Evaluation of a novel strategy, based in Coolant Flow Rate Control, for avoiding Knock in a SI engine

Abstract

An experimental study is carried out for investigating the possibility to limit knock occurrence on a SI engine by proper engine thermal management. The control of the wall temperature is realized by means of an electrically driven water pump. The coolant flow rate can be varied regardless of the engine speed. Preliminarily, an experimental campaign aimed at evaluating the effects of the coolant flow rate on the in-cylinder pressure fluctuations, under steady state engine operation, namely WOT@1500 rpm, is presented. In the experiments, the spark advance and the equivalence ratio are controlled by the ECU according to the production engine map and the coolant flow rate is varied from 1500 up to 4500 dm3/h. In a subsequent set of tests, a variation on spark advance is operated and, for each value of the spark advance, different coolant flow rates are enforced with the aim of evaluating the possibility to increase the spark advance as close as possible to the maximum brake torque condition and of mitigating knock occurrence with increased coolant flow rates. The benefits in terms of fuel economy and increase engine performance, in comparison to the traditional approaches for knock mitigation, are evaluated.