I have a generator with carburetor. It seems to consume a bit more fuel than I expected, 0.44 liters per hour for 386 watt production, or 1.14 liters per kWh. I'm also bit more annoyed by the exhaust fumes than I expected to be for a 4-stroke engine.
One factor that might affect the fuel consumption and exhaust fumes is the type of gasoline used. I understand that today nearly every location on this planet is using E10 gasoline (10% ethanol, 90% fossil fuel). However, I'm not using that and I'm not using E0 either; I'm using "small engine gasoline" that consists of only simple chain hydrocarbons and contains no aromatic hydrocarbons. The small engine gasoline has been specifically created to stay useful for 3-5 years in storage, to never block carburetors even if aged, and to evaporate completely without leaving any residue.
The small engine gasoline has bit different properties that normal gasoline:
- 95 E0 without oxygen: 32.7 MJ/l, 755 kg/m3, H/C 1.78
- 95 E10: 31.1 MJ/l, 743 kg/m3, H/C 1.89; 3.2% O
- small engine gasoline: 30.8 MJ/l, 685 kg/m3, H/C 2.17
I'm trying to understand how a carburetor works. If I have a carburetor and one cubic meter of air passes through it, it picks up some amount of fuel. I understand that the fuel is in the liquid state, so the carburetor isn't pulling evaporated gas but rather liquid that forms droplets and evaporates in the cylinder.
But how is the amount of fuel picked up by the carburetor determined?
Does it pick a certain volume of liquid fuel, such as always one liter of fuel per one cubic meter of air (just an example, not to suggest that would be correct air/fuel ratio)?
Or does it pick a certain mass of liquid fuel, such as always one kilogram of fuel per one cubic meter of air?
Or does it pick a certain number of fuel molecules, such as 4*1024 molecules per one cubic meter of air?
Of course the air pressure affects the operation of the carburetor, so let's assume the altitude is fixed, and the position of the choke valve is fixed.
I quickly calculated that one liter of both 95 E10 and small engine gasoline require almost the same number of external oxygen atoms to burn (only 0.5% difference), but that one kilogram of small engine gasoline requires 8% more oxygen atoms to burn than one kilogram of 95 E10. So if the carburetor is "picking kilograms" rather than "picking liters", then its adjustment might be off for the small engine gasoline, which might explain the annoying exhaust and little bit higher fuel consumption than what I expected (however, the little bit higher fuel consumption can also be explained by 6% lower energy density of small engine gasoline when compared with oxygenless 95 E0 -- it's possible the manufacturer has stated the fuel consumption with oxygenless 95 E0).