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Nội dung: <blockquote data-quote="Butchi" data-source="post: 63518" data-attributes="member: 7">Mô phỏng động cơ xăng 4 kỳ[MEDIA=youtube]AqnJVthBziM&feature[/MEDIA]Considering the energy crises and pollution problemstoday, investigations have concentrated on decreasing fuel consumption by using alternative fuels andon lowering the concentration of toxic componentsin combustion products. Hydrogen is considered anideal alternative fuel. The use of hydrogen as an automotive fuel, as a primary or supplementary fuel,appears to promise a signiﬁcant improvement in theperformance of a spark ignition engine. Besides being the cleanest burning chemical fuel, hydrogen canbe produced from water (using non-fossil energy)and, conversely, on combustion forms water againby closed cycle (Veziroglu et al. 1989; Vezirogluand Barbir, 1991, 1992). A small amount of hydrogen mixed with gasoline and air produces a combustible mixture, which can be burned in a conventional spark ignition engine at an equivalence ratiobelow the lean ﬂammability limit of a gasoline/airmixture. The resulting ultra-lean combustion produces a low ﬂame temperature and leads directly tolower heat transfer to the walls, higher engine eﬃ-ciency and lower exhaust of CO and NOx (Sher andHacohen, 1987; Al-Baghdadi, 2000, 2002).Ethanol is a likely alternative automotive fuel inthat it has properties that would allow its use inpresent engines with minor modiﬁcations. Alcoholfuels can be made from renewable resources like locally grown crops and even waste products such as331AL-BAGHDADIwaste paper or grass and tree trimmings (Morris,1992). As a fuel for spark-ignition engines, ethanolhas some advantages over gasoline, such as betteranti-knock characteristics and reduction of CO andUHC emissions. Ethanol fuel has a high heat ofvaporization; therefore, it reduces the peak temperature inside the cylinder and hence reduces theNOx emissions and increases the engine power (WeiDong et al., 2002; Al-Hasan, 2003; Bang-Quan et al.,2003).One of the major areas of development in the internal combustion engine is the development of computer simulations of various types of engines. Theireconomic value is in the reduction in time and costsfor the development of new engines and their technical value is in the identiﬁcation of areas that require speciﬁc attention as the design study evolves.Computer simulations of internal combustion enginecycles are desirable because of the aid they providein design studies, in predicting trends, in serving asdiagnostic tools, in giving more data than are normally obtainable from experiments, and in helpingone to understand the complex processes that occurin the combustion chamber. In the present work,a quasi-dimensional model was developed to simulate a 4-stroke cycle of a spark ignition engine fueledwith various types of fuels, i.e. gasoline, hydrogen,ethanol, and their mixture.Modeling of The Spark Ignition Engine(Power Cycle)The combustion chamber was generally divided intoburned and unburned zones separated by a ﬂamefront (Figure 1). The ﬁrst law of thermodynamics,equation of state and conservation of mass and volume were applied to the burned and unburned zones.The pressure was assumed to be uniform throughout the cylinder charge. A system of ﬁrst-order ordinary diﬀerential equations was obtained for the pressure, mass, volume, temperature of the burned andunburned zones, heat transfer from burned and unburned zone, and mass ﬂow into and out of crevices.BurnedzoneRHeat transfer(from burned zone)Heat transfer(from unburned zone)Flow into crevices(from unburned zone)Flow into crevices(from burned zone)Work doneFigure 1. Two-zone thermodynamic model of combustion.The mass burning rate was modeled by the following equation (Heywood, 1989):dMbdt= Af l.ρ.ST (1)The turbulent ﬂame front speed (ST) was modeled by the following equation (Heywood, 1989):ST = SL.f.(ρu/ρb)[(ρu/ρb) − 1]Xmb + 1(2)where f is a turbulent ﬂame factor, deﬁned with thefollowing formula:f = 1 + 0.0018 × rpm (3)The laminar ﬂame front speed for mixtures of hydrocarbon and/or alcohol with hydrogen, air, andresidual gas was modeled by the following equation(Yu et al., 1986):SL = SLo.where YH2 is an indication of the relative amount ofhydrogen addition, which was deﬁned by the following formula:</blockquote>

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