Generally, you will find two types of IC engines in the market
  1. PETROL ENGINE
  2. DIESEL ENGINE
So what is the difference between a PETROL ENGINE and a DIESEL ENGINE?




If we consider a  FOUR-STROKE ENGINE. It has four strokes  SUCTION, COMPRESSION, COMBUSTION, EXHAUST. 


                   four-stroke-engine-cycle
                                               (Credits--Aero toolbox)
 1. SUCTION:

          The intake valve opens up, letting in air and moving the piston down.

           Generally, during suction in PETROL ENGINE, the air and fuel enter into the cylinder as a mixture but in DIESEL ENGINE, during suction, only air enters into the cylinder.


  2.COMPRESSION:

          The piston moves back up and compresses the air.

            During compression, the pressure in the cylinder will be around 10bars in a PETROL ENGINE whereas in the DIESEL ENGINE the pressure will be around 33 bars because the air in the cylinder is not a mixture but only fresh air.


  3. COMBUSTION:

           As the piston reaches the top, fuel is ignited, forcing the piston back down.

      During the combustion, the air-fuel mixture in the cylinder will get ignited in the PETROL ENGINE with the help of a spark plug.

      Whereas in the DIESEL ENGINE, Diesel will be injected with the help of an Injector and combustion occurs without any external source because its auto-ignition temperature is low.

       So that is the reason why PETROL ENGINE is called SPARK IGNITION (SI) ENGINE   and   DIESEL ENGINE is called COMPRESSION IGNITION (CI) ENGINE.

 4. EXHAUST:

         The piston moves back to the top, pushing out the exhaust created from the combustion out of the exhaust valve.

  5. CYCLE:

           The PETROL ENGINE works on a Constant Volume cycle called OTTO CYCLE whereas the DIESEL ENGINE works on a Constant Pressure cycle called DIESEL CYCLE.

  6. STARTING:

          As PETROL ENGINE has a spark plug, there will be no difficulty in starting in cold weather conditions but DIESEL ENGINE has to rely on the COMPRESSION stroke so there might be a problem while starting the engine in cold weather conditions.

  7. COMPRESSION RATIO:

            The compression ratio is defined as the ratio of the volume of the cylinder and its headspace. Petrol engines have a compression ratio in the range of 10.0:1 to 13.5:1, while diesel engines have a compression ratio in the range of 15:1 and 23:1.

  8. EFFICIENCY:

       Because of the higher compression ratios, DIESEL ENGINES are more efficient when compared to PETROL ENGINES. As a result DIESEL ENGINES give more mileage.

  9. TORQUE:

         PETROL ENGINES make less torque and DIESEL ENGINES make more torque.

  10. FLYWHEEL:

         The flywheel used in PETROL ENGINE is lighter when compared to the flywheel used in DIESEL ENGINE. So the weight of PETROL ENGINE will be less than DIESEL ENGINE.
Image: Slideshare



So finally the conclusion is 

PETROL ENGINE is lightweight, Silent, Less expensive.
DIESEL ENGINE is more powerful, more efficient.




Which engine do you think is better?? let me know in the comments....