|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. 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|
|Engine||Type||Inline 6 cylinder|
|Valve type||OHV, two valves per cylinder|
|Bore/stroke||108mm / 126mm|
|Aspiration||Turbocharged with intercooler|
|Max power||199 kW|
|Max torque||750 Nm|
|Emission reduction system (cc)||EGR, Oxidation catalyst, NOx storage reduction catalyst|