CO2-neutral vehicles

April 1, 2008
Volvo group used the occasion of the recent Washington International Renewable Energy Conference (WIREC) to unveil a group of functional heavy-duty alternative-powered trucks

Volvo group used the occasion of the recent Washington International Renewable Energy Conference (WIREC) to unveil a group of functional heavy-duty alternative-powered trucks. These were a Mack Pinnacle, two Volvo VNs, and four European-spec'd Volvo FM cabovers, all carbon-dioxide-neutral, powered by fuels produced from renewable raw materials.

Also on display was a heavy-duty Mack Granite dump truck with a hybrid driveline.

In addition, Volvo put on two seminars. One was on renewable fuels for CO2-neutral road transport. The other dealt with alternative fuels and alternative drivelines.

Held March 4-6 in Washington, DC, the WIREC is intended to bring together government, society, and private business leaders to address the possibilities, challenges, benefits, and costs of a major and rapid scale-up in the global deployment of renewable energy technology. The US Government, in cooperation with the American Council On Renewable Energy, hosted the event.

In presenting the alternative-fueled trucks to WIREC attendees, Volvo Group chief executive officer (CEO) Leif Johansson explained: “CO2-neutral vehicles are powered by fuels produced from renewable raw materials which, unlike fossil fuels, can be driven without any net contribution of carbon dioxide to the atmosphere. The combustion process generates exactly the same amount of carbon dioxide as that absorbed by the source material during its growth. No increase in atmospheric carbon dioxide will result, provided that crop re-growth matches the quantities harvested.”

Power sources

With the aid of sophisticated engine technology and minor modifications, Volvo has adapted the diesel engine to run on a wide range of renewable fuels. It decided to work with the diesel engine rather than other power sources because “diesel engines are the most efficient energy converter, and they can be modified to run on fuels other than diesel,” Johansson said. What's more, the diesel engine forms the basis for a variety of hybrids in parallel with electric motors, batteries, and fuel cells.

The seven fuels Volvo is evaluating are: biodiesel, synthetic diesel, DME (dimethyl ether), methanol/ethanol, biogas, biogas plus biodiesel, and hydrogen plus biogas.

These fuels were chosen because they have the least amount of impact on the climate, energy efficiency, land use efficiency, fuel potential, vehicle adaptation, fuel cost, and fuel infrastructure (handling and distribution).

“Our real desire, along with providing the best transport efficiency and lowest operating costs, is to provide transport that has as little impact as possible on the environment,” said Johansson. “We know we need to reduce CO2, but we also need to decrease the dependency on oil. Oil is running low as demand is outstripping supply. There is the threat from terrorists disrupting the oil supply, and there is political uncertainty in many oil regions.

“Alternative fuels and hybrid technology can help solve these problems. Plus, our customers are seeking ways to reduce their fuel costs, which for many fleets is more than one-third of their total operating costs.”

Volvo views tomorrow's fuels and drivelines from what it calls a “well-to-wheel” perspective. This is a concept in which all relevant stages of the fuel chain are considered. This includes the cultivation (including fertilization) and harvesting of the raw material, its transport to the fuel production plant, production and distribution of the fuel to refueling stations, and use in vehicles.

The aim is to obtain the maximum possible energy efficiency from the energy source itself, all the way to the vehicle's wheels but with the lowest possible emissions along the way.

Each alternative fuel Volvo is evaluating presents challenges and benefits, according to Volvo Powertrain North America's Anthony Greszler, vice president-advanced engineering, and Greg Shank, coordinator lubricants, fuels and coolants technology. With regard to liquid fuels:

  • Biodiesel, produced by the esterification of vegetable oils, comes in a wide variety of formulations and quality. It provides slightly reduced fuel performance (5 to 10 percent), is corrosive to certain materials, and causes an increased need for maintenance.

    Esterification is a chemical process in which raw vegetable oils are converted into esters and given enhanced physical properties, particularly greater stability.

