Knock Phenomena under Very Lean Conditions in Gasoline Powered SI-Engines
Artikel i vetenskaplig tidskrift, 2018

Homogeneous lean operation is a well-known strategy for enhancing the thermal efficiency of SI-engines. At higher load points the efficiency is often compromised by the need to suppress knock. Experiments were performed to determine the knock characteristics of SI engines using homogeneous lean operation at λ values of up to 1.8 with various hardware configurations that are commonly used to increase the lean limit. Changing λ altered the eigenfrequencies of the combustion chamber and the highest energy excitation mode. Increasing λ from 1.0 to 1.2 increased the knock tendency and led to an earlier knock onset. However, further increases in λ significantly reduced the knock tendency and retarded the knock onset. The knock signal energy increased for higher λ values and constant knock tendencies. The differences in knock characteristics between the various λ values became more pronounced upon raising the intake temperature from 40 °C to 90 °C. The trends in knock tendency and knock onset largely parallels that observed for engine out NOxemissions and thus the NOxconcentration in the internal EGR. The increased knock signal energy under lean conditions is partly attributed to the change in eigenfrequencies in the combustion chamber.

SI-engines

High frequency ignition

Knock

Heated intake air

Lean combustion

Författare

Gerben Doornbos

Chalmers, Mekanik och maritima vetenskaper, Förbränning

Stina Hemdal

Chalmers, Mekanik och maritima vetenskaper, Förbränning

Ingemar Denbratt

Chalmers, Mekanik och maritima vetenskaper, Förbränning

Daniel Dahl

Volvo Cars

SAE International Journal of Engines

1946-3936 (ISSN)

Vol. 11

Ämneskategorier

Annan maskinteknik

Energiteknik

Atom- och molekylfysik och optik

DOI

10.4271/03-11-01-0003