Advance Powertrain Systems - Vehicle Energy Consumption

Vehicle Energy Consumption (kWh)

• Efficiency Rating:
  • Expressed in miles per kilowatt-hour (miles/kWh) or kilometers per kilowatt-hour (km/kWh).
• Factors Affecting Energy Consumption:
  • Driving Behavior:
    • Aggressive driving (rapid acceleration, heavy braking) increases energy consumption.
    • Smooth, gradual driving is more efficient.
  • Terrain and Elevation:
    • Hilly terrain or higher elevations increase energy consumption.
  • Temperature:
    • Extreme temperatures (especially cold) reduce battery efficiency.
    • Increases energy consumption for heating/cooling.
  • Speed:
    • Higher speeds require more energy due to aerodynamic drag.
  • Payload and Weight:
    • Additional weight reduces energy efficiency
  • Tire Pressure:
    • Underinflated tires increase rolling resistance.
  • Auxiliary Features:
    • Air conditioning, heating, infotainment systems increase energy usage.
• Formula:
  • $Vehicle\ Efficiency\ (km\ per\ kWh) = \frac{Distance\ Driven\ (km)}{Vehicle\ Energy\ Consumption\ (kWh)}$

Energy Loss in Vehicles

• Gasoline-Powered Vehicle:
  • Approximately 80% of the energy is lost due to inefficiencies.
  • Engine losses: 62-69%.
  • Drivetrain losses: 5-7%.
  • Parasitic losses: 4-6%.
  • Auxiliary electricity use: 0-4%.
  • Aerodynamic losses: 3-11%.
  • Rolling losses: 16-25%.
  • Braking losses:
    • Urban driving: 3%. Recaptures 22% of original energy through regenerative braking.
    • Highway driving: 2%.
  • 16-25% of original energy goes to wheels.
• Electric Vehicle (EV):
  • Approximately 11% of energy is lost.
  • Charging loss: 10%.
  • Drivetrain losses: 0-2%.
  • Auxiliary electricity use: 2-4%.
  • 87-91% of original energy goes to wheels.

EV vs. ICE Vehicle Efficiency

• Energy Efficiency:
  • EVs: 85-90% efficiency in converting grid energy to movement.
  • ICE Vehicles: 20-30% efficiency in converting gasoline energy to motion, with significant heat loss.
• Energy Consumption per Mile:
  • EVs: 0.25-0.35 kWh per mile (15-22 kWh per 100 km).
  • Petrol Cars: 0.3-0.35 litres per mile (8-10 litres per 100 km).
• Energy Consumption Comparison :
  • EVs: Approximately 0.3 kWh per mile.
  • Petrol Vehicles: Approximately 3.4 kWh per mile (after converting fuel to energy).
• Energy Cost Comparison:
  • Electricity: £0.10-£0.30 per kWh, resulting in £0.03-£0.09 per mile.
  • Petrol: Assuming £1.40 per litre and 0.35 litres per mile consumption, the cost is around £0.4 per mile.
• Environmental Impact:
  • EVs: Zero tailpipe emissions; overall impact depends on electricity source (renewables vs. fossil fuels).
  • ICE Vehicles: Significant CO2 and other pollutants from exhaust.
• Overall Efficiency:
  • EVs are 3-4 times more efficient than petrol vehicles.
• Cost: EVs generally cheaper per mile in terms of energy cost.

Drive Cycles

• Essential for vehicle development, testing, and regulation.
• Used to measure fuel consumption and emissions under standardized conditions.
• Regulatory agencies require manufacturers to meet emission and fuel economy standards.
• Simulate real-world vehicle operation under controlled conditions for:
  1. Emissions and Fuel Economy Testing
  2. Battery and Energy Management in EVs
  3. Vehicle Performance Evaluation
  4. Powertrain Development and Calibration
  5. Standardization and Comparisons

WLTP vs NEDC

• Fuel Consumption Measurement:
  • Europe: Fuel consumption (urban, extra-urban, combined) and $CO_2$ emissions measured in litres/100 km and g/km using chassis dynamometer tests.
  • Since September 2018: WLTP (Worldwide Harmonised Light Vehicle Test Procedure) replaced NEDC (New European Driving Cycle).
  • NEDC fuel consumption determined from CVS dilute sample emission measurements.
  • Similar procedures used in other countries (e.g., FTP75 in the USA).