    On the positive side, biodiesel is currently available and is an acceptable alternative due to incentives for using it. Its operational range is almost equal to diesel fuel, and there are only minor vehicle adaptation requirements.

    Greszler and Shank noted that biodiesel is the most common renewable fuel, but it needs a common standard.

  • Synthetic diesel is a blend of synthetically generated hydrocarbons produced by the gasification of biomass that can be blended with conventional diesel oil without problem. It presents the fewest challenges. Chief among them is reduced lubricity, which is treatable with additives.

    Gasification is a process in which an organic material, such as biomass (any organic material made from plants or animals), is converted into synthetic gas, a mixture of hydrogen gas, and carbon monoxide. The synthetic gas can then be used to produce various synthetic fuel constituents.

    Among the benefits of using synthetic diesel are very low CO2 emission levels, the same performance and operating range as diesel fuel, and no need for vehicle modifications.

  • Methanol/Ethanol are alcohol fuels. Methanol is a product of biomass gasification. Ethanol is produced by fermentation from crops with a high sugar or starch content.

Challenges with this fuel are that it is difficult to ignite and has reduced energy density, which diminishes the operational range (60 percent less than diesel). In addition, methanol/ethanol is more corrosive than diesel, and has increased hydrocarbon and carbon monoxide emissions.


Biogases, said Shank and Greszler, are gaseous fuels consisting mainly of the hydrocarbon methane, which can be extracted from sewage treatment plants, landfills, and other sources of biologically degradable material. This alternative fuel also can be produced by biomass gasification.

Biogas can be mixed with hydrogen in low concentrations. Hydrogen is a gas produced by electrolysis of water using renewable electricity.

Because both gases have a low cetane index, ignition with a spark plug is required. Both biogas and hydrogen have low volumetric energy, so this fuel's operational range is lessened.

When biogas is used in combination with biodiesel, there must be separate tanks and fuel injection systems. A small percentage (10 percent) of biodiesel (or synthetic diesel) is used to achieve compression ignition. In this option, biogas is used in cooled, liquid form.

As for the benefits from these gaseous fuels, Greszler and Shank said hydrogen and biogas have very low well-to-wheel CO2 emissions, virtually no particulates or smoke, good throttle response, and very low noise levels.

Biogas and biodiesel offer these same benefits, but there is some particulate emissions and smoke. Additionally, biogas and biodiesel have the added benefit of high engine efficiency.

Greszler and Shank said there is potential for biogas and biodiesel being optimized for long-haul operations, or in the case of unreliable fuel supply. They said there are good possibilities for hydrogen and biogas for urban operations, where lower noise is needed and operating range is less critical.

The final alternative fuel shown by the Volvo Group was DME (dimethyl ether). A gas that is handled in liquid form at low pressure, DME is produced by the gasification of biomass. It also is a byproduct of wood pulp operations.

Among the challenges of this fuel are low viscosity and lubricity, high compressibility (requires a common rail fuel system), and a limited operational range — about 55 percent of diesel. What's more, DME dissolves most rubber and plastic materials.

Nevertheless, the fuel offers a variety of benefits, including diesel efficiency and performance, high torque at low engine speed, low CO2 emissions from biosources, reduced noise levels, and simplified exhaust aftertreatment systems. Only modest modifications are required to convert a diesel engine to run on DME

The Volvo Group feels “DME is a concept with great potential, especially for long-haul applications.” Volvo has been working with this alternative fuel for a number of years in Europe. It is being commonly used in some Asian countries.


In his presentation to the WIREC, Paul Vikner, president and CEO of Mack Trucks, part of the Volvo Group, outlined the company's North American market perspective on the hybrid technology, pointing out: “It is part of the strategy to accelerate the transition to CO2-neutral transport. Hybrids not only provide better fuel efficiency, they reduce emissions and enhance operating performance.”

