Potential of the combustion engine to reach future CO2 emissions

Abstract

Potential of the combustion engine to reach future CO2 emissions 746 Abstract Within the upcoming emission legislations, engine exhaust pollutants and the fuel con-sumption respectively CO2 emissions will become more stringent worldwide. Since there is typically a trade-off between reducing tailpipe pollutants and the car's fuel effi-ciency meeting both limits simultaneously will be challenging. However, the CO2-saving potential of both gasoline and diesel engines is not outbid yet but further improv-ing the engines efficiency will require an accurate balancing of their benefits and costs. For all types of engines thermal management and friction reduction will be in the main focus for all segments. Efficient exhaust gas aftertreatment systems will be a key meas-ure for reducing CO2-emissions and pollutants particularly for diesel engines. Addition-ally, engine hardware measures as e.g. variable valve timing and valve lift will be intro-duced and combined high-and low-pressure exhaust gas recirculation will be used more frequently. Another potential for engine optimization is in coupling of different technol-ogies, e.g. 2-stage turbo-charging in combination with a gearbox featuring a wider gear spread for load point shift into more favourable regions. For spark ignited engines there will be an increase of engines equipped with valve train variability in order to utilize Miller-and Atkinson cycles for de-throttling the engine. At high and full load operation recirculation of cooled exhaust gas can reduce the knock tendency giving the potential to further increase the compression ratio and thus the thermal efficiency at part load opera-tion. By utilizing a variable compression ratio high efficiency at part load can be achieved while simultaneously not sacrificing power output at full load. Further, this technology enables to fully exploit the potential of fuels with high knock resistance and stretch the operational area of unconventional combustion processes as e.g. controlled auto ignition. For both types of engines different fuels help meeting the emission limits as well. E.g., compressed natural gas (CNG) is an interesting fuel candidate for SI en-gines since it features a very high knock resistance on the one hand and a higher hydro-gen to carbon ratio on the other hand.