Advanced Automotive Technology: Visions of a Super-Efficient Family Car

cycle PM10 emissions estimated in this study.^42 The EVs cause 200-400 percent increases in per-
mile SOX emissions. Also, the lead acid EV causes an increase in NOX of nearly 90 percent, with
the Ni-MH EV causing a small increase.

The 2015 EV results are somewhat better. Again, both the lead acid and Ni-MH almost
eliminate emissions of HC and CO, and they achieve a 60 percent to 70 percent reduction in
PM10 emissions. SOX emissions still increase, as they must considering the high forecasted coal
use in power generation, but the increases are basically cut in half from the 2005 results. The
changes in NOX emissions vary substantially with the battery technologies, with Ni-MH achieving
nearly a 30 percent reduction, while the Pb-acid still causes NOX emissions to increase, by 20
percent.

These results are generally in line with the results of other studies except for the NOX results.
Past studies often have projected a more uniform reduction in NOX emissions from the use of
EVS,^43 though this is by no means universal. OTA’s projections for gasoline vehicles’ NOX
emissions may be optimistic, however. Unless there are strong improvements in inspection and
maintenance programs, and excellent success for projected changes in EPA’s certification testing
program (designed to reduce emissions during vehicle acceleration and other high-load
conditions), gasoline vehicles may have substantially higher on-road emissions than projected in
this analysis--especially as they age. Given the virtual certainty of obtaining low EV fuel cycle
emissions, these results indicate that EVs generally will yield significant emissions benefits on a
“per-vehicle” basis.

HYBRID VEHICLES

As noted in the introduction to this section, hybrid vehicles combine two energy sources with
an electric drivetrain, with one or both sources providing electric power to the motor. This
section examines hybrids that incorporate an internal combustion engine as one of the energy
sources, with batteries, flywheels, or ultracapacitors also providing electric energy to the motor.
Moreover, although gas turbines can be used in a hybrid, turbines of the size optimal for 1ight-
duty vehicles are unlikely to be more efficient than piston engines of the same performance
capacity; consequently, only piston engines are considered in this section. Other combinations of
energy sources, such as a fuel cell and a battery, can also be used in a hybrid, however.

The conceptual advantage of a hybrid is that it gains the range provided by an engine using a

high-density fuel, but avoids the energy losses associated with forcing the engine to operate at

speed/load combinations that degrade its efficiency. In other words, the engine can run at nearly

constant output, near its optimum operating point, with the other energy source providing much

of the load-following capability that undermines the engine’s efficiency in a conventional vehicle.

The term hybrid is applied to a wide variety of designs with different conceptual strategies on

the use and size of the two drivetrains. One form of classification for hybrids is a division into so-