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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.

A drivetrain model incorporating detailed crankshaft and drivetrain dynamics has been incorporated into an unsteady gas dynamic computer simulation of a single-cylinder two-stroke engine. This study examines the change in predicted engine performance caused by relaxing the conventional assumption of constant crankshaft velocity, and a comparison of results is presented. Relaxing the assumption changed the predicted brake mean effective pressures by over 10%. Experimental validation of the simulation involved mounting an engine to a test bed and driving an inertia wheel through a fully characterized drivetrain. A high-speed data acquisition system measured signals from a position encoder mounted on the crankshaft and from a non-contact torque transducer. The time and position data were used to calculate instantaneous crankshaft speed, and these results were compared to the predicted profiles. Simulation results and experimental measurements are presented and discussed.

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.

The paper discusses the design of a racing motorcycle engine to compete in World Superbike racing. This class of motorcycle racing is based on production machines with four-stroke engines only. The rules allow three engine variants to be used, a 750 cm3 four-cylinder engine, a 1000 cm3 twin-cylinder engine, and a 900 cm3 three-cylinder engine. To date only the first two variations have been employed but this paper shows that the 900 cm3 engine has the highest potential power output of the set. This is demonstrated using engine simulation software and the finest detail of the design of the engine and its ducting are supplied within the discussion. The input data for the engine simulation is provided by empiricism so that the design is initially well-matched from the intake bellmouth to the end of the exhaust system. The outcome of this empirical process is confirmed by the engine simulation to be a relevant initial design procedure.