Ethanol or gasoline, which is the better option for my vehicle in terms of fuel economy, performance? Before we go further, and for the sake of CYA on my end, I’m going to refer you to your vehicle’s owner manual for the right fuel to use in your vehicle. Now that that little bit of housekeeping’s been taken care of it’s time to jump into the mysterious or unknown world of gasoline blends and ethanol. It might be confusing will all the advertising out there today on television, websites, and the host of other sources providing complicated explanations, confusing marketing/brand names or contradictory information about whether ethanol is in fuel, how much of it is there, benefits provided, and what is simply myth. I felt the same way.
But before we go down the rabbit hole let’s start with a basic understanding of fuel, and how cars process it.
Are you ready? Great, let’s dive in!
Most vehicles utilize an internal combustion engine. If it doesn’t then it’s either an EV (all electric vehicle) or diesel powered vehicle. All internal combustion engines run on a mixture of fuel and air that is ignited. That reaction transforms the potential energy to actual energy causing work to be done, in this case propelling the vehicle. For the purposes of this exercise we’ll simply look at the workings of a gasoline powered internal combustion engine. The processes for both rotary and diesel engines are slightly different, but both combust fuel to transform fuel into energy to perform work (i.e. generate propulsion). Before we get to which is better we need to understand the building blocks before we finish our pyramid.
Fuel is issued a “pump” octane rating using a simple formula; adding the RON (Research Octane) and MON (Motor Octane) ratings then dividing by 2 or (R+M)/2. Octane gets its name from its chemical structure (fun fact, right?). Octane has eight carbon atoms in a chain, and can be compressed nicely with no ill effect (pre-detonation). The seven variants that come before octane just can’t get the job done (methane-propane-butane-pentane-hexane-heptane), but lucky 8 octane’s a winner! Octane with its delightful eight carbon atoms in a straight chain creates the gasoline we know and love today.
Now an octane rating is simply a measure of how much any gasoline can be compressed before it explodes/ignites without assistance from the spark plug. The higher the number the more stable and compressable (real word?) the fuel is. Gasoline with an octane rating of 87 means that 87% of gas is composed of octane while the remaining 13% is comprised of some other fuel combination-additive-blends equivalent to 87% octane and 13% heptane. Therefore gasoline with an octane rating of 87 could not be compressed as much as gasoline that has an octane rating of 91. Savvy? Typically your economy/fuel efficient engines place emphasis on fuel efficiency and may be lower compression requiring lower octane rated fuels. Conversely your Corvette ZR1 will possess a higher compression engine requiring a higher octane fuel. It’s important to keep in mind that deviating from the recommended octane ratings listed in the vehicle’s owner manual can cause a drop in performance on one end, and possibly engine damage at the other end of the spectrum so know what the manufacturer recommends for your vehicle! A higher compression engine running a lower than specified octane fuel will cause early detonation or knocking that could damage internal engine components that could be costly to replace.
With the exception of rotary engines, the basic premise is that the fuel, gasoline in this case, is part of the power cycle that we will briefly look at below.
The Power Cycle
Fuel is drawn into the combustion chamber when the piston travels downward toward Bottom Dead Center (BDC). As the piston is moving down the injectors atomize the fuel and inject it into the combustion chamber just above the tops of the pistons. When the piston reaches BDC, stroke 1 has finished.
The piston next starts back towards the top of the engine which in turn compresses the fuel mixture that was injected in the first stroke. When the piston travels to the Top Dead Center (TDC) position stroke 3 is ready to begin.
At TDC the spark plugs provide a spark causing the fuel mixture to explode, simultaneously starting the 4th stroke, exhaust.
Fuel is delivered to the carburation/injection system, mixed with air, atomized and injected into the engine’s combustion chamber on the 3rd of the 4 motions after 1) the piston travels down sucking in the fuel-air mixture, and 2) the piston travels back to the top compressing the mixture at TDC when 3) the spark plugs provide detonation of the fuel mixture sending the piston back down to BDC thereby converting the fuel into energy realized and converted to motion.
According to the US Energy Information Administration (EIA) gasoline is a fuel made from crude oil and other petroleum liquids. From one 42 gallon barrel of crude oil refineries are able to extract approximately 19 gallons of gasoline. Federal law requires gasoline to be mixed with blending agents that reduce the amount of oil contained in a gallon sold at the pump as well to comply with the Clean Air Act.
Gasoline is typically sold in three grades at retail stations; regular, midgrade, and premium.
Prior to 1996 gasoline could contain lead, which acted as a lubricant.
Gasoline changes by the season; winter and summer. The change relates to the vapor pressure. During the winter months fuel providers are allowed by the government to increase the vapor pressure in the gasoline to allow the cars to start more easily in the colder months while in summer they providers must reduce the vapor pressures to limit the VOC’s that are emitted during evaporation which occurs more rapidly in warmer temperatures.
Burning one gallon of gasoline with any ethanol generates 19.6 pounds of carbon dioxide whereas a mixture of gasoline and ethanol such as E10 produce what is considered “atmospheric carbon-neutral CO2”.
