Analysis of a Novel Two-Stroke Engine Scavenging Arrangement: The Neutron Engine

A unique two-stroke engine design is investigated in which fresh mixture is introduced into the cylinder through a valve in the piston crown, and exhausted through peripheral cylinder ports. The engine behaves as a free-piston engine through a portion of the cycle when the piston lifts off the valve seat. The fresh air jet rising along the cylinder centerline effectively displaces the burned gases with little mixing of the two streams.

The concept was analyzed by a combination of dynamic cycle simulation and prediction of the in-cylinder flow characteristics by multidimensional modeling. The cycle simulation program considered the dynamics of the piston during its free motion as well as under the kinematic constraints of the crank system. A zero-dimensional thermodynamic model of the cylinder was used to predict cycle pressure and temperature, indicated power, fuel consumption, and flow in and out of the cylinder. The flow results were used as boundary conditions to a Computational Fluid Dynamic simulation of the two-dimensional cylinder flow. Results, in terms of performance and two-dimensional maps of fluid velocity and density, were compared to a uniflow-scavenged engine predicted by the same modeling techniques. The results indicate that, while the concept may not be particularly attractive from the performance and fuel consumption standpoint, it may result in substantially reduced short-circuiting losses of fresh charge during scavenging. This is of particular interest for classes of engines that are currently carbureted and significantly impacted by current and upcoming emissions regulations.