Efficient tracking of knock onset for a wide range of fuel surrogates

Corinna Netzer, Lars Seidel, Harry Lehtiniemi, Frédéric Ravet, Fabian Mauss

Abstract

Fuel properties have a major impact on engine knock and therefore need to be considered in detail in spark ignition engine simulations to find the knock limit spark advance. In our method, the auto-ignition and emissions are calculated based on a reaction scheme for mixtures of iso-octane, n-heptane, toluene and ethanol (ETRF) that allows for a flexible surrogate formulation with close agreement to the physical and chemical properties of the commercial gasoline. The
combustion is predicted using a combination of the level-set method with tabulated laminar flame speed and the wellstirred reactor model in 3D RANS. The transition from harmless deflagration to knocking combustion is evaluated using Bradley’s detonation diagram. Through the use of the suggested tool-chain, the knock limit spark advance and the
indicated mean effective pressure can be determined as function of fuel quality with low computational effort. This information can be used to consider regional varieties in fuel composition and find the optimal engine design in terms of efficiency, emissions, and reliability.