What is the correct sequence, from minimum to maximum, of soot emissions from vehicles running on different types of fuels?

A. CNG fuelled vehicle
B. Petrol fuelled vehicle
C. Diesel fuelled vehicle
D. Hydrogen energy fuelled vehicles

​Choose the correct answer from the options given below:​

Correct option is C

Let's determine the correct sequence of soot emissions from minimum to maximum for vehicles running on different types of fuels. Soot is primarily unburnt carbon particles.

1. Hydrogen energy fuelled vehicles (D): Hydrogen combustion primarily produces water (H2​O) and trace amounts of nitrogen oxides (NOx​) if air is used as the oxidant. It produces virtually no soot because there's no carbon in the fuel. This would be the absolute minimum.

2. CNG fuelled vehicles (A): Compressed Natural Gas (CNG) is predominantly methane (CH4​). Methane is a relatively simple hydrocarbon that burns very cleanly compared to liquid fuels. While some incomplete combustion can occur, soot emissions are significantly lower than petrol or diesel.

3. Petrol fuelled vehicles (B): Petrol (gasoline) is a mixture of various hydrocarbons. While petrol engines generally produce less visible smoke than diesel engines, especially older ones, they do produce particulate matter (soot), particularly with direct injection engines. However, they are still generally cleaner than diesel in terms of soot.

4. Diesel fuelled vehicles (C): Diesel fuel is a heavier, more complex mixture of hydrocarbons. Diesel engines operate with lean combustion and heterogeneous mixing, which can lead to localized fuel-rich zones and incomplete combustion, historically resulting in the highest soot emissions among these options. Although modern diesel engines are equipped with Diesel Particulate Filters (DPFs) to trap soot, inherently, the combustion process generates more.

Therefore, the order from minimum to maximum soot emissions is:

1. Hydrogen (D)
2. CNG (A)
3. Petrol (B)
4. Diesel (C)

The sequence is Option C  D, A, B, C .