The paper reports an experimental study on the effect of compression ratio variation on the performance and pollutant emissions of a single-cylinder light-duty research diesel engine operating in DF mode.
The architecture of the combustion system as well as the injection system represents the state-of-the-art of the automotive diesel technology. Two pistons with different bowl volume were selected for the experimental campaign, corresponding to two CR values: 16.5 and 14.5. The designs of the piston bowls were carefully performed with the 3D simulation in order to maintain the same air flow structure at the piston top dead center, thus keeping the same in-cylinder flow characteristics versus CR.
The engine tests choice was performed to be representative of actual working conditions of an automotive light-duty diesel engine. Moreover, the test methodology was designed in order to carry out emission and fuel consumption (FC) estimation on New European Driving Cycle (NEDC) test procedure. A proper engine Dual-Fuel calibration was set-up respecting prefixed limits in terms of in-cylinder peak firing pressure, cylinder pressure rise, IMEP cycle-to-cycle variation, and gaseous emissions.
The results evidence a significant impact of CR on the THC level (mainly CH4), as well as on the combustion efficiency. Benefits on combustion noise and full load performance in DF mode can be attained reducing the CR. The results also show a great potential on the CO2 reduction beyond a NG substitution rate of 50%. Moreover, the study indicates that such limit could be overcome with specific combustion system design as well as a proper engine calibration.
