Miller cycle and exhaust gas recirculation for a naturally aspirated lean-burn gas engine

Abstract

Motivated by tightening emission standards for small natural gas driven cogeneration gas engines, this thesis explores an alternative working process that extends the pre-vailing lean-burn operation with Miller cycle and cooled exhaust gas recirculation (EGR). The combination of these well-established means is expected to improve the trade-off between engine efficiency, NOx emissions and indicated mean effective pres-sure (IMEP) of a naturally aspirated gas engine.Comprehensive series of measurements were carried out in engine operation with Mil-ler valve timing and varying EGR rate. The main focus was put on the potential that the working process offers in improving the trade-off between engine efficiency and NOx emissions at constant IMEP of the baseline engine’s reference operating point.