Criteria S.I. Engine (Petrol or Spark Ignition Engine) C.I. Engine (Diesel or Compression Ignition Engine) Working Cycle Works on Otto Cycle or Constant Volume Cycle. Works on Diesel Cycle. Mixture During Suction Stroke Takes a mixture of air and petrol during the suction stroke. Takes only air during the suction stroke. Fuel Used Uses petrol as fuel. Uses diesel as fuel. Compression Ratio Has a compression ratio that varies from 6 to 10. Has a compression ratio that varies from 16 to 20. Engine Weight and Cost S.I. engines are lighter and cheaper. C.I. engines are heavier and costlier. Initial Cost Initial cost is lower compared to C.I. engines. Initial cost is high due to high compression ratio. Starting Starting is easy. Starting is difficult, especially in cold conditions. ...
STRESS AND STRAIN -
Stress- it is defined as the force acting per unit area of the cross- section of a body.
it is denoted by f, P or σ ( Sigma ) .
σ = P/A ( mathematically)
Unit of stress :- N/m², N/ mm² = Pascal
TYPES OF STRESS:- Mainly 2 types of stress
1.) Direct stress
2.) Shear stress
1.) Direct Stress - The force is applied perpendicular to the cross section of the body then the stress induce in body is known as direct stress.
The direct stress either tensile or compressive.
a.) Tensile Stress - when the axial pull is applied to the cross-section of a body then the stress induce is known as tensile stress.
( In a simple way tensile stress is the force whose effect tend to increase the length of the body)
σ = P/A
b.) Compressive Stress - when the axial push is applied on the cross- section of a body, then the stress induce is known as compressive Stress.
σ = P/A
2.) Shear Stress - when two equal and opposite forces are applied tengentially to the cross section of a body, then the stress induced is known as shear stress.
σ = P/A
STRAIN - It may be defined as the ratio of change in dimension to its original dimension .
ε = change in dimension / original dimension
it is denoted by epsilon ε
TYPES OF STRAIN - There are 4 types
1.) TENSILE STRAIN - The ratio of increase in length to its original length.
ε =
2.) Compressive Strain: The ratio of decrease in length to it's original length of the body.
3. )Shear Strain: When a body is subjected to two equal and opposite parallel forces not in same line, it tends to shear off across the resisting section.
OR
The ratio of angular deformation to original Length along the force is known as shear strain.
4. )Volumetric Strain: The ratio between the change in volume to its original volume of a body is known as volumetric strain or bulk strain.