Mode Switching to Improve Low Load Efficiency of an Ethanol-diesel Dual-fuel Engine

Paper #:
  • 2017-01-0771

Published:
  • 2017-03-28
Abstract:
Diesel engines suffer from the oxides of nitrogen (NOx) versus smoke trade-off, wherein the application of EGR for NOx reduction often results in an increase in the smoke emissions. By implementing the ethanol-diesel dual-fuel combustion, the smoke penalty associated with the use of EGR can be suppressed when high ethanol fractions are used. However, at low load levels, the increased carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions contribute to a large reduction in the thermal efficiency in the dual-fuel mode. In this work, tests are conducted on a high compression ratio, single cylinder dual-fuel engine, that incorporates the direct-injection of diesel and port-injection of ethanol. Engine load levels are identified, at which, diesel combustion is more efficient than the dual-fuel combustion while attaining low NOx and smoke emissions. Thereafter, a cycle-to-cycle based closed-loop controller is implemented for the combustion phasing and engine load control in both the diesel and dual-fuel combustion regimes. The controller actively regulates the fuelling rate and the injection timing of the diesel direct-injection. A mode switching scheme for switching between diesel and dual-fuel combustion modes is realized, using the closed-loop controller, without compromising the combustion stability. The continuous measurements of NOx and PM emissions demonstrate the effectiveness of the mode switching on achieving low exhaust emissions, whereas the fuel flow measurements illustrate the thermal efficiency benefits of conducting the switching. By applying the mode switching strategy in the dual-fuel engine, stable, efficient, and clean combustion is obtained from idle (3 bar IMEP) to full-load (19.2 bar IMEP) conditions.
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