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Fundamentals of turbocharger behaviour and spray formation in HCCI diesel engine operation at medium loads

Several turbocharger-engine configurations were investigated through numerical simulation. While in HCCI mode - mainly at medium load -, the turbo matching is quite tricky since high EGR rates and charge cooling are needed in the cylinder. This could lead to reduced mass flow rates and higher compression ratios through the turbo compared to a normal Diesel operation.

The turbo working conditions approach the surge line and actions have to be taken to avoid stalling. A computer model was thus developed in order to predict the turbocharger working conditions and the overall engine performances while in HCCI mode.

In parallel, the innovative injection system developed by IFP was fully characterised in an experimental test rig with multiple optical access windows. Thermodynamic conditions similar to those existing in the cylinder during advanced fuel injection were generated in a vessel and the spray development was recorded and analysed trough laser imaging.

Correlations among fuel pressure, injection pulse duration, air density, air temperature and spray penetration were generated mainly for those situations that are poorly covered in the literature (i.e. small fuel injected quantities and high air temperatures).

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