Name How Does Diesel Compare to Other Sources of Energy? Diesel and Gasoline are common fuel sources in Alaska. How do they compare? Both diesel and gasoline are made from crude oil. Crude oil is a liquid fossil fuel that formed from dead organisms (usually zooplankton and algae) that were buried underground under heat and pressure for millions of years. Crude oil is a mixture of different lengths of hydrocarbons (long molecular chains of carbon and hydrogen atoms) that can be separated out depending on the length of the hydrocarbons to produce fuels including diesel and gasoline. Diesel is made up of hydrocarbon chains with 10-20 carbon atoms while gasoline has hydrocarbon chains that are slightly shorter at 7-11 carbon atoms. Diesel is used for running generators to produce electricity and to fuel certain types of vehicles (some cars and large trucks, airplanes, ships, and heavy equipment); gasoline is used to fuel vehicles (most cars and trucks, snow machines, 4- wheelers), and it is mixed with oil for running two- stroke engines in chain saws and outboard motors. 1. If the energy in diesel and gasoline is stored in the chemical bonds between the atoms, which fuel do you think would have more energy? Explain your answer. British Thermal Unit One unit used to measure energy is the British Thermal Unit (BTU). A BTU is defined as the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit and it is equivalent to 1055 joules. A BTU is approximately the amount of energy that one match stick gives off. 1
2. On average, 1 gallon of diesel contains 139,200 BTUs and, on average, 1 gallon of gasoline contains 125,000 BTUs. Volumetrically, which is more energy dense diesel or gasoline? Explain your answer. Converting the energy in diesel to electricity Diesel fuel can run a generator that converts the energy into another usable form it can either convert the energy into mechanical energy to do physical work or it can convert the energy into electricity to power appliances. The First Law of Thermodynamics addresses the conservation of energy. It states that the amount of energy in a system stays constant energy can neither be created nor destroyed. However, not all of the energy output of a generator is usable energy. Much of the energy output is heat and trace amounts of energy are converted into noise and light from the combustion flame. About a third of the energy in the diesel is converted into electricity. Some newer, more efficient generators can convert ~ 40% of the energy in the diesel into electricity. 2
3. If we put a gallon of diesel with 139,200 BTUs into a generator, how many BTUs of electricity will we produce? Watt, Kilowatt, and Kilowatt- hour What will a gallon of diesel power? Energy is defined as the ability to do work, and power is the rate at which energy is used, so measurements of power include a length of time. A watt is a measurement of power that equals one joule per second and wattage refers to the amount of power an appliance uses; 1000 watts equal 1 kilowatt. Watt and kilowatt both measure power. A kilowatt- hour (kwh) sounds like it should be a measurement of power, but it is actually a measurement of energy. A kilowatt- hour is the amount of energy used if you use 1000 watts for one hour (or use 2000 watts for half an hour). kwh = watts kilowatt 1000 watts hours Since 1 kilowatt hour (kwh) = 3,412 BTUs, BTUs can be converted into kwh with the following equation: kwh = BTUs 1 kwh 3414 BTUs 4. Using your answer from Question 2, calculate how many kwh are produced from a generator with one gallon of diesel: 5. Using the amount of kwh you calculated in Question 3 and the following equations (rearranged from the first kwh equation), calculate how long a generator with one gallon of diesel will power the items with in the following table: hours 1 gallon of diesel = 1 wattage 1000 watts 1 kilowatt kilowatt hours kwh 1 gallon of diesel 3
Appliance Wattage (w) 1 Hours powered Incandescent light bulb 100 CFL light bulb 23 LED light bulb 12 Laptop computer 45 Large plasma TV 475 PS3 or Xbox 190 Microwave oven 1440 Coffee maker 900 Clock radio 4 How far can one gallon of gas power a vehicle? 6. How much does a gallon of gasoline cost in your community? $ A vehicle s miles per gallon (mpg) rating measures how far one gallon of gas will power that vehicle. This rating depends on a number of factors including the engine, the weight of the vehicle, acceleration, and friction. 1 Available from http://michaelbluejay.com/electricity/howmuch.html 4
7. Considering the following line of vehicles from the Ford Company and the vehicles mpg, one gallon of gasoline does an impressive amount of work. It can move quite a bit of weight a long distance. For the price of a gallon of gasoline in your community, would you be willing to do the amount of work a gallon of gasoline does and push these vehicles the following distance? Vehicle Weight (lbs) Miles per gallon (mpg) Ford E- 150 15 passenger vehicle 5250 13 Would you be willing to push this vehicle this far for the price of one gallon of gas? Ford F- 150 truck 5500 17 Ford Explorer SUV 4050 18 Ford Fiesta car 1100 28 Ford Fusion hybrid engine car 3250 41 5