The ideal fuel air mixture for gasoline is 14.7:1.
- Gasoline represents 60% of the transportation sectors fuel use. This equates to being the favored form of fuel to power vehicles.
- Readily available, and generally sold in 3 octane grades: 87, 91, and 93.
- Generates greenhouse gasses
- Fossil fuel
- Higher octane gasolines used in racing (100-110) can cost more per gallon than E85.
Ethanol has been in use as a fuel source since the 1850’s first for lighting, and later for cars. Henry Ford used a mixture early in his career, and the Model T could run on either ethanol or gasoline. According to the US Department of Energy, Ethanol is listed as a renewable fuel derived from corn or other plant material known as biomass. It is utilized in 97% of the gasoline sold in the US.
The EPA mandates incorporating oxygenating agents such as ethanol to comply with facets of the Clean Air Act.
Ethanol is a clear, colorless liquid. It also commonly known as grain alcohol.
It has a higher octane rating than gasoline, around 105, which makes it a good blending agent
That higher octane rating means that it provides a performance advantage when used in high compression engines
The most common ethanol/gasoline blends are E10, E15, and E85. E10 is the most widely available in the US. The number after the letter refers to the percentage of the total composition that is ethanol, therefore an E10 blend would be made up of 10% ethanol, and 90% gasoline.
The cost to manufacture a gallon of either gasoline or ethanol is roughly equivalent* with the tie breaker going to ethanol due to its “green” credentials of being sustainably raised/grown and lower greenhouse emissions than pure gasoline.
Ethanol works best performance-wise in blends where the octane rating is above 110.
The ideal fuel air mixture for ethanol is 9.79:1.
According to Bell Performance the following are the pros/cons of using ethanol in your vehicle:
- Blends containing ethanol burn cleaner than pure gasoline fuel loads, and ethanol and similar oxygenates are mandated by the EPA to meet Clean Air Act standards
- Ethanol cuts a car’s greenhouse gas emission
- Water accumulation in gas tank – ethanol absorbs water from the air
- lower energy content that the equivalent amount of gasoline
- Deposit build up
- Loss of power
- Rough running
- Lower fuel mileage, between 25%-30% worse than gasoline
- Can corrode internal engine components for older vehicles. Late model vehicles, if ethanol friendly, are usually designed to run on a blend up to E20.
- Contaminants in fuel system
- Fuel phase separation – cannot be restored
- Encourages microbial growth in fuel
- Short shelf life -as short as 90 days
- Older vehicles typically have problems processing Ethanol-Gasoline blends often requiring the same modifications to upgrade leaded fuel engines to run on unleaded fuels.
- Some argue that it is a negative energy source, meaning it takes more energy to produce than it generates. Which is not dissimilar to the process in making rechargeable batteries used in hybrid cars.
What about E85 being a performance fuel?
First there are three fuel grade varieties of E85, class 1, 2, and 3. Class 1 is made of 80-84% ethanol while class 2 is comprised of 75-79% (E75), and class 3 has 70-74% (E70) ethanol content. Edmunds conducted a test running one vehicle in similar conditions with one trip being fueled by gasoline, and the other by ethanol. What they found is that of the 4 performance benchmarks they used (0-60mph, 1/4 mile time, overtaking, etc…) only one tilted in ethanol’s favor, overtaking speeding from 50mph to 70mph. The margin using ethanol was four tenths of a second quicker than the time gasoline posted.
But wait! That’s not the whole story as with many things. We know that ethanol, particularly E85 has a higher jump octane rating than the comparable gasoline choices at the filling station which means you can buy race equivalent fuel for commuter prices. The fact that E85 has a higher “pump” octane rating means engines (properly setup to run E85) that call for premium grade fuel would benefit due to the high compression aspect inherent in its composition. Couple that with the fact that E85 in a vehicle tuned to burn ethanol can produce more horsepower than using a similar quantity of gasoline, and you start to see the competitive advantages over gasoline. An article in the Hot Rod Network mentions another advantage of E85 has a much greater latent heat of vaporization, cooling the intake charge like intercooling or water alcohol injection. So it’s got that going for it.
Applying What We’ve Learned
We know is that virtually all of the gas available at the pump will have ethanol or similar oxygenating agent to comply with federal emission standards. We know ethanol blends have lower energy content than gasoline, and fuel economy may also be reduced as a result.
The good news is for performance fans. E85 has a higher pump octane rating than those of the premium grades of gasoline available at retail outlets, and E85 is sold at a discount when compared to gasoline grades sold at racetracks. The downside is the vehicle needs to be tuned to harness the potential gains of this blend, and cannot easily go back to running lesser blends without additional tuning which in turn makes it less flexible than simply using normal pump gasoline.
Ethanol is here today. Does it makes sense to run E85? That’s up to you. My goal was to provide you with a basic understanding as well as a starting point for you to continue your own research on fuels and additives if this particular rabbit hole is one you want to continue down.
*Critics argue it actually takes more energy to produce the equivalent amount of ethanol.