VANCOUVER, British Columbia — Cummins Westport has begun development on the ISB6.7 G, a mid-range 6.7-liter natural gas engine, the company announced on Thursday.

The new engine will target the school bus, medium-duty truck and vocational vehicle markets. Company officials said that it is being “designed to meet the increasing demand for on-highway vehicles powered by lower cost, cleaner and increasingly abundant natural gas.”

Cummins Westport currently offers the ISL G natural gas engine for school bus applications.

The new ISB6.7 G engine will be based on the Cummins ISB6.7 diesel engine and will use Cummins Westport's spark-ignited, stoichiometric cooled exhaust gas recirculation technology. Exhaust aftertreatment will be provided by a simple, maintenance-free three-way catalyst, company officials said.

The engine will run on compressed natural gas (CNG), although fuel could be stored on the vehicle in a liquefied natural gas state or as CNG.

Company officials said that the ISB6.7 G is expected to be in production by 2015 and will be designed to meet U.S. EPA and California Air Resources Board regulations that are in force at the time of launch.

"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 8.9-liter ISL G, with over 16,000 engines in service, and the 11.9-liter ISX12 G, which will start production in 2013, to give our customers a broad range of natural gas engines for on-highway applications."