Cummins Westport is broadening its offerings in natural gas engines for commercial vehicles. The ISB6.7 G model is a 6.7 liter factory-built medium-duty engine for medium-duty truck and vocational applications as well as for school bus and shuttle bus work.

Based on Cummins ISB6.7 diesel platform, it will operate exclusively on compressed natural gas (CNG) or liquefied natural gas (LNG). It uses Cummins Westport’s proprietary spark-ignited, stoichiometric combustion system with cooled exhaust gas recirculation emissions control, first introduced with the 8.9 liter ISL G model engine.

The new engine features three-way catalyst aftertreatment, which is packaged as a muffler and is maintenance-free. No diesel particulate filter or selective catalytic reduction aftertreatment will be required, according to the company.

Preliminary specs include a range of ratings up to 260 hp and 660 lb ft of torque, with automatic transmission capability.

It is expected to be certified at launch to meet the U.S. Environmental Protection Agency and California Air Resources Board emission standards including 2016 U.S. greenhouse gas and fuel economy regulations.

The engine is currently in field trials, with full production set to begin in mid-2016 at Cummins’ medium-duty engine plant in Rocky Mount, NC, as part of the joint venture between Cummins and B.C.-based Westport Innovations.