PASCO TD-8577 User Manual
Instruction Manual
®
Outer Safety
Tube
(polycarbonate)
Piston
Removable
Base
Bottom
Removable Top
Knob
Loading/Cleaning
Rod
“O” rings
“O” rings
Replacement
Glass Tube
Small O-ring (4)
Inner Glass
Tube
Medium O-ring (1)
IMPORTANT!
Piston Starting
Position label
Large O-ring (1)
Replacement
O-rings (6)
PASCO Compression Igniter
TD-8577
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012-13028B
PASCO Compression Igniter 012-13028B Introduction
®
PVconstant=
PVP0V
0
=
PVP015V
=
P 15
P
0
=
The ignition temperature of
paper is about 451 °F.
See the science fiction
novel Fahrenheit 451
by
Ray Bradbury.
P0V
0
nRT0 and =
PV nRT=
Included Equipment Included Equipment
PASCO Compression Igniter Replacement Glass Tube*
Loading/Cleaning Rod Replacement O-rings* (6)
Lubricant, silicone compound, (2 packets), not shown Material Safety Data Sheet for Lubricant
Additional Item Needed Cotton, tissue paper, “flash paper”
* The TD-8498A Replaceable Glass Tubes includes two replacement tubes and twelve O-rings.
Introduction
The TD-8577 PASCO Compression Igniter (or “fire syringe”) illustrates what happens inside the cylinder of a diesel engine. It demon s trat es the high temperatures produced during adiabatic compression of air by igniting a small amount of cotton, tissue
paper, or magician’s “flash paper” inside a replaceable, thick-wall glass tube. The
glass tube is encased in a polycarbonate safety tube that protects users from injury if
the glass tube breaks. The piston has two rubber “O” rings at its end that provide a
tight seal against the inside of the glass tube. When the piston is rapidly pressed down
into the glass tube, the temperature inside the tube rises quickly.
The Compression Igniter comes with one replacement glass tube and six O-rings. The
large O-ring is a replacement for the ring at the top of the inner glass tube. The
medium O-ring is a replacement for the ring at the top of the piston rod where it joins
the knob. The small O-rings are replacements for the rings on the end of the piston
rod and for the rings on the post that is part of the removable base.
Theory
The compression of air inside a hollow cylinder is an adiabatic process since the
compression is so fast that there is no time for thermal energy to leave or enter the
cylinder.
For an adiabatic compression of gas, , where P is the pressure of the
gas, V is the volume of the gas, and is the ratio of specific heats of the gas (specific
heat at constant pressure divided by specific heat at constant volume)
Therefore, when the gas in the cylinder is at its original volume V
and then is compressed to a small volume V and pressure P,
With the compression igniter, it is possible to compress the gas in the cylinder by a
factor of about 15, so V
= 15V. With this assumption, the final pressure at maximum
0
compression can be calculated in terms of the initial (atmospheric) pressure:
and pressure P0
0
2
The quantity that is of interest is the final temperature: Is it high enough to ignite
paper? To arrive at the temperature, assume that the gas is air and that it is an ideal
gas. For an ideal gas,
Model No.TD-8577 012-13028B Operation
®
PV
P
0V0
T
T
0
----------------
=
T
PV
P
0V0
------------
T
0
15P0V
P
0
15V
-------------------- -
T
0
==
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P
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Combustible
material
Piston
Push knob
down rapidly
Grip
tube
firmly
Watch
here
Piston Starting
Position label
Bottom
Top
Safety Tube
Glass Tube
Insert combustible
material here.
Removable
Base
where n is the number of moles of gas, R is the gas constant, and T is the absolute
(thermodynamic) temperature. Solving the initial equation for nR and substituting the
expression into the final equation gives:
Solving for the final temperature, T, and substituting the final pressure, P, derived
from the adiabatic equation and the final volume, V, which is 1/15 the initial volume
gives:
Simplifying this expression gives T = 15
1.4, so this gives T = 15
(297 K), then T = 15
0.4
T0. Assuming that the initial temperature is about 24 °C
0.4
(297 K) = 877 K. Converting to celsius, T = 604 °C. Since
( - 1)
T0. For air, which is mainly diatomic , =
604 °C = 1120 °F, the temperature is high enough to ignite paper.
Operation
1. Turn the removable base counterclockwise to unscrew it from the bottom of the
igniter. Remove the base and set it aside.
2. Insert a small piece (~ 1 cm
pulled from the end of a cotton swab) into the bottom of the glass tube.
2
) of tissue paper or a few strands of cotton fiber (e.g.,
3. Use the loading/cleaning rod to push the material up into the lower part of the
glass tube. Carefully remove the loading/cleaning rod without pulling the material out of the lower part of the glass tube.
4. IMPORTANT: Insert the piston into the top of the igniter and push it in far
enough that the end of the piston lines up with or is slightly below the
“Piston Starting Position” label on the outer tube 2.5 cm (1 inch) below the top.
5. Replace the removable base by screwing it clockwise into the bottom.
6. Place the base of the igniter on a sturdy horizontal surface and securely hold the
tube with one hand. Make sure that the combustible material in the bottom of the
glass tube is visible.
7. Watch the piece of combustible material at the bottom of the glass cylinder.
8. With the palm of your other hand, quickly slap down on the knob of the piston so
the end of the piston goes down into the cylinder rapidly.
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