Simulation Analysis of the Scavenging Process of a Uniflow and Loop Scavenging Concept

Abstract

<div class="section abstract"><div class="htmlview paragraph">The two-stroke engine, as a today unconventional concept in automotive applications, has a great potential for a relaunch in the fast-growing market of Plugin Hybrid Electric Vehicle (PHEV) or Range Extender Electric Vehicle (REX) [<span class="xref">2</span>, <span class="xref">3</span>, <span class="xref">4</span>, <span class="xref">8</span>, <span class="xref">9</span>]. An efficient scavenging to remove the in-cylinder burnt gases and to fill the cylinder with fresh charge, performed at the same time is one of the major challenges, as losses of fresh air and fuel towards the exhaust line should be avoided when operating a lambda = 1 concept necessary for a 3-way catalyst aftertreatment system.</div><div class="htmlview paragraph">A prior study [<span class="xref">1</span>] of different gas exchange designs for two-stroke engines concludes that two possible concepts cover this purpose. In this paper, 3D-CFD simulation is used to compare these two different scavenging concepts, a uniflow and a loop scavenging type with control elements for the gas exchange process. As boundary conditions, it is assumed that both concept types have nearly the same displacement, are used with an external scavenging blower and have a lubrication system like a conventional oil sump similar to a four-stroke engine. Additionally, a high-pressure direct injection fuel system is applied to guarantee oil- and fuel-free air for the scavenging process.</div><div class="htmlview paragraph">To compare these different two-stroke scavenging concepts, this study focuses on the scavenging and compression phase using 3D-CFD simulation in order to evaluate the scavenging characteristics and the in-cylinder charge motion. The goal of this study is to prepare a basis for discussion of the best configuration, which will be designed, built and tested on the engine test-bench.</div></div>