2018 Cummins “Near-Zero” and “Optional Low-NOx” natural gas engines
FTA has evaluated the changes made by Cummins to its natural gas bus engines for model year 2018. Cummins has indicated that the ISLG and ISX12G are being replaced in 2018 with updated versions that include a “Near-Zero” emissions package. The Near-Zero emissions packages include changes to the engine electronic control unit, closed crankcase ventilation, and a larger and upgraded 3-way catalytic converter. These changes reduced the EPA-certified NOx emissions of these engines from 0.2 g/bhp-hr to 0.02 g/bhp-hr. The resulting Near-Zero engines are designated L9N and ISX12N, respectively. Similar changes have been made to the ISB6.7G, reducing its EPA-certified NOx emissions from 0.2 g/bhp-hr to 0.1 g/bhp-hr. This version is designated B6.7N and is certified to the California Air Resources Board Optional Low NOx standard of 0.1 g/bhp-hr.
The greenhouse gas emissions of these engines are projected to be approximately 9 percent lower, corresponding to a similar improvement in fuel economy. The power and torque ratings are unchanged, and the weight differences of the engines and aftertreatment systems between the G and the Near-Zero/Optional Low-NOx versions of each engine are insignificant. In addition, no major changes are required in the mounting or interconnections of the engines to the vehicle.
Based on this information, FTA has determined that bus models that have previously satisfied Bus Testing requirements when equipped with the ISB6.7G, ISLG, or ISX12G will not require additional testing when offered with the corresponding Near-Zero/Optional Low-NOx engine.
The changes Cummins has made to these engines are limited to the 2018 emissions package, which is comprised of improved versions of mature technologies. While we would expect testing of buses equipped with the Near-Zero versions of these engines to result in approximately 9 percent improvement in fuel economy data and approximately 90 percent improvement in NOx emissions data (50 percent for the B6.7N), these changes are in a favorable direction and they have been validated through engine dynamometer certification testing by EPA and CARB. We would not anticipate changes in other data measured during FTA Bus Testing of bus models equipped with these engines. (Posted February 6, 2018)
Buses manufactured on a gasoline-fueled third-party chassis and then converted to a compressed natural gas (CNG) fuel system by a fourth-party converter, upfitter, and/or dealer prior to final acceptance of the vehicle(s) by an FTA grantee
A change in a previously-tested bus model’s fuel system from gasoline to CNG is a major change and triggers Partial Testing requirements; tests in which FTA might reasonably expect to obtain different data (compared to the baseline gasoline-fueled version of the bus) would need to be repeated. Accordingly, each newly-offered fourth-party conversion to a CNG fueling system (consisting of a particular design, specific major components [whether produced in-house or by outside suppliers], installation techniques, and calibration) must have completed testing at the Bus Testing Center that includes at least the Maintainability, Safety, Performance, Structural Durability (test 5.7), Fuel Economy, dynamic Noise (i.e., noise tests involving engine operation), and (if the conversion was contracted for testing on or after January 1, 2010) Emissions tests, since these are the tests in which we would expect to obtain significantly different data due to the conversion. Once a particular fourth-party CNG conversion of a particular chassis has completed the testing specified above, it may be substituted for the corresponding gasoline chassis in bus models that have satisfied FTA Bus Testing requirements on that corresponding gasoline chassis. Versions with fewer CNG tanks could also be substituted, but versions with more tanks would require an individual determination of testing requirements. In this context, “corresponding chassis” means the same make and model chassis powered by the same make and model engine. In order for a proposed CNG bus model to meet the requirements of the Bus Testing Regulation, the Partial Bus Testing Report resulting from the test of the corresponding converted CNG chassis must be provided to the grantee along with the full Bus Testing Report for the baseline gasoline-powered version of that bus model. (posted January 5, 2011)
2010 Freightliner MB-65 Chassis
FTA has reviewed the new-for-2010 Freightliner MB-65 chassis and has determined that it is a variant of the MB-55 chassis, which has been tested several times at the Altoona Bus Testing Center. FTA’s view is that the structural interface between the similar chassis frame rails and an unmodified bus body would not generate substantially different stresses compared to that of similar buses previously tested on the MB-55 chassis. However, FTA has also determined that the MB-65 incorporates several significant differences from the MB-55 that qualify under the Bus Testing Regulation (49 CFR Part 665) as major changes and that could be expected to produce significantly different data if certain tests are repeated:
- New front axle with 20% increased GAWR
- New front suspension
- Upgraded rear suspension with higher ride height
- Lowered engine
- Revised crossmember locations, affecting driveshaft angles
- 2010 emissions package
Based on these changes, FTA has determined that significantly different data could be expected from repeating the Maintainability, Reliability, Safety, and Structural Durability tests on a bus built on the MB-65. We could also expect moderately different data from repeating the Performance, Fuel Economy, and Noise tests; these differences would not necessarily trigger additional testing on their own, but including them would be justified if a bus built on the MB-65 is already undergoing the other tests. In addition, we would expect to obtain significantly different data from conducting the new Braking Performance and Emissions tests that became effective January 1, 2010 because these tests have never been performed on the MB-55.
