Optimization of Heat Release Shapes and Their Impact on Engine Performance

This study analyzes the heat release rate (HRR) shape and the performance of the G95 marine engine (NOx and Specific Fuel Oil Consumption SFOC), developed by MAN En[1]ergy Solutions. The tools used for the analysis are the simulation software GT-Power and MATLAB for post-processing the results. The engine was studied in both diesel and dual fuel mode (methane main injection with a diesel pilot). For each case, the analysis was done in two conditions: - with "control on" (where parameters like maximum cylinder pressure, compression pressure, Indicated Mean Effective Pressure IMEP, and maximum injection pressure are kept fixed), and with "control off", where fewer limits are applied. Several engine parameters were changed in order to see the effects on HRR shape and engine performance. These include the fuel nozzle diameter, number of holes, EGR level, and the geometric compression ratio. For the dual fuel mode, pilot injection parameters such as Start Of Injection (SOI), duration, and pilot fuel mass were also varied. The results show that both engines are already well optimized. In fact, when all the controllers are active, it’s hard to get better SFOC values. However, with fewer constraints, better improvements can be reached. For the diesel engine: - With all controls on, reducing the EGR level from 18.7% to 11.5% results in a slight improvement in SFOC, with a reduction of 0.27%. However, this also causes a significant increase in NOx emissions, by about 24.45%. Increasing the Geometric compression ratio form 29 to 31 lead to a reduction in NOx of 5.01% without affecting the SFOC When the control constraints are relaxed (control off), increasing the maximum cylinder pressure from 199 bar to 219 bar leads to a more noticeable SFOC reduction of 1.37%, while the corresponding NOx increase is 8.92%. For the dual fuel engine: - With all controls on, lowering the EGR level from 17.8% to 10.5% allows for a 0.51% reduction in SFOC, though NOx emissions rise by 18.46%. Similarly, increasing the geometric compression ratio from 29 to 33 results in a 0.39% decrease in SFOC, with a NOx increase of 9.69%. Removing the diesel pilot lead to a reduction of both SFOC and NOx respectively of 0.33% and 7.65% When the constraints are removed, increasing the maximum cylinder pressure from 198.5 bar to 218.5 bar gives the best SFOC improvement of 1.62%, accompanied by a 16.88% rise in NOx.