Menoufia University Subject: ICE (2)

Faculty of Engineering, Shebin El-kom Code: MPE411

Mechanical Power Department Year: 2021-2022
First Semester Examination, 2021-2022 ‫جامعة المنوفية‬ Time Allowed : 3 hours
Date of Exam: 23 / 1 / 2022 Total Marks : 90 marks
‫ يجب أن يبدأ كل سؤال رئيسى فى صفحة جديدة على أن تبدأ اإلجابة من السؤال األول من يسار كراسة اإلجابة‬-1 :‫تبيهات مهمة‬
‫ ضرورة تنظيم اإلجابة ووضوح الخط والرسم واألرقام‬- 2
Answer the following questions:
Question (1) (25 marks)
a- Compare between different methods used for supercharging ICE and show the limitation of
supercharging SIE. (6 marks)
b- Discuss the role of mixture quality of SIE on resultant emission. Show how to reduce such
harmful emission. (6 marks)
c- List the major lubricant properties used in ICE and explain why multi-grade oil is more
suitable than the conventional one. (7 marks)
d- A six-cylinder, four-stroke engine gasoline engine having a bore of 90 mm and stroke of 100
mm has a compression ratio 8. The relative efficiency is 60%. When the indicated specific fuel
consumption is 3009 g/kWh. Estimate
1- The calorific value of the fuel
2- Corresponding fuel consumption given that imep is 8.5 bar and speed is 2500 rpm.
(6 marks)
Question (2) (25 marks)
a- Discuss with suitable diagram the combined effect of engine speed and valve timing on
volumetric efficiency. What is the modern solution to bad effect of variable engine speed on
volumetric efficiency? (6 marks)
b- Describe with the help of schematic diagram the working principle of evaporative cooling
system. (5 marks)
c- Mention four detrimental effects of pollutants from ICE. (4 marks)
d- A four-stroke cycle gasoline engine has six acting cylinders of 8 cm bore and 10 cm stroke.
The engine is coupled to a brake having a torque radius of 40 cm. at 3200 rpm with all
cylinders operating the net brake load is 350 N. When each cylinder in turn is rendered
inoperative, the average net brake load produced at the same speed by the remaining 5
cylinders is 250 N. estimate the indicated mean effective pressure of the engine. With all
cylinders operating the fuel consumption is 0.33 Kg/min, calorific value is 43 MJ/Kg, the
cooling water flow rate and temperature rise is 70 Kg/min and 10ᵒC respectively. On test the
engine is enclosed in a thermally and acoustically insulated box through which the output
drive, water, fuel, air, and exhaust connections pass. Ventilating air blown up through the box
at the rate of 15 Kg/min at 17ᵒC and leaves at 62ᵒC. draw up a heat balance of the engine
stating the items as percentage of the heat input. (10 marks)
Question (3) (20 marks)
a- How are the exhaust valve and piston of an internal combustion engine cooled? (6 marks)
b- Derive an expression to evaluate piston displacement from TDC position in terms of crank
angle (Ɵ), crank radius (r) and connecting rod length (L). (6 marks)
c- A four-cylinder, four-stroke cycle, 2.8 litre, opposed-cylinder SI engine has brake mean
effective pressure and mechanical efficiency as follows:
At N = 1000 rpm bmep = 828 kPa mechanical efficiency ηm = 90%
N = 2000 rpm bmep = 828 kPa mechanical efficiency ηm = 88%
N = 3000 rpm bmep = 646 kPa mechanical efficiency ηm = 82%
Calculate:
1- Brake power at 2000 rpm [kW]
2- Fmep at 2500 rpm [kPa]
3- Friction power lost at 2500 rpm[kW] (8 marks)
Question (4) (20 marks)
a- Derive the following expression that evaluate the side thrust on the cylinder wall when the
piston is in expansion stroke and the rotation of crank shaft is clockwise direction in naturally
aspirated SIE.
𝑹
𝒅𝒖
𝒕𝒂𝒏 [ 𝒔𝒊𝒏 ( 𝒔𝒊𝒏 𝜽)]
𝑳
Fth = [ P . A – m
𝒅𝒕
][ 𝑹 ]
𝟏+ 𝝁 . 𝒕𝒂𝒏 [𝒔𝒊𝒏 ( 𝒔𝒊𝒏𝜽)]
𝑳
Where: Fth : Side thrust P : Gas pressure on piston
m: piston mass A : Cross section area of piston
𝒅𝒖
: Acceleration of the piston 𝝁 : Coefficient of friction
𝒅𝒕
R : Crank radius L: Connecting rod length 𝜽: Crank angle degree (5 marks)
b- Draw the typical variable speed characteristic curves for an SI engine at wide open throttle.
Discuss the nature of the curves. (4 marks)
c- What are the positive and negative characteristics of hybrid vehicles? (3 marks)
d- A six-cylinder, 4.5 liter, four-stroke, super charged engine operating at 4000 rpm has an
overall volumetric efficiency of 150%. The compressor has an isentropic efficiency of 90%
and a mechanical efficiency of 85% in its link with the engine. The compressed air is delivered
to the engine cylinders at 57 oC and 1.8 bar. The ambient conditions are 17 oC and 1 bar. The
arrangement is shown in the figure below.