Basically, hybrid drivelines consist of a diesel engine, an electric machine (“the heart of the hybrid system”), an automated manual transmission, ultra-capacitor storage devices (batteries), and conventional drive axles. The batteries absorb energy during vehicle braking. This stored energy is transferred via an electric turbo-compounder to provide torque to the wheels.

Under vehicle start, initial acceleration, and slow speeds, a hybrid truck functions in full electric mode for reduced noise and exhaust emissions and efficient operation. The diesel engine cuts out depending on the truck's load and speed. Engine idling during stops is avoided.

A key feature of Mack's hybrid driveline is its auxiliary vehicle electrification system, said Vikner. It replaces parasitic, belt- and gear-driven components — such as air compressors, coolant pumps, power steering pumps, refrigerant compressors, and cooling fans — with electrically driven components.

Electrification of such components not only improves operating efficiency, he added, it permits 120-volt alternating current auxiliary power generation for hotel loads.

“The potential fuel savings in hybrid operation is dependent upon the application,” said Vikner. “Hybrid systems are particularly suited to those vehicles that operate in continuous stop-and-go conditions, because the systems harness the retardation energy that builds up every time the brakes are applied.” In particular, he cited refuse trucks, which can realize “anywhere from a 15 to 33 percent decrease in fuel consumption.”

He noted that long-haul hybrids could have significant impact on overall diesel emissions, given the two million over-the-road tractors in operation in the US today.

Even though in long-haul operations trucks are running at higher speeds for longer miles, Vikner said fuel economy improvement of 5 to 8 percent is still possible with hybrid technology. “For the fleets operating hundreds and thousands of trucks and running tens of millions of miles a year, that increase in fuel mileage is huge, and that brings greater profitability to a fleet.”

To capture the benefits of hybrids, “we need to continue and expand public-private sector research and development partnerships — a key to successful commercialization, he said. “We also need to encourage hybrid truck purchases by government entities and create meaningful incentives for commercial customers to purchase hybrids. The faster we can bring this technology and alternate fuels to market, the faster we can achieve exactly what this conference is all about.”

“One of the foremost challenges to alternative fuels,” Johansson added, “is determining what fuels to pursue, creating standards for the fuels, and making sure supply is available. As we have demonstrated with our vehicles for renewable fuel options, the technology and resources exist, but we need the fuels.”


Both he and Vikner concurred that making CO2-neutral transport a reality will require the active participation of politicians, government agencies, and fuel producers. “Politicians and government agencies must take international decisions to enable stable, long-term regulations to be implemented, while fuel producers must provide the answers as to when production and distribution can begin,” said Johansson.

In his comments at WIREC, US Department of Energy's Assistant Secretary For Energy Efficiency And Renewable Energy Andy Karsner observed: “We are addicted to oil in an unsustainable way that degrades our planet, undermines our security, affects our long-term prosperity, and must be dealt with as the highest priority. We're working on this not just in the US, but with partners around the world.”

A good example of this, he said, is a specific international public-private environmental agreement developed by the American and Swedish governments, in which the Volvo Group participated. The agreement is aimed at reducing the use of fossil fuels in the transportation sector through cooperative projects in the areas of energy and automotive development, including advanced hybrid and alternative driveline technology.

“Sweden is the first country to do this,” Karsner pointed out.

Energy efficiency

The Volvo Group's ongoing efforts to improve energy efficiency have not only been with its vehicles. It has been reducing energy consumption in its manufacturing process as well.

Its New River Valley truck plant in Dublin, Virginia, has reduced green house gases emissions by 40 percent. The engine plant in Hagerstown, Maryland, has gone from 2.25 megawatts of power to make an engine to just above 1 megawatt. Its Macungie, Pennsylvania, truck plant has trimmed down its greenhouse emissions by 50 percent.

Perhaps most notable is Volvo's plant in Ghent, Belgium. It is the world's first carbon dioxide neutral vehicle production plant.

About the Author

David Kolman