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. ...
• Maximum OR Ultimate Tensile stress:- it
Is the ratio of Maximum load on a body to the Original cross section of a body.
• WORKING STRESS - it is the ratio of Ultimate stress to suitable Factor of safety (F.O.S). It is also known as allowable stress or permissible stress.
• FACTOR OF SAFETY ( F.O.S) - It is the ratio of Ultimate stress to the working stress
F.O.S is depend on following factors :-
1. Degree of safety required
2. Loading type
3. Degree of economy required
4. Life span of the body ( structure)
• BREAKING STRESS - It is the load at breaking point and the Original cross section area of a body.