Mechanical Engineering - Thermodynamics - Discussion

Awesome, Thanks @Sairohit Sandela.

Since too much unburnt carbon available in the combustion gas.

High air to the fuel ratio.
More air for a given amount of fuel.
Less fuel for the selected amount of air.

More fuel =more heat input=more energy release = more may be unused heat at exit hence more exhaust temperature.

Hence less fuel means less exhaust temperature.
Also, since more air is supplied for a given amount of fuel complete combustion takes place.

Air standard efficiency of a cycle is always higher compared to the air-fuel mixture cycle. When the mixture is made leaner, the cycle efficiency increases.

So answer B must be correct.

Not understood, Please explain.

The air fuel ratio is the most common reference term used for mixtures in internal combustion engines. The term is also used to define mixtures used for industrial furnace heated by combustion.

The AFR in mass units is employed in fuel oil fired furnaces, while volume (or mole) units are used for natural gas fired furnaces.