In this article, we will discuss about the difference between SI engine and CI engine. The Spark Ignition (SI) engine, as its name indicates uses spark to ignite the fuel. And in Compression Ignition (CI) engine, the air is compressed within the cylinder and the heat of this compression air is used to ignite the fuel. Since spark and compressed air is used to ignite the fuel in these engines, so they are called as spark ignition (SI) engine and compression ignition (CI) engine.
SI Engine (Spark Ignition Engine)
Spark Ignition (SI) Engine is a type of engine in which the combustion takes place by the spark generated by the spark plug. It uses petrol as fuel and works on Otto cycle. In the spark ignition engine, the air-fuel mixture is inserted into the cylinder with help of carburetor. The compression of the fuel takes place but it has low compression ratio. The fuel is ignited by the spark generated by the spark plug. SI engine produces less noise and vibration and their starting is very easy. They are light in weight and have less maintenance cost. They are mostly used in light commercial vehicles such as scooters, motorcycles cars, etc.
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CI Engine (Compression Ignition Engine)
Compression Ignition (CI) Engine is an engine in which the combustion of fuel takes place by the heat of the compressed air. It uses diesel as fuel and works on the Diesel cycle. In the compressed ignition engine, only air enters into the cylinder during suction stroke. It has high compression ratio because of the high ignition temperature of the diesel fuel. The heat of the compressed air ignites the fuel. Due to the high compression ratio it produces more power. Due to incomplete combustion of the fuel, it produces more hydrocarbons which lead to air pollution. The noise and vibration problem is there in the CI engines. The maintenance cost of the CI engine is more as compared with the SI engines. They are mostly used in heavy duty vehicles such as buses, trucks, railways, ships etc.
Difference Between SI Engine and CI Engine in Tabular Form
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S.no
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Parameter
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SI Engine
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CI Engine
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1.
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Definition
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It is an engine in which the spark is used to burn the fuel.
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It is an engine in which heat of compressed air is used to burn the fuel.
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2.
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Fuel used
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Petrol is used as fuel.
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Diesel is used as fuel.
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3.
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Operating cycle
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It operates on Otto cycle.
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It operates on Diesel cycle.
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4.
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Compression ratio
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Low compression ratio.
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High compression ratio.
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|
5.
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Thermal efficiency
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High thermal efficiency.
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Less thermal efficiency.
|
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6.
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Method of ignition
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Spark plug is used to produce spark for the ignition.
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Heat of compressed air is used for the ignition.
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7.
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Engine Speed
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High speed engines.
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Low speed engines.
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8.
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Pressure generated
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Low pressure is generated after combustion.
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High pressure is generated
after combustion. |
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9.
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Constant parameter during cycle
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Constant volume cycle.
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Constant pressure cycle.
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10.
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Intake
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Air + fuel.
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Only air.
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Weight of engine
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Si engine has less weight.
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CI engine are heavier.
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|
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12.
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Noise production
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It produces less noise.
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It produces more noise.
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13.
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Production of hydrocarbon
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Less Hydrocarbon is produced.
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More hydrocarbon is produced.
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14.
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Starting
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The starting of SI engine is easy.
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The starting of CI engine is difficult.
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15.
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Maintenance cost
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Low
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High
|
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16.
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Vibration problem
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Less
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Very High
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17.
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Cost of engine
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Less cost
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High cost
|
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18.
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Volume to power ratio
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Less
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High
|
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19.
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Fuel supply
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||
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20.
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application
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It is used in light commercial vehicles like motorcycle, cars etc.
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It is used in heavy duty vehicles likes bus, trucks, ships etc.
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So now, I hope you have clearly understood the difference between SI engine and CI engine. If you have any confusion related to that then feel free to ask through your comments. If you find it informative or useful than share it for others.
Modern Diesels are easy starting, lighter weight, rev much higher, are far more flexible and very efficient.
Can si engine be two stroke as well as four stroke engine?
Thank u