Worldwide Harmonised Light Vehicle Test Procedure (WLTP)

• Developed by the European Union as a new test procedure.
• WLTP uses real-driving data gathered globally, unlike the theoretical driving profile of NEDC.
• Came into force in 2017.
• Driving cycle divided into four parts with different average speeds: low, medium, high, and extra high.
• Each part includes driving phases, stops, acceleration, and braking.
• Each powertrain configuration is tested for the lightest and heaviest version of a car type.
• Aims to be a global test cycle for comparable emission and fuel consumption values worldwide.
• Classes are defined based on power to mass ratio (PMR).

New European Drive Cycle (NEDC)

• Carried out at a constant ambient temperature of $22 ± 2°C$, following a temperature soak of at least 6 hours.
• Robot driver typically controls engine speed and gear changes on manual transmission vehicles.
• Distance = 11.007 km, Time = 1180 s (280 s idling), Maximum speed = 120 km/h, Average speed = 33.6 km/h.
• Standardized test procedure used in Europe to assess:
  • Vehicle emissions ($CO_2$, NOx, etc.)
  • Fuel consumption
  • Electric vehicle range
• Simulates typical urban and non-urban driving conditions.
• Replaced by WLTP due to criticisms regarding its realism.

NEDC Composition

• Made up of two main cycles: urban and extra-urban.
• Urban cycle: Four repeated ECE-15 driving cycles commencing immediately on engine start.
  • Distance = 4.052 km
  • Time = 780 s (195 s per ECE-15 cycle)
  • Maximum speed = 50 km/h
  • Average speed = 18.7 km/h (including idling)
• Extra Urban cycle:
  • Distance = 6.955 km
  • Time = 400 s
  • Maximum speed = 120 km/h
  • Average speed = 62.6 km/h

NEDC Illustration

• Larger distance covered in the extra urban part.
• Only gears 1, 2, and 3 are used for the urban cycle.
• Fuel consumption:
  • Urban: 8.2 litres/100 km
  • Extra-Urban: 5.1 litres/100 km

WLTP vs NEDC: Key Differences

Chassis Dynamometer Review

• Rolling road
• Aerodynamic and rolling resistance loads programmed from coast down test
• Road speed fan for cooling air
• Legislative cycles programmed
• Robot driver possible

ICE Vehicle Fuel Consumption and CO2 Emissions

• Fuel economy values (litres/100 km) for urban and extra urban cycles are determined separately based on exhaust gas samples and fuel chemical composition.
• Combined cycle fuel consumption is calculated based on the distance covered in urban and extra urban parts.
  • Example (NEDC): 4.05 km / 11.0 km = 37% in the urban cycle
• Combined fuel consumption formula:
  • $Combined\ fuel\ consumption = 0.37 \times Urban + 0.63 \times Extra\ Urban$
• Example: 2009 Ford Fiesta (1.25 litre gasoline engine)
  • Urban: 7.3 litres/100 km
  • Extra urban: 4.3 litres/100 km
  • Combined: $0.37 \times 7.3 + 0.63 \times 4.3 = 5.4$ litres/100 km

Fuel Properties and $CO_2$ Emission

• Fuel consumption is a volumetric quantity, and $CO_2$ emission is a gravimetric unit; therefore, liquid fuel density is required.
• Ratio of $CO_2$ mass to fuel mass is based on the carbon content of the fuel.
• Typical Fuel Properties:
  

  Fuel Type	Fuel Density ρ (kg/m3)	Carbon Content % by mass
  Gasoline	750	86.5
  Diesel	840	86.5

