Research On Cold Plasma Gasoline Reforming And The Influence On Lean Burn Engine

Development of low emission and low fuel consumption engine becomes more important because of running out of fossil fuels, air pollution and global warming up problems. Previous research has shown that using hydrogen to enhance combustion, the engine's lean burn limits can be further expanded. Therefor engine can still work stably with higher air-fuel ratio than the flammability limits of gasoline, and very low NOx emission can be achieved. However this technique is restricted by the short of hydrogen facilities on vehicle. In light of this situation, this paper presents a solution to use the exhaust gas, by the aid of cold plasma, to reform part of the fuel to hydrogen-rich gas, to improve lean burn of gasoline engine, for that the engine's efficiency can be increased and the plane engine's NOx emission can meet current regulations without any after treatment.Thermodynamic analysis of the reforming system shows that the reforming efficiency with the engine exhaust is higher than partial oxidation reforming with pure air. For supporting engine's lean burn combustion, reforming will not have a significant negative impact on volumetric efficiency and maximum power of the engine. Since the traditional catalytic reformer has many shortcomings as easy poisoning, bulky, and slow response, this paper designed a new type of plasma reformer, presented a method to produce rotating gliding arc plasma, and an experiment power system is also contrived. Experimental studies show that using this system to reform gasoline with exhaust gas, the achieved reforming efficiency is more than 80%.With applying this reforming system to one lean burn engine, experimental study shows that the lean limit of engine is gradually increased when the reforming proportion is increased, and the NOx emission is sharply lowered. When 30% fuel is reformed to hydrogen rich gas, NOx emissions is lower than 70ppm, and even can be below 40ppm at low load conditions. NOx reduction rate is higher than 97% when compared with stoichiometric working conditions. Although reforming efficiency is lower than one, reforming part of fuel will not have much influence on engine efficiency. In the examined working conditions, the engine efficiency is increased by about 12~20%. In addition, this paper discusses using of the heat of the reforming system for heating intake air. The results show that, gas heating can also play a role in expanding the lean burn limit, and the engine efficiency is also improved. With the lean limits is increased, NOx emissions is getting lower.This paper establishes a quasi-dimensional combustion engine model. By analyzing the cylinder pressure, the mass burn ratio, flame speed, cylinder temperature, and NOx emissions can be predicted. The result of MBR and flame speed indicates that when the proportion of reforming is increased, the flame speed is gradually increasing, so the stability of combustion is enhanced, and the lean limit is also increased. With the engine's lean limit increasing, the temperature is dropped and the maximum cylinder temperature is decreased to a very low level. At some conditions temperature is even below 1900K, and NOx formation rate is greatly lowered.