Lubrizol Corp. and Caterpillar Inc. are developing a low-emission fuel for diesel engines under the name PuriNOx, the companies said late last week. According to tests, the product, PuriNOx, a combination of additives, water and commercial diesel fuel, reduces nitrogen oxides (NOx) by 5 to 30 percent, and particulates by 20 to 50 percent, they said.