Volvo’s DME technology will be available in a Volvo D13 13-liter engine, and the company’s I-Shift automated manual transmission will be standard on DME-powered trucks. DME-powered vehicles will join a line-up that already includes CNG-powered Volvo VNM and VNL model day-cabs. The company will also introduce its own proprietary LNG engine—North America’s first fully integrated natural gas solution—in VNL day-cabs and sleepers next year.

Volvo said it decided to invest in DME technology and introduce it to the North American market because of the numerous benefits DME offers as a heavy-truck fuel. DME’s high cetane number delivers performance and efficiency comparable to diesel, and it packages densely enough on a truck to support long range transports, or to allow room for vocational equipment on the frame. It is an excellent compression ignition fuel which, like diesel, requires no separate ignition mechanism.

Comparing packaging attributes for LNG, CNG and DME on-board storage. Source: Volvo Trucks. Click to enlarge.

Unlike LNG, it does not require cryogenic temperatures; it is handled and stored like propane, with tank pressures of only 75 psi (vs. 3,600 psi for CNG). On-board storage is much simpler and lighter than that required for LNG or CNG; instead of a double-wall stainless steel tank with cryogenics for LNG, or a carbon graphite tank for CNG, DME requires just a single-wall steel tank. It can safely be stored on-site for extended periods of time. It also performs exceedingly well in cold temperatures with no extra measures required.

Because DME produces no soot, no diesel particulate filter (DPF) is necessary. In addition to the weight savings from the removal of the DPF, DME tanks are considerably lighter than comparable CNG or LNG tanks and considerably less complex.

DME engine in 2015. Volvo is currently in development with the DME engine that will enter production in 2015. For now, noted Ed Saxman, Volvo Trucks’ Product Marketing Manager, Alternative Fuels, the engines in the customer fleet test trucks in the US are the same as those currently under test in Europe.

The base engine of the new DME engine will be identical to the D13 13-liter diesel. However, a new injection system is required; because DME has half the energy density of diesel, twice the volume of the fuel must be injected to offer comparable diesel performance. The requirement of the new injection system alone argues against a retrofit implementation of DME, Saxman said.

DME is injected as a liquid, but requires much lower pressure injection.

Additionally, because DME burns with no soot or particulates, no diesel particulate filter (DPF) is needed; no regeneration, active or passive, is needed; no seventh injector is needed. There is no need for Exhaust Gas Recirculation, EGR cooler, and EGR valve, Saxman said.

[Although others (Arcoumanis et al.) have suggested that NO_x emissions from DME-fueled engines could meet future regulations with high exhaust gas recirculation in combination with a lean NO_x trap.]

Nor is a Variable Geometry Turbocharger required on the new DME engine—a much simpler turbo can be used. Although the engine will initially be introduced with SCR for NO_xreduction, there is the potential for removing that requirement down the road. In short, Saxman said, the 2015 DME engine will be simpler and lighter than its diesel equivalent, but meet all the emissions standards.

Initially, Volvo Trucks will use a 17:1 compression ratio with the DME engine—the same as with the diesel variant. The initial rating will be 425 hp (317 kW), with 1,750 lb-ft (2,373 N·m) of torque. This will be followed by a 500 hp (373 kW) rating with the same torque.

Selecting DME. Volvo Truck’s DME announcement comes in the context of many years of alternative fuel and driveline development. In 2007, Volvo showcased in Brussels seven commercial vehicles powered by seven different CO₂-neutral fuels, one of which was DME. (Earlier post.) The company demonstrated these vehicles in US operation in 2008, in conjunction with the Washington International Renewable Energy Conference (WIREC).

The company then went on to evaluate the performance of the seven fuels—Biodiesel (B100); Methanol/Ethanol (Spark Ignition); Hydrogen + Biogas (Spark Ignition); CNG (Spark Ignition): LNG (Compression Ignition + pilot injection); Synthetic Diesel; and DME (Compression Ignition). Criteria in the evaluation were climate impact; energy efficiency; land use efficiency; fuel potential; vehicle adoption; fuel cost; and fuel infrastructure.

