Dirty Diesel: How Bad Is It Really and Can We Do Without It?

If diesel engines are as harmful as they are made out to be, why are they still so much in demand?

Diesel is still the most efficient fuel for transport applications. 

(Photo iStock)

It’s easy to slam diesel for being the root of the world’s pollution woes. Let’s face it, the fuel has caused considerable harm to the environment.

Well, I drive a diesel SUV too, but I don’t quite regret it, as there is some merit to the fuel. Why else it would be so popular? It powers everything from trucks, buses, generators, and heavy machinery right down to fuel-efficient hatchbacks.

Therein lies the issue. We just cannot do without this supposed harmful fossil fuel. Fact is, there are inherent benefits that cannot be ignored. Let’s talk about some of them.

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Diesel Is More Energy Efficient

I’m not going to bore you with a physics lesson here, but here’s a fun fact – diesel is more energy efficient than all the other fossil fuels put together. A litre of diesel contains about 39.4 Mega Joules of energy, while petrol packs in only 34.3 Mega Joules of energy. Let’s just say if diesel was a student that scored a 100 in its physics paper, petrol would only get 87 percent. Oh, and in comparison, CNG would be a loser, as it packs in only 9.9 Mega Joules (that would be just 25 percent of the energy efficiency of diesel).

Diesel has the most energy density among fossil fuels. (Photo: The Quint)

Diesel Not So Bad For Global Warming

Pop quiz: Which is the biggest greenhouse gas responsible for global warming? Carbon dioxide. Which fuel emits more carbon dioxide per kilometre? Petrol. That’s right. Now here’s the tricky part. Diesel is better than petrol when it comes to some pollutants, but much worse when it comes to others.

Diesel engines emit far less carbon dioxide than petrol engines. (Photo: The Quint)

If you look at Euro IV diesel – which is the current norm in India – you will find that for emissions of carbon dioxide, diesel is much cleaner than petrol.

For an average small car with a 1.2 litre petrol engine or a 1.2 litre diesel engine, the diesel car emits about 120 gms per km of carbon dioxide, while an equivalent petrol car emits 200 gms per km.

But if you look at nitrous oxide emissions, a diesel car emits about 30 percent more nitrous oxide than a petrol car. Nitrous oxides are responsible for respiratory illnesses.

No Spark, No Problem

Diesel engines are compression ignition engines. This means that they don’t need spark plugs. They work by compressing air in the ratio of 18:1 or 21:1, and in the process, generating heat beyond 210 degree centigrade – which is the auto ignition temperature of diesel. A small spray of diesel into this compressed air sets off combustion.

This means that diesel can’t be ignited by just a spark, and hence, is much safer than petrol. But if temperatures are too low, you could face ignition issues, which is why you may have come across truckers in the hills lighting a bonfire under their diesel tanks, or pouring hot water over the engine to warm it up.

Diesels Make More Torque

Since diesel engines are high compression engines, they need heavier parts and longer connecting rods to achieve this. The longer stroke in a diesel engine, along with the better thermal efficiency (more bang for your buck), helps it develop much better torque than an equivalent petrol engine. Torque is the turning force or the ability to accelerate better that an engine develops. In a diesel engine, this heavy torque comes in at lower RPM than a petrol, also making it far more fuel efficient.

Diesel Is More Fuel Efficient

As modern diesel engines have precise computer-controlled injection, they use minimal amount of fuel. And since diesel has a higher energy value compared to petrol, it produces the same amount of power using lower, much lower, amounts of fuel. If you compared a 1.2 litre petrol engine and a 1.2 litre diesel engine, the diesel is likely to be at least 25 percent more fuel efficient than the petrol motor.

Diesels get more kilometres per litre than a petrol car. (Photo: The Quint)

Hence, those who are obsessed with “average kitna deti hai” will always be happier with a diesel car. Oh, and the fact that diesel is still about Rs 10 cheaper than petrol per litre in India is a bonus. A big bonus!

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