| After the 4190ZLC-2 diesel engine electronic control transformation,under the permission of the economy,the emission of NOx has droped largely through the load-characteristic test,but it is still beyond the emission requirements of Tier II not to metion the requirements of Tier III;obviously,the only electronic control transformation is unable to meet the more stringent requirements in the future.By using simulation software AVL_Fire on this basis,the simulation study on diesel /natural gas dual fuel reactivity controlled compression ignition(RCCI)engine is carried out for 4190ZLC-2 diesel engine in the paper;reactions inside the cylinder are controlled by controlling the combustion phase,which ensure the economy and power,at the same time,super low NOx emission is achieved.The results of the study are as follows:Firstly,the influence of the replacement rate of the natural gas on the perf ormance of the engine is studied by using of double equivalent diesel injections and timings.It shows that: with the increase of the replacement rate,the ignition delay will increase gradually,and the starting point of combustion will be postponed,and the power output will increase,and the cylinder pressure,the temperature and the emission of NOx will reduce;but the phenomenon of non-ignition occurs,when the replacement rate is 93%.Secondly,the influences of the first and the second injection timi ngs on the performance of the engine are studied respectively with the condition of 86% replacement rate.It turns out: after retard the first injection timing,the starting point of combustion will gradually advance,and the power,the cylinder pressure,the temperature and the NOx emission will gradually increase.The refered fuel consumption decreased gradually,and the unburened HC compounds will decrease first and then increase,and then decrease rapidly again.It shows that the earlier first injection timing is benefit for the low temperature combustion.When the second injection timing is postponed,the powe,the cylinder pressure,the temperature and the other parameters do not change linearly;the peak values occur at 15°CA BTDC;before 15°CA BTDC,the later the second injection timing,the earlier the starting point of the combustion,and the higher the power,the cylinder pressure and the NOx emission;after 15°CA BTDC,the starting point of combustion began to postpone,the parameters began to dro p.The refered fuel comsumption began to decrease first and then increase,and the lowest point occurres when the second injection timing is 15°CA BTDC.Thirdly,the influence of the fuel ratios of the double injections on the performance of the engine is studied.The results shows that: with the increase of the proportion of the first injection of fuel,the combustion phase is delayed,and the power,the cylinder pressure,the maximum temperature in the cylinder and other parameters gradually decreases,and the change amplitudes are large.the NOx emission gradually decreases,but the refered fuel consumption increases.Therefore,the power is greatly influenced by the proportion of double fuel injections when the economy and the environmental protection are guaranteed first.Fourthly,the phenomenon of non-ignition is further studied with 93% replacement rate.The results shows that: the ignition starts when the second injection timing is delayed to the 25°CA BTDC;and if the second injection timing is further postponed,the starting point of combustion is earlier,and the change law of each parameter coincides with the law of the previous study on the second injection timing.Finally,the simulation research on the load characteristic of dual fuel RCCI engine is carried out and the result is compared with the load characteristic test data of the engine after the electric control transformation.It shows that: the NOx emissions are very low in the full load range,and the refered fuel consumption is lower than the test data in the medium and high load range,but the emission of the unburned HC compound is higher in the low load;the weighting NOx emission of dual fuel RCCI engine is much lower than that of Tier III through calculation.The control of the combustion phase can be achieved by changing the double injection timings and proportions,and thus the control of the engine performance can be realized;the study of this paper provides a theoretical basis for the transformation of 4190ZLC-2 diesel engine into diesel/natural gas RCCI engine. |
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