An Experimental Investigation On Combustion And Emissions In Engine With Variable Intake-air Composition

The study on behavior and mechanism of combustion with variable intake-air composition in engines aims at improving the performance of engines applied in the high plateau regions or other air-special environment, and exploring an innovative way of controlling combustion and emission by means of variable intake-air composition in engines.The study work in this thesis gained sustentation fund from NSFC programme . This paper firstly studied theoretically the influence of oxygen concentration to the combustion performance of gasoline. Based on the theoretical analysis, this paper carried out some experiments to prove the theoretics. The self-designed test bench included the development of fiber optical sensor, the design of photoelectric system, and the design of ignition signal collection system. In consideration of the results of both engine bench test and the theoretical analysis, we determined to use the oxygen of concentration range from 15% to 27% in experiments. Covered with the combustion and emission tests in condition of both oxygen-enriched in-take and nitrogen-enriched in-take, the experiments included tests of in-cylinder pressure, flame light intensity and emissions in order to study the combustion characters.In this paper, three style of experiments are made in condition of oxygen-enriched air(oxygen concentration Co=21～27%), they are: normal steady state test, normal temperature start test and transient in-take switch test. The tests shew: with the increasing of oxygen concentration, instantaneous speed change coefficient decreases in steady state, and the rate of fire missing descends in start process; the exhaust of CO, HC become less, and especially in start process, the decrease of CO, HC is evident with NOx increasing obviously but still 1/4～1/8 to steady stage conditions. We can conclude from the tests that it can get much better effect if the oxygen concentration is from 23% to 25% when exhaust of HC, CO decrease evidently with NOx increases less. In codition of other concentrations, HC,,CO decrease slowly but NOx increases obviously.In the nitrogen-enriched(nitrogen concentration Cn=79%～85%) in-take test we can conclude that: with the increasing of nitrogen concentration, ignition lag and combustion duration protract, instantaneous speed change coefficient increases; NOx decreases with the increase, however, CO,HC increase. We can conclude from the test that it can get best effect if the nitrogen concentration is from 81%～83% when the exhaust of NOx, HC,CO is in a best state.It can reach similar effiect with EGR. simultaneously nitrogen-enriched in-take can improve NOx emission, however, We must analyze the causes according to condition comprehensively and obtain much better emission control,At the least price of HC,CO emissions.In a word, this paper researches and explores combustion and emissions in engine with variable Intake-air composition systemly.the technique of integrate combustion control taking the form of variable in-take with differen composition of oxygen and nitrogen finds a new way to optimize the combustion performance of engines.