Question

The combustion in a gasoline engine may be approximated by a constant volume heat addition process. The cylinder contains the air-fuel mixture before combustion and the combustion gases after it, and both may be approximated as air, an ideal gas. In a gasoline engine, the cylinder conditions are 1.18 MPa and 450°C before the combustion and 1900°C after it. Determine the pressure at the end of the combustion process. Combustion chamber P MPa 450°C The pressure is MPa.

Answer 1

Given that the gases behave as ideal gases.

Ideal gases are those which obeys gas laws at all temperatures and pressures.

So from the ideal gas equation at constant volume we can write,

P₁ / T₁ = P₂ / T₂

Given that

Initial temperature (T₁) of gasoline engine is 450^oC = 450 + 273 K = 723 K

Final temperature (T₂) of gasoline engine is 1900^oC = 1900 + 273 K = 2173 K

Initial pressure (P₁) in the gasoline engine is 1.18 MPa = 1180 kPa

Final pressure (P₂) can be calculated from the above equation

1180 kPa / 723 K = P₂ / 2173 K

P₂ = 3547 kPa or 3.547 MPa

Therefore the required pressure at the end of the combustion is 3.547 MPa