Evaluation of an optimal engine configuration for a SI Engine Fueled with Ethanol for Stationary Applications

This work aims at investigating the optimal configuration of an internal combustion engine fueled with bio-ethanol for improving its brake power and efficiency as well as for reducing the NOx emissions, in stationary applications. A turbocharged spark ignition engine characterized by a single-point injection was preliminarily considered; subsequently, a direct injection configuration was investigated. For both cases, a 1-D numerical model was developed to compare the injection configurations under stoichiometric conditions and different spark timings. The analysis shows that the direct injection guarantees: a limited improvement of brake power and efficiency when the same spark timing is adopted, while NOx emissions increases by 20%; an increase of 6% in brake power and 2 percentage points in brake thermal efficiency by adopting the knock limited spark advance, but an almost double NOx emissions increase. In order to exploit the advantages of the direct injection, an engine configuration characterized by higher compression ratio, lower boost pressure and different cam phasing was proposed. By adopting a spark timing of 23°CA BTDC and a lean mixture (ϕ = 0.8), the engine provides a brake power of 232 kW, a brake thermal efficiency of 42%, which are 4% and 14 percentage points higher than single point configuration, respectively, and NOx emissions, amounting to 3 g/kWh, 9% lower with respect to single point injection.