QUESTION PAPER: EME-505, IC ENGINES & COMPRESSORS

FIRST MINOR TEST: IC ENGINES IN SGIT

Shree Ganpati Institute of Technology; Ghaziabad
From 23rd September, 2013 to 26th September first minor test has been organised. This semester, I am teaching IC Engines and Compressors (EME-505) and Thermodynamics (ME-301).
Here is the Question paper of EME-505

  

snapshot of the question paper
ME-301; Thermodynamics
3rd Semester; Mechanical Engg

ASSUMPTIONS CONSIDERED IN ANALYZING AIR STANDARD CYCLE:

AIR STANDARD CYCLE:

• In true sense, internal combustion engines in which combustion of fuels occurs inside the engine cylinder can not be defined as cyclic heat engines. The temperature generated during combustion is very high so that engines must be water cooled to prevent the damage of the engine due to thermal shock. The working fluid here is a mixture of air and fuel that undergoes permanent chemical changes due to combustion and the products of combustions must be exhausted and driven out of the cylinder so that fresh charges can be admitted. Therefore, it does not complete a full thermodynamic cycle.
• The engine cycle analysis is an important tool in the design and study of
• Internal Combustion Engines. 
•  A thermodynamic cycle is defined as a series of processes through which the working fluid progresses and ultimately return to the original state. 
•  Although the thermodynamic cycles are closed cycles and actual engine 
• A real thermodynamic analysis of such an engine quite complex. Hence, we simplified the operation of an I.C. Engine by introducing somewhat idealized version of a real thermodynamic processes occur inside an IC Engine, and this idealized thermodynamic cycles are called "Air standard cycle." In an air standard cycle, a certain mass of a perfect gas like air operates in a complete thermodynamic cycle, where heat is added and rejected reversibly with external heat reservoirs, and all the processes in the cycle are reversible. Air is assumed to behave like a perfect gas, and like a perfect gas, its specific heats are assumed to be constant (although they are certain functions of temperature). These air standard cycles are conceived in such a manner that they may correspond to the operations of internal combustion engines.
•  Although, there are numerous such air standard cycles, the important of them are

a) Otto Cycle (used for petrol engine)

b) Diesel Cycle (used for diesel engine)

c) Mixed, limited pressure or Dual Cycle (used for hot spot engine)

d) Stirling Cycle

e) Ericsson Cycle

To make the analysis simpler, certain assumptions are made during the analysis of air standard cycle. They are as following,

• i) The working substance is a perfect gas obeying the gas equation pV = mRT.
• ii) The working fluid is a fixed mass of air either contained in a closed system or flowing at a constant rate round a closed cycle.
• iii) The physical constants of the working fluid will be those of air.
• iv) The working medium has constant specific heats.
• v) The working media doesn't undergo any chemical change throughout the cycle.

OTTO CYCLE:

The Otto cycle is a thermodynamic cycle used in gasoline (petrol) engines to convert the chemical energy stored in fuel into useful work. It is a four-stroke cycle, consisting of four processes: intake, compression, combustion, and exhaust.

During the intake stroke, the fuel-air mixture is drawn into the engine cylinder as the piston moves downward. During the compression stroke, the mixture is compressed by the upward motion of the piston, which raises the temperature and pressure of the mixture. Near the end of the compression stroke, the spark plug ignites the mixture, causing a rapid combustion that generates a high-pressure wave that drives the piston downward, producing power. This is the power stroke. Finally, during the exhaust stroke, the spent gases are expelled from the cylinder as the piston moves upward.

The Otto cycle is an idealized model of the engine, assuming that the combustion occurs instantaneously and that there are no losses due to friction, heat transfer, or other factors. In practice, real engines operate less efficiently than the idealized model, due to these losses.

The Otto cycle is named after its inventor, Nikolaus Otto, a German engineer who patented the four-stroke engine in 1876. The cycle is widely used in modern gasoline engines, which have been refined and optimized over more than a century of development to achieve high levels of performance, efficiency, and reliability.

DIESEL CYCLE:

The Diesel cycle is a thermodynamic cycle used in diesel engines to convert the chemical energy stored in fuel into useful work. It is a four-stroke cycle, consisting of four processes: intake, compression, combustion, and exhaust.

During the intake stroke, air is drawn into the engine cylinder as the piston moves downward. During the compression stroke, the air is compressed by the upward motion of the piston, which raises the temperature and pressure of the air. Near the end of the compression stroke, fuel is injected into the cylinder, which ignites due to the high temperature and pressure of the air. The fuel-air mixture combusts, generating a high-pressure wave that drives the piston downward, producing power. This is the power stroke. Finally, during the exhaust stroke, the spent gases are expelled from the cylinder as the piston moves upward.

