Ethanol Alternative Fuel - E85 Secrets
Ethanol Alternative Fuel - E85 Secrets
http://images.hotrod.com/techarticle...tive_fuel+.jpgEthanol-the fuel distilled from corn instead of crude oil-is a controversial topic in political circles these days. It seems to hit every hot button in public policy, from global warming to farm subsidies to oil dependence. However, we are not going anywhere near that pie fight. This is HOT ROD. Lucky us: We get to bypass all the left-wing poppycock and right-wing folderol and focus on this issue solely as it relates to hot rodding. The bottom line here is that ethanol looks like a pretty darn good performance fuel.
Since hot rodders are all about looking for a performance edge, not to mention doing it on the cheap, it didn't take them long to notice something interesting: E85 ethanol actually retails for less than regular gasoline-from 20 to 40 cents per gallon cheaper in most areas. But its pump octane rating is 105, considerably higher than premium pump gas (93 to 94 octane) and comparable to racing fuels. Since 100-octane racing gas may sell for five to six bucks per gallon, and 105-octane can knock you back as much as 10 to 12 dollars per gallon, at less than three bucks per gallon E85 starts to look very attractive. Also, E85 is perfectly legal for road use, and depending on where you live, it is available straight off the fueling island at your local gas station. So ethanol appears to be a sweet deal if you are in need of a high-octane street fuel. But wouldn't you know it, there is more to the story. There usually is.
The first thing we need to know is that E85, the most common of the ethanol fuel blends, is actually three fuel grades. Class 1 or "pure" E85 contains 80 to 84 percent ethanol, while the remainder of the blend is commercial-grade (around 85 pump octane) gasoline. Class 2 or E75 is 75 to 79 percent ethanol, while Class 3 or E70 is 70 to 74 percent ethanol. However, all three classes of fuel may be marketed as E85 at various times during the year. While it seems confusing, this is done mainly to offer better cold-starting performance-which is a problem with ethanol fuels. Since straight ethanol has a relatively low Reid vapor pressure (meaning it doesn't like to light off at low temperatures), greater percentages of gasoline are added to the blend for colder weather. So while E85 is often described as 105 pump octane, its actual rating can vary depending upon the seasonal blend. Naturally, higher gasoline content will tend to lower the pump octane from 105 for "pure" E85 to perhaps 100 for E75-though these figures are approximations, it is important to note. Since ethanol is relatively new on the consumer scene, it is just not as thoroughly documented or standardized as gasoline. This is why, in part, you may see E85 described as anywhere from 100 to 106 octane.
Next, just as with conventional gasoline, with E85 and other ethanol blends there are multiple ways to measure octane. When we speak of the pump or road octane of a fuel generally we mean the (R+M)/2 method, where two separately derived ratings, research octane (RON) and motor octane (MON), are added together and their sum divided by 2. For example, if the motor octane of a gasoline is 90 and its research octane is 98, its (R+M)/2 or pump octane is 94. This averaged value, also known as antiknock index or AKI, is the number shown on gas pumps here in North America.
The research octane of ethanol is impressively high, which is a beautiful thing for high-compression and high-boost applications. However, its motor octane (the more extreme standard) is relatively low when compared to racing gasolines of similar (R+M)/2 octane. What this means is that E85 is highly resistant to knock but somewhat sensitive to preignition, comparatively speaking. (Knock and preignition are two different conditions: Knock is spontaneous combustion in the end gases before the flame-front can arrive, while preignition takes place before the timed ignition spark occurs, typically due to localized incandescence or hot spots in the combustion chamber.) But it's no huge deal: Simply know that when running E85 and other ethanol blends, you need to step down one to two heat ranges cooler on the spark plugs, and watch for other potential hot spots such as sharp edges on the piston domes and chambers.
Of course, the biggest tuning change when switching from gasoline to E85 is in fuel delivery. Yes, you will need more, just as you have heard-considerably more, in the range of 25 percent. Josh Ksiazkiewsicz is a GM Powertrain engineer and one of GM Performance Division's resident E85 gurus. A recent graduate of Kettering University, he is currently writing a rather thick master's thesis on ethanol fuels. And just to let you know where he is coming from: The 730hp, 496ci Rat motor in his personal hot rod, a '69 Chevy half-ton pickup, runs on E85 with a Demon carburetor. He says, "If you compare gasoline and E85, they have roughly a 20 to 25 percent differential in energy density by mass. We can't change that. What we can do is compensate for it by delivering more fuel mass to make up the difference."
And that points directly to one of the clear tradeoffs with E85: When you pump in roughly 25 percent more fuel, you take an approximate 25 percent hit in fuel economy as well, though it can be offset somewhat with careful tuning. And while drivers can switch back and forth from gasoline to E85 at will with the flex-fuel vehicles currently offered by the automakers, that is some fairly advanced technology beyond the reach of most backyard tuners. Once you've recalibrated your fuel system for ethanol, you're committed to ethanol until you change the calibration back again.
