Blending E85 at the pumpPosted on November 10th, 2007 2 comments
I previously wrote about using ethanol as an aviation fuel. After noticing that the national average for aviation fuel is now around $4.60/gallon, and E85 is available for $2.19/gallon, it seems fitting to revisit the subject. As oil heads toward $100/barrel, pushing regular gasoline over $3/gallon again it would seem that E85 is poised see some renewed interest at the fuel pumps around the country.
In order to take advantage of E85’s lower pricing in comparison to gasoline, it requires that you have a ‘flex-fuel’ vehicle that is approved for use with E85…or does it? I began to ponder the question of whether you can safely run E85 in a vehicle that is not specifically designed for it. I decided to do some research and experimentation on the subject. There is a lot of misinformation floating around about ethanol, much of it by people who don’t have the slightest understanding of fuel chemistry. It’s sometimes so often repeated that you have to wonder if there is some sort of conspiracy against ethanol. I have a little more experience than the average man off the street about gasoline and ethanol. I worked in HP’s Chemical Analysis group for 7 years (now part of Agilent Technologies) where one of the instruments I helped to design and support measured oxygenate content in gasoline. So I am constantly amazed at how people with no technical background in the subject will confidently repeat common myths about ethanol. I covered a few of those in the aviation fuel article so I won’t repeat them here.
I was interested to know if anyone had developed a kit to convert a conventional car into an E85 flex fuel vehicle. I found that there are several conversion products on the market that splice into a car’s fuel injection system that allow any fuel-injected vehicle to use E85 fuel. Just about all cars manufactured in the past 15 years use fuel injection systems instead of carburetors to adjust the air-to-fuel ratio to the engine. The advantage of fuel injection is that it can be computer-controlled to vary the air-to-fuel ratio based on a number of factors such as throttle position, engine speed, manifold pressure, engine temperature, and oxygen content of the car’s exhaust. The ability to monitor all of these parameters and adjust the mixture accordingly has helped significantly with advances in fuel economy and emissions reductions. The computer is able to adjust the fuel amount by pulsing the fuel injection valves to allow just the right amount of fuel to enter the intake manifold. The air-to-fuel ratio is thus determined by how many milliseconds the injector valve is opened each cycle. By monitoring the oxygen content in the exhaust, it’s possible to tell whether the fuel injectors are providing too much fuel (too rich a mixture) or too little fuel (too lean a mixture) and that information can be used to help close this control loop. Although I haven’t been able to find any technical descriptions on the theory of operation of these conversion devices, the only thing that one can assume that they do is to stretch the pulse generated by the car’s computer to compensate for the air-to-fuel ratio difference required by E85 to extend it beyond what the car’s computer had included in the lookup table for the air-to-fuel ratio settings. It needs to do this because the air-to-fuel ratio for ethanol is about 30% lower than it is for gasoline. So the effect of adding one of these devices to your car is to shift the lookup table to favor E85 fuel in the event that the standard lookup table cannot reach the lower air-to-fuel ratio required to keep the mixture rich enough when running ethanol.
I would estimate that the cost of the electrical components to implement a simple scheme like this would be well under $50, and so you would think a conversion kit would sell for somewhere around $150 or less, but they are charging as much as $500 to $750, which is more that I wanted spend to run some E85 experiments. So I won’t be discussing the efficacy of E85 conversion kits. Instead, I will concentrate on blending ethanol with gasoline at the pump.
Ethanol has about 28% less thermal energy (measured in BTUs) than gasoline. However, the process to convert the BTUs into mechanical energy on cars is rather inefficient, usually less than 30%. Thus it doesn’t automatically follow that your fuel economy will be reduced by exactly 28% when you run E85 in place of gasoline if you can improve the conversion efficiency. In fact, E85 may deliver similar fuel mileage if your car’s computer can advance the timing of the ignition and convert more of the BTUs into usable mechanical energy. This is possible due to ethanol’s superior octane rating, which is a measure of resistance to engine knocking, also known as ‘pinging’ or detonation.
