Mechanical Engineering Written Exam Questions (BOF, Year-2016)
Kelvin-Plank Statement: It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy from a single thermal reservoir into an equivalent amount of work.
Clausius Statement: It is impossible for a self acting machine working on a cyclic process, to transfer heat from a body at a lower temperature to a body at a higher temperature without the aid of an external agency.
Fire tube boiler | Water tube boiler | |
1 | In Fire-tube boilers hot flue gases pass through tubes and water is surrounds them. | In Water-tube boilers water passes through tubes and hot flue gasses is surround them. |
2 | The working pressure is low up to 20 bar. | The working pressure is high enough, up to 250 bar. |
3 | The steam generation rate and quality of steam are very low, therefore, not suitable for power generation. | The steam generation rate and quality of steam are better and suitable for power generation. |
4 | It is generally internally fired. | It is externally fired. |
5 | It occupies more floor area for a given output. | It occupies less floor area for a given output. |
6 | These are bulky and transportation is difficult. | These are light in weight, hence transportation is simple. |
7 | Its overall efficiency is up to 75%. | Its overall efficiency with an economizer is up to 90%. |
8 | Water treatment is not necessary. | Water treatment is necessary. |
9 | The drum size is large and damage caused by bursting is large. | If any water tube is damaged, it can be easily replaced or repaired. |
10 | The bursting chance of fire tube boiler is less. | The bursting chance of water tube boiler is more. |
11 | Simple in design, easy to erect and low maintenance cost. | Complex, design, difficult to erect and high maintenance cost. |
12 | Skilled operators are not necessary for efficient operation. | Skilled operators are required for efficient operation. |
13 | Its operating cost is less. | Its operating cost is more |
14 | Fire tube boiler is used in process industry. | Water tube boiler is used in large power plants. |
→ EFI = Electronic Fuel Injection
→ VVT = Variable Valve Timing
→ VVTI = Variable Valve Timing with Intelligence
→ ABS = Anti Lock Braking System
→ VTEC = Variable Valve Timing and Lift Electronic Control
❖ ❖ Describe
the Cetane number and Octane number.
Cetane Number: (For more details, click here)
→ The percentage, by volume, of cetane in a mixture of cetane and alpha-methyl naphthalene that produces the same ignitions lag as the fuel tested, in the same engine and under the same operating conditions is termed as the cetane number rating of that fuel.
→ The cetane number of Diesel oil, generally available is 40 to 55.
→ For examples: If a fuel has cetane number 45, it means that the fuel is having the same ignition quality as a mixture of 45% cetane & 55% α-methyl naphthalene by volume.
Octane Number: (For more details, click here)
→ The percentage, by volume of, iso-octane in a mixture of iso-octane and normal heptane, which exactly matches the knocking intensity of a given fuel, in a standard engine, under given standard operating conditions, is termed as the octane number rating of that fuel.
→ Octane number for Petrol, generally available is 80 to 100.
→ Octane Number of Natural gas is 130.
→ For examples: If a fuel has octane number as 80 it means that the fuel is having the same knocking tendency as a mixture of 80% iso-octane and 20% n-haptane by volume.
❖❖ What are the difference between reciprocating and rotary Engine?
❖❖ Write down the significance of Mohr’s Circle?
❖❖ What is difference between nominal stress and true stress?
❖❖ What is difference between nominal stress and true stress?
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