Volvo will add DME to alternative fuel options in North America

[kscarbel]

Fleet Owner / June 6, 2013

Volvo says it will begin limited production of VNL trucks powered by the alternative fuel dimethyl ether (DME) in 2015.

In a related development, Safeway Inc. will begin field testing two VNLs with Volvo D13 engines modified to use the new fuel option under a $500,000 grant from California’s San Joaquin Valley Air Pollution Control District, the truck maker said today at a press conference in the state’s capitol.

DME can be produced from a variety of biomass waste materials or natural gas, offering CO2 reductions of up to 95% compared to diesel. Modifications to the D13 are relatively minor and will not require the use of diesel particulate filters (DPFs), according to Volvo. Handling and storage is similar to propane and does not require cryogenic or high-pressure storage, the company said.

“We decided to test Volvo DME technology in our fleet because it is a natural fit with our sustainability strategy,” said Tom Nartker, VP of transportation at Safeway.

“With the addition of DME-powered vehicles to our previously announced CNG and LNG offering, Volvo’s Blue Power line-up will offer the industry’s most comprehensive approach to the developing North American alternative fuel market,” said Göran Nyberg, president of Volvo Trucks North American sales and marketing.

As part of the California field test, Oberon Fuels will begin commercial production of DME in the Imperial Valley using new skid-mounted, small-scale units.

“Our small-scale process enables the utilization of regional feedstocks to produce DME,” said Rebecca Boudreaux, Ph.D., president of Oberon Fuels. “Cost-effective, regional fuel production addresses the distribution issue, and offers the potential to bypass the need for a national fueling infrastructure, while reducing the carbon footprint associated with transporting the feedstock and the fuel produced.”

Earlier this year Volvo began field testing its first DME-powered VNL in the U.S. with a bulk hauler. Calling the test “highly successful,” Nyberg said customer feedback and early test results led to its decision to begin commercial production of DME-fueled heavy trucks for the North American market.

In addition to the CO2 reduction and handling benefits, DME is similar to diesel in performance and efficiency, according to Volvo. Unlike natural gas, it is a compression ignition fuel that does not require spark or diesel-pilot injection, and it has enough storage density to be suitable for long-haul applications or trucks carrying vocational bodies. It is also non-toxic and is already widely used as an aerosol propellant in cosmetics and other household products, the company pointed out during the press announcement.

The DME fuel systems could eventually be installed on the D13 engines at the company’s Hagerstown, MD, powertrain plant, but initial low volumes will be handled outside of Hagerstown, according to the company. Volvo already offers CNG-powered VNL and VNM day cab models in North America and has previously announced that it will introduce a proprietary LNG heavy-duty engine in VNL day-cab and sleeper models next year.

Note:

Dimethyl ether (DME), also known as methoxymethane, wood ether, dimethyl oxide or methyl ether, is a colorless, slightly narcotic, non-toxic gas. Highly flammable gas at ambient conditions, it can be handled as a liquid when lightly pressurized. The properties of DME are similar to Liquefied Petroleum Gas (LPG). DME is degradable in the atmosphere and is not a greenhouse gas.

DME is entirely in the experimental stage and is only “technically” feasible if the cost of crude oil is above US$100 a barrel. With the lack of an established supply and fueling infrastructure, DME fuel is more likely to be used in niche applications rather than as a wide-scale alternative to diesel fuel.

Volvo has been promoting it because of the funding the program is receiving from the Swedish Energy Agency and 7th Framework Program.

Not wanting to be left in the cold should the technology become available to actually make DME practical, Chemrec (Sweden), Haldor (Denmark), Preem (Sweden) and Total (France) are onboard as investors.

Under political pressure in Scandinavia to also experiment with DME, Scania has done an equal amount of experimentation and come to the conclusion that DME is not yet cost-effective and practical.

Because the entire fuel system must be redesigned, the larger emissions reductions DME can yield are offset by the high price and complexity of the necessary fuel storage and injection system including a pressurized fuel tank. Like LPG, DME is stored in the liquid state under relatively low pressure of 73 psi (to limit the number of modifications required to the engine).

DME can be produced from forest products (pulp-mill byproduct), agricultural by-products, organic waste, energy crops and black liquor.

Like methanol, DME contains oxygen and no carbon-carbon bonds. But unlike methanol, DME has a high enough cetane number to work a compression-ignition (diesel engine) fuel. Also unlike methanol, DME is a gas at ambient temperature and pressure, so it must be stored under pressure as a liquid similar to LPG (liquefied petroleum gas).

When used as a diesel fuel, DME provides reduced PM and NOx emissions, but increased CO and HC.

DME is produced by converting natural gas, organic waste or biomass to synthesis gas (syngas). The syngas is then converted into DME via a two-step synthesis, first to methanol in the presence of catalyst (usually copper-based), and then by subsequent methanol dehydration in the presence of a different catalyst (e.g. silica-alumina) into DME.

DME can also be produced through direct synthesis using a dual-catalyst system causing both methanol synthesis and dehydration in the same process unit, with no intermediate methanol separation. The licensors of this process, by eliminating the intermediate methanol synthesis stage, claim efficiency advantages and cost benefits.

Currently there’s only one DME plant in the world, a demonstration facility in Piteå, Sweden from 2010. It’s the first gasification plant worldwide producing high-quality synthesis gas based on 100% renewable feedstocks. The raw material used is black liquor, a high-energy residual product of chemical paper and pulp manufacture which is usually burnt to recover the spent sulfur.

With good ignition quality and a high cetane number, DME can be used as a diesel fuel substitute. But DME has two issues. Compared to diesel fuel, DME has a lower viscosity (insufficient). Also, because DME does not provide sufficient lubrication to the injection system, a lubrication additive must be added. Volvo chose Lubrizol LZ539N but was also challenged by blending problems.

For safety reasons, ethyl mercaptan was added as an odor additive, as DME has no noticeable odor (Ethyl mercaptan is used as an odor additive in LPG)

Volvo was challenged in trying to minimize the use of the lubrication and odor additives to avoid a negative impact on exhaust emissions, while still providing adequate lubricity for the fuel system.

So DME's lack of lubricity seems to be a key issue. It’s a trade-off between an engine with a well-lubricated fuel system that doesn’t meet the DME hopeful’s emissions expectations versus a low emission engine that will have a high maintenance injection system.

Pros:

• High Thermal Efficiency = Equal to direct injection diesel
• Compression Ignition = about 60 cetane number
• Smokeless Combustion = nearly zero PM
• High EGR Tolerance = NOx can be reduced
• Combustion Noise Reduced
• LPG Infra can be Used = Liquefied at 5∼6 bar

Cons:

• Low Lubricity & Viscosity = Wear & Leakage Problems
• High Compressibility = Difficult to Injection Control
• Elastomer Attack = Sealing Problem