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DME Comes to DC in a Truck Beating EPA 2010 Emissions Requirements

Nissan Diesel’s DME demo truck.

The Japan International Transport Institute and the National Traffic Safety and Environment Laboratory are hosting a half-day conference in Washington, DC, on the development and promotion of environmentally-friendly heavy-duty vehicles—with a specific emphasis on DME (dimethyl ether).

Not well-known as a fuel alternative in the US, DME is a synthetic substitute for diesel that has attracted attention and development in Japan, China and Europe. Volvo Trucks, for example, introduced its second-generation DME truck in 2005 (earlier post.)

DME as a synthetic fuel is to diesel what LPG is to gasoline: while gaseous at ambient conditions it can be liquefied at moderate pressure. With a high cetane number, DME is clean-burning, sulfur-free, and with extremely low particulates. These are attractive characteristics for a worldwide heavy-duty vehicle industry being faced with increasingly stringent emissions requirements.

DME truck emissions profile. The DME truck exceeds the EPA 2010 emissions requirements.

Specifically, dimethyl ether (DME) trucks developed and tested jointly by the National Traffic Safety and Environment Laboratory and Nissan Diesel Motor Co., have exceeded the upcoming 2010 US heavy-duty emissions regulations.

With its high cetane number, DME is very suitable for use in a compression ignition (diesel) engine. In building the DME truck prototype, Nissan applied a different fuel system to compensate for the lower heat value of DME compared to diesel, and a different emissions-control system.

Fuel system. Since DME becomes gas at normal atmosphere and pressure, DME vehicles pressurize fuel pipes to liquefy DME. To compensate for the lower heat value of the DME, and to retain the same output power provided by diesel, the Nissan DME truck uses a fuel supply system capable of spraying double the amount of fuel.

DME can match the BSFC of diesel.

Through the optimization of the combustion system and the combination of emission reduction technologies, the DME truck achieves the same level of fuel efficiency—measured as brake specific fuel consumption (BSFC)—as conventional diesel vehicles, while significantly reducing emissions.

BSFC measures efficiency by the amount of fuel consumption divided by the power production—grams of fuel per kilowatt-hour in this case.

Emissions system

Emissions system. DME causes no carbon bond when combusted, and therefore, it generates no PM or soot. For this reason, measures to control emissions from DME combustion are focused on NOx reduction. The truck does not require the use of a separate particulate filter.

As an emissions-control strategy, the Nissan DME truck applies a large volume Exhaust Gas Recirculation (EGR) system with a high-performance NOx catalyst system.

Nissan Diesel PW25A DME Truck
Gross Vehicle Weight 20 tons
DME tank capacity 342 liters
Range 627 km
Engine Type Inline 6 cylinder
Valve type OHV, two valves per cylinder
Bore/stroke 108mm / 126mm
Displacement 6,925 cc
Aspiration Turbocharged with intercooler
Max power 199 kW
Max torque 750 Nm
Emission reduction system (cc) EGR, Oxidation catalyst, NOx storage reduction catalyst




Verry interesting. Can say 10%DME remain in ULSD/BioD in one tank and without Adblue but with minor timing adjustments meet 2010 specs? Surely they tried that.

Rafael Seidl

If you mix diesel and DME in a single (pressurized) tank, the substantially less dense DME will rise to to the top, producing unpredictable fuel properties.

DME does not magically eliminate NOx, because the combustion temperature in the diffusion flame is a function of the compression ratio of the engine and the total fuel energy injected. Therefore, you still need NOx aftertreatment to meet 2010 standards.

What DME does eliminate is engine-out PM emissions so you can avoid the use of a particulate filter. The downsides are higher cost for the fuel and the fuel system components and, sharply reduced range on a single tank.

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