# Thermodynamic-Fuel and efficiency

Why is the maximum theoretical efficiency of Ar engine higher than that of Nitrogen engine? On a molecular level.

For an Otto Cycle

• $\mathrm{Eff} \le\left(1-r^{1-\gamma}\right)$
• $\gamma=\dfrac{C_p}{C_v}$
• $r=\dfrac{v_1}{v_2}$

Sys. Fluid

• Nitrogen, $\gamma=1.4,\ r=10,\ \mathrm{eff(max)}=60.2%$
• Argon, $\gamma=1.67,\ r=10,\ \mathrm{eff(max)}=78.5%$