H3051
THE UNIVERSITY OF SUSSEX
BEng (final year) and MEng (year 3) EXAMINATION 2022
January 2022 (A1)
Low Emission Vehicle Propulsion
Candidates must attempt THREE out of FOUR questions
Exam Duration: 3 hours
If all four questions are attempted, all will be marked, but the lowest mark
will not be counted in the total for the paper.
Write your answers on A4 paper, scan and save as a single PDF file and
upload to Canvas
PDF file name: candidate number_module title
Examination handout: Formula Sheet (available to download from Canvas)
Read Academic Integrity Statement
You are reminded that you should not access online materials, notes etc. during this
examination or discuss this assessment with others before the end of its 24 hour
window.
By submitting this assessment you confirm that you have read the above Statement
and are responsible for understanding and complying with Academic Misconduct
regulations as they relate to this assessment.
H3051 Low Emission Vehicle Propulsion
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Question 1
a) Using Figure Q1-1, suggest a specification for a four-stroke naturally
aspired engine with the maximum power of 250 kW and the maximum
torque of 1000 Nm. The specification will include the suggested stroke of
cylinders, number of cylinders. the bore of pistons and the resulting swept
area. Assume that the maximum power density on the piston must be
2.7 MW/m2 and must be less than or equal to 9 .
Hint: As the best practice, the bore of the pistons should be slightly less
than their stroke.
Figure Q1-1: Maximum torque and power curves of the engine at different rotational
speeds
[10 marks]
b) For the results of (a), calculate the Mach number of airflow through the
intake valve of the engine and estimate the volumetric efficiency using
Figure Q1-2. Assume four valves per cylinder (two valves for intake and
the other two for exhaust gas), = 0.21 and = 33℃. The specific gas
constant and the heat capacity ratio of air are respectively 287 / /
and 1.40 ( ).
Hint: the maximum diameter of the intake valves in a 16-valve structure is
41% of the bore. Using this ratio, you should calculate the equivalent
diameter of an imaginary circular valve with the same area as the sum of
the areas of two intake valves. Theis equivalent diameter will be used to
calculate the Mach number.
/Question continued on next page
0
50
100
150
200
250
0
200
400
600
800
1000
1200
0 1000 2000 3000 4000
Speed (rpm)
Power (kW)
Torque (Nm)
H3051 Low Emission Vehicle Propulsion
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Figure Q1-2 Volumetric efficiency of the engine in terms of Mach number of airflow
[6 marks]
c) Exhaust Gas is often recirculated (EGR) to reduce NOx; Explain the
impact of EGR on NOx and Soot emissions. Figure Q1-3 illustrates the
challenge of EGR flow when the turbocharger increases the pressure of
the intake manifold. What drives the EGR to flow from the exhaust to the
high-pressure intake manifold in Figure Q1-3 How can this flow rate be
increased
Figure Q1-3 An engine with the turbocharger and EGR circuits
Also, explain the reasons behind the fact that the engine of large ships is
normally 2-stroke with lower rotational speed than the engines of passenger
cars.
[4 marks]
End of Question 1
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7
Valve Flow Mach Number (-)
EGR circuit
EGR valve
EGR flow
Volumetric Efficiency (-)
High-pressure air
H3051 Low Emission Vehicle Propulsion
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Question 2:
a) A fully loaded passenger car is driving up an incline of 7 degrees at a
constant speed of 130 (km/h). Figure Q2-1 illustrates the BSFC map of the
engine of the car.
Figure Q2-1 BSFC map of engine
Having the car parameters as below, calculate the engine operating point
(engine speed and torque) assuming the driver has selected the most efficient
gear. Assume air with a density of = 1.225 ( / 3
).
The engine is a 2.5 litre, 4-stroke, SI engine with engine operating
range from 1000 ( ) to 6500 ( )
Vehicle Parameters:
o Final Drive ratio = 3.5:1 efficiency 95%
o Gear ratios all with efficiency 93%
1
st = 3.86: 1
2
nd = 2.18:1
3
rd = 1.32: 1
4
th = 1.1: 1
5
th = 0.75:1
o Tyres Rolling Radius = 0.33 ( )
o Fully loaded mass = 1500 ( )
o Rolling resistance coefficient = 0.015 ( )
o Cd = 0.25 ( )
o Frontal Area = 1.9 ( 2
)
[10 marks]
b) As in Figure Q2-2, the intake air path consisting of a carburettor and a
compressor can be with either of the following configurations:
a. the carburettor placed before the compressor;
b. the carburettor placed after the compressor.
H3051 Low Emission Vehicle Propulsion
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Compare the cooling effect of fuel evaporation on charge temperature in a
turbocharged spark-ignition engine for these two cases. Explain which
configuration is preferable.
Assume that the air/fuel ratio is 14.7: 1 and the evaporation of the fuel at
this ratio causes a 25 ℃ drop in mixture temperature. The pressure ratio is
1.70 and the corresponding isentropic efficiency of the compressor is 80%.
The ambient air is 32℃, the specific heat capacity and the ratio of air are
respectively , = 1.02 ( . ) and = 1.40 ( ). The ones of the air_xFFFE_fuel mixture are also , _ = 1.06 ( . ) and = 1.29
( ).
