A pair of Cummins Westport, Inc. natural gas engines have gained approval from the U.S. Environmental Protection Agency and California Air Resources Board for medium-duty vehicles, the engine maker announced.

The 2018 L9N and B6.7N engines meet California's Low NOx standards and the 2017 EPA greenhouse gas emissions requirements for the engines, which are used in medium-duty trucks, including refuse haulers, school buses, and transit shuttles.

The L9N has been certified to Californial's optional Low NOx standard of 0.02 g/bhp-hr, which is a 90% reduction from engines operating at the current EPA NOx limit of 0.2 g/bhp-hr. The L9N offers ratings from 250 hp to 320 hp and 1,000 lb.-ft. peak torque.   

The B6.7N has been certified to California's optional Low NOx standard of 0.1 g/bhp-hr, which is a 50% reduction from current EPA levels. The engine is available with ratings from 200 hp to 240 hp and 560 lb.-ft. peak torque.

The company plans to introduce a third natural gas engine — the ISX12N — that's expected to meet the optional Low NOx emissions level of 0.02 g/bhp-hr. Production of the three engines will begin by April 1.