Working Of Four Stroke Compression Ignition Engine with PV Diagram

 Compression Ignition Engine running

CI has no carburetor and spark plug, but has a fuel injector. This engine work on the principle of diesel cycle. Similar to SI engine CI engine also has the four stroke in one complete burning cycle. The four strokes are known as intake, compression, expansion and exhaust. These four-stroke or one cycle of operation completed in two revolutions of crankshaft.

Working Of Four Stroke Spark Ignition Engine with PV Diagram

4-Stroke si-Engine-with-airflows animated

🔗Basic components of IC engine and their functions
🔗Comparison between SI engine and CI engine

SI engine is an internal combustion engine, where the fuel is burned with the help of spark plug. SI engine working the principle of the Otto cycle. As the name suggests, in a four-stroke engine, the one cycle of combustion operation is completed in four strokes. Each stroke consists of 180° rotation of the crankshaft and hence four stroke completed in 720° rotation of the crankshaft. The engine takes two revolutions of crankshaft to complete this four stroke. The four-stroke for a spark ignition engines are

Nomenclature or Terminology Used In Study of IC Engine

engine nomenclature

Read: IC engine basic components

The common terms used in calculations and study of IC engine is listed below.

Cylinder Bore (d): Cylinder bore is the inner diameter of working cylinder. It is represented in millimetre (mm).

Piston Area (A): Piston area is defined as the area of a circle of diameter equal to the cylinder bore. It is usually represented in square centimetre (cm2).
A= (π/4) d2

Basic Components of IC Engine and Their Function

ic engine components

Even though there are different type of internal combustion engine and each engine has hundreds of components, there are some basic components that are present in almost all engine. Those who are study IC engines should know this basic component, and often used terminology in IC engine.
Figure shows the cross section of an SI engine, various components and its function is described below.

What Is Machinability Index? Criteria Considered In Evaluating Machinability?

drilling cutting fluid

🔗What Is Machinability? Factors affecting and advantages of machinability

What is machinability index of metal?

Machinability index is used to compare the machinability of different materials in the various cutting process. It is an attempt to quantify the relative machinability of different material. The rated machinability may vary for different cutting operation such as turning, milling, forming etc. In order to find the machinability index, factors like tool material, tool geometry, tool life and other cutting conditions are fixed except the speed. Then find the speed at which tool cut the material for a pre-determined tool life. Then it is compared with a standard material. Here machinability of standard steel is arbitrarily fixed as 100%. The slower speed indicates, low metal removal rate and hence poor machinability.

Machinability index, I (%)=  V_i/V_s ×100

Vi = Cutting speed of metal investigated for 20 minute tool life
Vs = Cutting speed of standard steel for 20 minute tool life

What are the criteria considered in evaluating machinability?

Following are parameters needs to considered for machinability measurement

  • Tool life, and types of wear tool subjected to. Crater wear, flank wear etc.
  • Cutting forces Power consumption.
  • Shape, size, type of chips. Tendency to burr. Cutting ratio of chip.
  • Efficiency and rate of chip removal.
  • Quality and properties of workpiece material.
  • Quality of surface finish and dimensional accuracy.
  • Temperature at cutting zone.

What Is Machinability? Factors Affecting Machinability and Advantages of Machinability

lathe running

What is machinability?

Machinability is defined as the ease with which a material can be machined to intended geometry and purpose at a satisfactory cost. The machinability often regarded as the work piece material property, however, the ease of machining also depends on other factors such as rigidity of cutting tool. Good machinability related to removal of material with moderate forces, good surface finish, small chips, and with minimum tool wear. It is difficult to maintain all these objectives at once for a machining operation. For example, the fine-grained material results in good surface finish but have high resistance to machining. So it is always a challenge to engineers to find ways to improve machinability without spoiling the performance.

What are the Factors that affect machinability?

It is difficult to predict machinability because of various factors affecting machinability. The machinability depends on the following machining process parameters, conditions and physical properties of workpiece.

Material variables:

  • Microstructure and grain size of workpiece
  • Heat treatment of material
  • Chemical composition of workpiece such as presence of alloying metal.
  • Hardness, tensile strength and ductility of workpiece

Machining variables:

  • Rigidity of tool, fixture, and work holding devices.
  • Tool geometry, tool dullness etc. indirectly affects the machinability.
  • Cutting parameters such as feed, speed, cutting force etc. are directly affect machinability.
  • Use of cutting fluid.

Generally, hardness decreases machinability because of high power consumption, high temperature and high tool wear. The coarse-grained steel shows better machinability than fine grained steel because fine grain will have better strength and hardness. Presence of alloying materials has much greater effect on the machinability than the effect of hardness on machinability. The small amount of alloying metal (less than 0.2%) of Sulphur S and lead Pb can improve machinability without having a noticeable change in mechanical properties. Heat resisting steels and superalloys are generally shown poor machinability. Poor thermal conductivity causes heat build-up at cutting zone, which eventually degrades the tool life.

One of the major factor to be considered during machining is the condition of tool. The dull cutting tools drive at too small feed may fail to cut chips and cause work hardening of material surface.

🔗What is machinability index?

Advantages of machinability

Result of good machinability are listed below

  • High cutting speed can be used.
  • High material removal rate
  • Low power consumption.
  • Tool wear rate is very low and good tool life.
  • Good surface finish
  • Minimum idle time.