Cummins Westport has started developing a medium-duty natural gas engine for the school bus, medium-duty truck and vocational vehicle markets. The ISB6.7 G, a mid-range 6.7L natural gas engine will be based on the Cummins ISB6.7 diesel, the company said.

“The addition of the ISB6.7 G will round out our family of high performance natural gas engines,” said Jim Arthurs, president of Cummins Westport. “It joins the 8.9L ISL G, with over 16,000 engines in service, and the 11.9L ISX12 G, which will start production in 2013, to give our customers a broad range of natural gas engines for on-highway applications.”

The new engine will utilize the company’s spark-ignited, stoichiometric cooled exhaust gas recirculation (SEGR) technology. Exhaust aftertreatment will be provided by a maintenance-free three-way catalyst, Cummins Westport said.

The engine will run on compressed natural gas (CNG), but the natural gas may be stored on the vehicle in liquefied natural gas (LNG) state or as CNG.

Production is set to begin in 2015.