Following up, it looks like Mahle has actually been tying to address the NOx production. The OP links to this article [1] from 2010, which is mostly taken from

Following up, it looks like Mahle has actually been tying to address the NOx production. The OP links to this article [1] from 2010, which is mostly taken from three SAE papers that indicate they have been able to constrain the NOx in jet injection engines to "single digit ppm engine out NOx emissions" [2]. The EPA seems to indicate [3] that less than 1 ppm NOx post-catalytic converter is targeted. I don't know if their advancements allow for three-way catalytic converters on a lean burn engine, but that would be pretty impressive. [1] http://www.greencarcongress.com/2010/10/tji-20101027.html http://www.greencarcongress.com/2010/10/tji-20101027.html [2] http://papers.sae.org/2010-01-2196/ http://papers.sae.org/2010-01-2196/ [3, PDF] https://www3.epa.gov/ttncatc1/dir1/fnoxdoc.pdf https://www3.epa.gov/ttncatc1/dir1/fnoxdoc.pdf