In an internal combustion engine (either gasoline or diesel), the upstroke of the piston reduces the volume of the cylinder. Using the kinetic theory of matter, what happens to the temperature and pressure of the air/fuel blend in the cylinder?

A. The volume is forced smaller, the temperature goes up and the pressure goes

up

B. The volume is forced smaller, the temperature goes up and the pressure goes

down

C. The volume is forced smaller, the temperature goes down and the pressure

goes up

D. The volume is forced smaller, the temperature goes down and the pressure

goes down

In an internal combustion engine, the upstroke of the piston reduces the volume of cylinder leading to increase in the pressure and temperature. So option A is correct.

Answer: A

Explanation

According to kinetic theory of gases, the pressure of a gas is inversely proportional to the volume of the gas.

So when the piston is moved upward, the volume is forced to become smaller and the pressure of the gas tends to increase.

As there is an increase in the pressure due to compression of volume by an external force, the temperature of the gas also increases as the external force or the work done will transfer its energy to the gas molecules leading to the increase in temperature.

The best example for this is heating of the mechanical air pumping machine for cycle Tyre.

During filling of air in cycle Tyre, we have to give extra mechanical energy in the pumping piston to compress the volume of air in the pumping machine and that gas get transferred to the Tyre.

But while pumping, the mechanical pumping machine gets heated up due to the mechanical work done on the piston. This work done is transferred as heat to the gas molecules thus increasing the temperature of the gas on decreasing the volume and also the pressure will be increased when volume is compressed mechanically.