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Alternative Fuels for Transportation
headwind velocity (m/s), g ( = 9.8 m/s 2 ) the gravitational acceleration, and A
the frontal cross-sectional area (m 2 ) of the car.
From the parameters associated with a typical modern medium-size car;
that is, M = 1400 kg, A = 2.2 m 2 , C t = 0.01, C a = 0.3, d = 1.17 kg/m 3 , its power
requirements may be estimated from Equations 11.2 through 11.5. For the
irreversible losses, Equations 11.4 and 11.5 show that while P tires is linearly
dependent on velocity, P aero varies as the third power of velocity and although
negligible at low velocities, the latter becomes the dominant irreversible loss
at high speed. As an example, for these parameters, for a car traveling at about
50 km/h, tire friction is twice the aerodynamic drag and together amount to
about 3 kW. At 100 km/h highway cruising, aerodynamic drag increases considerably to over twice the tire friction, increasing the total power requirement to about 12 kW. It is noteworthy that for both these estimates, the wind
speed (w) has been taken to be zero for the sake of simplicity. But, in practice,
the effect of wind speed on the performance of the car could be quite substantial. For example, P aero at a favorable tailwind speed of 30 km/h will be
as low as 0.8 kW but would amount to 4 kW at a similar opposing tailwind
velocity. Accordingly, the energy performance of the car will drop from 40
km/kWh to 15 km/kWh (Wicks and Marchionne 1992). Taking the example of a hill with a substantial 10% gradient, climbing at 100 km/h requires
about 50 kW, including tire friction and aerodynamic drag. Acceleration is
more demanding, particularly at high velocities. For example, acceleration at
5 km/h/s requires 30 kW at 50 km/h but increases to 66 kW at 100 km/h.
The above estimates are for the power supplied to the wheel of the car and
do not include the losses incurred in delivering that power to the wheels.
At this time in the development of electric traction systems, a precise estimate of this is difficult to obtain but anecdotal information suggests that
the efficiency of the power conditioning electronics together with the electrical and mechanical drivetrain is likely to be about 0.85. Additional power
may also be required to power the accessories like radio, lights, steering, airconditioning, and so on, which is likely to add about 5 kW to the total power
demand of the car.
An analysis of this kind indicates that the power plant of a modern car
must be capable of delivering about 65 kW of sustained power for accessories
and hill climbing, with burst-power requirement for a few tens of seconds to
about 105 kW during acceleration. For a car with these performance characteristics, this sets the upper power limit, but in common usage rarely exceeds
20 kW while cruising.
The heating value of gasoline-fuel is 32.5 MJ/l but a heating value of only
6.5 MJ/l will be available with an ICEV of near 20% well-to-wheel efficiency.
This is about 1.82 kWh/l of gasoline-fuel and considering the average drive
range of the car with the parameters listed above as ~10 km/l, it would
amount to 182 Wh/km. The heating value of diesel fuel is 35.95 MJ/l and
accordingly the estimated energy will be 201 Wh/km for diesel-driven cars,
which have well-to-wheel efficiency of about 30% and a drive range of about
Alternative Fuels for Transportation
headwind velocity (m/s), g ( = 9.8 m/s 2 ) the gravitational acceleration, and A
the frontal cross-sectional area (m 2 ) of the car.
From the parameters associated with a typical modern medium-size car;
that is, M = 1400 kg, A = 2.2 m 2 , C t = 0.01, C a = 0.3, d = 1.17 kg/m 3 , its power
requirements may be estimated from Equations 11.2 through 11.5. For the
irreversible losses, Equations 11.4 and 11.5 show that while P tires is linearly
dependent on velocity, P aero varies as the third power of velocity and although
negligible at low velocities, the latter becomes the dominant irreversible loss
at high speed. As an example, for these parameters, for a car traveling at about
50 km/h, tire friction is twice the aerodynamic drag and together amount to
about 3 kW. At 100 km/h highway cruising, aerodynamic drag increases considerably to over twice the tire friction, increasing the total power requirement to about 12 kW. It is noteworthy that for both these estimates, the wind
speed (w) has been taken to be zero for the sake of simplicity. But, in practice,
the effect of wind speed on the performance of the car could be quite substantial. For example, P aero at a favorable tailwind speed of 30 km/h will be
as low as 0.8 kW but would amount to 4 kW at a similar opposing tailwind
velocity. Accordingly, the energy performance of the car will drop from 40
km/kWh to 15 km/kWh (Wicks and Marchionne 1992). Taking the example of a hill with a substantial 10% gradient, climbing at 100 km/h requires
about 50 kW, including tire friction and aerodynamic drag. Acceleration is
more demanding, particularly at high velocities. For example, acceleration at
5 km/h/s requires 30 kW at 50 km/h but increases to 66 kW at 100 km/h.
The above estimates are for the power supplied to the wheel of the car and
do not include the losses incurred in delivering that power to the wheels.
At this time in the development of electric traction systems, a precise estimate of this is difficult to obtain but anecdotal information suggests that
the efficiency of the power conditioning electronics together with the electrical and mechanical drivetrain is likely to be about 0.85. Additional power
may also be required to power the accessories like radio, lights, steering, airconditioning, and so on, which is likely to add about 5 kW to the total power
demand of the car.
An analysis of this kind indicates that the power plant of a modern car
must be capable of delivering about 65 kW of sustained power for accessories
and hill climbing, with burst-power requirement for a few tens of seconds to
about 105 kW during acceleration. For a car with these performance characteristics, this sets the upper power limit, but in common usage rarely exceeds
20 kW while cruising.
The heating value of gasoline-fuel is 32.5 MJ/l but a heating value of only
6.5 MJ/l will be available with an ICEV of near 20% well-to-wheel efficiency.
This is about 1.82 kWh/l of gasoline-fuel and considering the average drive
range of the car with the parameters listed above as ~10 km/l, it would
amount to 182 Wh/km. The heating value of diesel fuel is 35.95 MJ/l and
accordingly the estimated energy will be 201 Wh/km for diesel-driven cars,
which have well-to-wheel efficiency of about 30% and a drive range of about