The base FC value is
interpolated from the stationary
FC
map.
If necessary the base value is corrected to compensate for unconsidered
auxiliary energy consumption for vehicles with Start/Stop. In
Declaration Mode additionally the WHTC correction is applied, see below.
The CO
2 result for the actual mission profile is directly derived from the fuel consumption using a gravimetric
CO2/FC factor.
Fuel Map Interpolation
The interpolation is based on
Delaunay
Triangulation 
and
works as follows:
- Triangulate
the given rpm/torque/fuel points (= x,y,z) to create
a
network of triangles with each point of the map being part of at least
one triangle.
- Find the triangle where the to-be-interpolated
load point (x,y) is inside. If no triangle meets the criterion the
calculation will be aborted.
- Calculate the z-value (= fuel) of the given x,y-point in
the plane of the triangle
Delaunay Triangulation Example
Auxiliary - Start/Stop
Correction
For vehicles with
Start/Stop the fuel
consumption needs to be corrected to consider the wrong auxiliary
energy balance caused by engine stops because VECTO uses a constant
power demand for auxiliaries for the whole mission profile. The
correction consists of the following steps:
- From all 1Hz data points of the VECTO simulation, a linear
regression curve (y=k*x+d) for fuel consumption (unit: grams per hour)
over engine power (unit: kilo-watt) is calculated (see figure below).
- From the difference between the energy consumed by the
auxiliaries in the simulation with Start/Stop function and the target
value (unit kilowatt-hours), a cycle average change in mechanical power
“ΔPe” (unit kilowatt) of the internal combustion engine is calculated
(using an average alternator efficiency and the cycle time with running
engine).
- The correction of the fuel consumption is performed for all
1Hz time steps using: ΔFC (unit: grams per hour) = ΔPe * k
where k = gradient in the regression. If the engine is running
in motoring conditions ΔFC is set to zero.
Example of a linear regression between engine power and fuel consumption
WHTC Correction
The WHTC correction
aims to counter the disadvantages of using a stationary FC map. The
following steps are applied in VECTO for the WHTC correction method:
- VECTO interpolates the fuel consumption for the WHTC load
cycle from the engine fuel map based on the target speed and target
torque as determined based on the engine full-load curve. The results
are FC values for the Urban, Rural and Motorway part.
- The correction factor CFWHTC is calculated using the equation below considering the current mission profile's weighting factors for each
part.
- The factor is multiplied to the FC values for each time
step and the total FC result.
where:
CFWHTC = WHTC Correction Factor [-]
i = index for each part (Urban, Rural, Motorway)
fi = Weighting factor per part [-]
FCmeas_i = WHTC measurement result per part (input parameter) [g/kWh]
FCcalc_i = Calculated FC per part [g/kWh]