Browse Publications Technical Papers 2019-01-0240
2019-04-02

System Level 1-D Analysis of an Air-System for a Heavy-Duty Gasoline Compression Ignition Engine 2019-01-0240

A detailed study of various air system configurations has been conducted for a prototype gasoline compression ignition (GCI) engine using a Cummins MY2013 ISX15 heavy-duty diesel engine as the base platform. The study evaluated the configurations with the assumption that RON80 gasoline would be used as the fuel and the combustion chamber would have a geometric compression ratio (CR) of 16.5. Using 3-D computational fluid dynamics (CFD) simulations, a high efficiency & low engine-out NOx GCI combustion recipe was developed across five engine operating points from the SET cycle: A100, B25, B50, B75, and C100. Subsequently, the CFD generated air-thermal boundary conditions and the combustion burn-rate & injector rate-of-injection profiles were imported into a calibrated 1-D engine model for the air-handling systems analysis. Initially equipped with a single stage turbocharger and high pressure exhaust gas recirculation (HPEGR) system, the stock air-system performance for these GCI boundary conditions was established as a benchmark for comparison. Several boosting configurations, including both single stage (1-Stage) and two-stage (2-Stage) turbocharger systems, were investigated as part of the study. For the 1-Stage system, both variable geometry turbine (VGT) and waste-gated (WG) turbine options were examined. For the 2-Stage air systems, high-pressure (HP) and low-pressure (LP) compressor stages were analyzed in a series configuration with a waste-gated HP-turbine. Multiple exhaust gas recirculation (EGR) systems were also considered and these included a dedicated high-pressure EGR system, a dedicated low pressure EGR (LPEGR) system and a combination of the two with flow split between the HP and LP (DLEGR) systems. For DLEGR, a flow split sweep between the HP and the LP loop was carried out to optimize the pumping losses. For optimal compressor-turbine pairing, change in EGR strategy mandated variation in trims for the compressor and turbine wheels. Based on the 1-D system simulations, both the 1-Stage and the 2-Stage air-handling systems were able to meet the GCI air-system targets. A detailed energy balance analysis highlighted the best performing configurations.

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