BIODIESEL. Lesson 4a Test biodiesel in an oil lamp. Developed by Engineering and Technology Curriculum Team 2008

Transcription

1 BIODIESEL Lesson 4a Test biodiesel in an oil lamp

2 In a laboratory setting, test biodiesel in an oil lamp by estimating calories and Btu. define density, energy density, calories and Btu calculate density, energy density, calories and Btu convert values between the units of calories and Btu and between volumetric and mass energy densities

3 Fire Safety Always follow directions. Know where to locate and how to use the closest fire extinguisher. Do not use water to extinguish a fire involving biodiesel. Biodiesel is lighter than water, will float on the water, and spread the fire. Remember STOP, DROP, and ROLL! Know evacuation plan in case of fire.

4 The Big Picture We want to find out how much energy biodiesel has compared to a standard value of diesel fuel. We will do this by burning the biodiesel to heat water. From the energy that is transferred into the water, we will be able to estimate how much energy is in the fuel.

5 Steps Step 1 Find the density of the fuel. Step 2 Find the energy transferred from the burning fuel to the water. Step 3 Find the mass energy density. Step 4 Convert to volumetric energy density. Step 5 Convert from metric values to standard values. Step 6 Estimate the energy in biodiesel fuel Step 7 Estimate the energy ratio of biodiesel fuel to diesel fuel.

6 Density Density is a value of unit mass per unit volume. The Greek letter ρ (Rho) is often used to symbolize density. We will use the density of the liquid fuel to convert from a mass to a volumetric energy density. To find the density of a liquid, measure out a specific volume of the liquid and weigh it. Be sure that you do NOT include the weight of the container. ρ = mass volume

7 Step 1 - Find the density of biodiesel If 21.0mL of biodiesel weigh 18.07g, what is its density? = ρ 18.07g 21.0mL = 0.860g / ml

8 The calorie and the Calorie 1 calorie (small c, abbreviated cal) is the energy it takes to raise 1 g of H 2 O by 1ºC. 1 Kilocalorie or Calorie (capital C, abbreviated kcal) is the energy it takes to raise 1 kg of H 2 O by 1ºC. It is equivalent to 1,000 calories (small c). This is also the unit of food Calories.

9 Step 2 Find the energy transferred from the burning fuel to the water Calculating the calories added to water (E H20 ) is a two step process. 1 Calculate the temperature change ( T) of the water by subtracting the initial temperature (T i ) from the final temperature (T f ). 2 Multiply the mass of the water (Mass H2O ) by the temperature change. Use the equation: T E = T f T i H 2O = MassH 2 O x T

10 Calculating energy example If I have 247.4g of H 2 O and raise the temperature from 26.2ºC to 43.5ºC, how many calories were added to the H 2 O? T = 43.5ºC-26.2ºC = 17.3ºC 247.4g x 17.3ºC = 4.28kgºC or 4.28kcal Or E H 2 O = (247.4g) x( ) C = 4. 28kcal

11 Energy density Energy density is different than density. Mass energy density is the amount of energy per unit mass. ρ mass = energy mass Volumetric energy density is the amount of energy per unit volume ρ vol = energy volume

12 Step 3 Find the mass energy density If I burned 1.13g of biodiesel while adding 4.28 kilocalories to the H 2 O, how many calories were transferred into the water per gram of biodiesel? ρ 4.28kcal = = mass 1.13g kcal g

13 Step 4 Convert to volumetric energy density Because of the nature of the burner, in our experiment we measured the mass of the fuel burned. However, since liquid fuels are purchased by volume, most liquid fuels are measured in volumetric energy density. Thus, we will convert from mass to volumetric energy density. This is done by using the following equation. ρ = ρ xρ vol mass

14 Converting to volumetric energy density From step 1, biodiesel has 0.860g/mL and from step 3, 3.79kcal/g. How many calories are in 1 milliliter of biodiesel? ρ kcal g = 3.79 *0.860 = g ml vol kcal ml

15 Energy Density Our energy density is then 3.79kcal/g or 3.26kcal/mL, depending on whether you desire a mass energy density or a volumetric energy density.

