Vehicle-specific power

The concept of vehicle-specific power (VSP) is a formalism used in the evaluation of vehicle emissions. The idea was first developed by J. L. Jiménez Template:Harv at the Massachusetts Institute of Technology.Template:SfnTemplate:Sfn Informally, it is the sum of the loads resulting from aerodynamic drag, acceleration, rolling resistance, and hill climbing, all divided by the mass of the vehicle.Template:Sfn Conventionally, it is reported in kilowatts per tonne,Template:Sfn the instantaneous power demand of the vehicle divided by its mass.Template:Sfn VSP, combined with dynamometer and remote-sensing measurements, can be used to determine vehicle emissions.Template:Sfn

The United States Environmental Protection Agency held a "modelling shootout" in 2001, to help with the development of its (then) new MOVES (motor vehicle emissions simulator) vehicle emissions model. Two of the four modelling metholodogies in the shootout, one from North Carolina State University Template:Harv and one internal to the EPA, used vehicle-specific power metrics.Template:SfnTemplate:Sfn MOVES was eventually implemented using vehicle-specific power as its primary metric.Template:Sfn (See Template:Harvnb for the EPA MOVES draft VSP specification.)

Formulae

Jiménez's own formula is:

$\mathrm{V}\mathrm{S}\mathrm{P}=\frac{\mathrm{p}\mathrm{o}\mathrm{w}\mathrm{e}\mathrm{r}}{\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}}=\frac{\frac{\mathrm{d}}{\mathrm{d}t}(E_{\mathrm{k}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{t}\mathrm{i}\mathrm{c}}+E_{\mathrm{p}\mathrm{o}\mathrm{t}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}})+F_{\mathrm{r}\mathrm{o}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{g}}\cdot v+F_{\mathrm{a}\mathrm{e}\mathrm{r}\mathrm{o}\mathrm{d}\mathrm{y}\mathrm{n}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{c}}\cdot v+F_{\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{n}\mathrm{a}\mathrm{l}}\cdot v}{m}$Template:Harv

VSP can be simplified using typical coefficient values. Haibo Zhai of North Carolina State University provides the following formula for transit buses:

Template:MathTemplate:Sfn

where:

v

vehicle speed (in metres per second)

a

vehicle acceleration (in metres per second per second)

g

acceleration due to gravity (gee, in metres per second per second)

φ

road grade

ψ

rolling resistance coefficient (metres per second per second)

ζ

drag coefficient (reciprocal metres)

References

Sources

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Further reading

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