OPEN CHAMBER SPARK IGNITED COMBUSTION SYSTEM DEVELOPMENT FOR HIGH POWER DENSITY AND LOW EMISSIONS

摘要

High power density and thermal efficiency combined with very low NOx exhaust emissions are main challenges in today's gas engine development programmes. Until recently open chamber combustion systems using traditional spark ignition were considered to be limited by knock and misfire in their potential to achieve the above mentioned goals. The main task of the work reported here was to achieve a stable, knock-free combustion using a knock-prone gas fuel of 70 methane number for a specific power density of 25 kW/L at 250 mg/m_N~3 NO_x emission according to the TA Luft. The combustion system development was carried out on a single cylinder engine (SCE), thus, a special aspect of the work was to ensure transferability of the single cylinder engine combustion system development results to the targeted V12 multi-cylinder engine. Prior to engine testing, intensive simulation work was undertaken to specify the most promising engine hardware configurations. The main emphasis was on the 3D CFD analysis of the in-cylinder charge motion and its interaction with carefully chosen combustion chamber geometry variants. The ultimate scope was to generate high local turbulence levels during combustion, enabling a short combustion duration with low variation coefficients. The experimental phase included engine tests for several combustion relevant parameters and the detailed combustion analysis with respect to flame propagation and knock centre location using the optical combustion diagnosis system AVL VISIOLUTION. This paper describes the overall work procedure as well as the analytical and experimental methods and tools employed in the combustion system development programme. It also gives information on engine test results, the value and contribution of combustion visualisation, as well as on the engine performance which could be finally reached.