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The flow performance of the helical intake port has great influence on DI diesel engine combustion and performance and so the helical port is usually an important, well-designed and sophisticated engine part. However, many errors or deviations may occur during the casting and machining processes. In this paper, a few sets of mechanism were designed for simulating different kinds of port deviation e.g., port with inclination, vertical swelling and eccentric errors etc. The flow performance of the port was tested on a steady state flow rig to verify how and to what extent the errors or deviations affect the flow performance of the helical inlet port in order to improve the production precision so as to insure good engine performance.

The prediction of tumble speed in the cylinder of spark ignition engines is discussed in this paper. Based on the experimental results from the steady state flow rig and the flow field measurement in the cylinder of a motored engine by LDA system, a model for the physical process of the tumble formation is proposed. That is: during the early stage of induction and before the piston reaching a critical crank angle, tumble can't be formed effectively. This critical piston position or crank angle should correspond to the time when the in-cylinder tumble has to be distorted and destroyed by the upward moving piston during the late stage of compression stroke. A model for predicting the tumble speed is derived and verified by the in-cylinder flow measurement results by a LDA system.