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Combustion, performance and emission analysis of a natural gas-hydrous ethanol dual-fuel spark ignition engine with internal exhaust gas recirculation

da Costa, Roberto Berlini Rodrigues, Hernández, Juan J., Teixeira, Alysson Fernandes, Netto, Nilton Antonio Diniz, Valle, Ramón Molina, Roso, Vinícius Rückert, Coronado, Christian J.R.
Energy conversion and management 2019
carbon monoxide, combustion, emissions, energy, ethanol, heat transfer, hydrocarbons, liquids, natural gas, pollutants, spark ignition engines
This manuscript presents a deep analysis of natural gas-hydrous ethanol dual-fuel combustion in a spark ignition engine with a modified compression ratio and an advanced intake valve opening strategy to promote internal exhaust gas recirculation (iEGR). Both fuels were port-fuel injected and two different liquid fuel replacements by compressed natural gas (CNG) were tested (18 and 45% by energy). Combustion, performance and pollutant emissions were investigated under stoichiometric air-fuel conditions at 4 bar of net indicated mean effective pressure (IMEP) and 1800 rpm. Results show that dual-fuel mode improves fuel conversion efficiency when compared to CNG-only operation, due to lower carbon monoxide (CO) and unburnt hydrocarbons (HCs) emissions as well as to a better combustion phasing. The use of iEGR, despite deteriorating the combustion process as expected (ignition delay, combustion duration and combustion stability), improves efficiency because of a decrease in pumping losses and wall heat transfer, as well as pollutant emissions reduction. Nitrogen oxide (NOx) emissions increase with dual-fuel operation. However, the influence of iEGR was found to be more significant under dual-fuel mode than under single-fuel operation, with NOx reductions of up to 70% and fuel conversion efficiency improvements of around 2.5%.