Definition and evaluation of the gas exchange process of a two-stroke engine with external and internal mixture formation

Abstract

Problem. The transition from external to internal mixture formation requires adjusting the organization of gas exchange processes. The subject of the research is the gas exchange indicators of the 1D 8.2/8.7 engine with spark ignition with a carburetor and direct fuel injection (DFI) for the organization of stratified fuel-air charge (SFAC) and stratified weak fuel-air charge (SWFAC). Goal. The purpose of research is to determine ways to improve cylinder cleaning from combustion products and increasing its filling with fresh charge at DFI. Methodology: the following methods were used to conduct a study of the engine according to the load characteristic (n = 3000 min-1) and determine the gas exchange indicators by the coefficients: consumption μ of the purge and exhaust channels; purge air leakage υ; residual gases γ; excess purge air φо; filling ηv; purging φ; use of purge air ηв; k.k.d. purge ηs. Originality. The empirical dependences of changes in gas exchange indicators: μ, υ, γ, φ, ηv on the load were determined. Results. With a carburetor power system γ = 0.24-0.17, φo = 0.32-0.67 (bmep = 0.174-0.45 MPa). At the maximum load (bmep = 0.45 MPa) ηv = 0.5. The use of a hemispherical symmetric combustion chamber with an increase in volume and load creates conditions for reducing γ and increasing ηs to 0.86. With DFI and the organization of the SFAC γ = 0.15-0.13 (bmep = 0.21-0.45 MPa), SWFAC γ = 0.16-0.13 (bmep = 0.144-0.21 MPa), γ = 0.4 (bmep = 0.43 MPa). In the case of SFAC and SWFAC, the maximum values of φо = 0.7 and ηv = 0.52 (bmep = 0.42–0.44 MPa). As the load decreases, the values of φо and ηv from the SWFAC exceed the values from the SFAC by up to 9%. The largest values of ηs = 0.87-0.88 (bmep = 0.21-0.47 MPa) correspond to the SFAC and the hemispherical combustion chamber shifted to the exhaust window. The organization of SWFAC in a hemispherical symmetric combustion chamber of smaller volume contributes to the reduction of ηs from 0.875 to 0.71. Practical value. In order to reduce γ and increase ηv at SWFAC, it is necessary to direct the flow of purge air inside the combustion chamber by installing an additional purge channel opposite the exhaust window.