Simple carbon emissions from fuel and fire calculations I would like to get the simple carbon emissions calculations below written in the most Pythonic / straightforward way.

FUEL_FACTORS = {'diesel': {'energy_factor': 38.6,
                           'co2_emission_factor': 69.9,
                           'ch4_emission_factor': 0.1,
                           'n2o_emission_factor': 0.5
                          },
                'petrol': {'energy_factor': 34.2,
                           'co2_emission_factor': 67.4,
                           'ch4_emission_factor': 0.5,
                           'n2o_emission_factor': 1.8
                           },                
                'avgas':  {'energy_factor': 33.1,
                           'co2_emission_factor': 67.0,
                           'ch4_emission_factor': 0.05,
                           'n2o_emission_factor': 0.7}
                }

FIRE_FACTORS = {'gwp_co2': 1,
                'gwp_ch4': 25,
                'gwp_n2o': 298,
                'ch4_co2_mass_ratio': 7.182e-3,
                'n2o_co2_mass_ratio': 1.329e-5,
                }

def get_fuel_emission_factor(fuel):
    """Get fuel total CO2 emission factor."""
    factors = FUEL_FACTORS[fuel]
    energy_f = factors['energy_factor'] 
    fuel_emission_factor = 0
    for i in ['co2', 'ch4', 'n2o']:
        gas_emission_factor = factors[i + '_emission_factor']
        fuel_emission_factor += energy_f * gas_emission_factor * 1e-3
    return fuel_emission_factor

def fuel_to_co2(fuel, quantity):
    """Get total tCO2 emission by kL of fuel."""
    fuel_emission_factor = get_fuel_emission_factor(fuel)
    return fuel_emission_factor * quantity     


def burned_c_to_co2(tC):
    """Get CH4 and N2O emissions in tCO2 from tonnes of C burned"""
    ch4_emissions = tC * FIRE_FACTORS['gwp_ch4'] * FIRE_FACTORS['ch4_co2_mass_ratio']
    n2o_emissions = tC * FIRE_FACTORS['gwp_n2o'] * FIRE_FACTORS['n2o_co2_mass_ratio']
    return ch4_emissions + n2o_emissions

fuel_emissions = fuel_to_co2('petrol', 2.7395)
fire_emissions = burned_c_to_co2(5.74)
Define a constant for greenhouse gases GHG to avoid hard-coding them in separate functions:

GHG = ('co2', 'ch4', 'n2o')  # greenhouse gases



get_fuel_emission_factor function.
The for loop with accumulation is concisely replaced with builtin sum function on generator expression:

def get_fuel_emission_factor(fuel):
    """Get fuel total CO2 emission factor."""
    factors = FUEL_FACTORS[fuel]
    return sum(factors['energy_factor'] * factors[f'{gas}_emission_factor'] / 1000
               for gas in GHG)

fuel_to_co2 function.
Inline variable technique can be applied:

def fuel_to_co2(fuel, quantity):
    """Get total tCO2 emission by kL of fuel."""
    return get_fuel_emission_factor(fuel) * quantity