Vehicle Propulsion Systems

Modelling of Automotive Systems 1

Objectives To introduce mathematical models and optimization methods that allow a

systematic minimization of the energy consumption of vehicle systems.

VehicleA vehicle is a means of transport, such as bicycles, cars, motorcycles, trains, ships, and

aircraft. Vehicles that do not travel on land are often called crafts, such as watercraft, sailcraft, aircraft, hovercraft and spacecraft. Most land vehicles have wheels.

Scope of the vehicle: Passenger cars1. Autonomous2. Refuelling time short3. Transport 2-6 people4. Acceleration 10-15 seconds to 100km/h, and 5%ramp at legal top speed

Vehicle Propulsion Systems


PowertrainA group of components that generate power and deliver it to the road surface, water, or air, including the engine, transmission, driveshafts, differentials, and the final drive (drive wheels, caterpillar track, propeller, etc.).

The vehicle Powertrain consists primarily of •The Engine (Shown in orange), typically Diesel or Gasoline, but other combustionconcept exist or are on the “horizon”.•The Transmission (Shown in green), either a manual, automatic, continuously/infinitely variable transmission, or a hybrid Powertrain with additional electrical components!•After-treatment Systems such as catalysts or particulate traps (Shown in blue)•Electronic Control Units (ECU) and Control Software

EPSRC


Energy sourcesHydrocarbons: petroleum (Fossil/mineral or biofuel) , coal, and natural gasHydrogen – fuel cellBatteries

Biofuel (agrofuel) can be broadly defined as solid, liquid, or gas fuelconsisting of, or derived from biomass.

Biomass is grown from plants, including miscanthus, switchgrass, hemp, corn, poplar, willow and sugarcane

On-board energy carrier requirementsHigh energy densitySafe and no environmental hazards in production or operation.


Vegetable Oil Fuel

To reduce the viscosity, biodiesel recipe:1. 1 litre of vegetable oil.2. 200 millilitres of methanol (95% pure).3. 5 grams of sodium hydroxide.

Vegetable Oil Fuel HeatersVegetable Oil is much thicker than mineral diesel at typical ambient temperatures. Therefore, if a vehicle is to be powered by vegetable oil, the oil must be heated before it reaches the fuel filter and the engine's injectors,


3 energy conversion steps:

- well to tank

- tank to vehicle

- vehicle to miles


PP-power plant


Energy Densities

• From tank to wheel energy• CNG-compressed natural gas


Batteries as ‘fuel’

Electrochemical on-board energy carriers -Batteries have low density.Used as auxiliary energy storage to improve IC efficiency (hybrid)

• Lead-acid 30Wh/kg• Nickel-metal hydrides 60Wh/kg• ‘hot’ batteries 150Wh/kg (such as sodium-nickle chloride ‘zebra’ battery)• Improvements are slow• Take long time to ‘refuel’


Pathway to better fuel economy

• Improve well to tank efficiencyby optimizing upstream processes

• Improve tank to wheel efficiency by 1. improve the peak efficiency of components

2. improve the part load efficiency3. recuperate kinetic and potential energy in the vehicle4. control propulsion system configuration

• Improve wheel to mile efficiency by reducing the vehicle mass and aerodynamic and rolling losses


Vehicle Energy

• Kinetic energy when have speed

• Potential energy when have altitudes

Vehicle Energy Losses (after engine)

• Aerodynamic drag • Rolling friction• Brake dissipation


Forces acting on vehicle on motion

( )

forceedisturbancothertF

componentforcegravitytFfrictionrollingtF

frictioncaerodynamitFforcemoverprimetF

where

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tdvm

d

g

r

a

t

dgratv

__:)(

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_:)(__:)(

)()()()()()(+++−=

Courtesy L.Guzzella et al


Aerodynamic Friction

2

21)( vcAvF dfaa ρ=

Rolling Friction

etcconditionsurfaceroad

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t

r

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,__:..._:

__:

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Gravity force component

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rm

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++++−=

=

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where

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2γ


Performance and Drivability

Top speed

Maximum gradient at which vehicle reaches legal top speed

Acceleration time to 100km/h (60miles/h)

Top speed power (aerodynamic resistance dominant)

3maxmaxmax 2

1 vcAvFP dfaa ρ=≈


Performance and Drivability Uphill driving power maxminmax sinαgmvP v≈


Performance and Drivability Energy required to accelerate the vehicle from 0 to 0v (estimate)

200 2

1 vmE v=

Let mean power

0

0

tEP =

Take

2maxPP =

Time required to accelerate the vehicle from 0 to 0v

max

200

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e.g. seconds100 =t ,

( ) HPKWs

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0

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max ==×

==


Vehicle Operating Modes When coasting on horizontal road and without disturbances

rvdfav gcmtvcAdt

tdvm −−= )(21)( 2ρ

or

rdfav

rdfav

gccAm

where

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tdvor

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tdv

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−−=

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22

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βρβ

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ρ



( )

( ) ( )

( ) ( )

−=

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−=

−=

+

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00

ββββ

ββ

ββββ

ββ

ββ

ββ

ββββ

ββ

β

This is a slop with negative gradient – coasting gradient



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tdvm −−= )(21)( 2ρ

( ) ( )

−= tvtv 21

2

1

1

2 0arctantan ββββ

ββ

3 operating modes can be identified from the vehicle speed curve Traction mode: gradient > coasting gradient Braking mode: gradient < coasting gradient Coasting mode: gradient = coasting gradient


0 20 40 60 80 100 120 140 160-5

0

5

10

15

20

25

30Coasting velocity

t (s)

v (m

/s)

( )( )

( ) smttvor

ttvgc

cAm

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r

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/0060.09151.0tan37.21)(

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/78.27/100,013.0,7.02.05.3,1500vehiclesize full aFor :Example

2

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02

−=

−×=

=×==

=×××

==

====×==

β

ρβ


0 20 40 60 80 100 120 140 160-20

0

20

40

60

80

100

120

v (k

m/h

)

t (s)

Coasting velocity


Vehicle Operating Modes

Traction

0>tF

Braking

0<tF

Coasting

0=tF

L.Guzzella et al

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Vehicle Propulsion Systems