We all know that Diesel cars are the best mileage cars and also torque compared to petrol engines. Diesel has more energy than petrol. Each liter of diesel contains 38.6 Megajoules while petrol has only 34.8 Megajoules of energy. This means that diesel burns hotter than petrol and you would need 25% less diesel to produce the same amount of power compared to petrol.
Diesel can be ignited at high temperatures and this is the principle on which a diesel engine works. When the cylinder is compressed the temperature inside the cylinder increases, when it is above 210 degrees Celsius (it is the auto-ignition temperature of diesel) a small spray of diesel is sprayed into the cylinder which ignites the diesel spontaneously. This is why diesel engines will take a while to start in extremely cold conditions, some cars use heaters and glow plugs to pre-heat the engine. A diesel engine will have fuel injectors that precisely inject diesel at the right time due to which lesser fuel is consumed. Petrol engines also have direct fuel injection in the combustion chamber, but most petrol engines are Multi-point fuel injection.
Diesel engines can operate at a higher compression ratio than petrol engines. The efficiency of the engine is directly proportional to the compression ratio. The high compression ratio in a diesel engine means that it needs thicker engine components and longer pistons and connecting rods to compress air better. It has a higher thermal efficiency than a petrol engine. This increased length of pistons also means it has a better torque than petrol engines. Torque is the turning force that the engine generates and more of this comes at a lower rpm in a diesel engine, it is easier to move away without revving the engine too much and this also saves fuel. Diesel has more energy than petrol. Each liter of diesel contains 38.6 Megajoules while petrol has only 34.8 Mega joules of energy. This means that diesel burns hotter than petrol and you would need 25% less diesel to produce the same amount of power compared to petrol.
Because diesel is minutely directly sprayed into a cylinder, lesser fuel is used and since it has cetane (six-sided) rings in its makeup instead of octane (eight-sided hydrocarbon rings), diesel’s burning characteristics are better – it is more slow-burning and complete burning, allowing for a longer burn time and better efficiency. This is also the reason why diesel engines don’t reach high rpm ranges. Now some new-generation petrol engines are adopting similar technology like all the fleets of Maruti Suzuki.
The engine power is the product of torque and rpm. Petrol engines produce more power by revving high to about 5000-7000rpm. The diesel engines with longer pistons and connecting rods will not rev high but will produce more torque to manage power.