Mixture Formation and Combustion Evaluation of a Motorcycle Engine Concept Equipped with One Fuel Injector for Each Intake Valve

In light of a more stringent emission legislation and in anticipation of possible future measures to further reduce the real environmental impact of motorcycles, it is necessary to develop engine concepts which are efficient and low on emissions in a wide range of operating points. This poses an important challenge on the development of high performance motorcycles engines as their focus on full load behaviour conflicts sharply with the emission and efficiency demands of the remaining engine load map. The focus of this paper is to evaluate the potential of a port fuel injection (PFI) concept consisting of one individual fuel injector for each intake valve to solve this trade-off. Previous research shows a positive effect of such a setup on mixture formation due to better targeting and atomization, reducing HC emissions and cyclic variations. It also shows improved efficiency, performance and knocking characteristics caused by an enhanced charge cooling effect through open valve injection (OVI). Although the system has been previously investigated, the necessary layout considerations and impacts of the system for a high performance motorcycle engine have not yet been addressed. In this work the mentioned PFI concept was studied using a high performance two-cylinder motorcycle engine. Engine tests were conducted for two injector sets having different static flow values. The results showed improved efficiency and lower HC emissions for higher engine loads, but no performance gain at full load. The reasons for this behaviour were closely analysed by means of CFD simulation and thermodynamic loss analysis of the combustion process. These explanations were further confirmed by additional engine tests using exhaust gas sampling with fast FID. As a final result a set of recommendations for further concept improvement is proposed.