Calculate:
1- The rate of heat rejection from the aftercooler. [kJ/sec]
2- The power absorbed by the supercharger from the engine. [kW] (8 marks)

With my best wishes .

This exam contributes " by measuring in achieving Programme Academic Standards

according to NARS
Question No. 1-b 2-c 1-c 2-b 3-a 1-a 3-b 2-a 2-d 3-c 2-d 3-c 4-b
A6-1, A6-3,
Skills A5-1
A6-2 A6-1 A4-1 A4-1 B5-3 B5-2 B5-2 B5-1 B5-1 C5-1 C5-1 C5-1

Question No. 4-d 4-c 4-a 4-b 4-d 1-d

Skills A4-2 B12-1 B5-2 B5-1 C5-1 C5-1

Knowledge & Understanding Skills Intellectual Skills Professional Skills

 Model Answer of Final exam 2021/2022 of ICE (2)
Question (1)
a-
b-

Fig. (1)
Figure (1) shows the variation of HC, CO, and NOx emissions as a function of
equivalence ratio for an SI engine. It is already seen that all the three emissions are a
strong function of equivalence ratio.

c-
d-

Question (2)
a-
b-

c-The emissions exhausted into the surroundings pollute the atmospheric and
causes the following problems

i- global warming
ii- acid rain
iii-smog
iv-odours
v- respiratory and other health hazards

d-
Question (3)
a-
b-The high speed indicator diagram of pressure versus crank angle can be converted to a
plot of pressure versus piston displacement by using the geometry of the piston, the
connecting rod and the crank as shown in figure below. From figure below:
l sin Ɵ = r sin Ɵ
𝒓
Or sin Ɵ = sin Ɵ
Ɵ
𝒓
Or cos Ɵ = √𝟏 − 𝐬𝐢𝐧 Ɵ = √𝟏 − 𝐬𝐢𝐧 Ɵ
𝒍
The distance x between the crank axis and the wrist pin axis is given by
S = r cos Ɵ + l cos Ɵ
= r cos Ɵ + √𝒍 + 𝒓 𝒔𝒊𝒏 𝜽
The piston displacement from the TDC position is given by
x=l+r─s
= l + r ─ r cos Ɵ ─ √𝒍 − 𝒓 𝐬𝐢𝐧 𝜽

=r [(l ─ cos Ɵ ) + 𝒓𝒍 ─ √ 𝒓
𝒍
− 𝒔𝒊𝒏 𝜽 ]
Where
𝜽 = crank angle from the TDC position
r = crank radius
l = connecting rod length
Thus, the p-V diagram can be constructed. The area of the p-V diagram represents
the work done per cycle, from which the indicated power can be calculated.

Geometry of reciprocating engine

c-
Question (4)
a-

b- Variable speed characteristics of SI engines

Engine performance characteristics are a convenient graphical presentation of an
engine performance. They are constructed from the data obtained during actual test runs
of the engine and are particularly useful in comparing the performance of one engine with
that of another. In this section some of the important performance characteristics of the SI
engines are discussed.
It is to be noted that there is a certain speed, within the speed range of a particular
engine, at which the charge inducted per cylinder per cycle will be the maximum. At this
point, the maximum force can therefore be exerted on the piston. For all practical
purposes, the torque, or engine capacity to do work, will also be maximum at this point.
Thus, there is a particular engine speed at which the charge per cylinder per cycle is a
maximum, and at approximately this same speed, the torque of the engine will be a
maximum.
As the speed of the engine is increased above this speed the quantity of the inducted
charge will decrease. However, the power output of the engine increases with speed due to
a greater number of cycles is executed per unit time. It should be noted that the air
consumption will continue to increase with increased engine speed until some point is
reached where the charge per cylinder per stroke decreases very rapidly than the number
of strokes per unit time is increasing. Engines are so designed that the maximum air
consumption point is not reached within the operating speed of the engine. Increase in air
consumption means that increased quantities of fuel can be added per unit time increasing
the power output. In fact, the IP produced in the cylinder is almost directly proportional
to the engine air consumption.
The relationship between air charge per cylinder per cycle and torque, as well as
air consumption and IP is illustrated in Fig.2.1. Note that the maximum torque occurs at a
lower speed than the maximum IP.
 Figure 2.1 typical performance plot with respect to speed
c- the positive and negative characteristics of hybrid vehicles are:
1- positives:
a- Environmentally Friendly
b- Economical
c- Less fossil fuel dependent
d- Regulative braking system
e- Light build materials
f- Higher resale value
2- Negatives
a- Less power
b- Expensive to purchase
c- Poorer handling
d- High maintenance cost
e- High voltage battery
f- Battery disposal and recycling
g- Higher running cost
d-