• Mass of $CO_2$ per kg of gasoline or diesel fuel:
• $(\frac{44}{12}) \times 0.865 = 3.172 \frac{kg}{kg\ of\ fuel}$
• Published $CO<em>2$ emission figures are based on combined cycle fuel consumption and fuel properties (not a direct $CO</em>2$ measurement).
• $CO_2$ emissions = $(\frac{5.4}{100}) \times 750.0 \times 3.172 = 128.47 \frac{g}{km}$

$CO_2$ Emission Calculation

• For a gasoline engine, the combined fuel consumption is 5.4 litres/100 km.
• Therefore, the $CO_2$ emissions would be: $(\frac{5.4}{100}) \times 750.0 \times 3.172 = 128.47$ g/km (official figure is 128 g/km)
• $FE = Fuel\ Economy\ (\frac{litres}{Km})$
• Fiesta Gasoline (1.25 litre TDCi)
• Unit for $CO_2$ emissions: g / km
• The equivalent $CO_2$ calculation would give: $(\frac{4.2}{100}) \times 840 \times 3.172 = 111.9 \frac{g}{km}$

$CO_2$ Calculation Formula

• Given: combined fuel consumption of 4.2 litres/100 km for a diesel engine (1.6 litre TDCi).
• $CO_2\ (\frac{g}{km}) = FE\ (\frac{litres}{100\ km}) \times K$
  • Where:$K = (\frac{kg}{m^3}) \times (\frac{kg\ of\ CO_2}{kg\ of\ fuel})$
• Values of K for different fuel types:
  • K (gasoline) = 23.8 $\frac{100\ g\ CO_2}{litre\ fuel}$
  • K (diesel) = 26.6$\frac{100\ g\ CO_2}{litre\ fuel}$

Top Gear Steady-State Fuel Consumption Calculation

• Given data:

• M = Vehicle mass (including driver) = 1350.0 kg
• $g_t$ = Top gear ratio = 1.0
• $g_{fd}$ = Final drive axle ratio = 3.705
• r = Rolling radius = 0.281 m
• $A_d$ = Rolling resistance coefficient = 0.013
• $C_d$ = Aerodynamic drag coefficient = 0.32
• A = Projected frontal area = 1.95 m2
• Transmission efficiency = 92%
• Fuel density = 750 kg/m3
• Air density = 1.23 kg/m3

• Find Engine speed from vehicle speed of 100 kph

• Given:

  • M=1350.0 kg
  • gt =1.0
  • gfd = 3.705,
  • r = 0.281 m
  • Ad = 0.013
  • Cd = 0.32
  • A = 1.95 m2
  • ζT = 92%
  • ρf = 750 kg/m3
  • ρa = 1.23 kg/m3

Where:

• K1 = $\frac{2π}{60}$ engine speed

• wheel speed

• K2 = $ζT (\frac{1}{ grt })$

• K3 = r

• v= r ωw

• ζT = Transmission efficiency

• grt = overall gear ratio

BSFC Interpolation Calculation

\begin{aligned}
& BSFC = 345.0 - \frac{(38.56 - 35)}{(40-35)}*(345- 320)\
& BSFC = (345.0 – 17.8) = 327.2 g/kW.h
\end{aligned}

Steady State Fuel Consumption Calculation

• Given: Vehicle traveling at a constant 70 km/h, producing 8 kW of brake power, and engine fuel consumption is 300 g/kWh.

• Calculations:

  • Fuel consomption = $\frac{300 * 8 * 1000}{1000*750} = 3.2 litres/ h$

• BSFC = 300 g /kW h

  • liquid fuel density is ρf = 750 kg/m3
  • RMM $CO_2$ = 12+ 32 =44

• Fuel consumption in litres / 100 km = $\frac{3.2 * 100}{70} = 4.5 litres/ 100 km$

Battery Capacity

• Rated in kWh or AhV, battery energy capacity (stored energy) represents the amount of energy available when discharging from fully charged to the "cut-off voltage“ at a specified rate.
  • $Stored\ Energy\ E_s = i \cdot h \cdot V \ (kWh\ or\ AhV )$
  • Stored Energy Es of the battery determines the maximum EV range
  • Energy typically expressed in kWh
• Normal SI energy unit: Joule = 1 watt (W) x 1 second (s)
• ( 1 kWh = 3.6 MJ )

Battery Power Rating

• Determines how quickly the battery can be charged or discharged.
• Based on the current flow to/from the battery.
  • $C-rate = \frac{Charge\ or\ discharge\ current\ (A)}{Battery\ capacity\ (Ah)}$
• For a battery with a capacity of 100 Amp-hrs, 1C equates to a discharge current of 100 Amps.

