Reducing the Octane Appetite of Pressure-Charged Gasoline Engines using Charge Air Conditioning Systems

摘要

The knock-limited nature of pressure-charged gasoline engines enforces compromises in their configuration which are counter to any fuel economy improvement that may be realised through downsizing approaches. This is because detonation of the charge causes damage to the piston and so must be avoided; this is commonly achieved by retarding the ignition, diluting the mixture or reducing the compression ratio, or a combination of these. Since the knocking propensity of such engines is a function of the start-of-compression temperature in the cylinder, pressure and their compression ratio, any reduction in charge air temperature should result in an extension of the knock limit which could be used to increase the compression ratio. This will benefit the thermodynamic efficiency of the engine and consequently drive-cycle fuel economy of the vehicle. The present paper describes experimental work undertaken by the authors to investigate the magnitude of any possible benefit from this approach.