Strategy and potential of homogeneous lean combustion at high load points for turbocharged gasoline engines with direct
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ORIGINAL PAPER
Strategy and potential of homogeneous lean combustion at high load points for turbocharged gasoline engines with direct injection and small displacement Alexander Rurik1 · Frank Otto1 · Thomas Koch2 Received: 5 February 2020 / Accepted: 27 April 2020 © Springer Nature Switzerland AG 2020
Abstract In this paper, a homogeneous lean combustion concept for gasoline engines with direct injection, small displacement and turbocharging is investigated under high-load conditions. A representative operating point was selected for this purpose. The tests were carried out on a single-cylinder research engine. In particular, the influence of the center of combustion, charge motion and pressure ratio is discussed. It has been discovered that the center of combustion has a large influence on the stability of homogeneous lean combustion at high load points. The present investigations provide a method of how to achieve an early center of combustion in knock-limited load points of homogeneous lean combustion. Early centers of combustion enable a high air–fuel ratio with good, smooth running and low NOx emissions. In addition to the high charge motion, operation with a positive scavenging gradient and valve overlap can be applied to flush the hot internal residual gas out of the combustion chamber, whereby knocking can be reduced. With the high air–fuel ratio, specific fuel consumption can be reduced substantially and high combustion efficiency can be achieved. The results can be leveraged as a basis for future developments in gasoline engines. Keywords Gasoline engine · Homogeneous lean combustion · Charge motion · Center of combustion · Pressure ratio · Turbocharging List of symbols λ Air–fuel equivalence ratio of combustion N Engine speed η Efficiency p Pressure T Tumble number ω Angular velocity Abbreviations ATDC After top dead center AVT Active valve train * Alexander Rurik [email protected] Frank Otto [email protected] Thomas Koch [email protected] 1
Daimler AG, Mercedesstraße 137, 70327 Stuttgart, Germany
Institut für Kolbenmaschinen (IFKM), Karlsruher Institut für Technologie (KIT), Rintheimer Querallee 2, 76131 Karlsruhe, Germany
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bp Best point BTDC Before top dead center CAD Crank angle degrees CEI Controlled electronic ignition CFD Computational fluid dynamics CO2 Carbon dioxide COV Coefficient of variance EVC Exhaust valve closing IMEP Indicated mean effective pressure ISFC Indicated specific fuel consumption IVO Intake valve opening L Liter MFB05 05% Mass fraction burned MFB50 50% Mass fraction burned MFB90 90% Mass fraction burned NOx Nitrogen oxides SCR Selective catalytic reduction WLTC Worldwide harmonized light duty test cycle Subscripts C Crankshaft Exh. Exhaust
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i Indicated Int. Intake
1 Introduction The internal combustion engine faces a number of challenges in the future. These include the increasing environmental awareness of society as well as the challenging climate protection targets, such as those of
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