The LD/LDT/LDS engines are all in the 0.45-0.55 pounds of fuel per horsepower-hour range. It takes 1 Hp to generate 746 Watts if everything is perfectly efficient. With mechanical governors (all diesels are governed), typical engines have two horsepower for every kW of generator capacity...the old 5 kW MEP-017A used the 42 cubic inch AO-42 military standard 2-cylinder 10 Hp engine (42 cubic inch, 3600 RPM).
So while the stock governor should hold the RPM close enough for 60 Hz regulation with a PTO, it will only have the 27 Hp output at 1600 RPM . So at best, you could get 13 kW. Drop the RPM and you will have proportionally less power. So at 800 RPM, that would be 13 Hp or less and 6 kW generator output.
At 13 Hp, you are looking at 6 pounds per hour of fuel which is about a gallon. A MEP-002A diesel is rated at 5 kW but will do 7.5 easily and consume about 3/4 gallon per hour at that output.
The specific fuel consumption of a diesel is highly dependent on engine speed, load and temperature. It can be well over 1 pound per Hp-hour at lower RPM. Typically, it is least (most efficient, specific means specific to power output) at the engine's torque peak.