Rank-ordered, the scores (higher is better) were:

• DME: 28.5
• Methanol: 27.5
• Synthetic diesel: 26.5
• LNG: 23
• CNG: 22.5
• Hydrogen + biogas: 21
• Biodiesel: 19
• Ethanol: 17.5

Customer trials. Volvo Trucks in North America will partner with Safeway Inc., one of the largest food and drug retailers in North America, and Oberon Fuels to test heavy-duty commercial vehicles powered by dimethyl ether (DME) produced from biomass. The project received $500,000 in funding from California’s San Joaquin Valley Air Pollution Control District (SJVAPCD) and will be the second customer field test conducted by Volvo Trucks in the US.

DME trucks in the US have already been in testing with Martin Transport, which operates a fleet of tank trucks providing transportation of petroleum products, LP gas, molten sulfur, sulfuric acid, paper mill liquids, chemicals, dry bulk, and numerous other bulk liquid commodities. Martin Transport is an element of Martin Resource Management, founded and run by Ruben Martin, who is now also an investor in Oberon Fuels.

Between the trials in Europe and the work with Martin, Volvo DME trucks have already logged more than 650,000 kilometers (404,000 miles) of operational testing.

Oberon’s process. Click to enlarge.

Oberon. Founded in 2011, Oberon Fuels has developed a patented, skid-mounted, modular design for DME production. The small-scale process is envisioned to enable the development of regional fuel markets that can service local customers engaged in regional haul, initially bypassing the need for a national infrastructure.

A full Oberon plant will consist of three stages: the production of syngas, its conversion to methanol, and the subsequent catalytic dehydration of methanol to DME.

For the $500,000 grant collaboration with Volvo Trucks and Safeway, Oberon plans eventually to produce DME from renewable feedstocks such as animal, food and agricultural waste, preventing methane from being released into the atmosphere, and converting the waste to a usable, clean-burning fuel.

The Oberon plant supported by the funding from the SJVAPCD will be located in Brawley, California, in the Imperial Valley. The primary source of biogas will be cow manure.

Nameplate capacity for the Brawley plant will be 4,500 gallons per day. Phase 1 of the Brawley project—which consists of the distillation tower to produce DME (the third stage)—is coming online this month. The plant will run for a few months to produce fuel for the Volvo Truck trials, said Dr. Rebecca Boudreaux, Oberon’s president, then shut down for the installation of the “front-end” elements of the Oberon process (syngas and methanol production). The plant will begin production again in 2014 with the full process: biogas to DME.

Oberon intends to offer two unit size options: the 4,500 gpd unit, and a larger 10,000 gpd unit. The 4,500 gpd unit will require 950 kcf/day (60% methane, 40% CO₂) of biogas as input; the 10,000 gpd unit will require 2.1 Mcf/day biogas. The Oberon process can use biogas with CO₂ content of up to 50%

While in theory biomass gasification could be used to produce syngas for use in the Oberon process, the ratio (i.e., CH₄ to CO₂) is not as optimal for Oberon’s technology as in biogas, Dr. Boudreaux said. Therefore, Oberon will need to rely on the presence of anaerobic digesters to produce biogas or landfill methane to produce renewable DME, or use natural gas.

Oberon envisions a regional buildout for its technology, with the plants essentially going to where the feedstock is, rather than the other way around as is currently the case. With this as a basis, Oberon foresees a hub-and-spoke model for distribution—i.e., regional production of DME, which will then be delivered in propane-style tankers to customer terminals.

Resources

• US Patent Nº 8,378,159: Process and system for converting biogas to liquid fuels

  T.H. Fleisch, A. Basu, R.A. Sills (2012) Introduction and advancement of a new clean global fuel: The status of DME developments in China and beyond, Journal of Natural Gas Science and Engineering, Volume 9 Pages 94-107, doi: 10.1016/j.jngse.2012.05.012

• Constantine Arcoumanis, Choongsik Bae, Roy Crookes, Eiji Kinoshita (2008) The potential of di-methyl ether (DME) as an alternative fuel for compression-ignition engines: A review, Fuel, Volume 87, Issue 7 Pages 1014-1030 doi: 10.1016/j.fuel.2007.06.007

• T.H. Fleisch, A. Basu, M.J. Gradassi, J.G. Masin (1997) Dimethyl ether: A fuel for the 21^st century, In: M. de Pontes, R.L. Espinoza, C.P. Nicolaides, J.H. Scholtz and M.S. Scurrell, Editor(s), Studies in Surface Science and Catalysis, Elsevier, Volume 107, Pages 117-125, doi: 10.1016/S0167-2991(97)80323-0