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Presented is a study that expands the body of knowledge on the effect of in-cycle speed fluctuations on performance of small engines. It uses the methods developed previously by Callahan, et al. (1) to examine a variety of two-stroke engines and one four-stroke engine. The two-stroke engines were: a high performance single-cylinder, a low performance single-cylinder, a high performance multi-cylinder, and a medium performance multi-cylinder. The four-stroke engine was a high performance single-cylinder unit. Each engine was modeled in Virtual Engines, which is a fully detailed one-dimensional thermodynamic engine simulator. Measured or predicted in-cycle speed data were input into the engine models. Predicted performance changes due to drivetrain effects are shown in each case, and conclusions are drawn from those results.

Engine performance simulation software has become an integral part of the engine designer's toolkit. However, optimization of a particular design using such software is often difficult and time consuming. This is due primarily to the number of parameters required to adequately characterize the engine and the interdependency of these parameters on one another. This paper reports on the use of optimization algorithms embedded within the simulation software package, VIRTUAL 4-STROKE™ (1) 1, that help to automate the engine design process and shorten the development time to meet specific performance goals. A previous paper by Blair et al (2), presented to the society at SETC 2001, demonstrated the ability to predict the behavior of tuned exhaust systems on a single cylinder 4-stroke motorcycle engine using VIRTUAL 4-STROKE.