Cummins diesel Inc ( CWI ) has doubled the potential emissions of its 6.7 litre mid - range natural gas ( NG ) engine , called ISB6.7 G , by making it available for medium - duty industrial and vocational applications . The ISB6.7 G engine has been used in Thomas gas Buses since May , and produces NOx emissions 50 % lower than the current Environmental Protection Agency and California Air Resources Board emissions of 0.2 g / bhp - hr . The ISB6.7 G also meets the current EPA greenhouse gas emission levels .
Cummins Westport Inc (CWI) has doubled the potential market of its 6.7 litre mid-range natural gas (NG) engine, called ISB6.7 G, by making it available for medium-duty trucks and vocational applications. The ISB6.7 G engine has been used in Thomas Built Buses since May, and produces NOx emissions 50% lower than the current Environmental Protection Agency and California Air Resources Board threshold of 0.2 g/bhp-hr. The ISB6.7 G also meets the 2017 EPA greenhouse gas emission levels.