Spark Ignition (SI) Engine Vs Compression Ignition (CI) Engine

Spark Ignition (SI) Engine Vs Compression Ignition (CI) Engine

 

S.No	Aspects	S.I Engines	C.I Engines
1.	Thermodynamics Cycle	Otto Cycle	Diesel Cycle- For low speed engines Dual Cycle-For high speed engines
2.	Fuel Used	Petrol	Diesel
3.	Air-Fuel Ratio	10:1 to 20:1	18:1 to 100:1
4.	Compression Ratio	Up to 11 Average Value 7 to 9.	12 to 24 Average Value 15 to 18.
5.	Combustion	Spark Ignition	Compression Ignition
6.	Fuel Supply	By Carburetor	By Injection
7.	Operating Pressure    1. Operating Pressure    2. Maximum Pressure	7 bar to 15 bar  45 bar to 60 bar	30 bar to 50 bar  60 bar to 120 bar
8.	Operating Speed	High Speed- 2000 to 6000 R.P.M	Low Speed- 400 R.P.M
9.	Control of Power	Quantity Governing  by Throttle.	Quality Governing by rack.
10.	Calorific Value	44 MJ/Kg	42 MJ/Kg
11.	Cost of Running	High	Low
12.	Maintenance Cost	Low	High
13.	Super Charging	Limiting by detonation-Used only in aircraft engines.	Limited by blower power & mechanical & thermal stresses. widely used.
14.	2-Stroke Operation	Less Suitable, Fuel loss in Scavenging.	More Suitable, No fuel loss in Scavenging.
15.	High Power	No	Yes
16.	Distribution of Fuel	A/F ratio is not optimum in multi-cylinder engines.	Excellent Distribution of fuel in multi-cylinder engines.
17.	Starting	Easy, low cranking effort.	Difficult, high cranking efforts.
18.	Exhaust Gas Temperature	High, due to low thermal efficiency.	Low, due to high thermal efficiency.
19.	Weight Per Unit Power	Low (0.5 to 4.5 Kg/KW)	High (3.3 to 13.5 Kg/KW)
20.	Initial Capital Cost	Low	High
21.	Noise & Vibration	Less	More
22.	Uses	Mopeds, Scooters, Motorcycles, Passengers Cars, Aircraft. etc.	Buses, Trucks, Tractors, Earth moving machineries. etc.