Advanced IC engines notes PPT

Anna University- Chennai

Department of Mechanical Engineering

Subject : Advanced IC Engines

This post is useful for the students from Mechanical Engineering for the subject of Advanced IC engines as well as for IC Engines if you go to higher study.

The following images covers the Compression ignition engines which is the second unit of Advanced IC engines.

The following contents about the CI engines were discussed from the following images. Make download for your reference which will be more useful for understanding the concepts of Compression Ignition Engines.

UNIT 2

COMPRESSION IGNITION ENGINES

CONTENTS

- Stages of combustion-normal and abnormal combustion

-Direct and Indirect injection systems

-Turbocharger

-Factors afecting knock

-Thermodynamic analysis of CI Engine combustion process.

STAGES OF COMBUSTION:

•    Stages of combustion can be divided into four stages namely,
• —  Pre-flame combustion
• —  Uncontrolled combustion
• —  Controlled combustion and
• —  After burning

   Pre-flame combustion

•    At the beginning of pre-flame combustion, the energy release rate is very less than rate of heat absorption by the fuel because the amount of fuel vapour is small. As a result, the pressure in the cylinder decreases with the progressive fuel vaporization. 
•     This decrease in pressure attains a maximum value when the energy release due to pre-flame reaction is equal to the rate of heat absorption by the fuel. This process of fuel vaporization and subsequent decrease in pressure in the cylinder is shown on fig by paths ‘ab’.

Uncontrolled combustion:
    A considerable amount of fuel is accumulated in the combustion chamber during the relay period (time between the start of injection of fuel and start of ignition of fuel).

    This accumulated fuel burns very rapidly causing a steep raise in the cylinder pressure. The rate of pressure raise increases with the increase in delay period because of the amount of fuel taking part in this combustion increase with an increasing delay period.

    This phase of combustion causing rapid pressure raise in the cylinder is known as “period of uncontrolled combustion”.

      

Controlled combustion

   All the accumulated fuel during the delay period generally burns during the period of controlled combustion. The fuel injected after this (after point d) burns at the same rate at which it is injected because, the vaporisation of fuel, mixing with the air and burning takes place almost instantaneously as the fuel leaves the nozzle.

   This is because, the temperature and pressure inside the cylinder are sufficiently high and sufficient turbulence is created due to precious burning, thus the delay period for the fuel injected after point “d” is almost zero. This period of combustion is known as “controlled combustion” because the rate of burning can be controlled by controlling the rate of injection. 

  After burning:

   The thermal decomposition of the part of fuel takes place during uncontrolled and controlled combustion. 

  The decomposed fuel molecules contain enough number of hydrocarbons and carbon particles which has lower reaction rates. 

  Some carbon and hydro carbon, decomposed from fuel are left in the combustion product because the rate of decomposition during uncontrolled and controlled combustion is more than the rate of reaction of these molecules during that period. 

   These unburned hydrocarbons and carbon generally burn after stopping the fuel injection during the expansion stroke. This process of combustion of decomposed carbon atoms is known as “after burning”.

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Advanced IC engines question bank

This Post contains Question bank ( 2 marks questions with answers and 16 marks questions) for BE-Mechanical Engineering VIII th Semester ,Automobile Engineering , IC Engines .

ME 2041 – ADVANCED IC ENGINES

         

Part-A (Two Marks Questions with answers

         

                             UNIT – 1    SPARK IGNITION ENGINES

          1. What are the stages of combustion in a SI engines?

         

          The stages of combustion in a SI engines are:

                    First Stage: Ignition lag (or) preparation phase

                    Second Stage: propagation of flame

                    Third Stage: After burning

         

          2. What are the various factors that affect the flame speed?

         

a) Turbulence

 b) A/F ratio

          c) Temperature (T), Pressure (P)

          d) Compression ratio

          e) Engine speed, size & output

         

          3. Define normal combustion?

         

In normal combustion, the flame initiated by the spark travels across the combustion chamber in a fairly uniform manner.

         

          4. Define abnormal combustion and its consequences?

Under certain operating conditions the combustion deviates from its normal Course leading to loss of performance and possible damage to the engine are termed as abnormal combustion (or) knocking combustion.

Consequences are

(1). Loss of power

(2). Recurring preignition

(3). Mechanical damage to the engine

         

         

5. What is equivalence ratio?

         

The ratio of the actual fuel-air ratio to the stoichiometric fuel –air ratio.

         

          6. Short note on SI engine equivalence ratio requirements?

         

          In a homogeneous mixture with equivalence ratio close to 1.0 the flame speed is normally of the order of 40cm/s .However in a SI engine the maximum flame speed is obtained when φ is between 1.1 and 1.2 (i.e.) when the mixture is slightly richer than stoichiometric.

         

          7. Write the desirable qualities for SI engine fuel?

         

          In order to avoid or inhibit detonation, a high auto ignition temperature and a long ignition lag are the desirable qualities for SI engine fuel.

         

          8. Explain the type of vibration produced when auto ignition occurs.

         

          Two different vibrations are produced.

          1. In one case, a large amount of mixture may auto ignite giving use to a very rapid increase in pressure throughout the chamber and there will be a direct blow on free vibration of the engine parts.

2. In another case, larger pressure differences may exit in the combustion chamber and the resulting gas vibration can force the walls of the chamber to vibrate at the

          same frequency as the gas.

          9. What is the method to detect the phenomenon of knocking?

         

          The scientific method to detect the phenomenon of knocking is to use a pressure transfer this transducer is connected, usually to a cathode ray oscilloscope. Thus pressure-time traces can be obtained from the pressure transducer.

