COMPONENTS OF AN IC ENGINE

COMPONENTS OF AN IC ENGINE

ABOUT THE ENGINE:

     An Engine is a mechanical system which transforms heat energy into mechanical energy using fuel.

   At one time the word, “Engine” (from Latin, via Old French, ingenious, “ability” meant any piece of machinery – a sense that persists in expressions such as “siege engine”. A “motor” is any machine that produces mechanical power. Traditionally, electric motors are not referred to as ‘Engines’; however, combustion engines are often referred to as motors.

   Internal combustion engines are most commonly used for mobile propulsions in vehicles and portable machinery. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel, these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in wide variety of aircrafts and locomotives).

   Where very low power-to-weight ratios are not required, internal combustion engines appear in the form of gas turbines. These applications include jet aircrafts, helicopters, large ships and generators.

   We are all aware that heat engine is used to convert heat energy to mechanical work in a cyclic process as per second law of thermodynamics. But the engine in which the combustion of fuel (liquid or gas) takes place inside the cylinder known as internal combustion engine briefly known as I.C Engines. I.C Engines working fluid is mixture of air-fuel.

Heat engines are classified into two types:
 External combustion engines

      Internal combustion engines

 In case of external combustion engines, the combustion of fuel takes place outside the cylinder.

    Eg. : steam engines, steam turbines, gas turbines etc.

  The steam is made to act on the piston of steam cylinder/blades of steam turbine.

                      Combustion phenomenon in I.C. Engine is complex. Therefore it is essential to know the stages of combustion in S.I and C.I engines. In the study of combustion in I.C engines we come across with the phenomenon is harmful to engine. Therefore we have to study the effects and remedies of detonations. Similarly for reducing the knock we have to study the characteristics of fuels i.e. Octane number and Cetane number. For effective combustion and effective running of I.C engine proper designed combustion chamber is required.

CLASSIFICATIONS OF I.C ENGINES:

    The Internal Combustion Engines may be classified on the basis of following factors:

              According to Type of Fuel used:

    Petrol Engines

    Diesel Engines

   Gas Engines

     According to the Method of Ignition:

     Spark Ignition Engines (S.I Engines)

    Compression Ignition Engines (C.I Engines)

     Hot – Spot Ignition Engines

    According to the Number of Strokes per Cycle:

    Four Stroke Engines

    Two Stroke Engines

    According to the Working Cycle:

    Otto Cycle Engine

    Diesel Cycle Engine Dual Combustion Cycle Engine

     Dual Combustion Cycle Engine

   According to the Number of Cylinders used:

    Single Cylinder Engine

    Multi  Cylinder Engine

    According to Arrangement of Cylinders:

    Horizontal Engine

    Vertical Engine

     Radial Engine

    Opposite Cylinder Engine

    V - Engine

    According to the Method of Fuel Ignition:

    Carburettor Engine

    Air Injection Engine

     Air less Injection or Solid Injection

    According to the type of Cooling System:

    Air Cooled Engine

    Water Cooled Engine

              According to Speed of the Engine:

    Slow Speed Engine

    Medium Speed Engine

     High Speed Engine

              According to the Valve Location:

    Over Head Valve Engine

    Side Valve Engine

          According to the Method of Governing:

    Qualitative Governing Engine

    Quantitative Governing Engine

    Hit and Miss Governing Engine

         According to the Field of Application:

    Stationary Engines

    Automotive Engines

     Marine Engines

    Air craft Engines

    Locomotive Engines

 

PARTS IN INTERNAL COMBUSTION ENGINE:

   Cylinder Block: The cylinder block is the main supporting structure for the various components. The cylinders of a multi cylinder engine are cast as a single unit, called cylinder block. The cylinder head is mounted on the cylinder block. The cylinder block is provided with water jackets in the case of water cooling are with cooling fins in the case of air cooling. Cylinder head gasket is incorporated between the cylinder block and head. The bottom portion of the cylinder is called crank case.

    Cylinder: As the name implies it is a cylindrical vessel or space in which the piston makes a reciprocating motion. The varying volume created in the cylinder during the operation of the engine is filled with the working fluid and subjected to different thermodynamic processes. The cylinder is supported in the cylinder block.

    Piston: It is a cylindrical component fitted into the cylinder forming the moving boundary of the combustion system. It fits perfectly into the cylinder providing a gas – tight space with the piston rings and the lubricant. It forms the first link in transmitting the gas forces to the output shaft.

    Piston rings: These are fitted in the slots around the piston; provide a tight seal between the piston and the cylinder wall thus preventing leakage of combustion gases.

    Connecting rods: It interconnects the piston and the crankshaft and transmits the gas forces from the piston to crankshaft. The two ends of the connecting rod are called as small end and the big end is connected to the crankshaft by crank pin.

