Increasing decentralization of production combined with just-in-time delivery of products and components calls for a flexible and reliable transportation system. So far, trucks offer the most versatile and efficient solution to those problems. In consideration of increasingly strict emission standards and customer demands for more engine power and less fuel consumption, further selective developments and optimization of DI-diesel engines are necessary. One step in this direction is the application of 4 valves per cylinder in heavy-duty diesel engines to improve mixture formation of fuel and air to get a cleaner combustion and a higher power output.
For visualizing the combustion processes inside the engine, an optically accessible heavy-duty DI-diesel engine was used. This engine is a slightly modified conventional heavy-duty MAN engine based on the D0824 LFL 06 series. In contrast to a former version of the engine, the 2-valve cylinder head was replaced by an up-to-date 4-valve cylinder head.
During the tests, the influence of the start of injection as well as an operating point with pre-injection were investigated. A major target of the investigations was the evaluation of the combustion process by separation of flame and liquid fuel phase signals. The liquid phase was detected by the 2D Mie scattering technique. Simultaneously, flame luminosity was detected two-dimensionally.
The pictures taken inside the piston bowl clearly show the influence of twist on the mixing of fuel and air. The spray exiting from the injection nozzle, which is placed in the center of the combustion bowl, is hardly affected by the twist whereas the fuel vapor is drifted away into the regions between two spray jets where it ignites and burns. For the operating point with pre-injection, the fuel of the main injection hits into the flame of the already burning pre-injection with possible negative effects on HC and soot emissions. At the end of the injection, after the closing of the needle, a flame is visible at the nozzle tip resulting from fuel evaporating from the sac-hole of the nozzle, which leads to increased HC emissions in the exhaust gas.