E85 has a 105 octane rating, which exceeds the octane rating of even the most expensive premium gasoline by a wide margin. For example, in Colorado we have 3 commonly available grades of fuel: 85 octane, 87 octane, and 91 octane. These are lower than what you’d find at sea level because at Colorado’s higher altitudes, the risk of detonation is lower and thus you can safely use lower octane fuels
Gasoline’s price goes up with increased octane rating because of its higher ‘grade’ and to cover the expense of the blending agents required to enhance the octane rating. I’ve noticed that the price goes up approximately 7% per grade here in Colorado. I’ve often wanted to use 85-octane gasoline since that’s the lowest price for fuel advertised on the gas station signs, but I know how destructive detonation can be to an engine, so I always use at least 87 grade on my Dodge Durango. On the few occasions I tried 85 octane, I could hear the tell tale signs of knocking when climbing hills. The knocking goes away in a few seconds since the computer is able to monitor a ‘knock sensor’ on the engine and retard the ignition timing accordingly but I still don’t like to hear that sound so I stick with 87 or higher octane.
I noticed that there is a rather extensive Wikipedia article dedicated to using E85 in standard engines. Although there are a number of warnings about all the things that could happen when running E85 in a vehicle not specifically designed to run on E85, most of them don’t apply to vehicles manufactured after 1990. For example, much of the rubber seal material in automotive fuel systems was changed after ethanol became a common blending agent. Ethanol is typically mixed at the rate of 10% ethanol to 90% gasoline to help reduce emissions, and most cars can run fine on a mixture with as much as 20% ethanol. I became curious to see what would happen if I tried running on 30% ethanol, so lately I’ve been filling my tank w
ith 2/3 of the less expensive 85 octane gasoline mixed with 1/3 of E85. This gives me something close to a 30% ethanol ratio (E30) with an expected octane rating of around 91 and a BTU content that would be 90% that of gasoline. Since I’m saving 7% per gallon on the gasoline, and 30% per gallon on the E85, my fuel bill effectively is reduced by about 15%.
I have a fuel computer in my Durango that gives me instantaneous and average MPG and I’ve noticed about a 10% drop in MPG on my E30 blend, so it’s still about 5% cheaper to do this than to fill up with regular gas.
I’m not blending my own E30 for the savings, but rather to satisfy a curiosity about using ethanol. I suppose if one is of a mindset to reduce our nation’s dependence on fossil fuels, blending in E85 at the pump could have an immediate impact of reducing our demand for gasoline by about 30%, or 40 billion gallons per year while increasing the demand for ethanol by a similar amount. The ethanol industry doesn’t produce enough to satisfy this level of demand yet, but if more people started blending E85 with regular gasoline at the pump it may help to drive demand for E85 to help to increase its availability. One of the common shortcomings of E85 is the fact that it’s only available in a relatively small number of locations. For example, in my own town of about 77,000 people, we have only two stations that carry it.
What I’d really like to do is reprogram my car’s computer, often referred to as the ECU (engine control unit) or PCM (powertrain control module), to accommodate E85. However, the information to do something like this isn’t readily available. If you’re an automotive engineer with Daimler-Chrysler and know how to reprogram the ECUs to be E85 compatible, please contact me ;-).
My nephew is currently in the process of installing an open source-based ECU called a MicroSquirt II in his 1981 DeLorean and I have become his technical support hotline, giving him tips on proper soldering techniques and electronic debugging issues with the device. The more I read about it, the more I like the idea of a completely user accessible and reprogrammable ECU. That would make it easy to experiment with various ethanol ratios and once it’s debugged, the data could easily be made available to anyone with a similar vehicle who wants it.
The EPA is concerned about aftermarket products in this category, of course, because the ECU is largely responsible for keeping the tailpipe emissions compliant with clean air regulations. But I see that as a relatively easy problem to solve because using oxygenated fuels such as alcohol and reducing tailpipe emissions tend to be mutually compatible goals. The EPA has issued laws against altering the ECU in a way that makes the vehicle non-compliant with clean air standards. This was a problem when people were converting cars to run on propane and natural gas back during the first energy crunch but today I think those laws are mainly aimed at companies selling ‘performance chips’ which tend to sacrifice fuel economy and tailpipe emissions for more power.
It will be interesting to see what happens with E85 because the stock market seems to be predicting a glut of ethanol in the near future, but with the recent increase in gas prices it may take care of any potential ethanol over supplies, especially if the idea of using it in standard vehicles becomes popular.
2 responses to “Blending E85 at the pump”
[...] expansion and construction. I’ve written about E85 ethanol previously, including using it in vehicles that were not designed for it as well as in [...]
John G July 5th, 2010 at 17:01
I am curious does blending e-85 with gasoline change your emissions for creating less harmfull exaust I would love to know and try it out .Any enfo would help thanks. John G [firstname.lastname@example.org]
Leave a reply