American Scientist

To the Editors:

I share Andrew A. Frank's preference for parallel hybrid electric vehicles (HEVs) ("Plug-in Hybrid Vehicles for a Sustainable Future," March-April) primarily because of their potential to control large instantaneous changes in power and torque. Such capability makes it practical to use much more efficient (and multi-fueled) external combustion engines in the hybrid. When you think about it, the only reason we use internal combustion engines (ICEs) rather than external combustion is their ability to change power/torque levels rapidly. An electric-Stirling cycle hybrid could have the clean, quiet, efficient, multi-fuel benefits of the Stirling cycle engine without the Rube Goldberg machinations needed to control it quickly. Yet I don't recall ever seeing any work toward an electric-Stirling HEV.

Another thing that instantaneous control allows is automated vehicle spacing on the highway. With the electric motor to provide rapid speed control, it becomes feasible to tie position sensors (sonar, lidar or the like) into the control circuitry and program the system to safely maintain a set, small distance behind the car in front. The reduction in wind resistance by safely drafting the car in front of you would greatly reduce the amount of petroleum used.

My one real disagreement with Dr. Frank is in regard to his suggested method for providing certainty to the automotive industry to encourage the continued development of plug-in HEVs. Artificially assuring rising fuel prices is distasteful at best. But there may be another way. Many cities around the country, indeed the world, still have air-quality issues. It seems reasonable to me to enact policies that will phase out permission to pollute the air in said cities with internal combustion engines. If the cities begin prohibiting ICEs in the downtown core, some sort of plug-in hybrid would be required. In such cases, even a 10- or 15-mile electric range would be beneficial. People would drive to the city core with hybrid electric and turn to pure electric when driving in the core. And as battery technology improves, the range can be enhanced and the core can be expanded. Eventually, we may have a viable all-electric America.

Dana Johansen
Alexandria, VA