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The manufacturers continually look for improved methods to design engines. Increased durability, enhanced engine performance, decreased emissions and low cost are all issues to consider during the early design stages. The purpose of this paper is to investigate the thermal flows and heat transfer phenomena occurring in the small engines and to suggest valid methods for their prediction to be used inside computer design software. A new approach to theoretically calculate the heat transfer based on the thermal vibrational convection theory is first proposed. The basic idea of this approach is that the heat transfer process can be correlated mainly with the thermal explosion and with the detonation wave produced by combustion. Later on, a simplified model based on energy balance method is investigated and its use in the engine computational software is proposed showing how it represents the best solution to develop a software procedure to simulate heat transfer.

In order to develop modern two-stroke engines with low fuel consumption, respectively with low exhaust emissions, two alternative development areas - the mixture formation and the scavenging system - have been correlated. For a satisfying mixture formation without fuel losses by scavenging, the direct injection seems to be one of the best solution for the high speed two-stroke engine of the future. On the other hand the modern development of two-stroke scavenging systems shows a large field of application and improvement methods of cross and loop scavenging [1]. Based on the specific optimisation factors of the injection system, respectively of the scavenging system, the aim off this common work of the Universities of Pisa and Zwickau is to correlate both the optimisation fields in an advantageous mixture formation process.