What is the lowest compression ratio in engine?

The lowest compression ratio in internal combustion engines typically falls around 6:1 to 7:1. Such low ratiOS are often found in engines designed for specific applications, like large diesel engines or certain types of low-performance gasoline engines. These lower ratiOS can help prevent engine knocking and allow for the use of lower-octane fuels. However, they generally result in decreased efficiency and power output compared to engines with higher compression ratiOS.