An Investigation On Spray And Combustion Characteristics Of Refitted Direct Injection Diesel Engine Fuelled With Biodiesel

Due to the unrenewable nature of oil resources and the strengthening environmental protection consciousness,countries everywhere pay more attention to clean alternative fuel for power machine.Biodiesel has been studied worldwide as one of the clean and alternative fuels,which is non-toxic,renewable,biodegradable,and applied directly to diesel engine structure without change.At present,biodiesel study is more on the characteristics & additive which will influence the diesel engine performance and mechanism of reducing exhaust emission,less on spray and combustion process especially on firing,combustion process,and different factors' influence on spray & combustion process.Study on spray & combustion mechanism of biodiesel can offer theoretical support for further promotion and application of biodiesel as one of the clean alternative fuel.So,our study work is very essential and significant.Basing on narrating the development of the biodiesel industry,the article has also analyzed in detail the physical & chemical properties biodiesel and whose impact on engine performance.This study,by using the self-developed dynamic visual test device of multi-purpose spray combustion,is carried out through comparison testing on spray & combustion mechanism of biodiesel and conventional diesel,and a comparative analysis of the two fuels.Conclusions got as follows:comparing to diesel 0#,injection time of biodiesel is earlier,injection delay is shorter;Both fuels spray out four oil beams which run into a blank wall and then rebound,biodiesel beams rebound stronger after collision,some of fuel expand with the swirl along the wall, and other spread reversely,then mix with the air,forming a combustible mixture; Biodiesel combustion first occurs at the edge of the combustion chamber wall,which is the edge of the liquid injection front-end,firing time is earlier than that of diesel 0#, firing delay duration is shorter and it gets burnt faster than diesel 0#,so under the same speed,biodiesel combustion area is bigger than that of diesel 0#;Combustion duration of biodiesel becomes longer,which shows that the biodiesel combustion speed is lower than that of diesel 0# in the stage of diffusing combustion.This article has also analyzed the impact of three different factors:fuel feature, engine speed and fuel injection pressure on biodiesel spray & combustion properties, the conclusion got is:spray impenetrate distance of the mixed fuel grows up along with increasing quantity of biodiesel,there is one optimum mixing ratio for biodiesel and diesel 0# which should be between 0 and 20%,when the combustion efficiency can be improved,ignition delay and combustion time shorter,and the thermal efficiency improved;Speed change has a little impact on spray & combustion properties of biodiesel,burning area of biodiesel at the high speed is bigger than that at the low speed,combustion speed is faster at high speed,rotated angles of crankshaft corresponding to combustion end point increase at high speed also,rotated angles prolong in combustion process,but the combustion absolute time become shorter;Biodiesel spray cone angle at high injection pressure is a little bigger,and impenetrate distance at the same rotate angle corresponding to the injection time is also a little bigger,and the fire delay period gets shorter as the increasing of injection pressure,as combustion ends in advance,so combustion duration gets shorter.