DISIMILARITIES OF S.I ENGINE AND C.I. ENGINE

           



                

Dissimilarities.

S. I. Engine.	C. I. Engine.
1.  Ignition system required	1.  Not required.
2.  Draws air and fuel into the system.	2.  Draws only air into the cylinder.
3. Compresses air and fuel together.	3.  Compresses air only.
4. Fuel is mixed with air at before compression starts.	4. Fuel is mixed with air at the end of compression.
5. As too much compression of air and fuel mixture causes pre ignition and detonation permissible compression ratio is not high(about 7).	5. Only air can be compresses without pre-ignition and detonation, so compression ratio can be high (about 16).
6. Efficiency, being proportional to compression, is limited due to less compression ratios.	6. Higher efficiencies can be obtained due to possible higher compression ratio.
7. Uses highly volatile liquid fuels so that it can mix with air at low temperature.	7. Uses less volatile liquid fuels
8. Fuel used is costly.	8. Cheaper fuel can be used
9. More fuel is used for same power.	9. Less fuel consumption.
10. Lighter in weight.	10. Heavier and stronger engines due  to   higher pressures involved.
11. Initial cost less.	11. Initial cost high.
12. Smooth operation.	12. Certain roughness in operation encountered, especially in high-speed engines at light loads.