Improving the Heat Transfer Rate for Multi Cylinder Engine Piston and Piston ...
ICEFinalReport
1. Internal Combustion Engines Final Report
Summer 2015
Team Members
Chris Bader
Shadae Boakye-Yiadom
Jane Modes
Spenser Pawlik
Anna Starodubtseva
Contents
Abstract…………………………………………………………………………..2
2. 1
1. The Engine Test-Beds……………………………………………………...3
1.1 The Mini Engine Test Bed…………………………………………………………4
1.2 The Real Engine Test Bed………………………………………………………...6
1.3 Comparison of Test Beds…………………………….……………………………8
1.4 Measurement Techniques………………………………………………………...8
2. Data Analysis……………………………………...……………………….10
2.1 General Analysis…………………………....…………………………………….11
2.2 Indicated Work and Efficiencies……………………..…………………………..14
2.3 Pressure Trace Analysis………………...…………………………………….....15
2.4 Rate of Heat Release, Cylinder Pressure, and Injector Current vs. Crank
Angle………………………………………………………...……….…………………17
2.5 Cumulative Heat Release…………….………………………………………….19
3. Engine and TurbochargerMaps………………………………………....20
Appendix…………………………………………………….………………… 24
References………………………………………..…………………………….25
3. 2
Abstract
As part of the IESS Internal Combustion Engines Lab, we were tasked with modeling and
analysing several internal combustion engine test beds under the instruction of the internal
combustion engines laboratory faculty. This report contains a general overview of the test beds
followed by detailed analyses of the given data. Using the information presented in lecture and
software such as Microsoft Excel, UniPlot, and Matlab’s Simulink and ThemosDVA, we
prepared figures and explanations detailing the process undergone by an internal combustion
engine and the resulting produced and evaluated values. The purpose of this report is to outline
the modeling and analyses we performed.
Each group member came in with limited experience in the field of internal combustion engines,
but developed an understanding for the basics of the field through lectures and hands-on
laboratory experience led by the faculty. Through the duration of the course we were able to
work with programs that simplify the process of simulating and evaluating the results from an
internal combustion engine.
This report is a compilation of the analyses we performed throughout the summer. Since the
course was very short, we had an accelerated schedule. We were first introduced to the
fundamentals of internal combustion engines. This was followed by lectures in turbocharging
and computational fluid dynamics. We also learned some basic engine parts by observing them
both in and out of an engine, and learned measurement principles.
During the second week of the course we learned about and worked with Matlab and Simulink.
These programs were used to model a throttle, engine, and intake manifold, which come
together to form a basic model for a full car.
The third week of the course was spent working on test bed 2, the turbocharger, and test bed
3/4, the real engine. We gained hands on experience setting up the test bed for the
turbocharger and collecting actual data from both the real engine and the turbocharger test
beds. We used data provided by the faculty to evaluate and analyze the turbocharger and real
engine. The conclusions they came to are included in this report.
The fourth week of the course was spent compiling all the work to present this final report.
We’ve completed the report and all other tasks by the deadlines given by the instructors. We
would be happy to answer any questions you may have about the models and analyses.
4. 3
1. The Engine Test-Beds
An engine test bed is a device used to develop, characterize, and test an engine. The test beds
we are using aim to characterize different engines by taking adiabatic measurements.
There are several components of the real engine test bed that are necessary to run and test the
engine. These components include the throttle, turbocharger, intercooler, coolant, and a catalyst
to reduce emissions.
There are also several sensors that we use in the real engine test bed such as the brake for
speed, piezoelectric and piezoresistive sensors for pressure (Figure 6), hot wire anemometers
for mass flow, dynamic mass flow meter for fuel mass (Figure 7), Pt-100s and thermocouples
for temperature (Figure 5), and turbine flowmeters for volume flow measurement. With all of
these components and sensors the test bed can provide data used to characterize the engine.