Figure Q2-2 Two possible topologies of the intake air path consisting of both
turbocharger and carburettor
[6 marks]
c) Figure Q2-3 illustrates the characteristics (in terms of specific energy vs.
specific power) of different energy storage available for a hybrid electric
car. Explain the difference between gasoline, Lithium-ion and super capacitors in terms of their advantages and disadvantages for being used
in a car. Also, using Figure Q2-3 (b) discuss the benefits of using hybrid
storage consisting of batteries and super-capacitors in a car.
(a)
(b)
H3051 Low Emission Vehicle Propulsion
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Figure Q2-3 (a) The Energy-Power specification of the different energy storages of
the hybrid electric powertrains, and (b) the Energy-Power specification of the
combination of batteries and super-capacitors as a hybrid storage
[4 marks]
End of Question 2
Specific Energy Wh/kg
(a) (b)
Super-Capacitor
Hybrid
Storage
Battery
Specific Energy (Wh/kg)
Specific Power W/kg
Logarithmic
Specific Power (W/kg)
H3051 Low Emission Vehicle Propulsion
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Question 3:
a) A Diesel truck is being developed with a Diesel Particulate Filter (DPF)
and NOx after-treatment. The DPF needs to be sized to allow a time
between regeneration events of 35 hours at an engine load of75 ( ).
The engine has been developed with the NOx versus soot trade-off curve
in Figure Q3-1. Answer the following questions:
Figure Q3-1: A NOx – Particulates engine out emissions
1. The target tailpipe NOx emission rate is 0.27 ( ). Assuming
the truck meets this target and has NOx after-treatment with 96%
conversion efficiency. What are the Particulate Emissions from the
engine (Use Figure Q3-1)
2. The backpressure characteristics of the DPF are shown in Figure
Q3-2. Calculate the minimum size of the filter assuming the filter is
regenerated when the back pressure at full load exceeds
0.12 ( ).
Figure Q3-2: Backpressure versus soot loading at full load
[6 marks]
H3051 Low Emission Vehicle Propulsion
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b) You are a designer of powertrains including engines and gearboxes.
Calculate the maximum power of the engine for a front-wheel-drive car
with the following parameters to reach the top speed of 180 ( ):
Vehicle mass: 1200 ( );
Aerodynamic frontal area: 1.2 ( 2
);
Free-Rolling resistance coefficients: 0.015 ( );
Aerodynamic drag coefficient: 0.25 ( );
The effective radius of tyres: 0.33 ( );
The efficiency from wheels to the shaft of engine: 90 (%);
The density of air: 1.225 ( / 3
).
If the BSFC map of the chosen Diesel engine is as in Figure Q3-3, calculate
the swept volume of the required engine and ratio of the highest gear (5th or
6
th) of the required gearbox. Assume a final drive (i.e., differential) with a gear
ratio of 3 ( ).
Figure Q3-3 BSFC map of the required engine
[8 marks]
c) Calculate the stoichiometric air/fuel ratio for a type of fuel with the following
gravimetric mixture. Assume that the air is consists of 79% of Nitrogen
( 2
) and 21% of Oxygen ( 2
). The molar mass of Oxygen and Nitrogen is,
respectively, 32 and 28 ( ).
Component
Name
Component The ratio of the
total mass
Molar Mass
(kg/kmol)
Hexane C6H14 45% 6×12+14
Octane C8H18 33% 8×12+18
Cyclohexane C6H12 17% 6×12+12
Benzene C6H6 5% 6×12+6
[6 marks]
End of Question 2
bsfc (g/kWh)
RPM
10
9
8
7
6
5
4
3
2
1
0
1000 1500 2000 2500 3000 3500 4000 4500
BMEP (bar)
H3051 Low Emission Vehicle Propulsion
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Question 4:
a) It is known that half of the energy lost from the engine goes to the engine
coolant. Assume that all the energy that passes to the coolant is rejected
by the radiator and the lower heating value for Gasoline is 43 MJ/kg. The
aerodynamic frontal area of the vehicle is 1.8 ( 2
). Answer the following
questions:
1. The following table shows the maximum torque and BSFC of the
engine at specific speeds. Calculate the maximum power being
rejected by the radiator.
Point 1 Point 1 Point 1 Point 1 Point 1 Point 1
Engine Speed (rpm) 1000 2000 3000 4000 5000 6000
Brake Torque (Nm) 150 175 195 190 165 130
BSFC (g/kWh) 260 245 248 255 278 320
2. Calculate the minimum coolant flow rate of the radiator to avoid
overheating under these conditions, assuming the fan is not
running, the radiator is only cooled by ram airflow with the cooling
capacity given by the graph in Figure Q2-2. The cooling capacity is
the rate at which the radiator can remove energy from the coolant
circuit.
Assume the frontal area of the radiator is 9% of the vehicle’s frontal
area and the airflow speed through the radiator is 18 ( ).
Density of air is 1.225 ( 3
).
Figure Q2-2: A graph of cooling capacity versus air flow for different coolant flow rates
[8 marks]
/Question continued on next page
Coolant
flow
rates
H3051 Low Emission Vehicle Propulsion
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b) 1. A 12 Litre 4-stroke diesel engine operates with a nominal compression
ratio of 18: 1. Assuming a mean expansion/cut-off ratio of 1.70,
calculate the ideal indicated efficiency of the engine. The specific gas
constant of air is 286.9J/kg.K.
2. Using the provided equations in the Formula Sheet to calculate bmep,
AFR and volumetric efficiency, extract the following equations to
calculate bmep ( ) and bsfc ( / ) of the engine at a given
operating point:
=