Engine Design for NOx Control

Magdi K. Khair

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Note: This paper will not be updated and its contents is gradually moved to other papers, including papers on Intake Air Management for Diesel Engines and Diesel fuel Injection.

Abstract: NOx emissions from heavy-duty engines had to be reduced by about 70% to meet emission standards of the 1990s. Major technologies which were employed included injection timing retard and intake air cooling. The negative effect of timing retard on fuel economy was prevented by implementing high injection pressures.


NOx emissions from heavy-duty engines were reduced by some 70% over the period of 1980s and 1990s. The NOx emission standards that were the driving force behind these changes are illustrated in Figure 1. Through the use of a combination of injection timing retard and charge air cooling, NOx emissions were eventually reduced to below 4 g/bhp-hr, as measured over the U.S. FTP Transient cycle.