To decrease NOx emissions the engine temperature has to be decreased which is equal to lower engine efficiency. There are other ways to reduce NOx emissions, s

To decrease NOx emissions the engine temperature has to be decreased which is equal to lower engine efficiency. There are other ways to reduce NOx emissions, such as selective catalytic reduction (SCR) with urea ("AdBlue") injection. This technology is pretty standard on modern HGVs, but rare on light diesels.