Drives: C6 Z06, 09 335i, 10 335xi
Join Date: Dec 2008
Location: www.TopGearSolutions.com
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Cp-e has actually already done this and made a thread.
They did it on the stock system. It might be on the other forum. I def read it though.
Quote:
Originally Posted by www.cp-e.com View Post
This thread is aimed at those that are at least vaguely familiar with EFI tuning, and understand the implications of running alternative fuels in modern engines. I've started this thread because I wasn't aware of anyone that's documented running E85 in a directed-injected engine, let alone an N54. So, I thought it'd be exciting for some to see how the ECU reacts to the new fuel. If you're interested to see how far we can take this wonderful engine from BMW, please read on. If you have personal experience using E85 in your own vehicle (good and bad) please do share!!
The gas station that's right down the street from my home had been undergoing "upgrades" for about a month and I was getting really ticked by the inconvenience. Anyway, I drove by a couple weeks ago and there was a big new yellow banner at the entrance that read, "Now featuring E85 ethanol." "Let the games begin," I thought to myself
I've always been a fan of E85 because it's basically race fuel for the street at 105-octane, is $0.30 cheaper per gallon than 93-octane (price varies by location, obviously), has inherent engine cleaning properties, and cools the cylinder better than gasoline does. Until now, E85 hadn't ever been readily available to me, and I've never had a car that was "Flex Fuel" compatible so I never gave it too much thought. But in doing some tuning recently it occurred to me that the N54 is already setup for E85. That isn't to say that E85 doesn't have some drawbacks, so I wanted to create a thread about E85 where people could ask questions and share experiences. And truth be told, I really don't expect a heck of a lot of people to go down this road either
Why run ethanol at all?
Ethanol is a pretty neat fuel and I’m excited that I now have access to it. One reason why ethanol is so great (aside from the octane benefits) is because of its incredibly effective evaporative cooling effect. What that means is, when the ethanol turns from a liquid into a vapor it sucks a lot of heat away from it’s surroundings. This is special because when ethanol is injected into the N54’s cylinders at 2000psi it absorbs a tremendous amount of heat. This allows the engine to run more boost and ignition timing without auto-igniting. To illustrate just how good ethanol is at evaporative cooling, it removes about three times as much heat as gasoline when it vaporizes. When you combine that with the fact that you have to run more volume of ethanol than gasoline for a stoich mixture, the cooling effect is even more powerful.
Power Potential
Just how much power can someone make on mixtures of E85? Several studies suggest that the knock limit can be more or less eliminated by combining ethanol and DI. Sound crazy? There are many many articles illustrating just how powerful direct-injected ethanol can be. Here are a few to check out:
http://www.ethanol**********/LFEE-2005-01.pdf
http://www.technologyreview.com/Energy/18304/
http://www.greencarcongress.com/2006...p_working.html
Apparently Ford is about to release E85 version of their yet to be released Eco-Boost (DI and turbocharged) line of engines code named "Bobcat":
http://jalopnik.com/5044276/next+gen...-diesel-market
http://www.autoblog.com/2008/09/02/f...nder-codename/
As you can see, some of the links indicate two to three fold increase in power potential by running ethanol under the correct conditions. Even if these numbers are optimistic (they sound like it to me!) the point still stands. With turbos that run out of breath at about 12psi, why not get all you can out of that boost pressure?
Fueling
I said the N54 is already set up for E85. That sounds crazy, but it's really true. The N54 uses a closed-loop fueling system, and it targets a lambda (actually an equivalence ratio, but basically the same idea) and not an air/fuel ratio. That distinction is important because air/fuel ratio is specific to any fuel, whereas lambda is not. It's also important that the N54 uses this closed-loop system because it will automatically account for the E85's richer mixture requirements and add more fuel as necessary. That means "hypothetically" you can go to your local E85 filling station and fill up with E85 and the ECU will automatically adapt to the new fuel. It's actually that advanced (not really, read on).
So why can't everyone just fill up with E85 then? I said the N54's fueling system is special because it's always in closed-loop and targets lambda. Typically, cars don't have a totally closed-loop fueling system and, at wide open throttle they open the loop the ECU is blind to the fuel mixture. This causes problems for two reasons. First, in order to maintain a stoichiometric air/fuel ratio at idle and during light cruise using E85, the injectors will need to flow an extra 30% more fuel by volume than gas. For vehicles that aren’t always in closed-loop this is a serious problem because they’ll run very lean under high engine loads. For vehicles like the N54 that always operate in closed-loop, they can account for certain concentrations of E85. If the concentration of ethanol gets too large, the resulting injector pulse-width will grow and the resulting fuel trims will almost undoubtedly trigger a check engine light, which is bad.
So there are two options N54 owners have. They may either run low concentrations of E85 (read 3-5 gallons) without any tuning compensations. A mixture of ~E30 (remember regular gasoline is 10% ethanol) will have an octane rating of about 96, so this can be a great supplement for folks stuck with 91-octane gas. Customers that are able to tune their vehicles may run higher concentrations with some slight adjustments. I have been running mixtures as high as E50 with no problems to report as of yet.
Why not run straight E85? In my reading about ethanol fuel I’ve found conflicting information as to how detrimental the alcohol fuel really is to fuel lines, seals, and other parts not technically rated for alcohol duty. All we really need are a few gallons anyway, so I’m happy running E40 at the moment, which should be just fine
My Experience Running E40
I recently filled my tank with 5 gallons of E85, which comes out to about 40% ethanol concentration if you consider what was already in the tank. I actually made a nifty Excel spreadsheet that automatically calculates your new stoich air/fuel ratio, octane rating, and ethanol content in percentage when you input the number of gallons of E85 you’re running (which I’m happy to share if anyone wants a copy). E40 has an octane rating of 98. I believe Sunoco has a 100-octane race fuel they offer for about $9 a gallon. I filled my entire tank with E40 for $24.70! Not to mention, E40 has 40% better evaporative cooling than gasoline, and also reduces our reliance on foreign oil, lol!!
