Investigation of Extreme Mean Effective and Maximum Cylinder Pressures in Medium Speed Diesel Engines
The current level of mean effective pressure (mep) of medium speed diesel engines is 25 to 28 bar. Maximum pressure is about 230 bar. At the Technical University Hamburg Harburg a research engine with an mep of 40 bar and a maximum pressure of 350 bar has been operated successfully with good results. This led the authors to investigate what can be expected when operating at even higher pressures. In a theoretical study the mep of a 320 mm bore medium speed engine was increased up to 80 bar. A zero dimensional cycle simulation program was used for the calculations. Compression ratio, stoichiometric air ratio, valve timing and mechanical efficiency were kept constant. Several strategies concerning combustion and turbocharger efficiency were investigated. Some results: With a constant turbocharger efficiency of 70 % and constant rate of heat release (ROHR) an increase of mep above 60 bar is not possible, because the scavenge pressure difference becomes negative. Specific fuel oil consumption (sfoc) increases slightly. The exhaust temperature before turbine rises significantly. With constant ROHR and a constant ratio of pressure before turbine and charge air pressure an mep of 80 bar is possible. Temperature before turbine decreases slightly, sfoc decreases by 5 %. The required turbocharger efficiency is above 80 %. Thermal load increases significantly. In all cases the required charge air and maximum pressure rise approximately proportional to mep. For an mep of 80 bar the first reaches 15 to 16 bar and the latter 750 to 800 bar. Using a jet mixing model two strategies for injection and combustion were investigated. In both the injection duration was kept constant. If the nozzle area is increased proportional to the injected fuel mass the ROHR is unchanged and so are the operating data. The nozzle hole diameters become very large so smoke problems have to be expected. Injection pressure rises only moderately. If the nozzle area is increased proportional to the square root of the injected fuel mass injection pressure rises above 3000 bar and the operating data improve. Sfoc for example is reduced by another 2.5 %. Summarized it can be stated that improvements in operating data are possible. The challenge is to control the high mechanical and thermal loads and to provide the required high efficiency of the turbocharging system.
Peter Eilts Claude-Pascal Stoeber-Schmidt
Technical University Braunschweig,Germany
国际会议
上海
英文
1-10
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）