Reliability And Sensitively Analysis Of The Multi-state Diesel Engine Fuel Supply System

With the increasing improvement of the level of science and technology,the structure of the diesel engine system is becoming more and more complex,function is getting more and more complete.The random failure,various failure mode,performance diversity and multistate are become the main problem of the reliability study.Once a link or a component fails during the operation,which has an influence on safety and reliability of the system.For the diesel engine fuel system,the tradition reliability theory is not applicable to the system due to the complexity and particularity of its internal structure and its component parts,which making the system have a variety of state and performance level beyond the good and failure.And then a multistate system reliability theory is used to analysis the reliability instead of the binary algorithm,which provides a strong support for solving this problem.Taking diesel engine as the research object,reliability assessment and sensitivity analysis for diesel engine fuel system based on Markov model and generation function method,the probability distribution function of the system components degradation is obtained,this result provides the theoretical and technological base for reliability evaluation,life predication and fault diagnosis and prevention of engine.The main works of paper are as follows:(1)Study the failure model of the fuel system.A study is conducted for structure of fuel system,the structure schematic diagram is draw,the system fault modes are listed.The state space of the system and its failure modes are one-to-one correspondence,which can be combined with multistate system theory.The fuel injector,as the key component,is introduced in details,including its working principle,classification and failure forms,from the angle of statistical,filter,statistic and preprocessing are carried on external feedback failure data of injector,and the failure regularity of the component is obtained.(2)A reliability analysis method of diesel engine fuel system based on universal generating function is proposed,a reliability of engine system is analyzed by using the combined method of Markov and UFG.In order to reduce the dimension in the Markov process,a reliability module analysis method of UGF-based is presented,which is mainly used for the situation of the system of each components mutually independent.Firstly,solve the equations of smaller dimension in system module respectively,secondly,apply the UGF(Universal Generating Function)to multiple the calculation of various module,finally,obtain the dynamic parameters of the system reliability.A simulation analysis is carred out by applying MATLAB software for the diesel engine fuel system,example results show that: this new method can not only divide the equations,but also realize the dimensionality reduction of equations.(3)A reliability analysis method of the diesel engine fuel system based on the degradation measure time intervals is proposed.Firstly,equivalence sets are used to establish the degradation probability models of each multi-state system under different states,which could be divided by the performance level.Then,degradation probability model under different states is contracted,and the new reliability indicators are used to evaluate the reliability,such as dynamic probability of multi-state system,the time staying in each state,dynamic expectation function and integrated expectation function of the performance.Finally,the sensitivity of the reliability of the multi-state system is captured.The proposed method can predice the staying time of the component and the system,which is contributed to the life prediction and fault warming early,meanwhile,it can also reflect the best-state component at a certain point in time or time interval,which is contributed to the structural optimization on system.(4)A method for determination the optimal maintenance time of a certain type diesel engine is introduced.For the diesel engine fuel system,following the characteristics of the system performance degradation,non-homogeneous multistate is considered,the degradation and maintenance following some certain rules is assumed,then the probability function expressions are obtained,the optimal maintenance time is calculated through the establishment of negative utility function and the maintenance costs expression.