What is the difference between CNG and LPG in dual-fuel vehicles?

In years when economic pressure and fuel costs have become one of the main challenges of transportation, dual-fuel vehicles focusing on LPG and CNG have been proposed as a solution to reduce gasoline consumption. However, the reality is that these two fuels not only have fundamental technical differences but also fully affect driving experience, engine wear, fueling infrastructure, and even countries' policies. To understand why in some situations CNG performs weaker than gasoline or why LPG was removed in Iran, one must delve into the physics of combustion, engine volumetric efficiency, and the global experience with these fuels.