[sid]

When I worked for Chrysler as a design engineer back in the late 1970's, we were working on lean burn engines. But we were having a lot of problems getting them to pass emissions tests. Nitrogen oxides (NOXs) were the big problem. They also tended to burn up catalytic converters if we tried to add them to cars. They may have fixed those problems after I left. But I also think the Feds tightened pollution standards since then, too, which effectively killed all lean burn vehicles in the US.

One reason the same cars in the US get poorer fuel economy than in other countries is that we have different pollution standards. Our standards are optimized to reduce smog and carcinogens. Other countries tend to optimize for minimum greenhouse gases. Optimizing for minimum greenhouse gases usually gets much better fuel economy than optimizing for minimum smog. It is hard to get the EPA to reconsider their pollution requirements, especially since some places in the US still have occasional smog problems.