Your numbers for the electric system indicate a current draw of less than 10 amps and watts of less than 200 to maintain 32 mph.. The Saito fg-14 is supposed to put out 1000 watts(1.2 horsepower) at full throttle and consume 8 cc/minute max. If your numbers are correct for the electric system, then you will surely be at less than half throttle with a consumption of less than 4 cc/minute.

This is getting up to over 8 hours of flight time on your two liters of gas. Much more and you are going to run out of daylight
Do you have a specific requirement for flight time? Do you already have the airframe? You mentioned a simulation. Is this a specific dynamic model where you can set up an extended flight and directly test your flight time?

i guess the real question is whether this is just a paper exercise or are you planning to build a model gas pipeline sniffer or similar product?

John