Establishment Of GA-BP Diesel Engine NOx Emissions Prediction Model And The Application Study On Board

With the rapid development of shipping industry and enhancement of people’s environmental protection consciousness, the control of ship exhaust emission is faced with more and more strict requirements. Among them, the control of the marine diesel engine NOx emission is one of the most important steps. Based on the background of MARPOL convention annex VI domestic implementation, GA-BP model of predicting W6L20C type diesel engine NOx emissions is established, and on this basis, a preliminary study is conducted about how to apply this model on board.Firstly, this paper analyzes NOx formation mechanism in the marine diesel engine and introduces the calculation method of NOx emission values of unit power and time and the basic knowledge of predicting NOx emission in the diesel engine.Then through deep analysis of the influence factors of diesel engine NOx emissions in bench test, engine speed and power are determined as model input parameters. L-M algorithm is used to train the BP network. Compared with the traditional gradient descent method, network can converge in a shorter period of time. In order to improve the global search ability of the network, genetic algorithm is applied to optimize the BP network’s initial weights and thresholds. On this basis, GA-BP model of predicting a marine diesel engine NOx emissions is established. And the prediction model is trained and validated with the bench test data of W6L20C type diesel engine as sample data. Compared to BP neural network model of predicting diesel engine NOx emission, GA-BP model established in this paper has a certain improvement in convergence rate and generalization ability. And W6L20C diesel engine NOx emissions performance is forecasted and analyzed with the validated GA-BP prediction model.Finally, the factors on board influencing the diesel engine NOx emission performance are analyzed, and the influence degree of environmental conditions on the marine diesel engine NOx emission performance is analyzed with an actual case. Proposes are offered about the selection of NOx emission test cycle operating points on board. According to the proposed test points, GA-BP model can be used to predict the NOx emission and then, the NOx emission values of unit power and time can be calculated with the corresponding weighing factors, providing a reference for the competent authority. The realization method of NOx emision monitoring system is studied, with GA-BP prediction model as the core of it.