Comparison between Spark ignition and combustion ignition engines

S.No.	Aspects	SI ENGINE	CI ENGINE
1.	THERMODYNAMIC CYCLE	It used the Otto cycle (constant volume cycle) [heat addition at constant volume and reject constant volume]	Diesel cycle(constant pressure cycle)[heat addition at constant pressure and reject at constant volume] Dual cycle(heat addition at constant pressure and volume and heat reject occur at constant volume)
2.	Fuel	Petrol	Diesel
3.	Ignition type/combustion type use	Spark plug is used for combustion(Spark ignition)	Combustion is occur due to high compression no spark plug is used
4.	Speed	High speed 2200 to 6500 rpm these kind are use in car and light vehicle	Low speed 500 to 3500 rpm They are used for heavy vehicles because of high torque capacity
5.	Cost	Low cost from the fact petrol engine are lighter than diesel engine. so less amount in making and running (lower the weight higher the energy utilization)	High cost Diesel engine are very bulky and heavy. for heavy vehicles there size is huge
6.	Power capacity	They are lower power producing engine that is the reason truck and other heavy vehicles does not made of engine that use petrol	They are high power producing. Nearly every heavy vehicle designed for diesel engine
7.	Air fuel ratio	10:1 to 20:1	18:1 to 100:1
8.	Repairing /maintenance cost	Low cost as define in point no.5	High cost due to heavy engine and parts
9.	Working under Two stroke	Not suitable due to scavenging effect which cause fuel loss	Better suitable
10.	Compression ratio	Normally it is 6to 9 and go maximum to 11 at maximum limit anti knock effect occur	Normally 13 to 19 Maximum 25 Maximum limit is thermal stress and mechanical stress
11.	Safety	Petrol is more volatile so it more dangerous than diesel	Diesel is less volatile so it is more safe
12.	Efficiency	Low efficiency	High efficiency
13	Calorific value of fuel	44MJ/kg	42MJ/kg
14	weight	Light in weight	Heavy in weight because of the heavy engine making