While the stoichiometric (chemically ideal) air/fuel mixture ratio for gasoline is approximately 14.7:1, with ethanol it is around 9.79:1. In carbureted applications you will usually need higher-flowing metering blocks calibrated for E85, while in fuel-injected applications you may need to upgrade the injectors to a greater lb/hr rating. In all cases, Ksiazkiewsicz notes, "You need to look over your entire fuel delivery system, including the pump and lines, to ensure it can deliver the additional fuel mass." And while you're there, here is another issue to consider: materials compatibility. Ethanol can be downright unfriendly to some traditional fuel-system materials-cork, for example. On late-model cars it's not a big problem since they are already designed for fuel blends up to E20 (20 percent ethanol). But on older cars in particular, gaskets, seals, and hoses will need to be updated to ethanol-compatible materials, as in the long term the exposure will shorten their service lives. Also, aluminum fuel lines must be fabricated from standard anodized tubing. Naked aluminum corrodes when exposed to ethanol. However, ethanol presents no hazard whatsoever to oxygen sensors and catalytic converters-a definite plus.
Those are some of the downsides and tradeoffs. The good news is that all things being equal, when tuned properly E85 will make at least as much power as gasoline of comparable octane, and often a little more. E85 has a much greater latent heat of vaporization than gasoline, cooling the intake charge and thus increasing its air density-rather like intercooling or water-alcohol injection. We've all seen Sprint cars and Alcohol dragsters frosting up after a good run. Ethanol has much the same property, just to a lesser degree. On some engines the resulting power increase could be as much as 5 percent. And when we compare the performance potential of E85 apples to apples-that is, to other retail pump fuels-really there is no comparison. With a pump octane of 105 instead of 87 to 94, you can run more compression, more boost, and more spark advance without damaging the engine with knock, and make more power.
You remember Kurt Urban, the guy wheeling the killer green Nova ("Sucker's Bet," Nov. '06). Well, when not out doing his Clark Kent thing with one of the most outrageous sleepers ever built, Urban handles engine development at Wheel to Wheel Powertrain (W2W) in Madison Heights, Michigan. Recently we looked in on a dyno shootout Urban conducted featuring gasoline versus E85. The test mule was W2W's standard LS2 crate engine, 402 ci with electronic fuel injection, Mahle 10.2:1 pistons, and ported cathedral heads.
To simplify the test, a BigStuff3 engine-control unit with both pump gas and E85 calibrations handy was plugged into the EFI harness. On 100-octane gasoline, the combination made 509 lb-ft of torque at 5,200 rpm and 540 hp at 6,000 rpm. (W2W tests its pump-gas engines on 100-octane for safety's sake, then performs its final validations with 93-octane pump fuel.) With no other changes except in the software calibrations, on E85 the engine made 524 lb-ft of torque and 546 hp. So the numbers were very similar for both fuels, with E85 squeaking out a slight edge. The real difference here, of course, is that one fuel is an expensive racing blend while the other sells for less than regular. And Urban felt that with some optimizing of the spark curve to exploit E85's greater octane, further gains were well within reach.
Just for fun, Urban then bolted up his standard turbocharger combination, a Garrett GT42 blower and Precision Turbo air/water intercooler, to the well-worn test mule. Still running 10.2:1 compression and E85, at 13 psi of boost the engine made an easy 833 lb-ft of torque at 5,000 rpm and 850 hp at 5,900 rpm. You will note there are no comparable test results for pump gas with this combination. "There's no sense even trying it with this boost and compression," Urban says. "You just can't do this with pump gas." With its knock-stifling 105 road octane, E85 is a pump fuel that performs like race fuel. "I love this stuff," Urban says. "It's high-octane fuel for everyone, 105 you can buy on the road."
But not everywhere, at least not yet. Supply can be a big problem depending on where you live. Naturally, availability is best in the Corn Belt. Minnesota residents have it made with 322 retail outlets. Wisconsinites (87), Michiganders (54), and Ohioans (46) are well set too. But as of this writing there were seven states with no E85 locations at all, mainly in New England. California of all places has only three. But it looks like the supply situation will continue to improve. While we promised we weren't going to go there, it appears that the political winds are shifting toward a permanent commitment to ethanol fuels. Funny, isn't it? Usually when environmental and social issues arise involving cars, hot rodders get to take it right in the neck. Not this time. Here the green solution may be the ideal performance solution as well.
Photo Gallery: What You Need to Know About E85 Ethanol Alternative Fuel - Hot Rod Magazine
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