Characteristics of Fuel Ethanol

Ethanol is more reactive than hydrocarbon fuels, such as gasoline. Since it is an alco­hol, its molecular structure shows a polar fraction due to the hydroxyl radical and a nonpolar fraction in its carbon chain. That explains why ethanol can be dissolved in both gasoline (nonpolar) and in water (polar). Due to its short carbon chain, the prop­erties of ethanol polar fraction overcome the nonpolar properties. The formation of hydrogen bridges in ethanol molecule results in higher boiling temperature in com­parison to that of gasoline (Table 5.1). Ethanol is less toxic than methanol—another alcohol used as fuel. The simple structure of ethanol molecule makes it suitable for spark ignition internal combustion engines operation. The high octane number of eth­anol allows for higher compression ratios in comparison to gasoline fueled engines (Table 5.1) (Costa and Sodre 2010). One of the main advantages of ethanol offers when compared to gasoline is its antiknock performance, allowing its use in higher compression ratio engines. At high temperature, ethanol produces superior thermal efficiency due to its higher heat of vaporization. As ethanol can burn richer fuel/ air mixtures, it allows for higher engine power output in comparison to gasoline. However, due to its lower heating value, the use of ethanol instead of gasoline results in higher fuel consumption. Engine cold start is also a problem for ethanol, due to its low vapor pressure (Owen and Coley 1995). Rasskazchikova et al. (2004) discussed the use of ethanol as high-octane additive to automotive gasoline. The authors con­cluded that, despite the high cost, ethanol is the most promising octane-raising addi­tive available. That is justified by the low toxicity, reduced environmental pressure when burning ethanol-containing fuel, and production from renewable raw material. Silva et al. (2005) evaluated the effect of ethanol and other additives on the antiknock properties and Reid vapor pressure (RVP) of gasoline. Addition of ethanol up to 25 % by volume in gasoline led to increased RVP and octane ratings.

Ethanol is used as an automotive fuel and can be used alone in specially designed engines, or blended with gasoline and used without any engine modifications.

Some excerpts taken from Bajpai (2007). PIRA Technology Report on Bioethanol with kind permission from Smithers PIRA

Table 5.1 Properties of hydrous ethanol blend and gasoline-ethanol blend


Hydrous ethanol

78 % Gasoline 22 % ethanol

Chemical structure

C2 H6.16 O1.08

C6.39 H13.60 O0.61

Carbon mass (%)



Hydrogen mass (%)



Oxygen mass (%)



Sulfur mass (%)



Self-ignition temperature (°C)



Temperature of vaporization (°C)



Heat of vaporization (kcal/kg)



Research octane number (RON)


Motor octane number (MON)



Vapor pressure (bar)



Laminar flame speed (m/s)



Density (kg/l) 0.74 0.81



Lower heating value (kcal/kg)



Stoichiometric air/fuel ratio



Based on Costa and Sodre (2010)

Motorboats, motorcycles, lawn mowers, chain saws, etc. can all utilize the cleaner gasoline/ethanol fuel. Ethanol is a high-octane fuel with high oxygen content. So, it allows the engine to more completely combust the fuel, resulting in fewer emissions. Ethanol has many advantages as an automotive fuel. Ethanol blends also reduces carbon monoxide emissions. When used in a correctly formulated fuel, ethanol can also reduce vehicle emissions which contribute to the formation of smog. It can also withstand cooler temperatures. Because of its low freezing point, it can be used as the fluid in thermometers for temperatures below -40 °C, and for other low tem­perature purposes, such as for antifreeze in automobile radiators.

The Energy Policy Act of 2005 established RFS, which mandates the use of ethanol and other renewable fuels in gasoline. Most of the fuel ethanol consumed in USA is E10. A blend of 85 % ethanol and 15 % unleaded gasoline (E85) is also being used. Currently, in USA, approximately 50 million gallons of ethanol are made into E85. E85 is available at 1,000 locations in the USA (including both public and private). The National Ethanol Vehicle Coalition estimates approxi­mately 6 million FFVs on America’s roads today as compared to approximately 230 million gasoline — and diesel-fueled vehicles. Most E85-capable vehicles are “flexible fuel vehicles” or FFVs (RFA 1999, 2001, 2006a, b, c, 2007a, b). This mixture has an octane rating of about 105. This is significantly lower from pure ethanol but still much higher than normal gasoline. The addition of a small amount of gasoline helps a conventional engine start when using this fuel under cold con­ditions. E85 does not always contain exactly 85 % ethanol. In winter, particu­larly in colder climates, additional gasoline is added to facilitate cold start. E85 has been similar in cost to gasoline, but with the large oil price rises of 2005, it is being sold for as much as $0.70 less per gallon than gasoline which makes it highly attractive to the small but growing number of motorists with cars capa­ble of burning it. Gasoline contains more energy, gallon for gallon than ethanol.

