Ice Qb_mech_6th_2018_02.docx

Santosh Rungta Group of Institutions

Question Bank

Branch

Mechanical Engineering

Semester

VI

Subject

Internal Combustion Engine

Subject Code

337653(37)

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Santosh Rungta Group of Institutions

Department of Mechanical Engineering Unit - I 1

From point of view of fuel air cycle analysis how does fuel air ratio effect efficiency, 8 maximum power, temperature and pressure in cycle?

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What are the reasons for differing the actual P-V diagram from ideal diagram?

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Discuss the dissociation loss and time losses? 3

State briefly construction, working and advantages of using Wankel rotary engine. Five 8 suitable sketch?

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Compare the following: a) Four stroke engines and two stroke engines

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b) S.I and C.I engines 5

Draw and explain valve timing diagram of four stroke petrol engine? Why the valves

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are opened before dead center and closed after dead center? 6

Explain valve timing diagram for two stroke diesel engine? Mention effect of valve

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timing and engine speed on volumetric efficiency of engines both S.I and C.I 7

The air fuel ratio of a diesel engine is 29:1. If the compression ratio is 16:1 and the

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temperature at the end of compression is 900K, find at what percentage of stroke is the combustion completed? Assume that the combustion begins at the top dead centre and takes place at constant temperature. Take calorific value of fuel as 48000KJ/Kg, R= 0.29KJ/KgK for gas and Cv= (0.71+18x10-5T )KJ/Kg K. 8

Show that the compression ratio for the maximum work to be done per second per 8 kilogram in an otto cycle engine between upper and lower limits of absolute 𝑇

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temperatures T3& T1 is given by 𝑅𝑐 = (𝑇3 )2(𝛾−1) 1

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What is supercharging? How is it achieved? Explain the thermodynamic cycle of 8 naturally aspirated engine and supercharged engine?

10

What is scavenging? What is exhaust blow down loss? Discuss the optimum opening 8 2

Santosh Rungta Group of Institutions position of exhaust valve to reduce this loss. What is pumping loss? 11

Discuss briefly the effect of compression ratio and mixture strength on thermal 8 efficiency. Also discuss the effect of variation of specific heat on cycle efficiency.

12

What is dual fuel? Define volumetric efficiency and relative efficiency? What is normal 8 range of compression ratio for S.I engine and C.I engine? Define mean effective pressure and specific fuel consumption?

Unit - II 13

Explain effect of fuel volatility on engine performance with reference to efficiency, 8 volumetric efficiency, carburetor icing, percolation and crank case dilution?

14

Explain the difference between detonation and preignition. Define octane number and 8 cetane number? What is surface ignition and cause of surface ignition?

15

Explain with suitable sketches the combustion phenomena in S.I engines and explain 8 the three stages of combustion in S.I engines?

16

Explain in detail the combustion in C.I engine with all phases?

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17

Explain what is meant by detonation, knocking and preignition. What is antiknock

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rating of fuel and how it is used in deciding octane number and cetane number? 18

Define HUCR,CCR, performance number and cetane number?

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19

A mixture of octane vapor(C8H18)and air is supplied to a petrol engine. The measured

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amount of CO2 is 13% by volume in the dry exhaust gases by volume. Assuming the combustion is complete, find out A:F ratio by volume and express this as a percentage of stoichiometric ratio. 20

A petrol used in S.I engine contains 84% carbon 16% H2 by mass. The dry exhaust gas 8 analysis showed that there is no CO and volume of CO2 was 4 times the volume of O2 in the exhaust. Determine (i) A:F ratio used by mass supplied to engine (ii) % excess air supplied air contains 77% N2 and 23% O2 by mass

21

Explain how proper fuel air mixing is achieved in diesel engines. What is detonation 8 and how does it occur. How detonation can be prevented?

22

Discuss the effect of fuel structure on knocking. What do you understand by cetane 8 number 52? 3

Santosh Rungta Group of Institutions 23

Explain the phenomenon of diesel knock with the help of pressure crank angle diagram. 8 How do injection timing and the fuel quality affect the engine knock?

24

The mixture of hexane C6H14 and air is supplied to an IC engine. Determine the 8 theoretical mass of air required for the complete combustion of one kg of fuel. Also Estimate the composition of the products formed by volume if the mixture is 25% rich. Air contains 23% O2 and 77% N2 by Mass.

Unit - III 25

Prove that in case of simple carburetor that the mixture becomes progressively richer 8 with increasing air flow or increasing altitude?

26

Why a very rich mixture is required for idling? Describe with suitable sketch idling 8 system of a carburetor?

27

Discuss the air fuel mixture requirement for normal power range. Describe with 8 suitable sketch the compensating jet device of modern carburetor?

28

What is petrol injection? What are its advantages and disadvantages

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29

Determine the size of fuel orifice to give A:F=12:1. The diameter of venturi throat is

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3.5cm and vacuum at the venturi is 6.9cm of Hg. The pressure and temperature of atmospheric air ore 1.013 bar and 25C. the nozzle lip=5mm Take the following Cda=0.9,Cdf=0.7 and ef=760kg/m3. Consider the compressibility of air 30

The diameter of venture throat and fuel nozzle of a carburetor are 8 cm and 5 mm

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respectively. The coefficients of discharge for air and fuel are 0.9 and 0.7 respectively. Assuming the density of air 1.3 kg/m3 and density of fuel 700 kg/m3. Find the following a) Velocity of air and mass flow of air through the carburetor b) Velocity of fuel and mass flow of fuel through the carburetor. c) A:F Ratio supplied by carburetor ( Neglect the nozzle lip and air compressibility. Assume head causing the flow as 100 cm of water) d) If the nozzle lip is 5 mm then find out A:F for above given data e) If the head causing the flow during idling is 2 cm of water, then find A:F ratio considering the lip. 4

Santosh Rungta Group of Institutions 31

A 4 cylinder, 4 stroke engine running at 2000 rpm is provided with a carburetor whose

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venturi throat is 3 cm. find the suction at the throat assuming the volumetric efficiency of the engine is 0.7. Take ρa = 1.2 kg/m3 and Cda = 0.8 and atmospheric pressure is 1.013 bar. Stroke and diameter of the engine cylinder are 12 cm and 10 cm respectively. 32

Describe any modern carburetor?