Battery Terminology

• State of Charge (SOC):
  • Defines instantaneous energy level as a function of the maximum possible stored energy.
  • Expressed as a percentage (%).
  • Normal operation limits SOC to between 20% & 95%.
• Depth of Discharge (DOD):
  • Inverse of SOC, ranging from 0% (@ 100% SOC) to 100% (@ 0% SOC).
• Cycle Life:
  • The number of charge-discharge cycles until the battery capacity falls to 80% of its initial value.

Sample EV problems

• Example 3

  1. A battery electric vehicle has a battery rated at 20 kWh. Assuming that the battery is fully charged at the start of a journey and that the cabin heater and other electrical ancillary devices consume an average of 2.5 kW, calculate the maximum distance (based on the battery being full discharged) that can be driven on a level road at a constant speed of 100 km/h assuming the following vehicle specification:-
     • Total vehicle mass M = 1500 kg
     • Rolling resistance μ= 0.01
     • Aerodynamic resistance Cd = 0.3
     • Frontal area A = 2.2 m2
     • Electrical propulsion system overall efficiency ξ = 82%
       Assume air density ρ= 1.2 kg/m3 [112.8 km]

• Example 4

  1. A 30kWh traction battery has a rated voltage of 300 V.
  • Calculate discharge current 𝑖 , for a 5 hours discharge current rating (0.2C).
  • If a version of the battery is rated for charging at 4C, calculate the maximum charging current. [20A, 400A]

• Example 5

  1. A 1500 kg vehicle travelling at 120 km/h is brought to rest with a constant deceleration rate of 1.0 m/s2 . Ignoring tyre and aerodynamic resistance effects, calculate the maximum total braking power and the battery SOC at the end of the braking operation assuming that 70% of the available kinetic is produced as electrical energy at the battery, the battery has a rating of 0.85 kW.h and an initial SOC of 60%.

• Example 6

  1. A battery electric vehicle has a battery rated at 20 kW.h. Assuming that the battery is fully charged at the start of a journey and that the cabin heater and other electrical ancillary devices consume an average of 2.5 kW, calculate the maximum distance (based on SOC = 0) that can be driven on a level road at a constant speed of 100 km/h assuming the following vehicle specification:-
     • Total vehicle mass = 1500 kg
     • Rolling resistance (Ad) = 0.01
     • Aerodynamic resistance (Cd) = 0.3
     • Frontal area = 2.2 m2
     • Electrical propulsion system overall efficiency = 82%

• Example 7

  1. An electric vehicle has the parameters shown in Table below. What is the range of the vehicle at a steady speed of 50 kmh-1? (Assume energy flow from the battery is without loss).

     • Air density ρ 1.2 kgm-2
     • Drive wheel radius r 0.29 m
     • Car mass M 1100 kg
     • Wheel inertia (all wheels) Iw 8 kgm2
     • Car rolling resistance coefficient AD 0.02
     • Driveline efficiency to transmission input η 0.93
     • Drag coefficient Cd 0.29
     • Car frontal area A 2.0m2
     • Overall gear ratio between motor and wheels gfd 4
     • Inertia of rotating parts of motor and driveline Ie 0.73 kgm2
     • Available battery capacity Ebat 25 kWh

Review

• EV technology developing rapidly
• Limited range the main problem
• Continuing efficiency improvements will occur
• Early vehicles basic, recent models much improved
• Markets very variable, high sales in Norway
• Regenerative braking aspects in future lecture