BioPHYSICAL chemistry

The goal of scientists and politicians is to significantly decrease our depend-

ence on petroleum for transportation (see Chapter 12). This equation tells

us that engines have an efficiency that is determined by the difference in

temperature (neglecting real-life factors such as friction), which cannot

be easily changed. Hybrid cars contain a new technological develop-

ment that improves efficiency compared to normal internal combustion

engines – an electric motor that is immediately adjacent to the gasoline

engine (Figure 3.10). The electric motor drives the car primarily during

the startup period until the traveling speed is reached because the effici-

ency of heat engines is best when the engine operates at a constant

rate of revolutions. Since the car is started with the electric motor, the

gasoline motor is turned off when the car is stationary, rather than burn-

ing gasoline while idling, and is only started after the car is moving again.

The energy needed to drive the electric motor comes from a battery that is

separate from the battery used to drive the starter motor and electrical

components. As the electric motor drives the car, the energy available from

this battery decreases. Hybrid cars do not need an additional energy source

to recharge the batteries because they make use of regenerative braking.

62 PARTI THERMODYNAMICS AND KINETICS

Brake

recovery

(a) ICE

(b) HICE

Energy in

100 Reformer

0

Reformer loss

100 18.2 12.6

0

62.4

Engine loss

Idle

17.2

Accessories

2.2

5.6

Drive train loss

5.8

Braking loss

Rolling

and air

resistance

6.8

Engine Drive train Wheels

Brake

recovery

Energy in

47.3 Reformer

0

Reformer loss

47.3 15.6 12.6

2.6 2.9

29.5

Engine loss

Idle

0

Accessories

2.2

5.6

Drive train loss

2.9

Braking loss

Rolling

and air

resistance

6.8

Engine Drive train Wheels

Figure 3.10Comparison of energy flows from an internal combustion engine (ICE) and hybrid
(HICE) car. The ICE makes use of a conventional internal combustion, spark-plug-ignition engine.
The hybrid car has an electric motor and parallel drive train to eliminate idling loss and capture some
of the energy normally lost during braking. Hybrids are much more efficient, with 12.6/47.3 =0.266,
than conventional cars, with 12.6/100 =0.126. Modified from Demirdoven and Deutch (2004).