The Influence of Residual Gases on Knock in Turbocharged SI-Engines

Abstract

<div class="htmlview paragraph">In this investigation the influence on knock from the residual gas in the cylinder is investigated. Gas was sampled from inside the cylinder prior to ignition, the Residual Gas Fraction, RGF, was determined and the Knock Intensity, KI, was measured. By altering the exhaust backpressure the RGF was changed. By measuring the knock intensity for different RGF the influence on knock from residual gas was investigated.</div> <div class="htmlview paragraph">It is shown that with increased residual gas fraction the knock propensity of the engine is increased, and subsequently, decreased RGF gives lower knock intensity. This is showed by the fact that, with maintained knock intensity at 30 kPa, the ignition timing can be advanced as much as 5 Crank Angle Degrees, CAD, if the RGF is reduced with 15%.</div>