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Combustion Workshop


This is a two hour workshop that was used for a high school introduction to engineering class that came to the combustion lab. The work shop was done in groups of 4 each with their own fume hood and graduate student assistant.  The experiments done in this workshop requires supervision.

 

Laboratory Data Sheet

 

Name:______________________

 

Date:_______________________

Note:  Whenever igniting any portion of these experiment always wear gloves and safety glasses.  Make sure any long hair is tied back, no hats or loose clothing is to be worn.  None of the combustibles are to be removed from the lab, no experiments are to be done except those explicitly stated in this document.  Follow the instructions of your graduate student teaching assistant.

 

Outline:

A.  Ignition

a.     Spark Ignition

b.    Electrical Ignition

c.     Flame Ignition

B.   Combustion

a.     Liquid Flame Spread Rate

b.    Solid Fuel Flame Spread Rate

c.     Re-ignition of Candle

d.    Flame Shape

e.     Flame Temperature

C.   Extinction

a.     Suffocation 1 – by mechanical means

b.    Suffocation 2 – CO2

c.     Flow Speed for Candle Flame Extinguishment

 

 

 

 

 

 

 

 

A. Ignition:

 

Spark Ignition:

For this experiment you will need a small candle, a pie pan, the flint & steel, and 10 ml of alcohol.  Practice using the flint & steel to create sparks (notice that the steal striker has an “up” marking to specify which way to hold it).  Practice until you can make sparks which fall away from the flint atleast 4 inches  To hold the steel in place and pull the flint back toward you.  Using the flint & steel attempt to ignite a candlewick using the flint & steel.  Using a pipette place 2 ml of Alcohol in the center of your AL pie pan.  Using the flint & steel attempt to ignite the alcohol, keep the flint atleast 3 inches above the watch glass containing the alcohol. Make sure not to strike the AL pan with any portion of the flint or your hand.

 

Place a small candle in the center of the pan, attempt to ignite the candle with the flint and steel.  

 

Which fuel ignites?  ______________________

 

Using what you know about ignition energies, discuss why does the other fuel not ignite?

 

______________________________________________________________

 

___________________________________________________________________

 

 

Electrical Ignition:

For this experiment you will need a pie pan,  4 bundles of steel wool, a 9 volt battery, 3 alligator clip extension wires, a 10 ohm, a 50 ohm, and a 100 ohm resistor.  You will use the pie pan to contain any combustibles during the experiment.  Place 1 of the bundles of steel wool in the pie pan, connect 2 of the alligator clips to the 9 volt positive and negative wires.  Make sure to keep these ends separated.  While wearing gloves touch the positive and negative leads to the steel wool approximately 2 cm apart for approximately 1 second. 

 

Does the steel wool ignite?_____________

 

To determine the current needed to ignite the steel wool you will increase the resistance in the system until the wool no longer ignites.  Connect the positive lead from the battery to the one side of the 10 ohm resister, connect another alligator clip to the other side of the resister.  While wearing gloves touch the new positive lead and the negative lead to the steel wool approximately 2 cm apart for approximately 1 second.  Repeat this process with the 50 and 100 ohm resistors.

Using the 10 ohm resistor does the steel wool ignite? ­­­­­­­­­­(yes/no)­ ­_______________________

Using the 50 ohm resistor does the steel wool ignite? ­­­­­­­­­­ (yes/no)­­_______________________

Using the 100 ohm resistor does the steel wool ignite? ­­­­­­­­ (yes/no)­­_______________________


 

 

 

 

 

Using ohm law (V=IR) to determine the current necessary to heat the steel wool to ignition.  Assume that the steel wool and connecting wires have a resistance of 100 ohms and is in series with the solid state resister (RT = R1+R2).

Note: If the wool ignites in every case, calculate the current in the case with the most resistance, this is the minimum current tested and is still a fire hazard.

 

 

 

 

 

 

 

 

What is the ignition current? ­­­­­­­­­­­­­­­­­­­­­­­__________________________(Amps)

 

 

Re-ignition of Candle:

Using the long candle provided ignite the wick and let the candle burn for 30 seconds.  Blow the candle out and use the long stem lighter place a flame in the smoke that remains after the flame is out.  Repeat the process 5 times, and estimate the maximum distance which the flame will reignite.

 

Trial 1:________________________

 

Trial 2:________________________

 

Trial 3:________________________

 

Trial 4:________________________

 

Trial 5:________________________

 

Maximum Re-ignition Distance ______________________________

 

Discuss why you think there is a maximum reigniting distance.

 

__________________________________________________________________________________________

 

__________________________________________________________________________________________

 

 

 

 

 

 

 

 

2. Combustion:

 

Liquid flame spread rate:
Alcohol-

For this experiment you will need the angle AL trough, an aluminium foil liner, the small bottle of alcohol, 1 pipette, and the long stem lighter.  Place the AL trough inside of the fume hood.  Fill a piped with 2ml of Alcohol, using the pipette spread a thin layer of alcohol along the bottom of the aluminium foil liner.  Measure the length of the fuel in the aluminium foil liner using a ruler. 
Note: Keep all combustibles out of the fume hood except what is being specifically used for each experiment.

