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Technical Paper

Heat Transfer Predictions and Experiments in a Motored Engine

In the first part of this study, a one-dimensional code was used to compare predictions from six different two-equation turbulence models. It is shown that the application of the traditional k-ε models to the viscous-dominated region of the boundary layer can produce errors in both the calculated heat flux and surface friction. A low-Reynolds-number model does not appear to predict similar non-physical effects. A new one-dimensional model, which includes the effect of compression, has been formulated by multiparameter fit to the numerical solution of the energy equation. This model can be used in place of the law-of-the-wall to calculate the surface heat flux. The experiments were performed in a specially-instrumented engine, allowing optical access to the clearance volume. Measurements of heat flux, swirl velocities, and momentum boundary layer thickness were made for different engine speeds.
Technical Paper

The Effect of Mixing Intensity and Degree of Premix on Soot Formation in a Backmixed Combustor

To date there is no universal agreement as to the interaction between fuel type, fuel-air mixture preparation and combustion chamber flow characteristics and their effect on soot formation. A propane fueled modified conical back-mixed steady flow reactor was built in which the fuel and air could be mixed together in varying degrees and reacted in at different mixing intensities. The onset of soot and soot loading were determined qualitatively by a photomultiplier focused on the volume inside the reactor. Increasing the degree of premix from a diffusion flame to a distribution of Φmax/Φavg = 5.0 resulted in increases of 3 to 17 percent of the soot-onset equivalence ratio and decreases in soot loading down to zero. Changes in the mixing intensity from 32.5 sec−1 to 75.7 sec−1 resulted in a change in the soot-onset equivalence ratio from 1.26 to 1.52. Soot loading was found to depend on both the mixing intensity, β, and the average number of mixes per mean residence time, β/α.
Technical Paper

Thermodynamic Benefits of Opposed-Piston Two-Stroke Engines

A detailed thermodynamic analysis was performed to demonstrate the fundamental efficiency advantage of an opposed-piston two-stroke engine over a standard four-stroke engine. Three engine configurations were considered: a baseline six-cylinder four-stroke engine, a hypothetical three-cylinder opposed-piston four-stroke engine, and a three-cylinder opposed-piston two-stroke engine. The bore and stroke per piston were held constant for all engine configurations to minimize any potential differences in friction. The closed-cycle performance of the engine configurations were compared using a custom analysis tool that allowed the sources of thermal efficiency differences to be identified and quantified.