The Diesel cycle is similar to the Otto cycle but differs in that it does not rely on a spark plug to ignite the fuel. Instead, the fuel is injected directly into the cylinder and ignites due to the heat of the compressed air. This allows diesel engines to operate at a higher compression ratio than gasoline engines, which leads to higher efficiency and better fuel economy.

The Diesel cycle is named after Rudolf Diesel, a German inventor who patented the diesel engine in 1892. Diesel engines are widely used in a variety of applications, including cars, trucks, buses, ships, and generators. They are known for their efficiency, durability, and reliability.

Mixed, limited pressure or Dual Cycle (used for hot spot engine):

The Mixed or Dual Cycle is a thermodynamic cycle used in hot-spot engines, which are a type of internal combustion engine that combines elements of diesel and gasoline engines. The cycle is also sometimes referred to as the Limited Pressure cycle.

The Dual Cycle is a combination of the Otto and Diesel cycles. It uses the diesel combustion process, where fuel is injected directly into the cylinder and ignited by the heat of compressed air, but also includes a spark plug like in the Otto cycle. During the intake stroke, air is drawn into the cylinder, and during the compression stroke, the air is compressed to a higher pressure and temperature than in the Otto cycle. Fuel is injected into the cylinder, and the spark plug ignites the fuel-air mixture, creating a flame that spreads through the cylinder. The combustion of the fuel-air mixture produces high pressure and temperature, which drives the piston downward, producing power. Finally, during the exhaust stroke, the spent gases are expelled from the cylinder as the piston moves upward.

The Dual Cycle is designed to provide the advantages of both the diesel and gasoline engines, namely high efficiency and low emissions. It allows for a higher compression ratio than the Otto cycle, which leads to better fuel economy, while also reducing the emission of pollutants like nitrogen oxides (NOx) and particulate matter. The Dual Cycle is used in some specialized applications, such as large marine engines and certain military vehicles. However, it is not as widely used as the Otto and Diesel cycles in most everyday applications.

STERLING CYCLE:

The Stirling cycle is a thermodynamic cycle used in Stirling engines, which are a type of heat engine that converts heat energy into mechanical work. Unlike traditional internal combustion engines, Stirling engines operate on an external heat source, which can be supplied by any fuel source that can produce heat, such as wood, coal, or natural gas.

The Stirling cycle consists of four processes: heating, expansion, cooling, and compression. During the heating process, the working fluid (typically a gas such as helium or hydrogen) is heated by an external heat source, causing it to expand and drive a piston outward. During the expansion process, the expanding gas continues to drive the piston outward, producing mechanical work. During the cooling process, the working fluid is cooled by a heat sink (usually air or water), causing it to contract and pull the piston inward. Finally, during the compression process, the compressed gas is pushed back to the starting point, ready to begin the cycle again.

The Stirling cycle is designed to maximize efficiency by minimizing the losses associated with traditional internal combustion engines, such as friction and heat transfer. However, Stirling engines have a relatively low power-to-weight ratio and are less suitable for high-speed applications. They are typically used in specialized applications, such as in submarines, where quiet operation and long running times are important.

The Stirling engine was invented in the early 19th century by Robert Stirling, a Scottish clergyman, and engineer. Despite its potential benefits, the Stirling engine has not been widely adopted in mainstream applications due to its complexity and high cost compared to other types of engines. However, research and development continue to explore ways to improve the efficiency and practicality of Stirling engines.

QUESTION PAPER: ENGINEERING MECHANICS

Vivekanand Institute of Technology & Science; Ghaziabad
PRE-SEMESTER EXAMINATION (odd SEMESTER 2009-10)
B.Tech…first Semester

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Sub Name: Engineering Mechanics Max. Marks: 100
Sub Code: EME-102 Max. Time: 3: 00 Hr

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(i) This paper is in three sections, section A carries 20 marks, section B carries 30 marks and section C carries 50 marks.
(ii) Attempt all the questions. Marks are indicated against each question
(iii) Assume missing data suitably if any.

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Group A

Q.1 Answer the following questions as per the instructions 2x20=20
Choose the correct answer of the following questions:

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(i) The magnitudes of the force of friction between two bodies, one lying above the another depends upon the roughness of the
(a) Upper body;                 (b) Lower body
(c) Both the bodies               (d) The body having more roughness

(ii)The moment of inertia of a circular section of diameter D about its centroidal axis is given by the expression
(a) π(D)⁴/16               (b) π(D)⁴/32
(c) π(D)⁴/64               (d) π(D)⁴/4

Fill in the blanks in the following questions:

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(iii)The distance of the centroid of an equilateral triangle with each side(a) is …………. From any of the three sides.
(iv)Poisson’s ratio is defined as the ratio between ……………………. and
………………………… .
(v)If two forces of equal magnitudes P having an angle 2Ө between them,
then their resultant force will be equal to ________ .

