ethanol.

As far as air/fuel ratios for cruising. I do not have the same initiative as oem manufacturers. They run slightly rich of stoich to keep NOx uHC and all of that nonsense under control. We obviously know that at stoich you get the maximum temp and pressure and therefore very likely maximum NOx so they run just a bit fat of it. Maximum temp is not likely going to make your engine/exhuast system very happy. I therefore choose to run as lean as will allow regular combustion at cruise. The idea that engines should be run at stoich is nonsense that people have generated due to oem polution initiatives (monkey see monkey do). Engines could give a rip what the a/f is as long as it allows regular combustion and doesnt foul the plugs or wash the oil off the walls they are happy with it. Less fuel also usually allows for enough energy to be available in the combustion space due to compression and heat transfer to vaporize the mixture and avoid puddling. You do want the fuel to vaporize completely, but only after its in the chamber with the valve shut. Using this I only see about a 20-23% loss. Of course if you do it like the oem's, you are going to lose 30% of your economy that is exactly how they have set it up. But we do not have the epa monkey on our back as individuals at least here.

Steve, I had guessed as much from the view you were looking at it from. I am an ME. I have worked in two different places doing engine R&D but I can't talk about anything I saw there without getting into trouble. All I can share is common knowledge and personal experience and it is really a difficult thing to skirt critical information. I agree about the diesel fuel. Imo tractor trailers should function in the same way that diesel trains do. They should also be equipped with two stroke turbocharged diesels as well instead of as they are. If the truck manufacturers would do that we would eliminate the large black clouds from semi trucks. The cost of a truck would go up but I bet in the life of the truck it would break even might be better even at nearly $5/gal and be much better for everyone. I have personally seen diesel engines run as lean as 35:1 a/f under load and still happy.

 

You know, the diesel-electric version of a semi has been thrown around for years, but with the proper battery developement and regenerative braking (not just air brakes, but kinetic fly wheels or electric motors per axle) I can see it happening some day.

The use of a low redline and multiple gears has served diesel engines well in keeping near max VE and more efficent tq levels, but I agree, the idea of a load-independant diesel engine using electric motors (which are most efficient at very low rpms and generate very high torque values from a standstill) seems like a perfect fit for semi's. The diesel-electric train will be with us for a VERY long time... espeically with biodiesel developments making fuel selection options more available.

Main problem with a diesel-electric design however is the weight overhead that has to be absorbed to make it work. The upside is that electric motors can be made to work without a transfer case, and if placed per wheel can replace driveshafts and axles, and if Li-Ion takes off for automotive sizes the weight could be decreased as well... the cost issue however is really prohibative.

If diesel-electric takes over semi's as it has trains and ships, you'll probably only see it in long haul over-the-road designs with multiple trailers at first and later in single trailers that haul near major ports and warehouses... maybe even a pure electric option in those cases.

E85 or E100 will not overtake diesel in these "infrastructure" applications, but in consumers which account for a major share of CO2/CO/NOx/CHx emmissions I see a real problem due to the volitility of the fuel in CHx pollution from pumping alone, and in an application reality there simply isn't enough land to support our economy by converting corn... you need more efficent EtOH production (ie. switch grass, algae, etc...) especially considering the reduced milage which makes for even worse efficiency due to consumer demand for a 300 mile tank... bigger tanks = more weight to carry around. In all but the most optimistic scenarios, ethanol is a very long way off from making any sort of change in our energy policy and may actually be doing more damage environmentally than the gas its replacing.

 

No doubt e85 is crap as far as a replacement, do not fuel your car with your food. It is however a cheap and available alternative to 8-12 dollar a gallon race gas. That is the extent of my interest in it. Making the most of the mileage from it is purely for my own pocket book. The performance increase is rather nice too. This summer it was about 2 dollars here and 93 was 4 on average. Well thats a 50% savings but its 20% less efficient for me, so i save 30% making my fuel cost for the same mileage about 2.80 a gallon. Bad in the big picture... really good for ole number 1 who I like taking care of.

On the diesel trucks it would be a complete redesign keeping likely only the chassis and perhaps the transmission setup. Ideally though you would drive all three axles with one motor per axle with some sort of slip detection. With enough battery capacity you could keep the revs pretty low on the engine and it would last for freaking ever. The key to it is though that you can design the engine to run at one data point optimize everything because its basicly always going to run right there. A two stroke industrial type diesel is a mean machine too as far as efficiency is concerned. Compound turbocharging and intercooling will bring along efficiency quite a bit as well. Under high power conditions perhaps you could pull current from the engine to the motors as well as from the batteries, maybe up the cut off ratio and rpm to a max power situation. That would allow a semi truck to take off in a hurry relatively speaking.

The big gain though would be in air quality around shipping yards and things of that nature where there are alot of diesel trucks running all the time. If you have ever been in an area like that i almost garentee you did not stay long it is highly unpleasant. Part of the reason for that is the big plumes of black uHC that they all puke out when trying to take off. The other thing is those big plumes of smoke is money just floating around in the air, and the exhaust is horrible for you. Funny thing is if the truckers just saw it squirt out liquid diesel in thier mirror, they would have a fit, but as a fog of smoke... whatever .

Its too expensive right now, I already know. Me and a few dozen other engineers all keep notebooks on ideas for this particular project in our spare time. Updating as things become smaller and sometimes rewriting how its done as we go. Then again in a 2 year span I have seen stuff go from filling a 747 from tip to tail, to fitting inside of a shoebox.

 

im running 12.8:1 SCR with a LT4 Hotcam (with more lift due to my 1.72:1 rocker arms) and E85... so my DCR should be 9 to 10:1

 

Looks like GM faced energy content issues with their E85 version of the corvette C6R:

Obviously they did just fine with the change over, but it's interesting they specifically pointed out the fuel economy issue. Seems like carrying MORE weight in fuel to drive the same distance isn't a great idea from a racing standpoint, but I'd imagine it's a moot issue compared to the weight of a full-bodied car... especially when the E10 version of the car was dominating the pack in 2007 with the same chassis. In 2007 their 2 cars finished 1-2 in 11 of 13 races. In 2008 they pulled off the same feat... exactly. Spooky.

Here's the engine spec comparison between the vette/ZO6/C6R in 2008: http://www.corvetteracing.com/cars/c...ne_specs.shtml

I wish they had the 2007 C6R engine specs on E10 as well... would have been interesting to see how the torque/hp peaks moved.

 

it makes sense to switch to a higher oxygenated fuel for an engine that is restricted in airflow.

Look at that torque number! I have to wonder what compression ratio they are using with the E85.

I applaud them for this. They are using their time racing to find the limits of E85 so hopefully it will migrate more into street vehicles in the future.

I do agree that it would be nice if they shared the E10 info with us.