The mini engine test bed is designed to simulate a real engine test bed on a smaller scale to
reduce the cost. The engine for the real engine test bed is taken from a model airplane, not a
car, so there are several components like the throttle, turbocharger, intercooler and coolant.
There are also several components that the mini engine test bed has but the real engine test
bed does not. These components include a starter to start the engine, carburetor for mixing air
and fuel, and muffler to dampen the noise of the engine.
The mini engine test bed also has sensors for some of the same variables such as speed,
pressure, fuel mass flow, and temperature. The mini engine test bed also uses a strain gauge
instead of a brake to test the torque output of the engine.
1.1 The Mini Engine Test Bed
Figure 1. Scheme of the mini engine test bed
9. 8
1.3 Comparison of Test Beds
Table 1. Comparison of components of the real and mini-engine test beds
Components Real Engine Test Bed Mini-Engine Test Bed
Speed Sensor ✔ ✔
Pressure Sensor ✔ ✔
Fuel Mass Flow Sensor ✔ ✔
Temperature Sensor ✔ ✔
Air Mass Flow Sensor ✔
Volume Flow Sensor ✔
Throttle ✔
Catalyst ✔
Turbocharger ✔
Intercooler ✔
Coolant ✔
Starter ✔
Strain Gauge ✔
Carburetor ✔
Muffler ✔
1.4 Measurement Techniques
Most important Measurements
● Engine Torque
● Fuel mass flow
10. 9
Important Measurement Techniques
● Thermocouples
● Pt-100
● Hot Wire Anemometer
● Piezo-resistive sensors
Figure 5. Thermocouples (left) and PT-100 (right) sensors used to measure temperature in the
real engine test bed
Figure 6. Piezo-resistive sensor used to measure pressure
in the real engine test bed.
11. 10
Figure 7. Dynamic mass flow meter used to measure fuel mass in the real engine test bed
2. Data Analysis
With the measurement techniques and sensors mentioned above we tested a 2.0 liter
Volkswagen TDI MDB EU5 engine with a turbocharger on our test bed. With the data we
collected we performed multiple forms of data analysis including general analysis, indicated
work and efficiency calculations, a pressure trace analysis, rate of heat release analysis, engine
maps, and a turbocharger map.
Table 2. Important Engine Specifications.
Stroke (s) 95.5 mm
Connecting Rod (l) 144 mm
Cylinder Diameter (r) 81 mm
λSt = (r/l) 0.332
Compression Ratio 16.2
Engine Volume (VH) 1968 cm3
12. 11
2.1 General Analysis
The general analysis we performed included a plot of cylinder pressure vs. crankshaft angle
(Figure 8), a pressure-volume diagram (Figure 9), and important measurements notes.
Figure 8. Cylinder pressure of the engine at 1500 RPM increases during the compression cycle
and is close to ambient pressure during the intake and exhaust strokes because the valves are
open. The engine pressure is greater for the higher loads. The peak value is 157.8 bar.
The blue line is when there is no combustion and the engine is being run with the brake
dynamometer. This line is smooth and shows only one peak at the end of the compression
stroke. The other lines show the engine running with combustion and there is no longer a max
at the end of the compression stroke because the pressure increases additionally during
combustion. The combustion increases the crank angle at which the maximum pressure occurs
and as the load increases the maximum pressure also increases.
13. 12
Figure 9. The pressure and volume of the cylinder are plotted for the 1500 rpm speed and at
a 2 bar p_me load and max load. There is a greater pressure for the max load.
Figure 10. The theoretical Otto cycle is similar to the actual engine cycle above
14. 13
To make the pressure-volume diagram we first calculated the volume from the crank angle and
then plotted this volume with the corresponding cylinder pressure. The actual pressure data
resembles the ideal Otto cycle but is different because there are no constant volume processes.
