Mechanism Analysis on the Effect of Fuel Properties on Knocking Performance at Boosted Conditions

摘要

In recent years, boosted and downsized engines have gained much attention as a promising technology to improve fuel economy; however, knocking is a common issue of such engines that requires attention. To understand the knocking phenomenon under downsized and boosted engine conditions deeply, fuels with different Research Octane Number (RON) and Motor Octane Number (MON) were prepared, and the knocking performances of these fuels were evaluated using a single cylinder engine, operated under a variety of conditions. Experimental results showed that the knocking performance at boosted conditions depend on both RON and MON. While higher RON showed better anti-knocking performance, lower MON showed better anti-knocking performance. Furthermore, the tendency for a reduced MON to be beneficial became stronger at lower engine speeds and higher boost pressures, in agreement with previously published modelling work. A new method of interpreting octane appetite is presented which relates the gradient of contour lines of MB50 in RON/MON space to K value. The results can be further interpreted by understanding the relative contribution of low temperature oxidation (LTO) pathways under the prevailing temperature/pressure conditions in the engine.