Study On Application And Characteristic Of Spark Ion Current In Si Engine

A novel thinking that burned gas is a plasma state in a special period of the engine combustion process is presented in this paper. it is based on the investigation of the ionization process of burned gas. The mechanism is expatiated about the generation and dissipation of charged particle in burned gas plasma, and a mathematical model of the spark plug ion current in SI engine is founded, based on the chemistry kinetics, thermodynamics and plasma physics. It founds a theoretic foundation for extensive application of the spark plug ion current signal. An ion current signal acquisition and analyzing system is developed based on Virtual Instrument. Its measure device has reasonable structure, cheap cost and simple installation. Its probe is only connected between the spark plug and ignition cable in series, dispense with any change for engine. Its signal disposing soft has convenience, agility and high efficiency that is developed in LabVIEW 7 Express. This system is a perfect experiment stage for researching the characteristic and application of spark plug ion current. A lot of conclusion is obtained that has important guiding significance to apply spark plug ion current signal, base on a great deal experiment research to characteristics of spark plug ion current. A new method for detecting the local air-fuel ratio in spark plug gap, λSS, is proposed and realized, that is based on a BP neural network as soft sensing model and some characteristic parameters of spark ion current as second variables. The basic thinking and technique approach of λSS method are elucidated in detail. On the basis of researching entirely into soft sensing technology and artificial neural network theory, a λSS neural network model is set up used Matlab. λSS set up a new technique approach which gives a new controlled strategy for optimizing the formation quasi-homogenous mixture. In the end, the λSS method based on spark ion current is first employed in researching for quasi-homogenous lean-burn system .The experiment shows which optimizes controlled fuel injection parameters to form a quasi-homogenous mixture: The 2nd fuel injection proportion should be optimized according to the average mixture strength (namely injected fuel gross) in 4-valve Lean-burn engine, when engine is in middle or lower engine speed and load; The second fuel injection timing has hardly impact on local mixture strength of spark plug before inlet valve is opened, and it has a best timing during the inlet valve opening period.