Analysis Of Combustion Process Of Medium Speed Diesel Using Heavy Fuel Oil

Combustion process inside the cylinder, which is determinant of the dynamic, economy andemission, plays a quite important role on the performance of the diesel engine. With the rise of oilprice and implementation of stringent emission regulations, it becomes more and more important toinsight into the combustion process. Nowadays, the research of combustion and emission on dieselengine is mainly focused on high speed diesel engine. People seldom do such research onhigh-power diesel engine and medium speed diesel engine using heavy fuel. This paper analyses thecombustion process of medium speed marine diesel using heavy fuel, and try to research theinfluence of different parameters to combustion and emission. Because of the limitation of testingcondition, it’s impossible to study the actual states of temperature field, concentration field and theregion where NOx generates. By using combustion simulation software–AVL FIRE, this papersimulates the combustion process of DN8340which is medium speed diesel engine using heavyfuel oil.This paper builds a monitoring system of combustion process in the platform of LabVIEW torealize the monitoring of combustion process, data acquirement and analysis. And building thissystem includes proposing testing method, hardware construction and software construction.Process the acquired data and calculate the heat release rate to provide initial condition and thebaseline of verification for numerical model.By using the ESE-Diesel model of FIRE, this paper sets up the combustion chamber model ofDN8340diesel engine and carries on the grid partition and simulates the combustion process fromthe inlet valve closed to the outlet valve opened. Through the comparison between the result fromtesting and the simulation results, the paper verifies the correctness of the numerical model. Alsothis paper makes a research on calculation results such as pressure, temperature, emissionconcentration, spray flow field and NOx concentration field at the rated speed (650r/min). Theresult shows: the maximum cylinder pressure is17.57MPa which appears around10°CA ATDC;and the maximum cylinder temperature is2008K, appears around21°CA ATDC; oil in cylinderreleases heat quickly at8°CA BTDC that leads to sharp increase of temperature. Most of the NOxgenerates after25°CA ATDC, and the concentration of NOx is0.12%which is generated at theedge of the combustion chamber where have high temperature with enriched oxygen content. As thetemperature drops, NOx growth comes to a “freezing period” and the NOx concentration keeps thesame. The soot formation started at12°CA BTDC and reaches the maximum value at8°CABTDC, then the soot be oxidized gradually.Based on the numerical model, this paper studies the influence of changing fuel injectionadvance angel and intake temperature to the combustion process, then do parameter optimization to DN8340. The result shows: the advance of oil injection is beneficial to the combination of oil andfresh air, and the pressure and temperature increases as well. But that also increases NOx emissionwhich is generated in high temperature with enriched oxygen content condition. The rise of intaketemperature is helpful to the fuel atomization, and a lot of combustible mixture forms at the front ofoil spray. With the effect of high temperature air in cylinder, the mixture is ignited in advance. Atthe same time, high intake temperature reduces charging efficiency that lead to the decrease ofcylinder pressure and combustion quality. What’s more, the temperature and the NOx emission bothrise. Adjusting the fuel injection advance angle to7°CAand lowering the intake temperature to40℃, lead to the delay of the start timing of combustion. The maximum combustion pressure andtemperature both be reduced. The NOx emission is reduced to1.9g/kWh, which satisfied IMO TierⅢ emission limitation.