Combustive Properties of Biodiesel: Methanol versus Ethanol

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1 Combustive Properties of Biodiesel: Methanol versus Ethanol Briana Young Alternative Energy/Green Science Team Abstract Have you ever wondered what gives biodiesel its kick? Every fuel has some form of combustion. Without it, energy will not be created. In biodiesel, the thermal energy is created by adding a combustion agent, such as methanol or ethanol. As the bioenergy industry matures, there will be a greater need to identify chemical recipes that will increase the energy output of the bio based fuels. In this report I examine the difference in thermal energy generated by methanol-based biodiesel and ethanol-based biodiesel. Introduction Biodiesel is a liquid fuel that is made from organic material such as vegetable oil. It is used to power a diesel engine. The benefits of biodiesel are numerous. For example, biodiesel contains virtually no sulfur or aromatics, and use of biodiesel in a conventional diesel engine results in substantial reduction of unburned hydrocarbons, carbon monoxide and particulate matter. A U.S. Department of Energy study showed that the production and use of biodiesel, compared to petroleum diesel, resulted in a 78.5% reduction in carbon dioxide emissions. Moreover, biodiesel has a positive energy balance. For every unit of energy needed to produce a gallon of biodiesel, at least 4.5 units of energy are gained (4). Page 1 of 5

2 Combustion is the burning of fuel that produces heat and energy. The substance that gives biodiesel its combustive property is alcohol. Two common combustive agents used in biodiesel are methanol and ethanol. Methanol has a chemical formula of CH 3 OH. It is produced naturally and when burned forms carbon dioxide and water. Ethanol (ethyl alcohol) is the same type of alcohol found in alcoholic beverages. It is most often used as a biofuel additive. Its chemical formula is C 2 H 6 O. World ethanol production for transport fuel tripled between 2000 and 2007 from 17 billion to more than 52 billion liters. From 2007 to 2008, the share of ethanol in global gasoline type fuel use increased from 3.7% to 5.4%. Combustion occurs when fuels, such as natural gas, coal or gasoline, react with oxygen in the air to produce heat. The heat from burning fuels is used for industrial processes, environmental heating or to expand gases in a cylinder and push a piston. Simple combustion involves the reaction of oxygen in the air with carbon and hydrogen in the fuel, to form carbon dioxide, water and produce heat. Combustion analysis is part of a process intended to improve fuel economy, reduce undesirable exhaust emissions and improve the safety of fuel burning equipment. Combustion analysis begins with the measurement of flue (exhaust) gas concentrations and gas temperature, and may include the measurement of draft pressure and soot level. A low-tech way to examine combustion properties of biodiesel is to use the fuel to run a Stirling engine. The Stirling engine is classified as an external combustion system. It was created by Robert Stirling in A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to Page 2 of 5

3 mechanical work. This is different than the internal combustion engine where heat input is by combustion of a fuel within the body of the working fluid. A Stirling engine system has at least one heat source, one heat sink and up to five heat exchangers. In this experiment I examine the difference in thermal energy generated by ethanol-based biodiesel versus methanol-based biodisesel. Hypothesis Based on my knowledge of bioenergy and combustion analysis, I believe that methanol will produce more thermal energy than ethanol, thus causing Stirling engine #1 to run longer and faster. Materials ECOTEK Biodiesel-In-A-Box Science Kit (contains supplies needed to make methyl and ethyl based biodiesel) Methods Make 50ml of ethyl ester biodiesel and 50ml of methyl ester biodiesel Pour 20ml ethyl ester biodiesel into beaker #1, then pour 20ml methyl ester biodiesel into beaker #2 Label each Stirling cycle engine (engine#1 and engine#2) Using a pipette, put 4ml of ethyl ester biodiesel into fuel tank of engine#1 Using a pipette, put 4ml of methyl ester biodiesel into fuel tank of engine#2 Light wicks on each engine using the ignitor Start Stirling cycle engines. Observe speed of each engine. Record maximum run time (minutes) for each Stirling engine. Page 3 of 5

4 Data/Results The Stirling engine that used the methanol based biodiesel (Stirling engine #1) ran longer and faster than the Stirling engine#2 that used the ethanol based biodiesel. The total run time for engine#1 was over 10 minutes, while the total run time for engine #2 was 4 minutes. Engine #2 constantly stopped and had to be restarted, while engine #1 ran at an average speed of 2 mph with no interruption. Below is a chart that shows the difference in run time. Figure 1 Combustion Property Chart Total Run Time (minutes) engine #1-Methanol Biodiesel Type of Biodiesel engine #2-Ethanol Biodiesel Discussion Ethanol based biodiesel does not generate as much thermal energy as methanol based biodiesel. The difference in energy output has to do with the molecular structure and concentration levels of the alcohols. My experiment looked at combustion properties at a basic level. For more advanced analysis, additional equipment is needed. Page 4 of 5

5 References 1. Ross.A., 2007.Sterling Cycle Engines. Solar Engines.Wellsville, New York 2. Purcella. G Do It Yourself Guide to Biodiesel. Ulysses Press. Berkley, California 3. Make Your Own Ethyl Ester Biodesel, 4. National Biodiesel Board Page 5 of 5