1. Energy Consumption & Power Requirements of A Vehicle
P M V Subbarao
Professor
Mechanical Engineering Department
Know the Requirements Before You develop an Engine…..

2. Resistance Force : Ra
The major components of the resisting forces to motion are comprised of :
Aerodynamic loads (Faero)
Acceleration forces (Faccel = ma & I forces)
Gradeability requirements (Fgrade)
Chassis losses (Froll resist ).

3. Aerodynamic Force : Flow Past A Bluff Body
Composed of:
Turbulent air flow around vehicle body (85%)
Friction of air over vehicle body (12%)
Vehicle component resistance, from radiators and air vents (3%)

4. Aerodynamic Resistance on Vehicle
Dynamic Pressure:
Drag Force:
Aero Power

5. Cd = coefficient of drag  = air density  1.2 kg/m3
A = projected frontal area (m2) f(Re) = Reynolds number
v = vehicle velocity (m/sec) V0 = head wind velocity
P = power (kw) A = area (m2)
V = velocity (KpH) V0 = headwind velocity
Cd = drag coefficient  = 1.2 kg/m3

6. Purpose, Shape & Drag

7. Shape & Components of Drag

8. Some examples of Cd:
The typical modern automobile achieves a drag coefficient of between 0.30 and 0.35.
SUVs, with their flatter shapes, typically achieve a Cd of 0.35–0.45.
Notably, certain cars can achieve figures of , although sometimes designers deliberately increase drag in order to reduce lift.
0.7 to typical values for a Formula 1 car (downforce settings change for each circuit)
0.7 - Caterham Seven
at least a typical truck
Hummer H2, 2003
Citroën 2CV
over Dodge Viper
Toyota Truck,

9. 0.42 - Lamborghini Countach, 1974
Triumph Spitfire Mk IV,
Plymouth Duster, 1994
Dodge Durango, 2004
Triumph Spitfire,
Volkswagen Beetle
Mazda Miata, 1989
Ford Capri Mk III,
Ferrari F50, 1996
Eagle Talon, mid-1990s
Citroën DS, 1955
Ferrari Testarossa, 1986
Opel GT, 1969
Honda Civic, 2001
Citroën CX, 1974 (the car was named after the term for drag coefficient)
NSU Ro 80, 1967

10. Ford Sierra, 1982
Ferrari F40, 1987
Chevrolet Caprice,
Chevrolet Corvette Z06, 2006
Chevrolet Camaro, 1995
Dodge Charger, 2006
Audi A3, 2006
Subaru Impreza WRX STi, 2004
Mazda RX-7 FC3C,
Citroen SM, 1970
Volkswagen GTI Mk V, 2006 ( with ground effects)
Toyota Celica,
Citroën AX, 1986
Citroën GS, 1970
Eagle Vision
Ford Falcon,
Mazda RX-7 FC3S,
Renault 25, 1984
Saab Sonett III, 1970
Audi 100, 1983
BMW E90, 2006
Porsche 996, 1997
Saab 92, 1947

11. General Motors EV1, 1996
Alfa Romeo BAT Concept, 1953
Dodge Intrepid ESX Concept , 1995
Mercedes-Benz "Bionic Car" Concept, 2005 ([2] mercedes_bionic.htm) (based on the boxfish)
Daihatsu UFEIII Concept, 2005
General Motors Precept Concept, 2000
Fiat Turbina Concept, 1954
Ford Probe V prototype, 1985

12. Rolling Resistance Composed primarily of
Resistance from tire deformation (90%)
Tire penetration and surface compression ( 4%)
Tire slippage and air circulation around wheel ( 6%)
Wide range of factors affect total rolling resistance
Simplifying approximation:

13. ROLLING RESISTANCE
Rolling resistance of a body is proportional to the weight of
the body normal to surface of travel.
where:
P = power (kW)
Crr = coefficient of rolling resistance
M = mass (kg)
V = velocity (KpH)

14. Contact Type
Crr
Steel wheel on rail
Car tire on road
Car tire energy safe
Tube 22mm, 8 bar
0.002
Race tyre 23 mm, 7 bar
0.003
Touring 32 mm, 5 bar
0.005
Tyre with leak protection 37 mm, 5 bar / 3 bar
0.007 / 0.01

15. Rolling Resistance And Drag Forces Versus Velocity

16. Composed of Grade Resistance Gravitational force acting on the vehicle
For small angles, θg Fg θg W

17. Inertial or Transient Forces
Transient forces are primarily comprised of acceleration related forces where a change in velocity is required.
These include:
The rotational inertia requirements (FI ) and
the translational mass (Fma).
If rotational mass is added it adds not only rotational inertia but also translational inertia.

18. Transient Force due to Rotational Mass
= angular acceleration k = radius of gyration t = time T = Torque
m = mass  = ratio between rotating component and the tire

19. Resistance power, Presistance
Therefore if the mass rotates on a vehicle which has translation,
Resistance power, Presistance

20. Power Demand Curve
Presistance
Vehicle Speed

21. Ideal Engine Powering Torque
The Powering Engine Torque is:
The speed of the vehicle in km/h is:
rtire = Tire Rolling Radius (meters)
G = Numerical Ratio between P.E. and Tire
Ideal capacity of Powering Engine:

22. Drive System Efficiency
Drive train inefficiencies further reduce the power available to produce the tractive forces.
These losses are typically a function of the system design and the torque being delivered through the system.

23. Actual Capacity of A Powering engine
Correction for Auxiliary power requirements:

24. MATLAB for Vehicle Torque Requirement

25. MATLAB Model for Transmission System

26. MATLAB Model for Engine Performance

27. Engine Characteristic Surface

28. Requirements of Vehicle on Road & Engine Power

29. Urban Driving Cycle

30. Engine RPM during Urban Driving Cycle

31. Engine Fuel Consumption During Urban Driving Cycle

32. Inverse of Carnot’s Question
How much fuel is required to generate required power?
Is it specific to the fuel?
A Thermodynamic model is required to predict the fuel requirements.
Carnot Model
Otto Model
Diesel Model
A Geometric Model is required to implement the thermodynamic model.