Numerical models for the assessment of the cylinder-kit performance of four-stroke internal combustion engines.

摘要

Governments across the globe are introducing more stringent emission standards, setting targets for higher engine efficiencies and looking into alternative fuels. At the same time the consumer demands have to be met: low cost, high fuel efficiency, long trouble-free life, low emissions and low noise and vibration. In order to meet all of these demands, a vast amount of design and testing is needed. This is where the numerical models for the assessment of cylinder-kit performance apply. Such models greatly reduce the amount of time from conception to launch of a new product. They reduce the number of expensive prototypes required to complete a design, and they allow for multiple design iterations to be tested in virtual space.;In this dissertation, numerical models for the assessment of cylinder-kit performance of four-stroke internal combustion engines are explored. A novel 3-D numerical model for predicting piston dynamics was developed. This model deviates from conventional ones, as in addition to the axial and thrust plane motions of the piston it also considers the secondary motion in the wrist-pin plane. It is shown that the motion in this additional dimension becomes important with the new generation pistons, especially when faced with asymmetric and eccentric cylinder bore deformations. The model is used to investigate piston dynamics for both gasoline and diesel engines, and the Andreas Petrou Panayi predicted results are compared with the actual operating pistons.;Also, a method for the optimization of piston skirt profiles used in internal combustion engine piston design is proposed. The method is based on a response surface approximation of standard performance measures used in piston design, namely, the RMS values of the piston's transverse and angular accelerations, used as indicators of piston slap and noise, and the friction work on the skirt. The method is intended to be used in conjunction with computationally-intensive piston simulation tools. As such, it can be used also as a paradigm for strategies to solve optimization problems that rely on computationally expensive simulation models. An example illustrates the capabilities of the method and the significant enhancements in performance that result from an optimized piston skirt profile.;Finally, the ring-pack performance of a newly developed gasoline engine is benchmarked against that of a similar production engine using CASE, a commercial ring dynamics simulation program. Some limitations of such models that perform the calculations at one cross-section of the ring-pack are identified, and an introduction is made to the initial developments of an advanced 3-D ring dynamics numerical model.