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An ignition delay correlation was developed for a toluene reference fuel (TRF) blend that is representative of automotive gasoline fuels exhibiting two-stage ignition. Ignition delay times for the autoignition of a TRF 91 blend with an antiknock index of 91 were predicted through extensive chemical kinetic modeling in CHEMKIN for a constant volume reactor. The development of the correlation involved determining nonlinear least squares curve fits for these ignition delay predictions corresponding to different inlet pressures and temperatures, a number of fuel-air equivalence ratios, and a range of exhaust gas recirculation (EGR) rates. In addition to NO control, EGR is increasingly being utilized for managing combustion phasing in spark ignition (SI) engines to mitigate knock. Therefore, along with other operating parameters, the effects of EGR on autoignition have been incorporated in the correlation to address the need for predicting ignition delay in SI engines operating with EGR.

The effectiveness of the Helmholtz resonator as a narrow band acoustic attenuator, particularly at low frequencies, makes it a highly desirable component in a wide variety of applications, including engine breathing systems. The present study investigates the influence of mean flow grazing over the neck of such a configuration on its acoustic performance both computationally and experimentally. Three-dimensional unsteady, turbulent, and compressible Navier-Stokes equations are solved by using the Pressure-Implicit-Splitting-of-Operators algorithm in STAR-CD to determine the time-dependent flow field. The introduction of mean flow in the main duct is shown to reduce the peak transmission loss and shift the fundamental resonance frequency to a higher value.