         

          10. List out some of the knock limited parameters?

         

          1. Knock limited compression ratio

          2. Knock limited into pressure

3. Knock limited Indicated mean effective pressure. (Klimep)

          11. Define performance number?

         

          Performance number is defined as the ratio. Of Knock limited Indicated mean effective pressure with the sample fuel to knock limited Indicated mean effective pressure with ISO-OCTANE,when the inlet pressure is kept constant.

         

12. List the factors that are involved in either producing (or) preventing knock.

         

The factors that are involved in either producing (or) preventing knock are temperature, pressure, density of the unburned charge and the time factor.

         

          13. List the parameters which are affecting knock in SI engine?

         

          The parameters which are directly (or) indirectly connected with knocking are inlet temperature of mixture compression ratio, mass of inducted charge, power output of the engine.

         

          14. List the parameters in time factors that reduce the knocking?

         

          (1)turbulence,

(2)engine speed,

(3)flame travel distance,

(4)combustionchamber shape and

                   (5)location of spark plug.

         

          15. List the composition factors in the knocking?

         

                    (1)Air –fuel ratio and

(2)octane value of the fuel are the composition factors.

         

16. What are the objectives to be kept in mind during design of combustion chamber?

         

          General objectives are 

                    (a) Smooth engine operation

                    (b) Moderate rate of pressure rise

                    (c) Reducing the possibility of knocking

          (d) High power output and

(e)thermal efficiency

         

17. What are the factors to be considered to obtain high thermal efficiency?

         

          Following are the factors:

         

                    1. A high volumetric efficiency.

2. Anti knock characteristic must be improved.

                    3. Compact combustion chamber reduces heat loss during combustion

                    increases the thermal efficiency.

         

         

          18. Write the different types of combustion chambering SI engine? 

         

                    (1)L-Head type,

(2) I- Head type,     (Assume LIFT)

(3)F- Head type,

(4) T- Head type.

         

          19. What are the components required in the fuel injection system?

         

                    (1)pumping element,

(2)metering element,

(3)mixing element,

                    (4)distributing element,

(5)Timing control, and

(6)ambient control.

         

         

20. What are the advantages of fuel –injection in an SI engine?

         

                    1. Increased volumetric efficiency.

                    2. Better thermal efficiency

                    3. Lower exhaust emissions

                    4. High quality fuel distribution.

         

          21. List the drawbacks of the carburetion?

         

                    1. Non uniform distribution of mixture in multi cylinder engines.

2. Loss of volumetric efficiency due to retraction for mixture flow and possibility of back firing.

         

          22. What are the functional requirements of an injection system?

         

          1. Accurate mixing of the fuel injected per cycle.

2. Timing the injection of the fuel.

                    3. Proper atomization of fuel into fine droplets

                    4. Proper spray pattern.

                    5. No lag during beginning and end of injection.

         

23. List some of the important requirements of an automobile carburetors?

         

1. Ease of starting the engine, particularly under low ambient conditions.

                    2. Good and quick acceleration of the engine.

                    3. Good fuel economy.

                    4. Ensuring full torque at low speeds.

         

          24. What are the general types of carburetors?

         

          Types are

1.Up Draught,

2.Down Draught, and

3.Cross Draught.

         

25. What are the essential parts, compensating device and additional system (modern) carburetors?

Parts

·         fuel strainer,

·        float chamber,

·        main metering and idling system,

·        the choke &the throttle.

Compensating device-

·        Air –bleed jet,

·        compensating jet,

·        Emulsion tube,

·        auxiliary valve and port,

·        back suction control mechanism.

         

          Additional system –

§  Ant dieseling,

§  richer coasting,

§  acceleration pump and

§  economic (or) power enrichment system.

         

         

          26. Define carburetion?

         

          The process of formation of a combustible fuel –air mixture by mixing the proper amount of fuel with air before admission to engine cylinder is called carburetion.

         

         

          27. What are the factors effecting carburetion?

         

                    1. The engine speed

         

                    2. The vaporization characteristic of fuel

         

                    3. The temperature of the incoming air

         

                    4. The design of the carburetor

         

         

28. What are the different types air –fuel mixtures?

         

                    1.Chemically correct mixture

2. Rich mixture

3. lean mixture.

         

          29. What are the different range of throttle operation?

         

                    1. Idling

2. cruising

3. High power .

Part- B

         

         

UNIT- I

         

          1. Discuses why a modern carburetor is being replaced by an injection system in SI engine?

         

          2. Explain the factors that affect the process of carburetion?

         

          3. What are different air –fuel mixture on which an engine can be operated?

         

          4. Explain the following1. Rich mixture, 2. Stoichiometric mixture 3. Lean mixture.

         

          5. How the power and efficiency of the SI engine vary with air- fuel ratio for different load and speed conditions?

         

          6. By means of suitable graph explain the necessary carburetor performance to fulfill engine requirements?

         

          7. Explain why a rich mixture is required for the following 1. Idling 2. Maximum power and sudden acceleration.

         

          8. Describe briefly the MPFI system with a neat sketch?

         

          9. Explain port injection and throttle body injection system?

         

          10. Describe D- MPFI and L-MPFI injection system?

         

          11. Briefly explain the stages of combustion in SI engines elaborating the flame front Propagation

         

          12. Explain the various factors that influence the phenomena of knock in SI engines?

          13. Explain the effete of various engine variables on SI engine knock.

         

          14. What are the various types of combustion chamber s used in SI engines? Explain them briefly? 


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