An Investigation of the Flow Through Check Valves in a Uniflowtype Two-Stroke Engine

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Fraser, Iain
Mechanical Engineering , Engine , Two-Stroke
An innovative two-stroke engine has been under development at Queen’s University. Traditional crankcase-scavenged two-stroke engines have laboured to meet emissions standards and achieve fuel economy comparable to four-stroke engines. The engine in question makes use of a modified Eaton-type supercharger to enable air-only scavenging, with this it utilizes direct fuel injection which occurs after the exhaust ports have closed, these two elements combine to eliminate the combustion of lubricating oil in the cylinder and short-circuiting of the fuel-air mixture into the exhaust. By having passive check valves in the cylinder head to regulate the inflow of scavenging air, and exhaust ports located near bottom centre this results in a top-down uniflow-scavenged configuration, as well as retaining a simplistic engine design. In the two-stroke cycle, using the intake charge to replace the combustion products with fresh air during scavenging is critical to engine performance. In this engine the scavenging charge is produced by a set of passive intake check valves, and because of this the scavenging timing is important. These valves are important because they govern the volume of combustion products that are forced out of the cylinder during scavenging, and hence the efficiency of combustion in the engine. To evaluate the engine design criteria, a validated computational fluid dynamic (CFD) model was used to offer insight into how the in-cylinder flow developed during scavenging. The CFD model of this engine was used to test different check-valve geometries to see how they affect the scavenging flow in the cylinder. The goal of this is to assist in entraining more of the combustion products which would result in more being exhausted from the cylinder. A more favourable design was found, and a design produced to be taken onto the next step of testing.
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