A new study sponsored by General Motors Corporation (GM) and supported by Argonne, BP, ExxonMobil, and Shell may bring us one step closer to finding the answer. On March 21, 2001, at a conference in New Orleans, GM announced the publication of a new study that the automaker hopes will help focus the public debate about which are the cleanest and most efficient fuels and propulsion systems for the next generation of vehicles.

GAPC Study Team The study team (seated, right to left): Dan Santini (Argonne), Tony Finizza (AJF Consultants), Jim Wallace (Wallace and Associates), Jean Cadu (Shell), and Marianne Mintz (Argonne). (Standing): Norm Brinkman (GM), Michael Wang (Argonne), Greg Ruselowski (GM), Gilbert Jersey (ExxonMobil), Mike Kerby (ExxonMobil), Jim Simnick (BP), and Chris Saricks (Argonne).

The study found that hydrogen-powered fuel-cell vehicles represent the best long-term solution in terms of combined energy use and greenhouse gas (GHG) emissions; other fuels can be used to pave the way for hydrogen fuel-cell vehicles. The study, titled Well-to-Wheel Energy Use and Greenhouse Gas Emissions Analysis of Alternative Fuel/Vehicle Systems, employed a common platform, the Chevrolet Silverado pickup, to examine the energy efficiency and GHG emissions associated with gasoline and diesel internal combustion engines and fuel-cell and hybrid electric vehicles (HEVs) powered by a variety of fuels. To increase the breadth and credibility of the study, GM recruited researchers at Argonne National Laboratory and representatives of the three largest privately owned energy companies (BP, ExxonMobil, and Shell).

TransForum sat down with some of the key players to learn their thoughts about the study's significance and its impact on future automotive and fuels research. Excerpts from the interviews are provided below.

TF: What is the significance of this study? How does it differ from other studies that compare various vehicle fuels and technologies?

Greg Ruselowski (GM): What we did was try to take a very holistic approach. We looked at 75 different fuel pathways and 15 different vehicle propulsion systems, so the scope is much broader than anything that we've seen done before. Also, we chose one very high-volume product and bench-marked all of our propulsion systems against that. In some of the other studies, it's not clear that they were truly apples-to-apples comparisons. The other thing that makes our report unique is that we not only involved Argonne to help lead the effort, but also got three of the world's largest energy companies involved. And it really worked out quite well much better than we thought. I think at the end of the day, everyone has been extremely satisfied with the results.

Jim Simnick (BP): There are a couple things that are significant. The first is that we had great cooperation among energy companies, an automotive company, and a national lab to try to put together a study that was objective, broad in scope, and that will have an impact. It's not one particular interest looking at their favorite fuel but rather an objective look at a whole slew of different fuels and fuel/vehicle combinations. Another significant feature of this study was that, rather than looking at the individual efficiencies of making gasoline or methanol or hydrogen, or even taking a car with a fuel-cell power plant or a hybrid power plant, we also reflected the uncertainty in the estimates.

Michael Wang (ANL): The study provides critical technical input to the current debate regarding fuel choices for fuel-cell vehicles. The participation by the energy companies forced the study team to examine their key assumptions much more thoroughly.

TF: How do you hope that this study will influence public and private decision makers regarding the introduction of advanced fuel/vehicle propulsion systems?

Greg Ruselowski (GM): The study can help influence public policy in terms of where we should focus our efforts what types of fuels and technologies make the most sense. I think it will help the auto and energy companies as well in developing business strategies to optimize the fuel choices and propulsion systems that really make the best long-term sense, not only for our companies but for society in general.

Gilbert Jersey (ExxonMobil): ExxonMobil is very oriented toward an approach of sound science for making sound decisions, so this study is really one opportunity for bringing outstanding science that has been developed in this area to the forefront to make it part of the technical dialogue.

Jean Cadu (Shell): I think that responsible people cannot ignore the conclusions of the study. I hope that it will help put some sort of flexibility into emissions legislation for passenger cars because some of the fuel/vehicle systems will have trade-offs among the different pollutants. In Europe, there are two sets of emissions standards, one for diesel and one for gasoline, which makes sense. In the United States, there is only one series of limits, and diesel is completely left out.

TF: How (and why) did GM decide to involve the energy companies and Argonne in its analysis?