Interestingly, I first filled my tank with E40 right before a cold front moved through my area. In fact, the first night I filled up with E40 the temperature dropped down to 8°F. I started my car the first morning and the idle rolled was noticeably choppier than normal. After about 20 seconds the ECU trimmed the fuel and the idle turned into the familiar smooth purr. Sometimes vehicles not specifically tuned for E85 can have trouble starting in extremely cold weather, but the N54 didn’t have too much trouble learning to use the E40. Mind you, I didn’t even reset my battery to clear my fuel trims.
I drove to work like any other and the car seemed to like the fuel so far as I could tell. I didn’t notice any hiccups, no check engine lights, and no power loss. The car pulled hard with my boost set at 8psi in the cold air, and I was encouraged by what I saw.
The Good, the Bad, and the Ugly
To be very clear, people won’t have any issues running a couple of gallons of E85 as an octane booster. The issues that I’ve encountered are from running higher concentrations of E85, and I’m deliberately trying to push the envelope a little bit to see what I can get away with in this application.
One thing that you can expect during this documentary is full disclosure. There are risks involved in running alcohol in an engine that was otherwise designed to operate on gasloline (a.k.a. E10 in the United States). Since I started using blends of ethanol I have experienced some hurdles. Some of them I believe I’ve overcome, and others I’m currently working on. Here’s the latest.
The first issue I encountered was an SES light that popped up the other day when I was on the highway. I grabbed the scan tool and it read P0171 and P0174, which translate into a “lean system” code. I switched to the “live data” display on my scan tool and looked at my fuel trims. Sure enough they were pegged at +25% at cruise, which means the computer is injecting as much fuel as it can to reach a stoich ratio, but isn’t quite getting there. Typically computers are limited to how much fuel trimming they can do because excessive trimming can be indicative of a serious problem (eg. Failed sensor, vacuum leak, etc.). So ECU’s will typically throw a CEL when they exceed a certain about 25%, this was no exception.
For traditional PFI cars there are several ways to get around this problem. People may install computer-controlled injector pulse-width extenders, larger fuel injectors, or higher fuel pressure regulators. Because I’m doing some testing for an engine management system, I have some nifty control over various engine functions, one of which happens to be fuel pressure. So instead of buying a new fuel pressure regulator (which you can’t really do with the N54!) I’ve instead modestly increased the fuel pressure when the computer really cares about the fuel trims. So far this seems to have fixed the problem, and my fuel trims when from over +25% at cruise to about 16%. At idle my trims went from about 18% to 6%. So far so good!
Another thing I noticed was my average mileage dropped precipitously after switching to E40. Whereas I typically average about 21mpg on 93-octane, I’m averaging about 18mpg on E40 with mixed city/highway driving. A drop in fuel mileage is to be expected because ethanol requires more fuel per volume than gasoline to reach a stoich mixture, but this was excessive. This change in mileage is going to be the next problem I tackle, and it’s likely due to the change in flame speed of the new fuel.
If spark timing isn’t well optimized then the engine isn’t getting the most out of the burning mixture in the cylinder. The trick is to ignite the mixture so it makes best use of both the burning mixture expanding in the cylinder and the relationship of the rod and crank journal for optimum mechanical leverage. Thankfully our facility should be receiving our load-based dyno in the next few weeks, and I plan to find minimum best timing while cruising using various blends of E85. For now, I’ll suffer with the crappier mileage.
Tuning At Wide Open Throttle
Okay finally, to the reason why this is all worth the trouble! Things get interesting when you put E85 in the N54. The N54 runs very high static compression for a turbocharged engine, which makes for an extremely efficient engine. Direct injection makes the combination of high compression and turbocharging possible because the fine fuel mist helps cool the cylinder before spark ignition. However, at wide open throttle I see the N54 sometimes running as little as 6° of ignition advance, which isn’t a whole lot. Minimum best timing for the engine is probably much higher, so assuming the rotating assembly can take the higher cylinder pressures, the engine should make more power with some more ignition advance. The tricky part however, is adding the timing wisely.
To tune the ignition advance at wide open throttle I tapped into the BMW knock sensor circuit. I figured hey, if BMW stuck a microphone to the engine block why not use it, right? So I grabbed a mono 1/8” audio jack and tapped into the factory knock sensor signal. I ran the cable into the cockpit and plugged it into the MIC input on my laptop. From there I was able to record the output of the knock sensor after WOT runs to evaluate them and see if I was knocking. This can be an incredibly valuable tool since the human ear is arguably better than any automated knock detection system on the planet. I’m working with our electrical engineer to filter out some of the noise in the signal, and I’ll post up some full throttle audio files if anyone is interested in hearing what your engine sounds like through the knock sensor, heh. It kind of reminds me of the inside of a jet turbine. So far at 10psi and the stock timing tables I'm not getting any audible knock on E40.
So that’s what I have so far. I’ll be happy to keep updating people on my progress if anyone is interested, and maybe even if not, lol. Once I get a laptop that actually works I'll be able to post some datalogs while running the new fuel. I’m also going to continue working on the knock sensor interface so I can smartly add some more timing at wide open throttle. When the dyno comes in I’ll be able to grab some baseline numbers for everyone, and hopefully be able to quantify exactly how useful ethanol really can be in the N54.
Please ask questions if you have any, post comments, criticisms, whatever makes you happy! I’ll be at the P3/Willow meet tomorrow with my ethanol-fueled 135i if anyone would like to see it in person.
http://www.1addicts.com/forums/showthread.php?t=226326
Thanks for reading!
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