MECH9761 Laboratory Report Instructions

The following instructions will assist you in processing data files obtained from the engine cycle
analyser software. You are required to complete the provided Matlab code for data processing and
discuss your findings. The report is to be typed up in a word processor and submitted to Turnitin
portal before Monday 4pm, Week 8 (Lab session 1-3)/Week 9 (Lab session 4-6). A formal style
report is not required; please just complete the following steps and discussion questions.
Provide all codes you used to complete the report at the end of the report.

Task 1 – General Questions

During the laboratory, your demonstrator made changes to the settings on both the engine and the
dynamometer. Answer the following questions using the explanation given to you in the lab and lab
instructions, as well as consulting lecture notes and other materials of your choice.

a) What is the purpose of a dynamometer and what performance parameter does it measure?
How were the demonstrators able to change the load on the engine?
b) How was the output of lab engines varied? Does the air/fuel ratio change while doing this?
(Please answer this questions separately for SI and CI engines)
c) With the engine-dynamometer setup, is it possible to alter the supplied fuel amount while
maintaining a constant engine speed?
d) For the tested SI engine, as shown and discussed during the lab session, within its intake
manifold there are three key components as the butterfly valve, throttle body and the
carburettor. Please explain the role of each of these components regarding to the engine
operation. For example, if applicable, under what circumstance the component is used, what
factor it controls and how, in what way it impacts the engine combustion process.
Task 2 – Performance evaluation of the SI engine
Unzip the provided ‘Labdata.zip’ file, open folder ‘Labdata Petrol’. You will find 5 ‘txxx_yyyy.mat’
files, which contain raw in-cylinder pressure data. The ‘xxx’s refer to the torque measured by the
dynamometer (045 = 4.5 Nm, 133 d= 13.3 Nm etc.) and the ‘yyyy’s refer to the engine speed in RPM.
Open one of these files in Matlab and you will see that the CrankAngle parameter ranges from -180 to
+539. These angles are specified in terms of the expansion stroke top dead centre, i.e. -180 to -1 is the
compression stroke, 0 to 179 is the expansion stroke, 180 to 359 is the exhaust stroke and 360 to 539
is the intake stroke. Step by step instruction on data processing using Matlab is as follow.

a) Open Petrol.m in Matlab. Note that on line 12 we are dealing with the 7.2 Nm @ 2410 RPM
case to begin with. Change lines 14 and 55 so that they point to your unzipped Labdata
directory
b) Using ‘CrankAngle’ and other parameters defined in lines 4-10, enter the formula for
combustion chamber volume in line 26.
c) Noting that there is a variable defined as ‘Pressure’ for each case, complete line 31 in order to
obtain PdV.
d) Following the instruction on line 33, complete line 34 to obtain the total work done on the
piston during all 4 engine strokes.
e) Recalling definitions from the lecture notes, complete line 36 to obtain IMEP (in MPa – the
next line will convert it into bar).
f) [Advanced] In lines 41-43, write a loop which will calculate the work done during just the
intake and exhaust strokes (WorkP).
g) [Advanced] From e) and f) complete line 46 to obtain pumping losses (PMEP). Note that this
is work done by the piston on the working fluid, as such, you will need to change the sign to
obtain a positive value. Make sure you put in the necessary conversion in order to get the
answer in bar.
h) Recalling definitions from the lecture notes, complete line 49 to obtain BMEP (in Pa – the
next line will convert it into bar).
i) Frictional losses are the difference between indicated and brake output. Complete line 53 to
obtain FMEP.
j) Run the Matlab code and selected the first data set you would like to process, create P-V
(Pressure-Volume) plots for the case. The code will automatically save the processed data
in the same folder.
k) Complete the same processes for the 4 other engine operating conditions. Ensure that you
change lines 14 and 55 to correct file names each time so that you don’t overwrite your
previous work. Display all P-V plots in your report document.
l) In your report document, complete the following table:

m) Use the P-V diagrams and the data calculated, discuss the effect of Torque and RPM on
PMEP and FMEP, and provide reasons respectively (If possible, refer your answer to the
P-V plots you showed previously).
n) Calculate the mechanical efficiency for each case, find which operating condition has the
highest mechanical efficiency and discuss why this is the case (Hint: Mechanical efficiency
can be thought of as the ratio between gross indicated output and brake output. Gross IMEP,
net IMEP and PMEP are related via the following formula: Gross IMEP = PMEP + net
IMEP).
Task 3 – Performance evaluation of the CI engine
Open the folder ‘Labdata Diesel’. You will find 2 ‘_load_diesel.mat’ files for raw in-cylinder pressure
data for high and low engine operating conditions, and 2 ‘m’ files for data reduction and plotting. In
the ‘Diesel.m’ file, geometric information of the diesel engine and operating conditions are provided.
You need to complete this code similar to that for petrol engine to obtain data for in-cylinder pressure
plot, IMEP calculation, and apparent heat release rate plot.
a) Load one of the “_load_diesel.mat” file by using ‘load’ function in the Matlab. Follow the
same procedure as for the petrol engine case and copy formulas up to line 35 to calculate the
IMEP.
b) Assuming a constant specific heat ratio of 1.35, we want to apply the first law of
thermodynamics and calculate apparent heat release rate. Since we’ve already obtained
Pressure(x), dV(x), Volume(x), and dP(x), we can complete line 50 for aHRR at a given
crank angle.
c) Execute the code and you will notice that 1 ‘mat’ file is created in the current folder. In line
61, we used a save function to record ‘CrankAngle’, ‘Pressure’, “HRR_filt”, and ‘IMEP’ for
further analysis.
d) Execute the ‘plotter.m’ in Matlab. This will draw two figures: in-cylinder pressure over crank
angle with notes for IMEP values and apparent heat release rate versus crank angle.
Following the instruction given in line 10 and 11, plot the other case and complete the
incylinder pressure viewgraph.
e) Discuss the effect of fuel quantity on the in-cylinder pressure traces and its impact on IMEP.
f) In the plotter.m file, follow the instruction in line 28~29 to plot apparent heat release rate
traces.
g) Discuss the effect of fuel quantity on the heat release rate traces and its impact on NOx
emissions.
Torque
(Nm)
RPM
IMEP
(bar)
PMEP
(bar)
BMEP
(bar)
FMEP
(bar)
4.5 2100
7.2 2410
8 2170
13.3 2425
13.3 2550