At the most recent meeting of the engine working group last Tuesday it emerged that constructors are looking for an engine formula that will provide simpler and lighter engines, following a considerable weight increase since the introduction of the Hybrid power units in 2014.
Because ethanol has much less energy density compared to the normal race fuel
Ethanol is not "the biofuel". Only one kind. I don't remember any particular restrictions on biofuel, from when I looked at it. Is there any?
In the F1 rules? Nope. So far the FIA didn't define what exactly they mean with "Biofuel".
Propably they go for BtL (Biomass to Liquid) which basically allows you to produce any kind of liquid fuel you want, even petrol.
propane/butane etc content is strongly limited by restriction on fuel composition by carbon atom count and vapour pressure
ok within those limits using bio propane/butane could make sense - minimising loss from biofuel overall
and isobutanol ie bioisobutanol matches gasoline in mass-specific energy
btw butanol could have been useful in 'old' F1
having much higher heat per mass of air than gasoline or the lower alcohols eg ethanol or methanol
In the 2021 fuel regulations, they go to some extent in describing "Advanced Sustainable component" and "Second generation biocomponents" in the Fuel definitions section, but then in the Composition of the fuel section the only mention of biofuel is this:
16.4.4 A minimum of 10% (m/m) of the fuel must comprise advanced sustainable Ethanol.
It seems the details are still work in progress, which would also explain the absence of the race fuel max allowance, while the max fuel flow rate is kept at 100kg/h.