A Study of Emissions from Yard Tractors Using Diesel and LNG Fuels

Yard tractors are the workhorse of the cargo handling equipment (CHE) and there are over 1,500 in the Ports of Los Angeles and Long Beach. Because of their high numbers and frequent use, they also are the primary contributor to the emissions inventory from cargo handling equipment. Over 50% of the NOx and PM emissions associated with CHEs come from yard tractors. Based on these facts the POLB, LBCT and CALSTART launched an investigation of the emission factors from yard tractors. There were two goals: first, measure the emission factors from a series of engines certified to ever increasingly more stringent emission standards, and second, investigate the emissions from an engine running on an alternative fuel, LNG. As direct emissions values are scarce, the report compares the results with earlier studies and EPA certification values. A number of yard tractors with various engine technologies meeting different levels of EPA emission standards were part of the planned project. The test matrix represented engines meeting Tier 1 and 2 non-road (industrial) standards, on-road (automotive) standards for 2004 and an engine fueled with LNG. Fuels The engines were tested in their yard tractors on a heavy-duty chassis dynamometer. Testing included: first, developing an engine map to establish a C1 ISO test cycle, and second, measuring the emissions at various C1 test points in duplicate. Both modal and overall emission factors were calculated from the test data.

About 75 emissions tests were carried out during the project. Results for the diesel fueled engines showed the weighted emission factors on grams per wheel horsepower-hour for NOx and PM decreased with engines manufactured to meet stricter EPA certification standards. Estimates of the emission factors on a brake horsepower basis indicate the values were within the EPA specifications for the C-2003 and ISB engines but not for the C-2001 engine. Unlike the earlier POLA testing, Donaldson control technology was used in the LBCT tests and reduced the CO, THC and PM emissions on the C-8.3L engines but unexpectedly did not reduce emissions on the ISB engine. Several issues were discussed in the analysis section. One issue was the C-2001 engine map in that the C1 load points were about 50% of Cummins’ engine map instead of the expected 75%. As detailed in the analysis, we believe the emissions factors are still valid. Another issue was the results comparing the ISB engines from 2004 and 2005. The 2005/LBCT engine had about 20% higher NOx emissions than the earlier POLA test unit and the reason for the difference was not clear. Several hypotheses were presented in the discussion. Finally, the LNG fueling system from the LBCT yard tractor was modified prior to testing and did not generate the fueling errors seen during the POLA test. Consequently the LBCT yard tractor had lower NOx emissions than the earlier POLA test. One frontier examined in this work was the activity data for the ISB engine. These data revealed that the engines spend considerable time in the idle mode. The use of the engine downloads appears to be useful information about how a yard tractor operates. Not examined in this study was the measurement of the in-use activity and emissions from yard tractors with portable instruments during actual use of moving containers. Obtaining those values is planned and those values should be very helpful in finalizing the most appropriate emission factors to use for yard tractors.