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The dynamic effects of a coolant flow rate variation on knock tendency are experimentally investigated on a small S.I. engine. The analysis concerns the transient response of the unburned gas temperature and the knock onset to a step variation in load and coolant flow rate. This phenomenological investigation aims at preventing knock through a proper thermal management as an efficient alternative to the currently adopted strategies. Moreover, the proposed approach may result particularly useful for hybrid-electric powertrain, where the engine is expected to operate in the highest efficiency region by adopting high compression ratios and full stoichiometric map. The analysis is carried out through an experimental campaign, where the control of cylinder wall temperature is achieved by means of an electrically driven water pump. The spark advance and the air/fuel ratio have been properly varied in order to operate with advanced spark timing and stoichiometric mixture at full load.

The possibility to mitigate the knock onset by means of a controlled coolant flow rate is investigated. The study is carried out on a small displacement, N.A. 4-valve per cylinder SI engine. The substitution of the standard belt-driven pump with an electrically driven one allows the variation of the coolant flow rate regardless of engine speed and permits, therefore, the adoption of a controlled coolant flow rate. The first set of experimental tests aims at evaluating the engine operating condition and the coolant flow rate, which are more favorable to the knock onset. Starting from this condition, subsequent experimental tests are carried out for transient engine operating conditions, by varying the coolant flow rates and evaluating, therefore, its effects on cylinder pressure fluctuations. In all the experiments, the spark advance and the equivalence ratio are controlled by the ECU according to the production engine map.