13 Experiment 7: Energy potential of various liquid fuels

http://matse1.matse.illinois.edu/energy/e.html

project 8

evaluating energy potential of various liquid fuels

objective:  to compare energy delivery of flammable fuels

learning points:

1. understand the relationship of energy content with chemical fuels
2. compare energy content of various liquid fuels
3. calculate energy content based on mass and calories of energy

It is the common properties of liquid fuels that make them attractive for use today, some of these properties include: 1) They are easy to transport; and 2) They can be handled with relative ease. Most of the liquid fuels used today come from petroleum. The most known of these is gasoline and gasoline is the most widely used liquid fuel.

It is not the liquid form of gasoline that actually burns, but its fumes ignite, which causes the remaining liquid to evaporate and then burn. Gasoline is considered to be extremely volatile and easily combusts, therefore making any leakage extremely dangerous.  Gasoline sold in many countries carries a known octane rating. The octane number is an empirical measure of the resistance of gasoline to combusting prematurely, an action that is known as “knocking”. The higher the octane rating, the more resistant the fuel is to auto ignition under conditions of high pressures, and this allows for a higher compression ratio.  Engines with a higher compression ratio can produce more power. Increasing the octane rating has been achieved by adding anti-knock additives to the gasoline such as lead-tetra-ethyl.  However, the lead found in the anti-knocking additives have an environmental impact.  Therefore, the octane rating is increased currently by refining out the impurities that cause the knocking event.

Ethanol is the first organic chemical produced by humans, but any alcohol can be burned as a fuel.  Ethanol is very commonly produced through fermentation of sugars.  Ethanol and methanol are the most common, being sufficiently inexpensive to be useful as fuels.  Methanol has lost much of its attraction as a liquid fuel in internal combustion engine due to its formation of the toxic and smog component known as formaldehyde.  A blend of fuel referred to as E85 is a fuel comprised of 85% ethanol blended with 15% gasoline. This fuel type has a higher octane than most premium gasolines.  Butanol is another alcohol which can be used in most gasoline internal combustion engines without the engine modification requirement. Methanol is the simpler molecule, and ethanol can be made from methanol. Methanol can be produced from many types of biomass, including animal waste, or from carbon dioxide and water or steam by first converting the biomass to a synthesis gas utilizing a gasifier.

Propanol and butanol are considerably less toxic, but less volatile than methanol. Butanol has a high flash point of 35 °C, which is a benefit for fire safety, but will have difficulty when applied for starting engines in cold weather. However, the issue of flash point is not directly applicable to internal combustion engines because the compression of the air in the cylinder means that the temperature is several hundred degrees Celsius before ignition takes place.

Liquid fuels are combustible and energy-generating molecules that can be harnessed to create mechanical energy (producing kinetic energy).  Generally, it is the fumes of liquid fuels that are flammable instead of the fluid by-itself.  Energy density is the amount of energy stored in a given system per unit volume or mass, and the  latter definition is accurately termed as specific energy.

Energy content of various materials (U.S. Energy Information Administration, April 2010 Conference: Meeting the Energy and Climate Challenge):

SAFETY

This project involves the dangers related to working with glassware and heating with a burner.  Avoid touching anything heated until it has cooled to a comfortable temperature.  Dispose of matches into the trash after dosing with water.

As always: return everything to its place, wipe your bench, lock your drawer, and return the key to the key cabinet.

PROCEDURE

1. Obtain a burner (containing the liquid fuel to be tested) and set up the apparatus to be used to test the energy per unit mass of the fuel.

2. Make sure you have a liquid fuel inside the burner and record the fuel type.  Now obtain an accurate mass of the burner with fuel by use of balance (record all numbers possible from the balance you use).
3. Obtain one of the aluminum cans you will place distilled water into. Weigh the empty can accurately on a balance and record.  Now obtain your large graduated cylinder and accurately measure out a total of 250 mL of distilled water into the can.  Re-weigh the can holding the water and record an accurate weight (you should use the triple-bean balances for this step).  The difference of these masses is the mass of the water.
4. Find a thick glass stir rod and insert it through the two holes in the top of the can and suspend it from the iron ring and above the liquid burner as depicted in step 1.
5. Place your thermometer into the water (but don’t touch the bottom of the can) and record the temperature of the water to the tenths reading (example: 23.5 oC).
6. Now you may light the liquid burner with a match (be sure the flame has contact with the bottom of the can). Note the appearance of the flame: color, size, and generation of smoke.  Follow the temperature change of the water with the thermometer, but you must hold the thermometer in the water without touching the bottom of the can.
7. When the water has warmed at least 40 degrees higher then blow out the flame and obtain an accurate final temperature of the water to the tenths. Again, weigh the burner by balance to get an accurate value (the difference from mass of step 2 is the mass of fuel consumed). Difference of the temperature before the heating and the final temperature after heating is the temperature change of the water.
8. Repeat these steps with another liquid fuel per directions of your instructor.
9. Collect all your data for your written report and calculations.

CALCULATIONS

Determination of calories of energy absorbed by water:

energy in calories = mass of water in grams  x temperature change OC x 1.00 cal/goC

Determination of calories produced per mass of liquid fuel:

calories/gram fuel   =  calories /[mass of burner before heating – mass of burner after heating]

Do these calculations for each liquid fuel you tested.

ANSWER THE FOLLOWING QUESTIONS:

1. Which liquid fuel produced the most calories of energy? Record.
2. Which liquid fuel produced the least amount of calories? Record.
3. Which fuel produced the most calories per gram of fuel? Record.
4. Which fuel produced the least amount of calories per gram of fuel? Record.
5. Which of your fuels were alcohols?
6. Why did you keep the thermometer off the bottom of the can during the heating?
7. Which fuel produced the cleanest flame (i.e. less smoke and less soot)?
8. From your data, decide which fuel burned the most efficient and explain why.