GREETing a cleaner, more energy-efficient future

ARGONNE, Ill. (Oct. 14, 2005) — With gas prices soaring, the fuel and vehicle options open to Americans are more varied than ever. But what fuel and vehicle combination provides the lowest total emissions with the highest energy efficiency?

Researchers in Argonne's Center for Transportation Research have been studying these questions and more for a quarter of century and have developed software that is now the government and industry standard for evaluating various vehicle and fuel combinations on a consistent fuel-cycle basis from extracting the energy feedstocks –petroleum and natural gas – through fuel production to final vehicle operation.

Called GREET– for Greenhouse gases, Regulated Emissions and Energy use in Transportation – the software "evaluates the energy and emission facts from the beginning of the whole process," explained Michael Wang, section leader of Systems Assessment in Argonne Center for Transportation Research. "For gasoline the fuel cycle starts with petroleum recovery, followed by petroleum transportation, refining to produce gasoline, transportation and distribution to refueling stations, and finally gasoline used in vehicles."

As researchers from government, industry and universities use GREET, they can calculate:

• Consumption of total energy – in renewable and non-renewable sources – of fossil fuels including petroleum, natural gas and coal, and petroleum only.
• Emissions of carbon-dioxide-equivalent greenhouse gases – primarily carbon dioxide, methane and nitrous oxide.
• Emissions of "criteria" pollutants – those for which the Environmental Protection Agency sets limits: volatile organic compounds, carbon monoxide, nitrogen oxide, sulfur oxides and particulate matter smaller than 10 microns.

Growing GREET

"In 1995," Wang said, "we were again performing fuel-cycle analyses for the U.S. Department of Energy on transportation fuels, and we proposed to automate some of our analysis to not repeat calculations. We developed a tool to share with others to save effort so researchers can concentrate on issues beyond the mechanics of the analysis."

The first version of GREET was published and made available for free in 1996. Since then, it has been continually updated to accommodate new fuels and vehicle technologies. It began as a multi-dimensional Excel spreadsheet, but a graphical user interface was added to make the program more user-friendly. GREET can be downloaded from the GREET Web page.

GREET was funded by the Department of Energy's Office of Energy Efficiency and Renewable Energy.

"As we were developing the GREET tool," Wang said, "we reached out to experts and stakeholders in energy companies, auto manufacturers and government agencies for input and feedback." Their expertise provided deeper insight into the issues and improved the tool.

"Our work with these groups is an iterative process," Wang said. There are intricacies to each fuel. The stakeholders provide input about the key issues that need to be analyzed.

The software tool has more than 2,000 registered users in North America, Europe and Asia. That number includes government agencies, the auto industry, the energy industry, research institutes, universities and public interest groups.

GREET has grown to include 88 fuel production pathways and 72 vehicle/fuel systems. Common fuel production pathways include petroleum, which can be turned into conventional and reformulated gasoline, conventional and low-sulfur diesel, crude naphtha and liquefied petroleum gas.

Everyday examples of vehicle/fuel systems include gasoline spark-ignition engines and diesel compression-ignition direct-injection engines. A more exotic example is a hydrogen internal combustion engine like the one Argonne researchers are studying in the Advanced Powertrain Research Facility.

Wang is an environmental scientist and finds his work fulfilling. "It is a rewarding experience," he said, "to collaborate with experts in this field and to provide assistance to fellow researchers.

"The transportation sector faces a large challenge – we use large amounts of petroleum. It is exciting to work to find solutions for this challenge, which affects the U.S. and the world."

A cleaner China helps us all

Wang is a Chinese native and earned his bachelor's degree there before continuing his studies at the University of California-Davis. He has maintained his professional connections in China and is using them to assist China and the world.

" China's economy is growing at 8 percent per year, and when people's income increases, their standard of living increases, requiring more energy," Wang said. Car ownership in China is increasing by 19 percent each year, and the nation has become the second largest oil consumer in the world, behind the United States.

"While China has a serious energy and air quality challenge," Wang said, "I believe they may offer some of the best opportunities to find a solution to the world's energy challenges." China is starting with a fresh mindset and without the sunken infrastructure investments we have, he explained. Their fresh perspectives may offer opportunities the rest of the world can learn from.

Wang and Argonne colleagues collaborate with the China Automotive Technology and Research Center (CATARC) – a research institute dedicated to automotive safety, emissions control and energy conservation. Argonne and CATARC have a memorandum of understanding to exchange information to promote the commercialization of energy-efficient vehicle technologies and clean transportation fuels in China.

In 2004 and 2005, Argonne trained four CATARC engineers in the necessary analytical skills to tackle transportation challenges. The training included months of work with the GREET tool and the Argonne-developed Powertrain Systems Analysis Toolkit (PSAT), which can be used to simulate and analyze almost all imaginable powertrains. PSAT analyzes fuel economy, emissions and performance for any driving cycle or profile for a broad range of vehicles from conventional to fuel-cell drivetrains and up to four-wheel-drive configurations.

"Energy efficiency and greenhouse gas emissions are a global issue," Wang said, "and so we expect that by improving vehicle efficiency, we can decrease those emissions in China as well as in the U.S. " — Evelyn Brown