Study On Emission Characteristics Of Marine LNG/Diesel Dual-fuel Engine

Global energy crisis and environmental issues make the research on alternative energy type internal combustion engine to become an important development direction. Due to its easy modification, economy, and high efficiency, the natural gas(NG)/diesel dual fuel engine based on a pure diesel have got more attention.The G128ZLCa2-WX marine diesel engine made by Shanghai Diesel co.Ltd has been converted into a Liquified Natual Gas(LN G) / diesel dual fuel engine, combining the engine bench test with propeller characteristics and power generation to study the characteristics of the dual-fuel engine emission characteristics.The main contents of this paper include the following aspects:1) After the analysis of the physic-chemical properties of the Liquefied natural gas, combining with the development of the domestic shipping markert, this paper has proposed the modification scheme and design scheme of the LNG/diesel dual fuel engine.2) According to the operating charateristics of the common marine engine, lauching the emission experimental of two different NG intaking mode under the engine test bench. Here also includes the following sections. a. The emission performance comparison of two different type dual fuel engine in thepropeller charateristics. b. Researching the emissions impact caused by the diesel mass replacement rate, load andspeed to the engine. c. The influence of the engine emission, which caused by the NG injection timing, hasbeen studied in the multi-point injection engine. d. The simple anslysis of the dual fuel engine has been researched by the cylinderpressure and exhaust temperature.3) Based on the current research status of the LNG/diesel dual fuel engine’s emission model, this paper has proposed a RBF(Radial Basic Function) network emission model. A RBF emission has been established by the Matlab software.Experimantal studies have shown that the CO/HC of the dual- fuel engine is significantly worse than the original. As the same time, the multi-point injection engine has better emission performance that the other type engine. Replacement rate, load and speed have a significant impact on the dual- fuel engine emissions. With the increasing of the diesel mass replacement rate, HC concentration has a almost linearly increasing trend, the growth of CO concentration is relatively small that HC’s. NOx concentration is almost no changed. With the growth of load, HC emission performance has largely improved. Meanwhile the higher speed has brought the worse emission perforemance during the same power output. When the NG injection timing is near of the top dead center position, the emission performance of the dual fuel engine is the best. The NG injection timing has little impact to the HC and CO emissions, but CO has shown a regular changing. During the small load, the cylinder pressure of the dual fuel engine has the same variation to the original. The slowing burning of natural gas is the main reason caused the high emissions of HC and CO. When it comes to the middle and large load, the buring in the cylinder is more intense. The higher cylinder temperature has lead to a higher NOx emission.The experimental data has been used to establish a RBF nerwork emission model as the samples. The model validation has shown a high accuracy of this model by the comparison data.Finally, this thesis has pointed out the shortcomings and improvement areas, proposing the application prospects of the dual-fuel engine.