Modelling, performance improvement and emission reduction of large two-stroke diesel engine using multi-zone combustion model

Abstract

The main energy source in marine industry is fossil fuel. Diesel engines are main power supply in sea transport at present times and will also be in the future. Energy conservation and environmental protection are the main problems that engine manufacturers are facing. Researchers have been making a lot of effort over the last decades to analyse energy conversion in large two-stroke engines. A 1-dimensional large two-stroke low-speed diesel engine model is developed, along with a multi-zone combustion model (MZCM), in which the losses of exchanging working medium and gas composition are calculated in the whole engine, unlike the preceding 0-dimensional and quasi-dimensional engine models that are only calculated in engine cylinder chamber. The model of a low-speed two-stroke marine diesel engine is calibrated and validated with experimental data and is used for simulation and analysis of the engine performance, combustion behaviour and emission of harmful exhaust gases. Large two-stroke marine diesel engines are problematic for modelling due to very few researches on this issue, due to the unsuitability of applying model on a low-speed two-stroke big diesel engines, large number of parameters that affect combustion behaviour, shape of ports and exhaust valves, working medium flow as well as because of shape of combustion chambers in these engines. For the reasons above, this research paper and its experiments contribute to better understanding large two-stroke low-speed marine diesel engine process. Analysis of engine characteristic was done by varying the most important parameters. Optimization of fuel injection characteristic and exhaust timing is achieved. The parameter of changing injection profile from classic to pre-injection was performed, and the effects on engine performance, NOx, CO and soot emissions were showed. With a pre-injection profile it is possible to reduce NOx emission by 9%, but a decrease in engine power is significant.