For 2013, two on-highway natural gas engines will be available from Cummins through its joint venture, Cummins Westport,” advises Jeff Campbell, Cummins Westport’s director of marketing.

“Both the 8.9L ISL G and the 11.9L ISX12 G feature SEGR (stoichiometric exhaust gas recirculation) combustion, with spark ignition and maintenance-free three-way catalyst aftertreatment.”

Campbell notes that the ISX12 G is new for 2013 while the ISL G was rolled out back in ’07. “The ISX12 G and ISL G have low-pressure fuel systems, which enable the use of both CNG and LNG. This flexibility allows customers to make the fuel choice that best suits their applications.”

He says that for engines with similar ratings, the torque capability of the ISL G and ISX12 G are similar to that of diesel powerplants. “Both the ISL G and ISX12 G are based on the proven Cummins ISL9 and ISX12 diesel engines,” Campbell states, “and they share up to 80% of the parent diesel’s components and this provides similar durability.

“NG engines utilize throttled air intakes rather than direct injection as found on diesels,” he continues. “While this creates a different engine response, the driving experience is similar to diesel. And the ISX12 G with manual transmission and engine-braking capability enhance driveability.”

According to Campbell, initial driver feedback during field-testing of the ISX12 G has been positive. “The engine pulls throughout the power curve and engine response is excellent.”

Campbell says the ISX12 G, which boasts up to 400 hp. and 1,450 lbs.-ft. of torque capacity, “provides the power and torque required for regional/local vocational truck applications up to 80,000 lbs. GCW.

“In most cases,” he points out, “the ratings available for diesel and NG are similar; however, the peak ratings for diesel are higher. For example, the ISX12 G’s peak rating is 400 hp. and 1,450 lbs.-ft. while the ISX12 diesel’s is 425 hp. and 1,650 lbs.-ft.”

According to Campbell, fleets will find there are incremental maintenance costs with NG engines, “but these are normally far outweighed by the fuel cost savings from running NG engines.

“And with over 80% of the components of NG and diesel engines being the same, durability targets are also similar,” he continues. “In terms of maintenance, the primary difference is that spark ignition requires changing spark plugs. This adds some cost, but that is partially offset by maintenance-free aftertreatment. There’s no DPF or SCR system maintenance or DEF expenses with Cummins Westport NG engines.”

Campbell reports that there are two more NG engines in development at Cummins Westport and Cummins.

“In 2015,” he relates, “Cummins Westport will release the ISB6.7 G [6.7L] and Cummins will offer the ISX15 G [15L]. Both engines will feature SEGR, spark ignition and three-way catalyst aftertreatment [as found now on the ISL G and ISX12 G]. Both will be capable of operating on CNG and LNG.”