One gallon of gasoline contains approximately 114,132 btu and ethanol contains 76,000 btu. Therefore, E85 contains approximately 27 % less btu then 100 % gasoline. However, when factoring in the fuel efficiency of gasoline and ethanol (which is more fuel efficient), it was found that E85 mileage reduction is only about 10-15 % instead of the 27 % based strictly on energy content.

E85 is environmentally friendly (Niven 2005). It has the highest oxygen con­tent of any fuel available today, making it burn cleaner than ordinary gasoline. The use of E85 reduces pollutants such as ozone and carbon monoxide and air toxins like benzene. E85 cars perform well with significant reductions in emis­sions when compared to vehicles using ordinary unleaded gasoline. Reductions in two particularly troublesome pollutants, carbon monoxide and hydrocarbons, are reduced significantly. Ethanol is one of only two liquid fuels available that com­bats global warming because of its raw material source. As corn grows, it converts carbon dioxide into oxygen. Auto makers are offering more flexible fuel vehicles. Purchase price of these vehicles has been comparable to the base price of gasoline models. Since E85 is a cleaner burning fuel, it is expected that the life of a flexible fuel vehicle will be somewhat longer than that of a comparable gasoline vehicle.

The key component in a variable fuel vehicle is a sensor that determines the percentage of ethanol in the fuel. With the help of a computer, the vehicle auto­matically adjusts for best performance and emissions. Chrysler began offering E85 minivans in the 1998 model year, and Ford offered the Taurus and added Windstar and Ranger to the E85 flexible fuel vehicles in the 1999 model year. Ford, GMC, Chevrolet, and Daimler-Chrysler are now offering E85 variable fuel vehicles.

The mileage decrease which occurs when operating a vehicle on E85 has been debated. Ford reports an average of 16 MPG for E85 Taurus (based on city and highway driving) and 22 MPG for gasoline (Ford Motor Company 1998). Daimler-Chrysler reports a 27 % range reduction when using E85 in their mini­vans (Chrysler Corporation 1997).

The color of ethanol fuel blends depends on the color of the gasoline in the blend. Blends may also have a gasoline-like odor. A gallon of E85 contains 27 % less energy. The energy content of a gallon of ethanol is equal to 76,000 BTU as compared to about 115,000 BTU for a gallon of conventional gasoline. It fol­lows that to replace the energy equivalent of a gallon of gasoline, we would need approximately 1.5 gallons of ethanol.

The average vehicle on the road today emits more than 600 pounds of pollution into the air each year in US. These harmful emissions include carbon monoxide, vol­atile organic compounds, particulate matter, oxides of nitrogen, and carbon dioxide. These emissions have significant health implications because they contribute to the amount of smog and carbon monoxide in air. Carbon monoxide emissions have also been implicated in global warming. One of the benefits of using E85 vehicles is a reduction in the amount of pollutants emitted into the air we breathe. The emissions control systems found on ethanol-powered vehicles manufactured today have been engineered to meet or exceed all federal and state emissions control regulations. Two types of emissions are released by E85 vehicles—exhaust and evaporative. Although compliance with federal and state regulations has already resulted in a decrease in exhaust emissions from gasoline-powered vehicles, ethanol-fueled vehicles can fur­ther reduce pollution from emissions by a modest amount. Most ethanol-fueled vehi­cles produce lower carbon monoxide and carbon dioxide emissions and the same or lower levels of hydrocarbon and non-methane hydrocarbon emissions compared with gasoline-fueled vehicles. Nitrogen oxide emissions are about the same for etha­nol and gasoline vehicles. Emissions resulting from fuel evaporation are a potential problem for any vehicle, regardless of the fuel. E85 has fewer highly volatile compo­nents than gasoline and so has fewer emissions resulting from evaporation.

Brazil has used ethanol blends since 1939. High oil prices in the 1970s prompted a government mandate in Brazil to produce vehicles fueled by pure eth­anol in order to reduce dependence on foreign oil and provide value-added mar­kets for its sugar cane producers. Today, there are several million ethanol-powered vehicles in Brazil that consume more than 4 billion gallons of ethanol annually.

Requirements in the Clean Air Act to make cleaner burning reformulated gaso­line with lower volatility and fewer toxic components have increased interest in ethanol-based ethers such as ethyl tertiary butyl ether. It is a chemical compound produced by reacting ethanol and isobutylene. ETBE has superior physical and combustion characteristics to other ethers. They include low volatility, high octane value, lower carbon monoxide and hydrocarbon emissions, and superior driveabil­ity. Ethanol and ETBE are among the oxygenates used in reformulated gasoline that is required in certain ozone non-attainment areas in the US.

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