Blended fuels by DEFRA
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The methodology
Emissions model
Blended fuels are made up from a mixture of conventional fuels (diesel, petrol compressed natural gas) and biofuels (biomethane, biodiesel, bioethanol). Given that each component is associated with different quantities of greenhouse gas emission, the type of blend together with the precise proportion of conventional to biofuel in the mixture determines the quantity of greenhouse gases emitted on combustion.
The emissions calculation methodology is based upon emissions factors which relate mass, volume, or energy-based quantities of biofuels and conventional fuels with their associated quantity of greenhouse gas emissions. By specifying the type of blend and the relative proportion of the conventional and biogenic components, the emissions arising from the combustion of the blended fuel can be calculated.
Because the biofuels components represented in this methodology are derived from recently grown biomass, the direct emissions they produce on combustion are mostly benign from the point of view of atmospheric warming: the carbon released from the biofuel has only recently been sequestered from the atmosphere (during plant growth) and therefore does not represent a net contributor to atmospheric CO2 concentrations. As such, emissions according to this methodology are differentiated into several types:
- 'direct' emissions represent those greenhouse gases emitted during combustion which do cause a net contribution to atmospheric CO2 concentrations.
- 'indirect' emissions represent those greenhouse gases emitted in association with stages in the fuel production chain such as raw material extraction and delivery, and therefore considered to 'embodied' within the fuel.
- 'life cycle' emissions are to sum of direct and indirect emissions which contribute to atmospheric CO2 concentrations.
- Emissions which are 'outside of scopes' are equivalent to the CO2 absorbed from the atmosphere during growth of the biomass. These do not cause a net contribution to atmospheric CO2 concentrations
Model data
The data used for this methodology are referenced from the DEFRA methodologies for biofuels and conventional fuels assocaited with biofuel blends. All bio- and conventional fuel components are represented by the following types of emissions factor:
- direct emissions by mass: direct CO2e emissions per unit fuel mass
- indirect emissions by mass: indirect CO2e emissions per unit fuel mass
- life-cycle emissions by mass: total/life-cycle CO2e emissions per unit fuel mass
- non-scope / biogenic emissions by mass: biogenic CO2 emissions per unit fuel mass
- direct emissions by volume: direct CO2e emissions per unit fuel volume
- indirect emissions by volume: indirect CO2e emissions per unit fuel volume
- life-cycle emissions by volume: total/life-cycle CO2e emissions per unit fuel volume
- non-scope / biogenic emissions by volume: biogenic CO2 emissions per unit fuel volume
- direct emissions by energy: direct CO2e emissions per unit fuel energy
- indirect emissions by energy: indirect CO2e emissions per unit fuel energy
- life-cycle emissions by energy: total/life-cycle CO2e emissions per unit fuel energy
- non-scope / biogenic emissions by energy: biogenic CO2 emissions per unit fuel energy
Similar methodologies
The DEFRA methodologies for biofuels and conventional fuels associated with biofuel blends are also available
How to use this category
Choosing a specific activity type
To use this methodology, specify the fuel type using the fuel drill down choice.
Activity data required
Since emisisons according to this methodology are directly proportionate to fuel quantity, the quantity of fuel used must be specified using either the mass, volume or energy profile item values. in addition, the proportion of biofuel within the blend must be specified using the biofuelPercentage profile item value, as a decimal percentage (i.e. 0-1). This value is set to 1 by default, which represents 100% conventional fuel.
Results and calculation
CarbonKit returns the quantity of greenhouse gas emissions associated with the quantity of blended fuel specified. The following discrete amounts are returned:
- directCO2e: direct CO2e emissions
- indirectCO2e: indirect CO2 emissions
- lifeCycleCO2e: life-cycle CO2e emissions
- bioCO2: biogenic CO2 emissions
Notes
The data for this category is based upon those within the DEFRA methodologies for biofuels and conventional fuels associated with biofuel blends. In both cases, CarbonKit has used fuel property data published in the same DEFRA GHG Conversion Factors source documentation in order to provide a full suite of emissions factors for use on the bases of mass, volume or energy quantities. This methodology follows that additional functionality in being able to calculate via each of these bases.
One exception is that of the biomethane/cng blended fuel. In this case, the density values provided by DEFRA for each of the respective fuels are incompatible - one be at standard atmospheric pressure (biomethane), the other in a compressed state (CNG). As such, the conversion of emissions factors from a mass basis into a volumetric basis for these fuels is not equivalent and therefore the combination of thus derived volumetric emissions factors into a calculation for their blend is not valid.
The volumetric option for biomethane/cng therefore returns 0, and any calculation for this blend must specify fuel quantity on either a mass or energetic basis.