The Available and Required Autoignition Quality of Gasoline - Like Fuels in HCCI Engines at High Temperatures 2004-01-1969
In previous work it has been shown that the autoignition quality of a fuel at a given operating condition can be described by its Octane Index, OI = (1-K)RON - KMON; the larger the OI, the more the resistance to autoignition. Here RON and MON are, respectively, the Research and Motor Octane numbers of the fuel and K is a constant depending only on the pressure and temperature history of the fuel / air mixture in the engine prior to autoignition. The value of K is empirically established at a given operating condition by ranking fuels of different RON and MON and of different chemical composition for their ease of autoignition. Another important parameter at a given operating condition is OI0, the Octane Index of the fuel for which heat release is centred at TDC. In previous work K and OI0 were measured at different operating conditions and were related empirically to pressure and temperature of the mixture before autoignition and to engine speed and mixture strength.
In this work K and OI0 have been measured in a different engine at different conditions that include much higher intake temperatures and engine speeds than considered before. The focus is also on wide-boiling-range complex fuels rather than simple fuel systems. K is again seen to depend primarily on the compression temperature at 15 bar, Tcomp15. However in the higher temperature range, K increases much more sharply with Tcomp15 than found previously. There is also an overlap between the new data and the old data, confirming that the variation of K is not engine dependent. The data for OI0 for the two engines can also be described by a combined model. OI0 increases with increasing Pmaxcomp and Tmaxcomp, the compression pressure and temperature at TDC, and decreases with increasing λ and engine speed.