You might have noticed that the majority of the taxi drivers opt for a diesel engine. There are two reasons for this. The first is that a diesel engine returns better fuel efficiency and the second one is that they last longer. Man people know about the first one, but the long life of diesel engines is something that people are still not familiar with.
So, why do diesel engines last longer than petrol engines?
To understand this we would need to understand some basics of an engine and how both the engines work. Both engines are based on a four-stroke cycle. As the name suggests the four-stroke engines have four cycles to complete the combustion and exhaust cycle. The four steps are known as intake, compression, combustion and exhaust.
First, the piston moves down, this is when the intake valve opens and a mixture of fuel and air enters the cylinder. This is known as intake stroke. Then the piston moves upwards causing the mixture to compress. Hence, it is called compression stroke. Then the combustion happens, this is where there is a difference between a petrol and diesel engine. And finally, the exhaust valve opens and the piston moves back up forcing the exhaust gases out of the exhaust valve and into the exhaust pipe.
Difference at combustion stage
Petrol evaporates quickly so it is mixed easily with air. The only thing required to ignite this mixture is a spark which is the duty of a spark plug. The spark plug produces a spark and generates the combustion stroke. Diesel, on the other hand, does not mix well with air. So, the diesel is compressed and atomized. Then it is sprayed into the high-temperature air so that combustion can occur.
Due to this, the petrol engine requires a spark plug whereas the diesel engine requires a fuel injector. Then there is the compression ratio. The diesel engine runs on a higher compression ratio as it has to compress air whereas a petrol engine has to compress a mixture of petrol and air. This is the reason why diesel engine returns better fuel efficiency.
We see diesel engines being used in pick-up trucks, SUVs and trucks. Basically, big vehicles and vehicles have to carry heavy loads for long durations. Diesel engines produce significantly more torque which is essential if the vehicle is hauling stuff. Torque is the movement force that is generated by the engine.
Back to the main question
The reason why diesel engine lasts longer than petrol engines is because diesel is light oil. The diesel burns in the engine and simultaneously lubricate the engine parts. This causes the engine components to move more smoothly and last longer. When compared, petrol is a detergent and it washes away the oil from engine components that dry the engine. Because of this, the petrol engine’s parts wear quickly.
The typical life of a petrol engine is around 3 lakh kilometres before it starts wearing. However, a diesel engine’s lifecycle can easily last 5 lakh kilometres. Mechanics says that if maintained properly a diesel engine would last for around 30 years. We have seen examples of a Toyota Qualis reaching upto 8 lakh kilometres and a Toyota Innova that has crossed 10 lakh kilometres in India.