Preparing BMW Motorrad’s Boxer Engine for the Future: Improving Performance, Driveability and Efficiency While Fulfilling Future Emission Standards

摘要

Engine development mostly revolves around the same competing goals. With the implementation of the EU4 and EU5 emission standards for motorcycles, the difficulty of increasing performance and improving driveability and efficiency, while simultaneously fulfilling the Emission standards becomes even higher. Though the automotive industry offers a variety of solutions for the named topics, their implementation in a high performance motorcycle engine with specific needs regarding packaging, a wide operating range and full load behavior, represents a special challenge. This paper presents the approach of BMW Motorrad to meet these goals on the example of the boxer engine, focusing on the methodology throughout the development process. The gas exchange system of the engine was optimized using 1D gas dynamic simulations and 3D CFD analysis for a redesign of the valve train, ports and valves. The results of the calculations were further confirmed by experiments at the flow test bench measuring discharge coefficients and using particle image velocimetry (PIV). Combined simulation and engine testing led to a newly developed exhaust manifold enabling a faster light-off and a more stable operating temperature of the catalyst, while reducing raw exhaust emissions through a new injector layout. Engine experiments showed lower emissions, an improved efficiency and a more stable combustion in part load as well as an increased performance at full load. These results translated into lower exhaust emissions and fuel consumption when testing the motorcycle in the world motorcycle harmonized test cycle (WMTC).