Question

An Otto cycle with air as the working fluid has a compression ratio of 8.2. Under cold air standard conditions, what is the thermal efficiency of this cycle?

Answer 1

Answer:

Under cold air standard conditions, the thermal efficiency of this cycle is 56.9 percent.

Explanation:

From Thermodynamics we remember that thermal efficiency of the ideal Otto cycle ($\eta_{th}$), dimensionless, is defined by the following formula:

$\eta_{th} = 1-\frac{1}{r^{\gamma-1}}$ (Eq. 1)

Where:

$r$ - Compression ratio, dimensionless.

$\gamma$ - Specific heat ratio, dimensionless.

Please notice that specific heat ratio under cold air standard conditions is $\gamma = 1.4$.

If we know that $r = 8.2$ and $\gamma = 1.4$, then thermal efficiency of the ideal Otto cycle is:

$\eta_{th} = 1-\frac{1}{8.2^{1.4-1}}$

$\eta_{th} = 0.569$

Under cold air standard conditions, the thermal efficiency of this cycle is 56.9 percent.