PASCO Compression Igniter
012-13028C
Introduction
®
2
* 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 hap-
pens inside the cylinder of a diesel engine. It demonstrates the high temperatures pro-
duced 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
0
and pressure
P
0
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
0
= 15
V.
With this assumption, the final pressure at maximum
compression can be calculated in terms of the initial (atmospheric) pressure:
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,
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”
PV
constant
=
PV
P
0
V
0
=
PV
P
0
15
V
=
P
15
P
0
=
The ignition temperature of
paper is about 451 °F.
See the science fiction
novel Fahrenheit 451 by
Ray Bradbury.
P
0
V
0
nRT
0
and
=
PV
nRT
=
