Analysis of Different Uniflow Scavenging Options for a Medium-Duty 2-Stroke Engine for a U.S. Light-Truck Application

Abstract

The work presented here seeks to compare different means of providing uniflow scavenging for a 2-stroke engine suitable to power a US light-duty truck. The three different configurations which could utilize this type of scavenging system that were investigated are (1) the opposed-piston engine, which has been applied to aircraft propulsion as well as engines for power generation and rail traction, (2) the poppet-valve uniflow configuration, as exemplified by the Detroit Diesel 2-stroke engine, and (3) the sleeve-valve uniflow engine, the unusual arrangement of which was used in the Rolls-Royce Crecy, intended for high-speed interceptor aircraft application. All of these concepts were compared in terms of indicated fuel consumption for the same cylinder swept volume, and a new methodology for optimization was developed using a one-dimensional engine simulation package which also took into account charging system work. As a result of this work it was found that the opposed-piston configuration provides the best attributes since it allows maximum expansion and minimum heat transfer. It was found that existing experiential guidelines for port angle-area specification for loop-scavenged, piston ported engines using crankcase compression could also be applied to all of the other scavenging types. This has not been demonstrated before.

Identification and analysis of the factors to realizing variable intake/exhaust phases in opposed-piston two-stroke diesel engines

“…The port width only affects the area of the intake and exhaust ports; the port height not only affects the port area but also affects the intake and exhaust phases. 17–19 The port inclination contains radial inclination and axial inclination. The radial inclination generates a swirling flow, 20,21 while the axial inclination angle creates a tumbling flow.…”

2-Stroke Engine Options for Automotive Use: A Fundamental Comparison of Different Potential Scavenging Arrangements for Medium-Duty Truck Applications

“…Conceptually it might be considered to be a hybrid of the Crecy and Clerk's engine of 1881. It was analyzed partly due to the findings of an earlier paper which compared it to the OP2S and port-poppet engines [34].…”

“…Since the Schnürle-loop scavenged configuration represents what many consider to be the conventionally-conceived 2-stroke engine, it represents something of a baseline for the other arrangements. It was not assessed as part of the previously-reported work [34] and so it was included here. However, in including it it was also decided to assess the most flexible of the exhaust timing adjustment mechanisms applied to this type, which was considered to be the Lotus charge trapping valve (CTV) described by Blundell and co-workers in several engine research projects [7,8,15,36].…”

“…Configurations ( 1), ( 2) and ( 3) were described in a previous paper in which only uniflow scavenging arrangements were compared [34].…”

“…In that work the OP2S engine emerged as a clear winner, with the port-poppet configuration second but only marginally better than the forward-uniflow type. In [34] the observation was made that the port-poppet type was severely restricted by valve train dynamics and as a consequence, since it is desmodromic and is not limited by such issues, it may well be that the forward-uniflow-sleeve might be superior under some situations. In the analysis of the angle-areas undertaken for the Crecy for the earlier work, it was determined that the flexibility provided by the sleeve's port layout could permit additional optimization possibilities.…”