Knock and knock intensity models for boosted SI conditions with gasoline-ethanol blends

Abstract

In this work, a previously developed, two-stage table-lookup kinetic method for surrogate Toluene Reference Fuels (TRF) was extended to gasoline-ethanol blends and exercised in a GT-POWER model of knock in several engines. Experimentally, the knock limit is normally determined by the magnitude of pressure oscillations, known as the knock intensity (KI), rather than the crank angle of initial pressure oscillations or the crank angle of auto-ignition, which is difficult to identify. A number of empirical expressions of knock intensity have been developed for modeling purposes which relate the knock intensity to the crank angle and conditions at auto-ignition, and are available in the literature. These models were implemented into a GT-POWER model and tested against experimental knock-limited data for gasoline and gasoline-ethanol blends. The KI models are phenomenological in nature and are based on varying conceptual views of the knock event. With calibration all methods gave satisfactory results at mid-speed conditions when compared with the experimental data. Some deviations were seen at low and high speeds. Low speeds are potentially important because both RON and MON testing occurs under such conditions. Implications of the results and their relationship to recent knock experimental work are discussed and suggestions offered for improved knock models.