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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