UCR study finds increased NOx, PM emissions from hybrid construction equipment

22 October 2013

Researchers at the University of California, Riverside completed a first-of-its-kind study that examined the real world performance of hybrid diesel-electric construction equipment.

Manufacturers reported the hybrids reduced fuel consumption and GHG emissions by 20% and reduce NOx emissions by 30%. But UC Riverside researchers found fuel savings of between 7% and 28% and NOx emission increases of up to 21% when compared to conventional diesel equipment. The tests also showed increased PM emissions in hybrids.

The increase in NOx emissions illustrates the difficulty in tuning engines to simultaneously reduce both NOx and GHG emissions. “The reason we see increased NOx in this first generation technology is simple—getting the best fuel economy is going to sell the equipment,” said Kent Johnson of UC Riverside, the principal investigator on the project. As the hybrids cost 20% more than new conventional diesel equipment, a fuel economy improvement is necessary to offset the added costs.

The research was conducted under the Hybrid Off-Road Equipment Pilot Project, sponsored by the California ARB, that provided vouchers to accelerate deployment of commercial hybrid dozers and excavators, while evaluating the emissions benefit of the equipment in real world applications. The UC Riverside’s Center for Environmental Research and Technology (CE-CERT) administered both the deployment and testing elements of the project.

Ten hybrid Caterpillar D7E bulldozers and six hybrid Komatsu HB215LC-1 excavators were deployed with eight California based fleets. The in-use D7E dozer and HB215LC-1 excavator activity was observed and logged at six locations to develop typical in-use hybrid dozer and excavator duty cycles. Since exact non-hybrid versions of the tested equipment do not exist, emission comparisons were made relative to the most similar non-hybrid dozer and excavator models—the Caterpillar D6T dozer and the Komatsu PC200 excavator.

The researchers used time lapse cameras, global positioning systems, engine control units and portable emission testing equipment during more than 2,000 hours of testing on both types of vehicles.

• The hybrid bulldozer was tested under six conditions, with a different distance and load amount. Fuel savings ranged from 7% to 28%. In general, the shorter the distance and lighter the load, the more fuel saved. The use-weighted average was a 14% fuel savings. Tests for NOx emissions showed a range from an increase of 21% to a decrease of 2%. The use-weighted average was a 13% increase in NOx.
• The hybrid excavator was also tested under six scenarios, ranging from demolition, which usually means longer swings of the arms, to general construction work, which consists of more trenching and backfilling. The fuel use ranged from a 28% savings to an increase of 1%. In general, more fuel was saved during the demolition test cycles. The use-weighted average was a 16% fuel savings. For emissions, the researchers tested for NOx, PM and other pollutants. For NOx there was a range from an 18% reduction to an 11% increase, with an average of a 1% increase. For PM, there was increase between 6% and 36%, with a use-weighted average of a 27% increase.

Other UC Riverside studies of today’s first generation heavy-duty hybrid vehicles and equipment have found varying results relating to emissions and fuel economy. Hybrid marine vessels performed well, while on-road heavy duty hybrids, such as tractor trailers, had mixed results.

The hybrid research complements efforts by the California ARB to expand the demonstration and deployment of hybrid and zero-emission technology to help meet the goals of AB 32, a 2006 state law that requires greenhouse gas emissions be reduced to 1990 levels by 2020. California Governor’s Executive Order S-#-05 also targets an 80% reduction by 2050.

Significant deployment of next generation hybrid and zero-emission technologies is also critical for California to meet the health-based federal eight-hour ozone standard.

UC researchers expressed hopes the findings in this first-of-its-kind study will help drive technology improvements to hybrids and could help engine manufacturers consider their designs not only from a fuel economy and certification level, but also from an in-use basis.

Source: UC Riverside | California ARB