The document contains questions and answers related to thermodynamics, engines, and mechanical engineering topics. Some key points addressed include: - The laws of thermodynamics including the zeroth, first, second, and third laws. - Octane and cetane numbers which are measures of rating for gasoline and diesel engines. - A differential mechanism is used in automobile gearing systems. - A real gas behaves like an ideal gas under conditions of low pressure and high temperature. - Thermodynamics deals with systems in equilibrium while heat transfer deals with energy transfer and can be out of equilibrium.

1. Q. Explain the Laws of Thermodynamics?
Ans: Zeroth law: If any two systems are in thermal equilibrium with the third system, then
they are also in thermal equilibrium with each other.
First law: First law of thermodynamic states that energy can neither be created nor be
destroyed but it can only be converted from one form to another.
Second law: This law states that “all processes in nature tend to occur with an increase in
entropy and the direction of change always lead to the increase in entropy.”
Third law: This law states that “The entropy of a perfect crystal of each element and a
compound is zero at absolute zero.”
Q. Definition of Octane Number and Cetane Number?
Ans: Octane No:-Octane number is defined as the percentage, by volume, of iso octane in
the mixture of iso octane and h-heptane. It is the measure of rating of SI engine.
Cetane No: - Cetane number is defined as the percentage, by volume, of n-cetane in the
mixture of n-cetane and alpha methyl naphthalene. It is the measure of rating of CI engine.
Q. Which Mechanism Is Used in Automobile Gearing System?
Ans: Differential mechanism
Q. How to Calculate Bearing Number Ti Diameter of The Inner and Outer?
Ans: Divide the shaft diameter size by 5, it will give last two digits of the bearing no. and
according to type of load we have to choose the type of bearing and that will give prior
number of the bearing.
Q. What Happens If Gasoline Is Used in A Diesel Engine, Diesel Engine Will Work?
Ans: No, it will not work, as the Compression ratio of Petrol engine is 6 to 10 & that of
Diesel engine is 15 to 22. Thus, on such high compression, gasoline gets highly compressed
& it may blast.

2. Q. When A Real Gas Behaves Like Ideal Gas?
Ans: A real gas behaves like an ideal gas in low pressure and high temperature conditions.
Q. What Is the Difference Between Heat Transfer and Thermodynamics?
Ans: Heat transfer deals with the energy analysis which in transition and depends on the
modes of heat transfer like conduction, convection and radiation or combination of any
modes. Heat transfer deals in non-equilibrium domain and conditions while thermodynamics
deals with study of system at equilibrium and does not depend on how heat transfer is
calculated.
Q. At Which Temperature Thermal Radiation Can Become Zero?
Ans: Not possible. Because thermal radiation becomes only zero at absolute zero
temperature which can never be attained by the third law of thermodynamics.
Q. Difference Between Tube and Pipe?
Ans: There always a debate between differentiation of pipe and tube.
o Pipe is always designated by its Inside Diameter (ID) because main purpose of pipe is to
carry fluid, while the
o Tube is always designated by its Outside Diameter (OD). Pipe's thickness is sometimes called
as schedule and tube's thickness is gauge.
o As per the tolerance basis, tubes require higher tolerances as to that of pipe and tubes are
costlier in manufacturing compared to pipe production.
Q. Difference Between Flywheel and Governor?
Ans: The function of flywheel is to store the energy/power produced during the power
stroke of an engine and this stored energy is used during remaining stroke to make piston up
and down during working of engine while governor tries control the speed of an engine due
to variation in load. It does this work by reducing or increasing the amount of fuel passing to
the engine.

3. Q. What Is the Importance of The Thermodynamics in The Field of Mechanical
Engineering?
Ans: All the mechanical engineering systems are studied with the help of thermodynamics.
Hence it is very important for the mechanical engineers.
Q. What Is Carnot Engine?
Ans: It was being designed by Carnot and let me tell you that Carnot engine is an
imaginary engine which follows the Carnot cycle and provides 100% efficiency.
Q. Which Has More Efficiency: Diesel Engine or Petrol Engines?
Ans: Off course Diesel engine has the better efficiency out of two.
Q. What Is Bending Moment?
Ans: When a moment is applied to bend an element, a bending moment exists in the
element.
Q. What Are the Points in The Stress Strain Curve for Steel?
Ans: Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.
Q. Define Reynolds Number.?
Ans: Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless
number. It determines the type of fluid flow.
Q. Explain the Nomenclature of A 6203-zz Bearing?
Ans: 6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means
light, 03 is the bore, which is 17 mm and ZZ is the suffix meaning double shielded bearing.
Q. What Is Gear Ratio?
Ans: It is the ratio of the number of revolutions of the pinion gear to one revolution of the
idler gear.

4. Q. What Is Annealing?
Ans: It is a process of heating a material above the re-crystallization temperature and
cooling after a specific time interval. This increases the hardness and strength if the material.
Q. What are the names given to (A) Constant temperature, (B) Constant pressure,
(C) Constant volume, (D) Constant Internal Energy, (E) Constant Enthalpy, and (F)
Constant Entropy Processes?
Ans: (A) Isothermal, (B) Isochoric, (C) Isochoric, (D) Free expression, (E) Throttling and (F)
Adiabatic processes respectively.
Q. Enthalpy and entropy are functions of one single parameter. Which is that?
Ans: Temperature.
Q. What is the compression ratio for petrol engines?
Ans: 5 to 8
Q. Why different types of sound are produced in different bikes, though they run on
SI Engines?
Ans: Engine specifications are different manufactures like as bore diameter (CC), Ignition
timing. Also, the exhaust passage takes more responsible for sound.
Q. How much watt means 1HP?
Ans: 746.2 Watts.