Three-dimensional CFD modelling, optic analyses of the combustion process, and operation on test engines have revealed a huge potential for optimization of the electronically controlled ME engine. During the last couple of years, investigations have been made and tested on the MAN Diesel research engine at constant engine speed, MEP (mean effective pressure) and max. cylinder pressure at 75 and 100% loads, respectively.
- The following issues were covered:
- injection timing
- exhaust valve open timing
- exhaust valve close timing
- compression volume configuration
- hydraulic pressure
- fuel valve flow area configuration
- injection profile including square profile & step profile.
The tests revealed that it is possible to obtain a variation in both SFOC and NOx of approximately 10 g/kWh with unchanged MEP and pmax, giving very widespread optimisation possibilities. Even though the tendency for low NOx values to give a high SFOC, the spread of values is so large that it is possible to obtain an improved NOx performance with improved SFOC. All data obtained for the 75% load test are given in Fig. 1
The injection pattern profiling is the main topic of our investigation of the ME control system. Fig. 2 shows four different heat release patterns related to four injection profiles. This shows that modelling the injection profile also means modelling the combustion pattern. All NOx is generated during combustion and the modelling possibilities offered by the combustion pattern represent an excellent tool for controlling the NOx formation and the cross-over between the NOx for notion and SFOC.
The very positive result from these tests will of course result in a continued effort to investigate the further potential of the unique ME system, and transfer these findings to production engines as soon as verified. The step profiling is already systemized in the ME-B software and utilised as a setup for the delivery of the S40ME-B and S35ME-B engines. Further tests on S60ME-C, K98ME and L70ME-C type engines have been performed successfully, see Fig. 3.