Dimethyl ether (DME) has been identified as a promising renewable fuel for use in compression ignition (CI) engines. When produced from renewable sources, it has the highest well-to-wheel energy efficiency and lowest greenhouse gas emissions of any biofuel currently available. The high cetane number (>55) and high volatility of DME make it ideal for CI engines. DME's lack of carbon-carbon bonds produces no soot through conventional pathways during combustion. Therefore, it is widely assumed that DME engines will meet U.S. particulate matter (PM) regulatory standards for vehicles without requiring a diesel particulate filter. However, nanoparticles emitted from combustion may still be emitted originating from the engine lubricating oil or from fuel lubricity additives required to protect fuel system hardware. This study examines nanoparticle emissions from DME operation in a diesel engine as a function of lubricity additive concentration in the fuel. The goals of the project include measuring baseline particulate matter (PM) and gaseous emissions at three steady-state engine load conditions (4, 6 and 8 bar indicated mean effective pressure) with diesel fuel and DME. Four levels of lubricity additive concentration (0, 100, 500, 1000 ppm) were tested at each engine load with DME. Our work tested the hypothesis that lubricity additive increases semi-volatile nanoparticle concentration in the exhaust. Results show that DME exhibits thermal efficiencies slightly lower than diesel fuel, has similar NOX emissions but higher CO. The PM from diesel fuel operation contained accumulation mode particles in addition to a large nucleation mode assumed to originate from the lubricating oil. PM from DME operation did not contain an accumulation (soot) mode as expected and the particles emitted were nearly all volatile and easily removed with a catalytic stripper prior to the particle sizer. Increasing fuel  lubricity additive concentration showed a small increase in nanoparticle size and concentration.

Nanoparticle emissions from dimethyl ether combustion in a compression ignition engine

248th National Meeting (2014)

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