I think I remember the article I read saying that prototypes had been installed, and they used them with positive results. When fuel prices dropped, companies probably ditched the concept to save money in the short term. Whenever fuel prices get so high that people get creative and innovative, fuel prices magically drop and the momentum for those new ideas disappears. Around that same time, I remember mainstream news interviewing a prodigy teen that made an engine (suitable for a car) that ran off of dried leaves, or something similarly odd and mundane. He was touring around, doing interviews, then gas dropped back from ~$4/gallon to ~$2/gallon and no one cared about efficiency any more.