Additionally, we noticed a few interesting points about the data we were given. First we saw that
the values for the turbine temperatures are implausible because the temperature coming out of
the turbine (T_nT) is greater than the temperature going into the turbine (T_vT) (Table 3). This
should not occur because the air would be coming from combustion and could not just gain
energy while in the turbine, so T_vT should be greater than T_nT. By looking at other data
points/looking at other engine data, we found that the temperature after the turbine was too
high, while the temperature before the turbine seemed reasonable.
Table 3. Turbine Temperatures (T_nT too high)
Next we saw that the oil pressure is nearly constant at low loads but increased at higher loads
(Table 4). At higher loads the engine will be moving faster and more oil pressure needed to cool
the parts and at higher loads the parts of the engine will be rotating faster which means the
bearings will need additional oil pressure to maintain proper lubrication and stabilize the oil
bearings.
15. 14
Table 4. Oil pressure measurements
2.2 Indicated Work and Efficiency
Figure 11. The indicated work is shown as the area under the curve. The four strokes of the
engine are also shown on the graph. The boundaries of the diagram are also shown. The
16. 15
pressure/volume diagram for the engine at y1500 rpm and maximum load.
This area is calculated using the following equation,
which quantifies the value of the area under the curve. This integral was approximated using the
Matlab function ‘trapz’.
Table 5. Work and efficiency of the engine at various mean effective pressures
Mean Effective
Pressure
2 bar 10 bar Maximum Load
Indicated Work 175.9 J 568.6 J 1083.4 J
Indicated Efficiency 50.9% 45.4% 44.4%
Effective Efficiency 28.4% 39% 39.7%
17. 16
The indicated efficiency is greater than the effective efficiency at any point because the
indicated efficiency only describes how much of the potential heat in the fuel is transformed into
work done by the gas in the cylinder while the effective efficiency looks at the power output of
the engine compared to the fuel input. The effective efficiency takes into account mechanical
losses in efficiency due to the friction between moving parts or energy used by auxiliary
components of the engine like oil and water pumps.
The indicated efficiency decreases at higher loads, as shown in Table 5, because it is inversely
proportional to the heat loss of the gas in the cylinder, which is greater at a higher pressure due
to higher temperatures and the resulting increase in the amount of heat lost to the surroundings.
Effective efficiency increases at higher loads because more air is able to be brought into the
engine as the mean effective pressure increases, so the air to fuel ratio ( λ ) more closely
approaches the ideal. This occurs when the exact amount of air needed to burn the total mass
of fuel is taken in and used for combustion. At higher pressures the air is also coming into the
cylinder at a higher temperature, so it can be more thoroughly mixed with the fuel, further
contributing to λ.
2.3 Pressure Trace Analysis
Pre-injection involves premixing fuel and air inside the engine prior to ignition. If the
compression temperature is not sufficient to start combustion, you can inject diesel oil as a pilot
fuel (pre-injection). This starts primary combustion to raise the temperature in the combustion
chamber before the main-injection. This improves combustion by allowing the fuel to burn
uniformly and completely. The purpose of pre-injections in a diesel engine is to reduce fuel
consumption and carbon emissions.
18. 17
Figure 12. Matlab ThemosDVA data for 1500 rpm and 10 bar p_me
For the 1500 rpm and 10 bar p_me operating point, pre-injections were used. The Heat Release
vs Crank Angle graph in Figure 12 portrays two different peaks: a small initial peak followed by
a much larger peak. The first small peak represents the pre-injection. There is a small amount
of fuel burned from the pre injection that releases a small amount of heat. The large peak
shows the heat release from the normal cycle, or main injection phase.
As shown in the Indicated Pressure vs. Crank Angle graph in Figure 12, the calculated pressure
diagram is aligned with the measured one up to a crank angle of approximately 347°.
