Lab3
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School
University of Texas, San Antonio *
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Course
2325
Subject
Aerospace Engineering
Date
Dec 6, 2023
Type
Pages
6
Uploaded by JusticeLapwingPerson2061
Gasoline Engine (Lab 3) 1.
For this lab, you will use the PhET simulation: https://phet.colorado.edu/sims/html/gas-properties/latest/gas-properties_en.html and click on the “Ideal” tab. 2.
Click on the following link to see a gif animating the Otto Cycle which is the process that the gasoline engine follows in order to power automobiles: https://images.app.goo.gl/kxpWeuZ2UpVNFZhu8 3.
The first step of the cycle (intake stroke) involves the piston moving downward and sucking in a large volume V
A
of a gaseous mixture of air and fuel. In practice, put in 650 of heavy particles in a chamber of width w
= 14.0 nm at room temperature T
A
= 72
o
F. Determine the pressure P
A
(in kPa) by averaging 10 pressure measurements (every fourth push) and calculate the volume V
A
(in nm
3
). 4.
The second step involves the piston moving upward and adiabatically compressing the air and fuel mixture. a.
In the chart below record pressure P
0
= P
A
and volume
V
0
= V
A
measurements in the first row coming from step 3. Decrease volume in width increments of 0.2 nm until you reach a volume of 10 nm and record all values in chart below (
V
0
, V
1
, …, V
20
= V
B
and P
0
, P
1
, …, P
20
= P
B
). Pressure values will be found by using the adiabatic equation !
!
"
!
"
= !
!#$
"
!#$
"
where γ =
%
&
.
Use Excel to calculate them in order to save time.
Points Pressure (kPa) Volume (nm
3
) A B b.
Plot the points: V
on horizontal axis (points
V
0
, V
1
, …, V
20 = V
B
) and P on vertical axis (points
P
0
, P
1
, …, P
20 = P
B
). Hold onto this plot for later additions. c.
Calculate the final temperature T
B
using the adiabatic equation +
'
"
'
"($
=
+
)
"
)
"($
where γ =
%
&
. d.
Under “Hold Constant” on simulation, click on “Nothing”. Adjust parameters in order to get gas in the state B conditions. Does the pressure match P
B
? e.
Determine the area Ar under the PV curve by doing the trapezoidal rule (approximation to integral): ,- = ∑
*
!"#
#*
!
+
(∆")
+,
!-$
where ∆" = "
$
− "
,
(Use Excel.)
Note that the units of the Ar
are 345 × 78
.
. Convert this Ar
value to units of joules (J). The Ar equals to the work (
9
')
> 0) done on the gas in the compression. 5.
The third step involves the combustion of the air-gas mixture where the temperature jumps to T
C
= 800
o
F with the volume remaining constant. a.
Treat the air-gas mixture as a monatomic ideal gas during the process. What is the heat (
Q
BC
> 0) produced in this process? b.
Crank the heat up in the simulation to T
C
. What is the pressure reading P
C
? 6.
The fourth step involves the piston moving downward and the exhaust gas adiabatically expanding (power stroke). This is the step where the engine does the work. a.
In the chart below record pressure P
0
= P
C
and volume
V
0
= V
C measurements in the first row coming from step 5. Increase volume in width increments of 0.2 nm until you reach a volume of 14.0 nm and record all values in chart below (
V
0
, V
1
, …, V
20
= V
D
and P
0
, P
1
, …, P
20
= P
D
). Pressure values will be found by using the adiabatic equation !
!
"
!
"
= !
!#$
"
!#$
"
where γ =
%
&
.
Use Excel to calculate them in order to save time.
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Points Pressure (kPa) Volume (nm
3
) C D b.
Plot the points: V
on horizontal axis (points
V
0
, V
1
, …, V
20 = V
D
) and P on vertical axis (points
P
0
, P
1
, …, P
20 = P
D
). Hold onto this plot for later additions. c.
Calculate the final temperature T
D
using the adiabatic equation +
/
"
/
"($
=
+
0
"
0
"($
where γ =
%
&
. d.
Under “Hold Constant” on simulation, click on “Nothing”. Adjust parameters in order to get gas in the state D conditions. Does the pressure match P
D
? e.
Determine the area Ar under the PV curve by doing the trapezoidal rule (approximation to integral): ,- = ∑
*
!"#
#*
!
+
(∆")
+,
!-$
where ∆" = "
$
− "
,
(Use Excel.)
Note that the units of the Ar
are 345 × 78
.
. Convert this Ar
value to units of joules (J). The negative of Ar equals to the work (
9
/0
< 0) done by the gas in the compression. 7.
The fifth step involves a valve opening releasing heat Q
DA
with the temperature dropping back to T
A
= 72
o
F and the volume remaining constant. a.
Treat the exhaust as a monatomic ideal gas during the process. What is the heat (
Q
DA
< 0) released in this process? b.
Cool down the gas in the simulation to T
A
. What is the pressure reading P
A
(should be close to what you started with in step 3.)? 8.
The sixth and final step involves the piston moving upward and pushing the exhaust out through the valve opening. a.
Based all of the previous calculations, fill in the chart below: Process Change in Internal Energy ∆
E
int
(J) Heat Q
(J) Work W
(J) A to B (adiabatic) B to C (isovolumetric) C to D (adiabatic) D to A (isovolumetric) b.
The total change in internal energy from A back to A (add up second column above) is J
. Is it close to 0? Which calculation could be introducing some error? Yes, it is two orders of magnitude lower than all of the other values…basically, close to 0. The trapezoidal rule introduces error when calculating work values.
c.
Attach Pressure Versus Volume Plot created in Excel.
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