So, why is diesel the fuel of choice for bigger vehicles? Apart from the fact that it is cheaper than petrol in India, the diesel engine is more efficient. The diesel combustion cycle yields a leaner fuel-air mixture to operate at optimal efficiency as compared to petrol engines. Measured by volume, diesel is more energy-dense than petrol. The combustion cycle itself works best at leaner mixtures, and diesels deliver a torque curve that works better for bigger cars and trucks as compared to petrol.
Plus, most diesels are equipped with a turbocharger, which offers a sharp surge in power delivery after a certain RPM, a feature that is popular with customers of bigger cars and SUVs. Modern diesels also emit lesser carbon dioxide than petrols, something that has been instrumental in the spread of diesels in markets such as Europe.
Diesel engines also emit higher levels of nitrogen oxides, and over seven times more particulates as compared to petrol engines — pollutants that cause respiratory ailments.
The big reason for the higher efficiency of diesel engines boils down to the engineering design. While both petrol and diesel engines work by internal combustion, they do so in slightly different ways.
In a petrol engine, fuel and air is injected into small metal cylinders, and then a piston compresses the mixture, making it explosive. A small electric spark from a sparking plug sets fire to it, which makes the mixture explode, generating thrust. This then pushes the piston down the cylinder, and through the crankshaft, turns the wheels.
In pure design terms, diesel engines are simpler. First, air is let into the cylinder and the piston compresses it, but in this case, much more than in a petrol engine. While in a petrol engine, the fuel-air mixture is compressed to about a tenth of its original volume, in a diesel engine, the air is compressed by anything between 15 and 25 times. Compressing a gas generates heat, and once the air is compressed, a mist of fuel is sprayed into the cylinder by an electronic fuel-injection system, which works a bit like an aerosol spray. The air is so hot that the fuel instantly ignites and explodes — without the need for a spark plug. This controlled explosion pushes the piston back out of the cylinder, producing the power that drives the vehicle.
Diesel engines tend to be up to twice as efficient as petrol engines. The reasons for this include the lack of a spark-plug ignition system. As a result, the fuel is compressed much more, which makes it burn more completely in combination with the air in the cylinder, thereby releasing more power.
Also, in a petrol engine that is working at less than full power, more fuel (less air) needs to be suppled to the cylinder to keep it running, while diesel engines actually consume less fuel when they are working at lower power. This lowers fuel usage while idling.
Plus, measured by volume, diesel fuel is more energy-dense than petrol, and thereby offers more energy per litre than petrol. Diesel — which is a lower-grade, less-refined product of petroleum made from heavier hydrocarbons — is also a better lubricant than petrol, with the result being that a diesel engine runs with less friction, thereby generating better efficiency.
Diesels are also noisy, and they produce a lot of unburnt soot particles and nitrogen oxides. However, since diesel engines are more efficient, they typically use less fuel and thereby produce lower carbon dioxide emissions.
Flashing Red- Diesel exhaust contains particulate matter and gases including benzene and nitrogen dioxide, which are agents of serious disease.
Possible Effects –
- Lung cancer, even for non-smokers; damage to lungs, possibly brain damage
- Exacerbated allergies, asthma; shortness of breath; eye irritation; nausea
- Stress responses in brain; cellular damage linked to Alzheimer’s, Parkinson’s