33

Explain why a very rich mixture is required for sudden acceleration. Describe with 8

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suitable sketch the acceleration system of a modern carburetor? 34

Discuss the air fuel ratio requirements of a petrol engine from no load to full load?

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What do you mean by MPFI system? What do you mean by nozzle lip? What are the 8

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factors affecting carburetion?

Unit - IV 36

What do you understand by ignition? Describe the battery ignition system with the help 8 of sketch?

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What do you mean by governing of I.C engine? Explain governing methods used for 8 S.I engine and C.I engines?

38

Define wet sump lubrication. What are their varieties? Explain anyone with suitable 8 figure

39

Discuss with circuit diagram of battery ignition system. Write the operation vacuum

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ignition advance? 40

Describe the battery and magneto system by separate figures and make comparison of

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advantages and disadvantages? 41

Describe dry sump and wet sump lubrication system for I.C engines. What is antifreeze

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mixture for coolants and where it is used? 42

Why cooling of an I.C engine is necessary? Discuss the disadvantages of overcooling?

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Describe with a sketch thermostatically controlled forced circulation system? 43

Compare merits and demerits of air and water cooling systems?

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44

Describe the types of diesel injection system?

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45

Discuss the function of the lubrication system in an engine and describe a typical mist 8 5

Santosh Rungta Group of Institutions lubrication system used for a two stroke engine? 46

What are the three main types of fuel injectors? Describe a typical automatic injector 8 with the help of neat sketch?

Unit - V 47

What do you mean by heat balance sheet of an I.C engine? Sketch heat balance curve 8 for a S.I engine at constant speed and discuss the nature of curves

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Sketch a typical variable speed test performance curves (I.P vs. speed, B.P vs. speed) at 8 full throttle of spark ignition engine and comment on the nature of curves

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Following data were obtained from a test on a single cylinder 4 stroke single cylinder 8 oil engine: Cylinder bore = 15 cm, stroke 25 cm, area of indicator diameter =450 sq. mm, Length of the indicator diagram =50mm, indicator spring rating = 1.2 mm for a pressure of 9.81 N/cm2, Engine Speed = 400 rpm, Brake torque = 225 Nm, Fuel consumption = 3 kg/ hr, Calorific value of fuel = 44200 kJ/kg, Cooling water flow rate = 4 kg/min, Cooling water temperature rise = 42 Deg C, find the following a) The Mechanical Efficiency b) The Brake thermal efficiency c) The Specific fuel consumption d) Draw the heat balance

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A 4 stroke gas engine has a diameter of 270 mm and stroke of 450 mm. The effective

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diameter of the brake wheel is 1620 mm. The observation made during test of the engine were as follows: Duration of the test = 38 mm, Total Number of Revolution = 8170, Total number of explosions = 3266, Net load on the break = 100 kgf, Mean Effective pressure = 5.75 bar, Gas Used = 8.0 m3, Pressure of Gas = 135mm of water above atmospheric pressure, Temperature of the Gas = 27 Deg. C, Height of Barometer = 750.06 mm Hg, Calorific value of gas = 18422 kj/m3 at NTP, mass of jacket cooling water = 183 kg, Rise in temperature of cooling water = 47 Deg. C Draw the heat balance sheet and calculate the indicated and brake thermal efficiency. 6

Santosh Rungta Group of Institutions 51

Explain the performance of I.C engine in respect of B.H.P, I.H.P, air consumption, fuel

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consumption, load and speed. 52

What are the methods of measurement of friction power of an I.C engine? Describe 8 Willian’s line method to find out friction power. To which type of engine is it applicable? What is accuracy of this method?

53

Define the following: (i) Indicated thermal efficiency (ii) Mechanical efficiency

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(iii) Brake thermal efficiency. What is the relation between the three? 54

An S.I engine has a fuel air ratio of 0.007:1. How many kilograms of air per hour are 8 required for an output of 75W at an overall efficiency of 20%? How many m3 of air are required per hour if the density of air is 1.2kg/m 3? If the fuel vapor has a density four time that of air, how many m3 per hour of the mixture is required? The calorific value of the fuel is 43700 kJ/kg.

55

A six cylinder, gasoline engine operates on the four stroke cycle. The bore of each 8 cylinder is 80mm and the stroke 100mm. The clearance volume per cylinder is 70cc. At a speed of 4000rpm the fuel consumption is 20kg/h and the torque developed is 150 Nm. Calculate: (i) The brake power (ii) The brake mean effective pressure (iii) Brake thermal efficiency if the calorific value of the fuel is 43000KJ/Kg (iv) The relative efficiency on a brake power basis assuming the engine works on the constant volume cycle. γ=1.4 for air.

56

Define Morse test. What are the assumptions made in this test?

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Discuss in brief S.I engine emissions. What are its effects on human health and 8

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biosphere? 58

Discuss the various methods of control for exhaust emission from petrol engines?

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Santosh Rungta Group of Institutions

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