Scavenge efficiency is the ratio of mass of air in the cylinder at the beginning of compression to end of compression.
Scavenge efficiency = Mass of air in the cylinder at the beginning of the cylinder/ Mass of air at the end of the compression
How scavenge efficiency depends on air temperature?
Scavenge efficiency depends largely on scavenge air temperature. Cooler the air, denser the air and hence more mass and hence more scavenge efficiency.