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Cummins Westport ISB6.7 G midrange natural gas engine now in full production

Cummins Westport’s ISB6.7 G, a 6.7 liter midrange, factory-built natural gas engine is now fully available as a production engine for shuttle bus, medium duty truck, and vocational applications in North America. (Earlier post.) As previously announced, the engine has been available for school bus applications since May 2016 from Thomas Built Buses. The 6.7 liter engine platform has large OEM availability for midrange trucks, vocational trucks and mid size buses and the expansion of applications potentially available for the ISB6.7 G engine more than doubles its addressable market.

The ISB6.7 G is based on the Cummins ISB6.7 diesel engine platform, the industry leader in the Cummins midrange engine family, and operates exclusively on natural gas, including compressed, liquid, or renewable natural gas (RNG). The ISB6.7 G is the second engine from Cummins Westport (CWI) to receive emission certification from the US Environmental Protection Agency (EPA) and the Air Resources Board (ARB) in California for meeting the Optional Low NOx Emissions standards.

An engine of this size is a natural addition to CWI’s portfolio of natural gas engines. Many customers using school and shuttle buses, medium duty trucks, or vocational vehicles operate within a local area where the return to base nature of their operation allows them to use fleet-owned or growing publicly available natural gas fueling infrastructure. The ISB6.7 G offers the midrange customer an ability to take advantage of the most cost effective overall solution with the benefit of a low emission natural gas engine that has proven performance, reliability, and durability. In addition, operating on RNG offers customers a tremendous greenhouse gas savings opportunity versus fossil fuels.

—Rob Neitzke, President of CWI

The ISB6.7 G features the same advanced combustion controls with Three-Way Catalyst (TWC) as Cummins Westport’s ISL G & ISX12 G engines. NOx emissions of the ISB6.7 G are 0.1 g/bhp-hr—50% lower than the current EPA and ARB NOx limit of 0.2 g/bhp-hr. CO2 emissions meet the 2017 EPA greenhouse gas (GHG) emission requirements. All CWI natural gas engines are lower than the 2010 EPA standard for particulate matter (0.01 g/bhp-hr).


The ISB6.7 G utilizes CWI proprietary spark-ignited, stoichiometric combustion with cooled exhaust gas recirculation (SEGR) technology. It features electronic control with programmable features, a closed crankcase ventilation system, and maintenance-free three-way catalyst aftertreatment. No diesel particulate filter or selective catalytic reduction aftertreatment is required.

The SEGR technology was introduced with the ISL G in 2007, and was developed to meet 2010 EPA emission requirements. The cooled-EGR system passes exhaust gas through a cooler to reduce temperatures before mixing it with fuel and the incoming air charge to the cylinder. Stoichiometric combustion in combination with cooled-EGR offers increased power density and thermal efficiency. It also reduces in-cylinder combustion temperatures and creates an oxygen-free exhaust, which then enables the use of a three-way catalyst (TWC) for NOx control.

The ISB6.7 G will be manufactured in the Cummins engine plant and offered in three ratings up to 240 hp (179 kW) and 560 lb-ft (759 N·m) torque. Power Take-Off and automatic transmission capability meet customer and original equipment manufacturer requirements. Base warranty is two years, with unlimited miles/kilometers. Extended Coverage options are also available.

Partial funding in support of the ISB6.7 G engine development has been received from the California Energy Commission through its Public Interest Energy Research (PIER) Program in conjunction with the Gas Technology Institute.


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