Issue Date: February 16, 2009
"MIMICKING Mother-of-Pearl," on the work of Robert Ritchie and others, shows a route that is likely to make tough high-temperature structural materials more readily available (C&EN, Dec. 8, 2008, page 8). This promises removal of a serious obstacle to increased use of high-temperature engines and the resulting improved fuel efficiency.
I know of two other obstacles, however, and one of them is purely chemical. The nonchemical obstacle is high exhaust temperature, and I will leave that for engineers to address. The chemical obstacle is emission of nitrogen oxides.
We have been making a trade-off in many engines since about 1975: lower combustion temperature to minimize NOx formation and a catalytic converter to reduce emission of unburned fuel and carbon monoxide. Can chemistry now offer a more efficient trade-off? Can we go to higher hot-end temperatures, reduce levels of partial combustion, and catalytically lower the NOx emissions? For fixed engines (obviously not for automobiles) it might even be acceptable to produce ammonia as a by-product.
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