    Crank shaft: It converts the reciprocating motion into useful rotary motion of the output shaft. In the crank shaft of a single cylinder engine there is a pair of crank arms and balance weights. The balance weights are provided for static and dynamic balancing of the rotating system. The crankshaft is enclosed in a crankcase.

    Cam shaft: The cam shaft and its associated parts control the opening and closing of the two valves. The associated parts are push rods, rocker arms, valve springs, and tappets. This shaft is also provided with the drive to the ignition system. The cam shaft is driven by the crankshaft through timing gear.

    Inlet and Exhaust valves: Valves are commonly mushroom shaped poppet type. They are provided either on cylinder head or on the either side of the cylinder for regulating the charge coming into the cylinder (inlet valve) and for discharging the products of combustion from the cylinder.

    Spark plug: It is a component to initiate the combustion process in a Spark - ignition engines and is usually located on the cylinder head.

 Fuel Injector:  It atomizes the fuel into very fine droplets; it increases the surface area of the fuel droplets resulting in better mixing and subsequent combustion. Atomization is done by forcing the fuel through a small orifice under high pressure.

 Flywheel:  The net torque imparted to the crankshaft during one complete cycle of operation of engine fluctuates causing a change in the angular velocity of the shaft. In order to achieve to the output shaft and this wheel is called the flywheel.

WORKING PROCEDURE OF ENGINE:

                      

                  Engines can be classified in many different ways:  By the engine cycle used, the layout of the engine, source of energy, the use of the engine, or by the cooling system employed.

Principles of operation

Reciprocating:

·         Two-stroke cycle

·         Four-stroke cycle

·         Six-stroke engine

·         Diesel engine

·         Atkinson cycle

        Rotary:

·         Wankel engine

        Continuous combustion:

·         Braton cycle

·         Gas turbine

·         Jet engine

 

TWO STROKE PETROL ENGINE:

                      In two-stroke petrol engine all the four operations are carried out in 2 strokes of piston, known as upward stroke and down ward stroke.  In two stroke engines ports are used instead of valves.  The exhaust gases are expelled out from the engine cylinder by the fresh charge of the fuel entering the cylinder.  In this type of engine the suction and exhaust strokes are eliminated.  In case of petrol engine, the mixture of air and petrol is ignited by means of electric spark produced by the spark plug.

The two strokes of the engine are:

·         First stroke

·         Second stroke

First Stroke:         

              Assume that the piston is at B.D.C. position.  During this stroke the piston moves upwards from bottom dead centre to top dead centre.  It closes the transfer port and exhaust port.  The charges air-petrol mixture, which is already there in the cylinder, is compressed.  Due to the upward movement of the piston, a partial vacuum is created in the crank case and a fresh charge is drawn in to the crank case through the uncovered inlet port.  At the end of this stroke, the piston reaches the T.D.C.

Second Stroke:

                The compressed charge is ignited in the combustion chamber by means of an electric spark produce by the spark plug, slightly before the completion of the compression stroke.  Due to the combustion of the air-petrol mixture, the piston is acted on by a large force is pushed in the downward direction produces the useful power.  During this stroke, the inlet port is covered by the piston and the piston uncovers the exhaust port and then the transfer port.  The expanded gases start escaping through the exhaust port and at the same time fresh charge, which is already compressed in the deflector, on the piston crown, rises to the top of the cylinder and pushes out most of the exhaust gases.  The piston is now at the bottom dead centre position.  The cylinder is completely filled with the fresh charge although it is some when deflector with the exhaust gases.  The cycle of events are completed.

TWO STOKE DIESEL ENGINE:

              In two-stroke cycle diesel engine, only pure air is compressed in the cylinder.  A nozzle is fitted in the head of the cylinder sprays fuel into the cylinder just before the completion of compression.  The remaining operations of the two stroke cycle C.I. Engine are similar to those of the S.I. Engine.

              Scavenging is generally a problem in two stroke engines.

              The operation of clearing the engine cylinder of exhaust gases and filling it most completely with fresh charge is called scavenging. In two stroke engine the piston is crowned for effective scavenging in which fresh charge is not allowed to go through exhausted port.

             As the scavenging in poor in two stroke engines, the two stroke engines are more polluting when compared to four stroke engines. There are chances of some fresh charge going out of exhaust port. We find un burnt hydrocarbons in the omissions of two stroke engines. The un burnt hydrocarbons cause pollution.

Use of Two Stroke Diesel Engines:

                        Due to excessive loss of charge with exhaust gases and high fuel consumption, the two stroke cycle S.I engine is not widely used except in the case of outboard Motors, Scooters, Motorcycles and light vehicles. The modern practice is that large two stroke engines are generally C.I. engines.  The two stroke C.I. Engines are better for new and moderate speeds.

                 The use of two stoke opposed piston C.I. engines is well suitable for marine installations where the engine room is small.