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Both petrol and diesel engines have the same mechanism. Both of them can be two-stroke or four-stroke , both have a cylinder , a piston , a piston pin , a connecting rod , a crank and a crank shaft but there are many differences between the two
| Diesel Engine | Petrol Engine |
|---|---|
| The mechanism of diesel engine involves that only air is supplied into the cylinder which is compressed during the compression strokes . At the end of the compression the air reaches to a very high temperature and fuel is injected in the form of fine spray by a nozzle. | The mechanism of petrol engines involves that a mixture of air and petrol is injected into the cylinder . The mixture is produced by the carburetor . This mixture is compressed inside the cylinder during compression stroke . After the compression , a spark plug produces a spark that leads to combustion of the mixture . |
| Compression Ratio in diesel engine is as high as 24 | Compression Ratio in petrol engines is below 12 . It is due to the phenomenon of knocking . |
| Due to higher compression ratio peak pressure is higher so , heavier components (cylinder , piston , connecting rod , crank) are required in diesel engine | Components are comparatively lighter in petrol engines. |
| Diesel Engine works on the Diesel Cycle | Petrol Engines work on the Otto Cycle. |
| Diesel engines are practically more efficient because they work at higher compression ratios | However , Otto Cycle is more efficient than Diesel Cycle for a given compression ratio but due to its low compression ratio it becomes practically less efficient . |