Straight form the manual about DIESEL fuels. Note the temperature changes and recommended fuel types:

DIESEL:

Diesel Generators — Use any of the following ASTM certified fuels for your quiet diesel:

ASTM-No.2-D (ambient temperature greater than 23°F) (No. 2 Diesel)
or ASTM-1-D (No. 1 Diesel)
No.2-DLS (ambient temperature greater than 23°F)
No.1-D (ambient temperature less than 23°F)
No.1-DLS (ambient temperature less than 23°F)
B5 Biodiesel (ambient temperature greater than 50°F)

Ensure the fuel selected for use has a minimum Cetane number of 45. No. 2-D or No.2-DLS diesel fuel gives the best economy and performance under most operating conditions. Use No. 1 diesel fuel when ambient temperatures are below 32°F and during long periods of light engine load. Use low sulfur or ultra low sulfur content fuel having a cloud point of at least 10°F below the lowest expected fuel temperature. Cloud point is the temperature at which wax crystals begin to form in diesel fuel.

B20 Biodiesel − The use of B20 biodiesel requires the generator to have an additional fuel/water separator. Long-term storage of biodiesel fuels can result in oxidation and/or mold growth. Consult your vehicle manufacturer and your generator owner’s manual to see if this option is applicable to your generator.