Cummins Westport Inc. has begun development on the ISB 6.7G, a mid-range 6.7-liter natural gas engine designed to meet the increasing demand for on-highway vehicles powered by natural gas. The ISB6.7 G engine will be based on the Cummins ISB6.7 diesel engine and will use Cummins Westport’s proven spark-ignited, stoichiometric cooled exhaust gas recirculation (SEGR) technology.
Exhaust aftertreatment will be provided by a simple, maintenance-free three-way catalyst (TWC). The engine will run on compressed natural gas (CNG); however, the natural gas may be stored on the vehicle in liquefied natural gas (LNG) state or as CNG.
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 TWC for NOx control.
In a keynote address on technology choices for new natural gas engines given at the ASME Internal Combustion Engine 2012 Fall Technical Conference last week, Dr. Patric Ouellette, VP and CTO, Westport Innovations, observed that, for the medium- and medium-heavy-duty market:
For years the approach there has been to take a good diesel engine and then do the best job you can making them spark ignition engines. In our experience, that has been a very good compromise for the use of natural gas in many applications. It is well suited for CNG or LNG, and one of the things that is quite attractive is the achievement of low emissions— EPA 2010 and soon to come Euro6— with a three-way catalyst instead of having to use a DPF or an SCR. In this segment, some of these technologies have been more challenged because of the low temperature exhaust regime associated with stop and go applications.
The base engine is...a diesel engine, and so today that offers some benefits and some constraints. It’s a very strong engine, but the air flow and the piston shapes are pretty much limited by what your base diesel engines are giving you. And so you have some lack of flexibility and optimization to some extent there. Firing pressure are higher, so your ignition systems need to be designed differently.
The ISB 6.7 G is expected to be in production by 2015 and will be designed to meet Environmental Protection Agency (EPA) and California Air Resources Board (CARB) regulations 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. 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.—Jim Arthurs, President of Cummins Westport
Cummins Westport is a joint venture of Cummins Inc. and Westport Innovations Inc., a leader in alternative fuel, low-emissions technologies that allow engines to operate on clean-burning fuels such as compressed natural gas (CNG), liquefied natural gas (LNG), hydrogen, and biofuels such as landfill gas.