A recent study co-authored by the Environmental Defense Fund suggests that a shift from diesel fuel to natural gas would not automatically lead to a reduction in greenhouse gases. It fact, making that switch for heavy-duty trucks right now could have an even worse impact on climate patterns over the next 50 to 90 years, says Jason Mathers, senior manager of corporate partnerships with EDF.
Five researchers, four from EDF and one from Columbia University, examined multiple engine technologies and fuels, including both liquefied and compressed natural gas. What they learned validated the findings of an EDF paper published in 2012, while addressing a wider range of vehicle types and taking a longer-term view of the issue.
The culprit is methane, the chief ingredient in natural gas. It exudes 84 times more climate-warming power than CO2 over a 20-year period, EDF says. According to the latest Greenhouse Gas Inventory Report by the Environmental Protection Agency, approximately 6.3 million metric tons of methane escaped from the natural-gas supply chain in 2013. Over 20 years, that leakage would have the same impact on the world’s climate as 111 million cars or 140 coal-fired plants.
Mathers says EDF’s latest analysis looked at three variables: methane emissions associated with the production of natural gas and its use in vehicles, as well as the relative efficiency of natural gas and diesel engines.
The study’s short-term negative outlook is based on current systems for creating, processing and transporting natural gas to fueling stations, as well as the relative inefficiency of natural-gas engines, Mathers says. At the moment, they are 5 to 15 percent less efficient than diesel-powered models, a disparity that would cut sharply into the savings derived from reduced carbon dioxide emissions.
In order for natural gas to emerge as a truly viable alternative to diesel power, methane emissions resulting from its use would have to be severely cut or eliminated, and natural gas engines would have to match diesel engines in efficiency.
That’s not an insurmountable goal. Mathers cites a recent study by ICF International, a technology consulting firm, which concludes that the oil and gas industry could achieve a reduction of at least 40 percent in methane emissions associated with processing and transporting natural gas, at the cost of one penny per thousand cubic feet of gas produced. The price of natural gas at the time of the study was $4 per thousand cubic feet.
Some of the tools for achieving that goal are available today, according to the ICF report. They include technologies for detecting leaks and making repairs at the wellhead and processing facilities.
The scenario takes the movement of gas as far as the fueling station. The EDF study doesn’t consider the options for reducing methane emissions in vehicles. For example, says Mathers, natural gas engines have open crankcases. Shifting to a closed design could significantly reduce leakage.
There’s no clear environmental advantage when comparing liquefied and compressed natural gas, he says. “They kind of canceled each other out.” LNG ends up spending less time in the distribution system, creating fewer opportunities for leakage. At the same time, LNG production requires much more energy than CNG. The former needs to be kept extremely cold, and gets vented from tanks when it warms up. There’s currently no reliable data on the frequency of boiler loss, Mathers says.
Provided issues of processing and supply are addressed, natural gas has the potential to slash greenhouse gas (GHG) emissions from heavy trucks. More information is needed before industry can assess the real impact, however. EDF and industry partners are working to publish 16 field studies on the science of methane emissions across the U.S. natural-gas production system. For now, Mathers says, there’s a “paucity of data” on the subject.
In the meantime, EDF and government regulators are pushing for reductions in emissions from traditional trucks. EPA and the National Highway Traffic Safety Administration recently proposed new fuel-efficiency standards for medium- and heavy-duty vehicles. The so-called Phase 2 program seeks to cut GHG emissions by some 1 billion metric tons. The action would result in a $170bn cut in fuel costs for trucks purchased under the program, the agencies said. Vehicle owners would recoup the extra cost of the technology within two years, they claimed.
According to EDF, a 40-percent reduction in fuel consumption would cut usage by 1.4 million barrels a day, reduce climate pollution by 270 million metric tons a year, and save the average tractor-trailer owner $30,000 a year in fuel costs by the year 2030. In 2013, the group said, fuel accounted for 39 percent of the cost of truck ownership.
Each solution has its price, and the long-term impacts are hard to quantify. Nor is it entirely clear which option will have the most beneficial effect on the environment. Nevertheless, fuel and trucking technologies are due for a major overhaul in the years ahead.
“We’re not here to pick one fuel over another, but to make sure we diversify,” says Mathers. “We need to move on all fronts…. Our end goal is to reduce the global-warming impact of moving freight.”
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