8. What would the price of a gallon of gasoline need to be for you to be willing to do the amount of work a gallon of gasoline and push a car 20 miles? Would you do it for $50? $100? $1,000? $1,000,000? How does the amount of energy in diesel and gasoline compare to other sources of fuel? In order to compare one type of fuel to another, we need to standardize our units. A therm is defined as 100,000 BTUs. The term therm is usually used when referring to quantities of natural gas a therm of natural gas is 100 cubic feet of natural gas. Natural gas is a fossil fuel that is in a gas state because of its low number of carbon- carbon bonds; it is comprised mostly of methane, which is a carbon atom bonded to four hydrogen atoms. Compressed natural gas is natural gas stored under pressure to make it more compact (similar to propane in a propane tank). While a therm isn t commonly applied to other types of fuel, it is a unit that we can use to standardize other fuels for a comparison. Use the following equation to calculate how many gallons of fuels are in a therm: gallons of fuels for a therm = gallon of fuel Btus 100,000 BTUs therm 9. How many gallons of diesel are needed for a therm? gallons of diesel/therm How many gallons of gasoline are needed for a therm? gallons of gasoline/therm To calculate weight of a therm of a fuel: 6
gallons of fuels for a therm = gallons of fuel therm pounds gallon 10. If a gallon of diesel weighs 7 pounds, one therm of diesel weighs pounds. If a gallon of gasoline weighs 6 pounds, one therm of gasoline weighs pounds. Coal the solid fossil fuel Coal is a solid fossil fuel. Like crude oil, it is formed from dead organisms that were buried underground under heat and pressure for millions of years. Instead of originating from zooplankton and algae (as crude oil did), coal originated from ancient plants. Coal is classified depending on its properties, including how much energy it contains. Four main types of coal Properties 2 BTUs per pound 3 lignite A very young coal (less than 20 million 7,750 4 years old) with a low energy content and a high moisture content. It is mined in Texas, North Dakota, Montana, and the Gulf States. sub- bituminous A young coal (10 million to 50 million 8,800 years old) with a medium to low energy content and a medium to high moisture content. In Alaska, it is mined at Usibelli Coal Mine in Healy. It is also mined in Wyoming and Montana. bituminous An old coal (50 million to 300 million years) with a high heat content and low moisture content. In Alaska, it is mined at Wishbone Hill Mine in Sutton. It is also mined in Appalachia, the Midwest, and the West. 11,500 2 http://www.usibelli.com/coal_formation.php 3 Available from http://www.generatorjoe.net/html/energy.html unless otherwise noted 4 Available from http://www.alaskawoodheating.com/energy_content.php 7
anthracite The oldest type of coal (over 300 million years) that is hard and shiny with a high heat content and low moisture content; it is primarily mined in Pennsylvania. 12,700 11. How many pounds of each type of coal are needed to have a therm? pounds of fuels for a therm = 1 pound BTUs 100,000 BTUs 1 therm Lignite: one therm of lignite coal weighs pounds Sub- bituminous: one therm of sub- bituminous coal weighs pounds Bituminous: one therm of bituminous coal weighs pounds Anthracite: one therm of anthracite coal weighs pounds Wood Energy: Wood is a much younger source of energy than fossil fuels. Trees capture the sun s energy through photosynthesis and store that energy as chemical bonds in their wood. Alaska s trees have different energy content depending on their species. Firewood is measured in cords. One cord is 128 ft 3 of wood (8 feet long x 4 feet wide x 4 feet tall). Data is available on how many BTUs are in a pound of different types of Alaska firewood 5. In order to compare it to diesel, gasoline, and coal, we must convert it to pounds per therm. 5 Available from http://www.alaskawoodheating.com/energy_content.php 8
12. Use the following equations to calculate how many pounds are needed for a therm of these 8 different types of Alaskan firewood: BTUs of firewood per pound = BTUs cord cord pounds pounds of firewood per therm = pound BTUs 100,000 BTUs therm Alaskan tree BTUs per cord Pounds per cord Calculate: BTUs per pound Hardwoods Calculate: pounds per therm Birch 23,600,000 3,485 Aspen 16,600,000 2,414 Poplar 15,000,000 2,168 Cottonwood 14,500,000 2,108 Softwoods White Spruce 18,100,000 2,550 Sitka Spruce 18,100,000 2,550 Black Spruce 15,900,000 2,482 Hemlock 22,000,000 2,856 9
13. Rank the different types of fuels (diesel, gasoline, the 4 types of coal, and the different Alaska firewoods) based on the number of pounds needed for a therm (100,000 BTUs) 14. What type of fuel do you need the least pounds of for a therm? What type of fuel do you need the most pounds of for a therm? What is the most concentrated fuel and what is the least concentrated fuel? 15. How does the concentration of energy in liquid fossil fuels (diesel and gasoline) compare to solid fossil fuels (coal) and wood energy (the different types of firewood)? 16. What are advantages of fossil fuels? What are disadvantages? What are advantages of wood energy? What are disadvantages? 10