Optimized Natural Gas Hybrid-Electric Drayage Truck Demonstration

Demonstrating hybridization of heavy-duty natural gas vehicles to achieve near-zero emission goals.

Institute of Gas Technology dba GTI Energy


Des Plaines, IL

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

Based on demonstration and test results from this project, the project team recommended that future hybrid demonstrations consider the new advanced Cummins Westport natural gas engine, which has shown in-use emissions as low as 0.001 g/bhp-hr NOx emissions (99% below the 2010 standard). Incorporation of this projects hybrid technology with advanced low-emission engine technology has the potential to bring significant fuel reductions while maintaining low-emissions port drayage activity in California's port areas. Additional benefits could be obtained from a charge depletion mode strategy where plug in charging is utilized. Such an approach is realistic if geofenced zero emissions regulations are adopted near ports. Such a strategy could maximize the potential of hybrids and 25% fuel economy benefits observed, but at the added cost of a dual power (engine plus electric) system.

The Issue

Medium and heavy-duty vehicles are critical to California’s economy, yet they contribute a significant amount of greenhouse gas GHG emissions and consume much of the fuel used in California fleets. The Energy Commission’s 2011 Integrated Energy Policy Report anticipates that diesel consumption will continue to grow by 22.3% from 2009 to 2030 due to increased use of diesel in freight. While hybridization is not a new concept, hybridization combined with the use of natural gas has not been fully explored, and the hybridization technologies and strategies being used do not offer a competitive option for fleets.

Project Innovation

Gas Technology Institute, US Hybrid Corporation, and University of California-Riverside performed research and development to design a natural gas engine hybrid-electric Class 8 truck to reduce NOx emissions and improve vehicle fuel efficiency. This project utilized a commercially available, dedicated NG, Cummins Westport Inc. (CWI) ISL G 8.9L engine and enhanced the system to make it representative of an engine meeting CARB's optional low NOx near-zero standard. Both engine technologies were reviewed and evaluated at UCR to provide an in-depth characterization of emissions and fuel consumption results. UCR updated the emissions test laboratory in order to quantify such low emission. Two primary observations were identified: 1) up to 90% of the emissions are the results of either rapid engine speed transients (i.e. hot start tests) or cold starts emissions and 2) the impact of transient and cold start emissions is more critical at the lower NOx emission standard (0.02 g/bhp-hr) when compared to the 2010 certified, ISL G standard. This suggests emissions differences may be significant between drivers, vocations, and vehicle configuration (automatic vs. manual transmissions).

Project Benefits

This project advances the heavy-duty natural gas vehicles through hybridization that proved beneficial for heavy-duty applications that have different power needs and duty cycles and in areas where geofencing is adopted where heavy-duty vehicles can operate in different modes, e.g. as all-electric in the port areas. The technology resulted in a 70% reduction in NOX emissions and a fuel economy improvement of 5% and provided valuable information on emission and fuel economy benefits of hybridization moving forward.

Environmental & Public Health

Environmental Sustainability

The hybrid equipped natural gas engine showed a hot transient emissions of 0.057 g/bhp-hr (70% lower than the 0.2 g/bhp-hr standard) and an overall cold start weighted emissions of 0.19 b/bhp-hr. The fuel economy of the hybrid system was slightly improved (5%) from the baseline system over the cycles tested.

Key Project Members

Project Member

Tyler Manley



University of California, Riverside


US Hybrid Corporation




Mac McClanahan


Match Partners


Institute of Gas Technology dba GTI Energy


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