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Downsized-Boosted Gasoline Engine with Exhaust Compound and Lean Advanced Combustion
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
This article presents the experimental results obtained with a disruptive engine platform, designed to maximize the engine efficiency through a synergetic implementation of downsizing, high compression-ratio, and importantly exhaust-heat energy recovery in conjunction with advanced lean/dilute low-temperature type combustion. The engine architecture is a supercharged high-power output, 1.1-liter engine with two-firing cylinders and a high compression ratio of 13.5:1. The integrated exhaust heat recovery system is an additional, larger displacement, non-fueled cylinder into which the exhaust gas from the two firing cylinders is alternately transferred to be further expended. The main goal of this work is to implement advanced lean/dilute combustion while minimizing NOx emissions and addressing the transition between the operating modes. The combustion modes include well-mixed charge compression-ignition at low-load, and a mixed-mode combustion strategy at higher loads. The mixed-mode combustion strategy is composed of a deflagration of a stratified mixture, triggering a controlled autoignition of the surrounding gas. The paper describes the key features of the engine and details regarding the combustion and multi-mode valve strategies. The experiments were performed under steady-state operation at 2000 rpm, from 1 to 11 bar IMEPn and naturally aspirated conditions. The results show that the engine demonstrated great efficiency gains compared to a conventional naturally-aspirated and downsized-boosted spark-ignited engines. The piston-compounding exhaust-heat recovery system contributes to up to 10% of the efficient improvement. NOx emissions target were met using high-levels of internal and external dilution, as well as by optimizing the injection and ignition strategy. Finally, the analysis shows that a seamless transition between the different valving strategies is achievable in support of robust transient operation.