Consequently, one bus built on the MB-65 chassis will need to complete partial testing, including at least the Maintainability, Reliability, Safety, Structural Durability, Braking Performance, and Emissions tests, before buses built on the MB-65 may be offered to FTA grantees. Once that bus has completed these tests, other buses that had previously satisfied Bus Testing requirements when built on the MB-55 chassis may be sold to FTA grantees using the combination of the original Bus Testing Report on that bus and a Partial Testing Report on a similar bus built on the MB-65. (posted June 22, 2010)
Manufacturers will not be required to re-test buses solely due to the use of engines compliant with EPA 2010 emissions standards
While FTA does anticipate performance, fuel economy and potentially noise differences due to the different aftertreatment equipment and calibrations of these engines, these differences are not anticipated to be major, however, if use of a 2010 engine requires significant modifications to a vehicle itself, then additional testing might be required. In addition, data on 2010-compliant engines will become available in the normal course of testing new bus models nearly as quickly as if existing models were required to be re-tested. Anyone wishing to obtain data on the performance and fuel economy of the 2010 engines can obtain copies of the Bus Testing Reports of buses equipped with these engines, which should begin to be available soon. However, buses equipped with 2010 engines that are submitted for Partial Testing and which have not had the Performance, Fuel Economy, dynamic (i.e., when the powertrain is operating) Noise, and Emissions tests performed on a 2010 engine will also need to have these tests performed. (posted October 9, 2009)
Clarification regarding unmodified mass-produced vans
While unmodified mass-produced vans are categorically exempted from testing by the Bus Testing Regulation, this exemption historically assumed that unmodified mass-produced vans would only be offered in the 4-year, 100,000-mile service life category. FTA wishes to clarify that unmodified mass-produced vans are categorically exempted from testing by the Bus Testing Regulation only in the 4-year, 100,000-mile service life category; unmodified mass-produced vans offered in the 5-year, 150,000-mile (or higher) service life category are subject to testing. (posted January 30, 2007)
Manufacturers will not be required to re-test buses solely due to the use of engines compliant with EPA 2007 emissions standards
While FTA does anticipate some degree of performance and fuel economy differences due to the different aftertreatment equipment and calibrations of these engines, these differences are not anticipated to be major, and perhaps more importantly, no manufacturer or bus purchaser has a choice not to use 2007-compliant engines (if the 2007 engines require significant modifications to the vehicle itself, then additional testing might be required). In addition, data on 2007-compliant engines will become available in the normal course of testing new bus models nearly as quickly as if existing models were required to be re-tested. Anyone wishing to obtain data on the performance and fuel economy of the 2007 engines can obtain copies of the Bus Testing Reports of buses equipped with these engines, which should begin to be available soon. (posted October 23, 2006)
Changing the primary structural material of a bus from mild steel to stainless steel will generally be considered a major change, and will generally require partial testing including the structure-related tests
FTA considers changing from mild steel to stainless steel to be a “major change in chassis design” as defined in the Bus Testing Regulation that triggers additional testing. Compared to mild steels, stainless steels have different physical properties, different microstructure, and different (generally more stringent) manufacturing requirements. Years ago, FTA allowed a bus model that had been tested with a mild steel chassis to be sold without additional testing with a stainless steel chassis; when the stainless steel model entered service, it experienced numerous structural problems. (posted May 26, 2006)