Laminar Burning Velocity of Market Type Gasoline Surrogates as a Performance Indicator in Internal Combustion Engines 2018-01-1667

The laminar burning velocity is an important parameter in various combustion models for engine simulations. With respect to computational time for computational fluid dynamics (CFD) and full system engine simulations, the calculation of laminar burning velocities using a detailed chemical mechanism can be replaced by incorporation of approximation formulas, based on rate-ratio asymptotics.

In the present study, a work flow is developed to analyze the engine efficiency performance of spark ignition engines with respect to the laminar burning velocity as a fundamental fuel property. Firstly, methane is used as a fuel to assess practicability of the approach. The procedure is subsequently adopted for market type gasoline surrogates, RON95 and RON100. Detailed chemistry calculations are carried out for the three target fuels using existing state of the art mechanisms, the Aramco [Zhou et al., Proc. Combust. Inst., pp. 403-411, 2017] and the ITV RWTH mechanism [Cai et al., Combust. Flame, pp. 1623-1637, 2015]. Subsequently, the asymptotic-based approximation formula by Göttgens et al. [Göttgens et al., Symp. (Intl.) Combust., pp. 129-135, 1992] is employed and fitted based on detailed simulations under engine relevant conditions. In order to compute fundamental engine performance parameters, such as the indicated mean effective pressures (IMEP), the deduced model is embedded in GT-POWER [Gamma Technologies, LCC.,“GT-SUITE”, 2018], an industry standard tool for engine simulations. Significant differences in IMEP can be observed between calculations with the newly incorporated model and the default model for the laminar burning velocity of methane/air mixtures. Higher burning velocities were found to decrease the burn duration. In order to optimize thermal efficiency, the center of combustion must be delayed by shifting spark timing. For gasoline surrogates, differences in IMEP and efficiency between the two flame speed models were found to be less pronounced. This implies that either the GT-POWER inbuilt flame speed model for gasoline is reasonably good or sensitivities to the laminar burning velocity might not be represented well by the code.