What is the length of the fuel in the AL liner? __________________ (cm)


Working as a team ignite the right side of the layer of alcohol and measure the time it takes for the flame to travel the length of the fuel.  Calculate the flame speed using S= distance/time.

Note: This flame travels quickly and is light blue in colour.

 

What is the flame speed of Alcohol?  ­­­­­­­_________________ (cm/s)

 

Heptane-

Using a new pipette, follow the same procedure used for the alcohol to calculate the flame spread rate of heptane. 

 

What is the flame speed of Heptane?  _________________ (cm/s)

 

Tiki Torch Fuel-

Using a new pipette, follow the same procedure used for alcohol to calculate the flame spread rate of tiki Torch Fuel.

 

What is the flame speed of Tiki Torch Fuel? ________________ (cm/s)

 

 

Knowing that the molecular formula for alcohol (Ethanol C2H6O) is  46 g/mol, Heptane (C7H16) is 100 g/mol. 

Is there a correlation between the weight of the molecular weight of the fuel and the flame spread rate?

 

 

 

 

 

 

 

If there is a correlation do you think the Tiki Torch Fuel’s molecular formula is  larger or smaller than the other fuels?  Explain why you think this?

 

 

 

 





Solid fuel Flame spread rate:
For this set of experiments you will need the AL trough, the long stem lighter, 1 piece of cellulose (printer paper), one piece of moderately nitrated nicrocellulose (flashpaper), and 1 piece of strongly nigrated nitrocellulose (flashcotton).

Note: Be very careful with the nitrocelluloses, while you are using small amounts these are classified as class 1.1D explosives and ignite very easily.

Cellulose (printer paper)-
Measure the length of  the piece of paper and nitrocellulose.  Place the piece of cellulose in the AL trough, while wearing gloves and working as a team ignite the paper at the base and measure the time it takes for the flame to reach the end of the paper.  Calculate the flame spread rate using S = distance/time.

 

What is the flame spread rate of cellulose? _______________________________ (cm/s)

 

Nitrocellulose (flashpaper)-

Using the same procedure used for cellulose, calculate the flame spread rate of nitrocellulose.

 

What is the flame spread rate of flashpaper? ______________________________ (cm/s)

 

Nitrocellulose (flashcotton): (Be extra careful with this)

Using the same procedure used for cellulose, calculate the flame spread rate of flashcotton.

 

What is the flame spread rate of flashcotton? _______________________________ (cm/s)

 

 

Flame Shape:

Reignite the candle wick, place a wire mesh over the top of the candle flame, is the center of the flame filled with combustion?

 

 ________________________________________________________

 

 

Flame Temperature:

Using a hand held thermocouple measure the temperature of the tip of the candle flame.

 

What is the flame temperature? _____________________________________

 

 

 

 

 

 

 

 

 

 

Extinction: You are to study the some of the ways flames are extinguished:

Suffocation 1:

For this experiment you will need the pie pan, the long stem lighter, 1 beaker, and 1 small candle. Working as a team ignite the small candle, place a beaker over the candle, and measure the time it takes for the flame to extinguish.  Measure the height and diameter of the beaker and estimate the internal volume.  V = π/4D2*H.  Knowing that the atmosphere is 21% oxygen estimate the average oxygen consumption rate of the candle using CR= O2/time.

What is the average CR of the small candle? ______________________________ (cm3 O2/s)

 

Suffocation 2:

For this experiment you will need 2 large, 1 medium, and 1 small beakers, 1 small candle, the long stem lighter, baking soda and vinegar.  Working as a team place a small candle inside of a large beaker, ignite the candle using a long stem lighter. Mix baking soda and vinegar in the second large beaker, slowly pour the vinegar so that the bubbles do not spill.  The chemical reaction creates CO2 which is heavier than air. Carefully pour the gaseous CO2 from the large beaker on top of the candle without pouring any of the liquid onto the candle. 

 

Does the candle go out using the large beaker full of CO2? __________________________

 

Gently blow out the beaker with the candle inside to remove the CO2.  Following the same procedure as above use the medium size beaker to try to put out the candle.

 

Does the candle go out using the medium beaker full of CO2? __________________________

 

Repeat the process above for the small beaker.

 

Does the candle go out using the small beaker full of CO2? __________________________

 

 

Measure the volume of smallest beaker which put out the candle. Assume that the volume of the liquid is legible.

 

What is the volume of CO2 required to put out the candle? _____________________________________ (cm3)

 

 

Flow Speed for Candle Flame Extinguishment:

For this experiment you will need the large candle, a fan, a ruler, and the long stem lighter.  Working as a team reignite the large candle, and using the fan determine the maximum distance away from the candle the fan will blow out the candle. 

 

What is the maximum distance away from the flame the fan will blow out the candle? _______________ (cm)

 

Using the Vane Anemometer determine the air speed of the air at the distance measured above away from the fan. (there is only 1 anemometer which will be at the front of the room).  This speed is basically the speed at which the combustion front travels at the same speed as the air moving past the candle.

 

 

What is the speed required to blow out a candle flame? ­­­­­­­­­­­­­­­­­­­­_______________________________________ (cm/s)




Disclaimer: This is meant to be an example handout, this workshop is meant to be supervised by qualified laboratory personnel.  This description is meant as a guide only, the experiments can cause harm to persons or property.  The author takes no responsibility the use of any information from this site.

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