Investigation and application of systematic design method for combustionchamber of diesel engine

Abstract：The effects of diesel engine combustion chamber design have important influences on the formation andcombustion processes of the gas mixture, and greatly affect the power capability, fuel economy, and emissions of the engines.In order to make the design of the diesel engine combustion chamber more systematic and rigorous, the concept of dieselengine combustion chamber systematic design was proposed, which was elaborated from five aspects of design experience,design parameters, design criteria, factor processing methods, and response analysis methods. Nine design methods ofcombustion chamber were classified through combining three factor processing methods and three response analysis methods.The design method consisting of the factor sampling design method and the second type of the response analysis method wasselected to illustrate its application process due to its effectiveness and convenience. A four-valve-head direct-injection dieselengine was analyzed, and a transient in-cylinder flow model was established. Under the assumption of an approximatelyconstant compression ratio, the impacts of four different ω - shape combustion chamber structures on gas flow motions incylinder were compared and analyzed. These four combustion chambers were named type A, B, C and D with shrinkage ratiosof 16.4%, 6.1%, 9.8%, and 9.8%, respectively. The design evaluation criteria were gas flow velocity and turbulence kineticenergy. The results showed that the geometrical structures of the combustion chambers had little influence on the in-cylindergas flow motions during the intake stroke and the early stage of the compression stroke, while they exhibited significantimpacts during the late stage of the compression stroke. The average squish velocity and reverse squish velocity of the Type Ccombustion chamber, which had a conical bottom shape, was greater than that of the Type D combustion chamber having aspherical bottom by 25.2% and 26.4% respectively during the crank angle interval from 20° before the top dead center(BTDC) to 20° after the top dead center (ATDC). The average turbulence kinetic energy of the Type A combustion chamberwith a shrinkage ratio of 16.4% was greater than that of the Type D combustion chamber with a shrinkage ratio of 9.8% by25.4% during the crank angle interval from 20° BTDC to 20° ATDC. Compared to the type A and D combustion chambers thathad a elliptic bottom shape and a spherical bottom shape, respectively, the type B and C combustion chambers that had a 45°conical bottom shape exhibited stronger capabilities of maintaining turbulence kinetic energy and reverse squish intensity. Theresults in this paper can provide good guidance for the structural design and optimization of diesel engine combustion chamber