Match the following columns for the following two parts:

(vi) Match the column I to an entry from the column II:

COLUMN – I	COLUMN - II
(i) BMD of an UDL	(a) stored strain energy per unit volume
(ii) Resilience is	(b) brittle materials
(iii) Bulk Modulus	(c) parabolic in nature
(iv) Yield Point	(d) volumetric stress & strain
	(e) Ductile materials
	(f) Shear stress

(vii) Match the Following columns:

COLUMN – I	COLUMN - II
(i) Square of side (b)	(p) π b4 / 64
(ii) Equilateral Triangle of side (b)	(q) b4 / 12
(iii) Circle of diameter (b)	(r) b4/ 36
(iv) Isosceles right angle triangle of base (b)	(s) b4/(32√3)
	(e) Ductile materials
	(f) Shear stress

Column II gives the value of Moment of Inertia Ixx about a centroidal axis.

Choose correct answer for the following parts:

(viii) Statement 1:
In stress strain graph of a ductile material, yield point starts at the end of
the elastic limit.

Statement 2:
At yielding point, the deformation becomes plastic by nature.

(i) Statement 1 is true, Statement 2 is true.
(ii) Statement 1 is true, Statement 2 is true and they are unrelated with
each other
(iii) Statement 1 is true, statement 2 is false.
(iv) Statement 1 is false, Statement 2 is false.

(ix) Statement 1:
It is easier to pull a body on a rough surface than to push the body on
the same surface.

Statement 2:
Frictional force always depends upon the magnitude of the normal force.

(i) Statement 1 is true, Statement 2 is true.
(ii) Statement 1 is true, Statement 2 is true and they are unrelated with
each other
(iii) Statement 1 is true, statement 2 is false.
(iv) Statement 1 is false, Statement 2 is false.

Choose the correct word/s.
(x) Two equal and opposite force acting at different points of a rigid body
is termed as (Bending Moment/ Torque/ Couple).

SECTION-B

Q.2: Answer any three parts of the followings: 10X3=30

(a)	Find the shear force and moment equation for the beam as shown in the figure. Also sketch SFD (shear force diagram) and BMD (bending moment diagram)
(b) Explain and prove “the parallel axis theorem of moment of inertia.” Also find the centroid of the following composite area.
(c) Find the centroidal Moment of Inertia of the following shaded area.
	(d) Two cylinders P and Q rest in a channel as shown in fig. below. The cylinder P has a diameter of 100 mm and weighs 200 kN, where as the cylinder Q has a diameter of 180 mm and weighs 500 kN. Find the support reactions at all the point of contact.
(e)	Two blocks A and B of weights 1 kN and 2 kN respectively are in equilibrium as Shown in the figure. If the co-efficient of friction everywhere is 0.3, find the force P required to move the block B.

SECTION C:

(3) Answer any two parts of the following 5X2=10

(a) A simply supported beam of 2 cm wide and 4 cm high having a length 2 m long
in concentrated load of 3 kN (acting perpendicular to the axis of beam) at a point
0.5 m from one of the supports. Determine
(i) the maximum fiber stress (σb max); (ii) the stress in a fiber located at a
distance of 1 cm from the top of the beam at mid-span.

(b) Explain and justify the assumptions taken during analysis of a perfect truss.

(c)A flywheel is making 180 rpm and after 20 second it is running at 120 rpm.
How many revolutions will it make and what time will elapse before it stops, if the retardation is constant.


(4) Answer any one part of the following: 1X10=10

(a) Explain the terms angular momentum and radius of gyration.
A wheel rotates for 5 seconds with a constant angular acceleration and
describes during this time 100 rotations. It then rotates with a constant angular
velocity and during the next five seconds describes 80 radians. Find the initial
angular velocity and the angular acceleration.

(b) Analyse the following truss:



(5) Answer any three question;                           3X10=30

(a) Compare the stress – strain diagrams of a ductile material to that of a brittle Material. Also explain the term bulk modulus and modulus of elasticity.

(b) Explain and prove the “Bending Equation” (M/I)=(б/y)=(E/ρ). What is
called as Section Modulus?

(c) A cylinder of radius R, length L and total mass M is suspended vertically
from the floor, if the modulus of elasticity of the cylinder be E, find the total
deflection and maximum stress induced in the cylinder.

(d) A cylinder of 200 mm diameter is subjected to a twisting moment of
250 kN-m, the length of the cylinders is 1 m, if the modulus of rigidity of the
cylinder material be 150 GPa, find the maximum shear stress induced in the
cylinder. Also find the total angular deformation.