MEEG425
Vehicle Powertrain Theory
Homework number 2, Chapter 4,
Homework Assignment 2
Due March 12, 2012
Work on these ALONE. Similar answers will result in zero credit. I guarantee you won’t have a buddy on the
exam. SHOW ALL WORK. Answers will be discussed in class so no late homework will be accepted.
1) What is the maximum, as a percentage of bore area, that the valve face areas can
occupy for the combustion chamber configurations. Use a 4” bore and give valve
diameters assuming equally sized valves:
a. 2V Flat
b. 2V hemi with 30 degree valve angle
c. 2V Hemi with 45 degree valve angle
d. 4V flat
e. 4V pent-roof -w- 20 degree valve angle (careful)
f. 4V pent-roof with 30 degree valve angle
2) What is the maximum, as a percentage of bore area, that the valve face areas can
occupy for the combustion chamber configurations. Use a 4” bore and give valve
diameters assuming equally sized valves for a 5V hemi
a. Try 0, 10, 20, 30, 45 degree layouts and show how results were obtained. Use
any method at your disposal that is reasonably accurate. Graph valve size
percentage results for all 5 cases
b. In the 5V case, what problems will arise as maximum valve size is used for a
given non-zero angle
c. In the 5V case, what is the relationship between valve angle, maximum lift and
maximum valve size?
d. Calculate for combustion chamber volume for each 5V case.
(excel and AutoCAD would be a good choice for this problem)
3) A V-8 engine is designed to displace 5.7 liters with a 4” bore. It uses 2.02” intakes and
1.58” exhaust valves. In wedge-head configuration with a 20 degree valve angle.
Pistons are flat-top and, as a first cut, design for zero squish at zero deck height.
Valves flat faced and their centerlines are parallel. Use SI units for consistency. Draw
each configuration.
a. Assuming the valves are tightly shrouded, and a line between their centers,
when retracted, is in the plane of the center of the cylinder parallel to the deck
plane, what is the minimum combustion chamber volume possible in this
configuration? By tightly shrouded, assume only a cylinder the size of the
valves is bored out of the combustion chamber along the valve centerline.
b. What is the corresponding compression ratio?
c. Is this a good design? Comment on it with regard to the four design goals for
combustion chambers
d. What methods could be employed to increase the compression ratio by only
modifying the combustion chamber?
e. Modify the design so that the area between the valves is removed and calculate
the volume and compression ratio. (combustion chamber is oval shaped)
f. What other methods could be used to decrease the compression ratio? List all
you can think of and the benefits of each.
MEEG425
Vehicle Powertrain Theory
Homework Assignment 2
4) The engine in (3) is designed with a hemi head, true hemisphere. The valve is centered
in it’s half of the combustion chamber so that it’s centerline is halfway between the axis
of the hemisphere and the line connecting the center of the radius of curvature to the
edge of the combustion chamber.
a. What is the maximum valve size, assuming the valves touch at the cener and
cylinder interface, and radius of curvature with a 30 degree valve angle?
b. What is the volume of the combustion chamber, assuming the combustion
chamber face of the valves are concave with the same 
c. What is the CR assuming flat top piston?
d. What size valves can be used if the valves are chosen to be 5% below the size in
which they touch the edge of the combustion chamber?
e. What is the ratio of total valve face area to cylinder top area? Assume the valve
faces are flat for simplicity.
MEEG425
Vehicle Powertrain Theory
Homework Assignment 2
5) The same engine in (3) is designed as a pent roof with a 20-degree valve angle.
a. What size valves can be used if the valves are chosen to be 5% below the size in
which they touch each other and the cylinder wall (use elliptical projection?)
Max is 1-3/4”1.75, so 5% off is 1.675
b. What is the ratio of total valve face area to cylinder top area?
70%
c. What is the maximum compression ratio with a true “pent roof” chamber with
equal intake and exhaust valve sizes? Assume the CC starts at the low point of
the valves. You may want to use symmetry. State any assumptions you make
to simplify geometry and justify.
6) Comment on the advantages and disadvantages of each as follows.
a. Address issues such as valve train complexity, torque vs. power, cost of
manufacture and reliability, etc. for address engines in 2-3-4-5
b. What difference would it make if this were a V8 vs. an in-line configuration for
refer to 3-4-5
c. Which can use rockers vs. overhead camshafts, and how which configurations
are available for each? Draw diagrams. Refer to 3-4-5
d. Suggest a configuration for the 5V head which uses two cams, no rockers and
non-zero valve angle(s), refer to 2 only. Hint – valve angles may vary.
7) Catalysts and Emissions
a. Describe Ozone creation and destruction
b. How were emissions first reduced:
Name 2 methods that preceded catalysts and describe why they work.
What effect did these have on economy, power, and engine longevity?
c. Describe and Oxidation Catalyst System
d. Describe a dual catalyst system
e. Describe how a three way catalyst works
f. Compare and contrast ceramic vs. metallic catalysts
g. What is the role of a single O2 sensor?
h. What is the role of a second O2 sensor?
i. Why is it important that mixtures be Stochiometric for the catalyst to work?
j. Describe light-off and what efforts are used to control it. What are the
implications of high light up temp and wide efficiency range?
k. What is the role of Cerium Oxide, and how is it like a sponge?
8) Discuss advantages and disadvantages of the DISI engine, both from efficiency and
manufacturing standpoints.