Independent Bioethanol Fumigation in a Brazilian Agricultural Diesel Engine: Diesel Displacement and Emission Trade-Offs

Agricultural compression-ignition engines require decarbonization strategies that can reduce fossil-diesel demand without replacing robust power units already operating in the field. This study experimentally evaluates an autonomous hydrous-ethanol port-fuel-injection retrofit applied to a John Deere PowerTech™ Plus 6068 engine, a six-cylinder, turbocharged, 6.8 L agricultural diesel engine with high-pressure common-rail direct injection and MAR-1/Tier 3 equivalent emission compliance. Brazilian Diesel S10/B14 was retained as the directly injected pilot fuel, while commercial hydrous ethanol was supplied upstream of the cylinders through a FuelTech FT550-controlled low-pressure injection system. Tests were performed at 1200 and 1600 rpm, under 200 and 800 N·m, using ethanol injection pulse widths of 0, 10, and 20 ms. The analysis combines fuel consumption, brake-specific fuel consumption (BSFC), diesel substitution ratio (DSR), energy substitution ratio (ESR), fuel conversion efficiency (FCE), and regulated emissions. The strategy achieved substantial diesel displacement at low load, with DSR and ESR reaching 61.9% and 71.6%, respectively. The most balanced operating point occurred at 1600 rpm and 800 N·m with 20 ms ethanol injection, where DSR and ESR reached 21.1% and 22.9% while FCE varied by only +0.03 percentage points relative to the diesel-only baseline (35.83% versus 35.80%). CO2 emissions decreased in all dual-fuel cases, with reductions up to 18.0%, and NOx generally decreased by as much as 35.2%. However, CO increased in all dual-fuel cases, and HC increased strongly at low load. At high load, NOx decreased by 7.1% and 13.0% with 10 and 20 ms injection at 1200 rpm, whereas at 1600 rpm, it increased by 23.3% with 10 ms and returned to the baseline level (−0.5%) with 20 ms. These results demonstrate that hydrous-ethanol fumigation is a technically promising retrofit route for Brazilian agricultural diesel engines, provided that future calibration manages the incomplete-combustion penalties while preserving the CO2 and NOx benefits.