What: Natural gas engine technology leader Westport Innovations Inc.'s (NASDAQ:WPRT) stock is up 9% today (Oct. 7), and more than 18% over the past two market days. 

So what: Westport's joint venture with Cummins, called Cummins Westport, just announced a near-zero NOx emissions version of its very popular ISL G natural gas engine, the ISL G NZ. This is a pretty big deal, since this new engine meets stringent long-term emissions standards for particulates like NOx, a major cause of urban air pollution. 

Cummins Westport will begin manufacturing the ISL G NZ in April 2016, and it will be available as a "first fit" (sold with new vehicles) engine, as well as a replacement for vehicles currently running the Cummins Westport ISL G natural gas engine. 

Now what: This is a big deal and a definite positive for Westport. The ISL G engine has been hugely successful, with major market share in the transit and waste-removal vehicle segments. But even with that past success, this lower-emissions version of that engine is not exactly a game changer.

Westport still faces the same cash-burn challenges, and the uncertainty of low oil prices weighing on the rate of adoption of natural gas engines, especially in heavy-duty trucking and automobiles.