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. 

Jason Hall owns shares of Westport Innovations. The Motley Fool owns shares of and recommends Cummins. The Motley Fool recommends Westport Innovations. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.