2.4 Rate of Heat Release and Cylinder Pressure vs. Crank Angle
19. 18
Using a pressure trace analysis, we calculated the Rate of Heat Release (ROHR) or burn rate
within the cylinder. The curve allows us to find the energy flux at specific points.The cylinder
pressure is also shown in the plot for comparison. Figure 14 shows the chemical and physical
delay between the peak of the ROHR and the time of maximum pressure in the cylinder
because the fuel needs time to fully combust. In comparing the three data points used, the full
load data has a greater cylinder pressure and heat release. Also the data for the rate of heat
release under full load conditions showed much more noise within the signal. This noise could
have been caused from variations in the measurements
Figure 15. Cylinder pressure and burn rate at 2500 rpm and 4 bar p_me. The red dashed line
represents a local peak in burn rate and the black dashed line represents a local maximum of
cylinder pressure. The delay between the peaks is due to the time needed for the fuel to
combust.
Figure 16. Cylinder pressure and burn rate at 1500 rpm and 10 bar p_me
20. 19
Figure 17. Cylinder pressure and burn rate at 4000 rpm and 10 bar p_me
2.5 Cumulative Heat Release
21. 20
Figure 18. Plot of Cumulative heat release for 1500 rpm and 10 bar
The duration of combustion is defined as 5%-95% of the cumulative heat release. The end of
heat release is at the 95% part of the graph, when the cumulative heat release starts to level off.
The start of heat release is defined at 5% of the cumulative heat release. And the center of heat
release is at the 50% mark. At the center of heat release, the rate of cumulative heat release
increases, leading to faster combustion and thus increasing the efficiency.
22. 21
3. Turbochargerand Engine Map
Figure 19. Plot of p_me vs. RPM with Lambda ratio contour lines
Figure 20. Plot of p_me vs. RPM with Specific Fuel Consumption contour lines.
23. 22
Min Speed: this is the minimum speed that the engine can effectively operate at
Surge Line: this is the line at which air goes the opposite way through the compressor, causing
the turbocharger to fail.
24. 23
Max Load: this is the maximum power that the engine can produce
Max Exhaust Temp: this is the maximum temperature that the turbine can withstand from the
exhaust gas from the engine.
Max Speed: this is the fastest rpm that the engine can operate at
The lambda ratio decreases as the load increases. This is because at higher loads, more fuel is
used to produce enough power. This increases the amount of fuel in the piston compared to the
amount of air. The lambda ratio is a ratio of mass flow of air divided by mass flow of fuel. If there
is more fuel in the piston compared to air, the lambda ratio will go down.
The lambda ratio getting closer to 1 as load increases is one factor that leads to the specific fuel
consumption decreasing as the load gets higher, leading to a more efficient engine at higher
loads which is evident in the engine map.
Figure 21. Compressor map and line of max load
The first engine map boundary and the compressor map boundary are the same. The surge line
is the limit of the air flow at the compressor inlet, before air begins. The max speed is the
maximum speed at which the compressor can operate. The choke line is the limit of the
25. 24
compressor volume flow rate. The line of full load shows us what parts of the map we can use.
Everything outside the line of full load is not usable.
Figure 22. Turbine map
Appendix
Equations
26. 25
References
Pre- and post-injection flow characterization in a heavy-duty diesel e. (2012, September 1).
Retrieved June 11, 2015, from http://link.springer.com/article/10.1007/s00348-012-1323-3
Engine test stand. (n.d.). Retrieved June 11, 2015, from
http://en.wikipedia.org/wiki/Engine_test_stand
Influence of Pre- and Post-Injection on the Performance and Pollutant Emissions in a HD Diesel
Engine. (n.d.). Retrieved June 11, 2015, from http://papers.sae.org/2001-01-0526/
27. 26
Mo, Y. (2008). HCCI HEAT RELEASE RATE AND COMBUSTION EFFICIENCY: A COUPLED
KIVA MULTI-ZONE MODELING STUDY. Retrieved June 11, 2015, from
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/60734/yanbinm_1.pdf?sequence=1
Compressor Map. (n.d.). Retrieved June 11, 2015, from
http://performancetrends.com/Definitions/Compressor-Map.htm
Baar. Technische Universität Berlin, FG Verbrennungskraftmaschinen
