This paper presents a prospective combustion study about dilution effects on turbocharged SI engine at full load. It proposes a comparative analysis between lean burn and cooled exhaust gas recirculation (EGR) operation as knock improvement artifice in substitute of enrichment.
The study was led on a four cylinder 2L engine on stationary test bench. A specific EGR circuit was designed in order to achieve high control of the temperature and mass flow of the recirculated gas. Thanks to instantaneous pressure cylinder transducers, a combustion analysis was carried out using an home-made code. 1-D simulations (WAVE code) were used to complete the analysis on volumetric efficiency and turbocharger behaviour.
A real advantage of cooled EGR was observed in the study compared to lean burn or enrichment in terms of performance, heat exchange and specific fuel consumption.
The coupling between engine and turbocharger presents a double synergy in terms of combustion and volumetric efficiency for the cooled EGR.
On the combustion side, this double synergy offers a high dilution potential and a reduction of the internal residual gas fraction. Main consequences are knock resistance and indicated efficiency improvement.
By limiting the pressure before turbine, this method also improves volumetric efficiency and increases the compressor pressure ratio in order to stay in better efficiency areas of the turbocharger.