Greg Ruselowski (GM): There are a lot of these studies out there. We wanted this to be the gold standard that everybody could look at. We felt that getting Argonne involved was absolutely critical because of the level of credibility that the Laboratory brings in terms of being impartial. Also, Michael Wang's GREET model has been recognized around the world. When we looked at a number of other organizations to perhaps participate in the effort, most of them were using Michael's model, so we figured, let's just go to the source. Getting the energy companies involved was also critical in terms of helping to put in the right assumptions and to add credibility to this study so that when it did come out, it would be perceived rightly so as the standard by which to measure future work.

TF: Did the results of the study surprise anyone, or did they confirm that the areas in which your companies had already been focusing their research were the right ones?

Greg Ruselowski (GM): Actually, the results were not unexpected. We all recognize that fuel cells are the ultimate solution, but there were a lot of questions about what fuel makes the most sense. I think one of the surprising things was how well diesel fared. It's a very efficient fuel for the vehicle, but it also turns out to be a very efficient fuel to make. The other thing that I'd like to focus on is the methanol versus gasoline debate for the fuel cell. We worked with methanol for many years and we knew it had an advantage on the vehicle side, but on the well-to-tank side, we knew that there was a disadvantage. The results confirmed what we had thought, but by laying it out in a very consistent manner, we made our conclusions readily apparent to anybody looking at it; there were a lot of different studies showing conflicting data.

Gilbert Jersey (ExxonMobil): I think we learned a few things that we didn't know before as a result of interacting with the various groups, particularly with General Motors. It was an opportunity for us to really understand the nuances of the vehicle technology.

Jean Cadu (Shell): I think what came as a great surprise was the ethanol pathway, especially on a CO2 basis. The success of the diesel hybrid was also a surprise. It verified the things we had already worked out, but this study is a real confirmation that diesel hybrids are a feasible option.

TF: What is planned for the next phase of the study?

Greg Ruselowski (GM): The next phase will focus on criteria pollutants and developing a European counterpart to the current study. Nobody has done any really good work on criteria pollutants. This one's going to be a real challenge. So we're looking forward to working with Argonne and the energy companies on that. Also, there are some issues specific to Europe in terms of some of the fuel pathways, which are a little different. The vehicles are smaller. We're not sure that we're going to see huge differences. But there are enough differences in the way people drive, where they get the fuel; the powertrains are a little smaller, a little more efficient than what's available here, and so it's worth doing.

Jean Cadu (Shell): Shell will be involved in both parts of the study. Estimating criteria pollutants along the various fuel chains will be more complex, but the challenge is worth it. Shell looks forward to contributing to the European counterpart of this study, also led by GM.

Jim Simnick (BP): We will be involved in both parts of the study; it should be interesting because this is uncharted territory. We look forward to working with this group again, and we believe the second part of the study will be as good as the first.

Study Results

Considering both total energy use and GHG emissions, the key findings of the study are as follows:

Among the crude oil- and natural gas-based pathways studied, the diesel compression-ignition direct-injection (CIDI) HEV, gasoline and naphtha fuel-cell HEVs, and the gaseous hydrogen (GH2) fuel-cell HEV were the best and nearly identical in terms of total system energy use. Among these pathways, however, expected GHG emissions were lowest for the GH2 fuel-cell HEV and highest for the diesel CIDI HEV.
Compared with the gasoline conventional vehicle, the gasoline and diesel CIDI HEVs and the diesel CIDI (conventional) vehicle yield significant total system energy use and GHG emission benefits.
The methanol fuel-cell HEV offers no significant advantages over the crude oil-based or other natural gas-based fuel-cell HEV pathways when both energy use and GHG emissions are considered.
Ethanol-based fuel and vehicle pathways have by far the lowest GHG emissions of the pathways studied; they also do well on well-to-tank energy use when fossil fuel consumption is the focus.
On a total system basis, the energy use and GHG emissions of compressed natural gas conventional and gasoline conventional pathways are nearly identical.
The crude oil-based diesel vehicle pathways offer slightly lower total system GHG emissions and considerably better total system energy use than the natural gas-based Fischer-Tropsch diesel CIDI vehicle pathways. (Note that criteria pollutants are not considered.)
Liquid hydrogen, Fischer-Tropsch naphtha, and electrolysis-based hydrogen fuel-cell HEVs have significantly higher total system energy use and the same or higher levels of GHG emissions than the gasoline and crude naphtha fuel-cell HEVs and the GH2 fuel-cell HEV.