16 A Btu Since we live in the U.S.A., we use Standard units. A Btu is a British thermal unit Similar to the calorie but is defined as the energy needed to raise 1 pound (lb) of water by 1ºF. We can use a direct conversion: 1 Btu = 253 calories

17 Step 5 Convert from metric values to standard values To convert our metric volumetric energy density into a volumetric energy density using standard units, we need to make two conversions: 1 convert kcal to Btu (253cal = 1Btu) 2 convert ml to gal (3790 ml = 1 gal) Using the following formula, we can make both the conversions in the same equation. kcal ρ Btu vol ρ ml vol = x3790 gal kcal Btu ml gal

18 Simplify the conversion By combining the two constants in the previous equation, we can use the simplified equation below. Btu ρ = gal vol ρ vol kcal ml x14,980

19 Energy density in Btu/gal From step 4, 3.26kcal/mL were transferred to the water. How many Btu/gal were transferred to the water? Btu kcal ρvol = 3.26 x14,980 = 48, 800 gal ml Btu gal

20 Starting with English units The energy density can be calculated in Btu directly. Simply begin with English units and follow the same calculations. For mass energy density ρ mass = ( mass ) x( T ) 2 mass H O biodiesel _ burned To convert to volumetric energy density ρ vol = ( ρ ) x( ρ) mass

21 Why an estimate? Loss to Environment The fuel actually contains more energy than what is transferred to the water. air is also heated flask is heated fuel may not completely burn Due to the loss to the environment, the energy transferred to the water is less than the total energy contained in the fuel. It is impossible to stop loss to the environment and impractical in this lesson to calculate the loss. Smoke indicates Incomplete combustion Glass is heated Air is heated

22 Why an estimate? Energy transferred Another factor that affects our measurement is the energy transferred from the flame to the water. Several variables affect this value. Flame size Distance from flame to flask Air flow Surrounding temperature In order to be consistent, as many of these factors should be kept constant as possible.

23 Flame adjustment and soot The larger the flame, the less complete the burn. The less complete the burn, the more soot the flame produces (after 15 min). Curriculum Team

24 Properly adjust the flame for consistency The flame should be adjusted to be about half blue flame and half (or a little less) yellow flame. Place it under the flask so that it is close enough to make the yellow flame disappear without extinguishing the flame entirely, which will happen if it is placed too close. The flame should be touching the flask. The distance between the flask and the burner should be kept constant from one test to another. Curriculum Team

25 Properly adjust the flame for consistency This is not the only way for the flame to be adjusted. The importance of adjusting the flame is to get consistency from measurements. It is OK to adjust the flame differently; just make sure that the flame is adjusted the same for each test.

26 Energy density of petrodiesel We can estimate the total value of Btu in biodiesel by making an estimate of how much energy we lose to the environment. Petrodiesel typically contains 128,700 Btu per US gallon. If petrodiesel is burned to heat water and 54,700 Btu per gallon is transferred to the water, then 43% (54,700/128,700) of the energy is transferred to the water and 57% of the energy is lost to the atmosphere. We will call the 57% our %loss.

27 Assume similar loss If we assume that the same percentage of energy will be lost to the environment when we burn the biodiesel, we can make an estimate of how much energy is in biodiesel. We start with two equations: E total = E % loss = H 2O E E loss total + E loss

28 Calculate estimate Using algebra, we come up with the equation E total = E H 2O 1 % loss The total energy is equal to the energy transferred to the H 2 O (from step 5) divided by the percent transferred or one minus the percent lost to the environment (i.e. 38% = 0.38).

29 Step 6 Estimate the energy in biodiesel fuel Using the previous equation, plug in the numbers to find an estimate of the energy density of biodiesel. Btu 48,800 gal E = = 114, 000 total Btu gal

30 Step 7 Estimate the energy ratio of biodiesel fuel to diesel fuel To find the energy ratio of our fuel to diesel fuel we divide the energy estimate by the value for diesel fuel. 114, ,700 x100% 89% This appears to be a good estimate since the average energy value of biodiesel is about 91% the average energy value of diesel fuel per volume. =

31 Better methods This method is not very consistent and yields poor values when compared to other methods. However, this method of testing is inexpensive and easy to accomplish. To get accurate values, we would use equipment such as a pycnometer (to measure density) and a bomb calorimeter (to measure energy).

32 Conclusion Now it is time for a demonstration! Do Class Demonstration Worksheet 4a Diesel Fuel. Burn biodiesel, not a tree!