| In recent years,the number of national vehicles has been increasing,and the problem of energy shortages has become increasingly significant.It is of great significance to seek alternative fuels to cope with the energy crisis.Among them,methanol is considered to be one of the most promising alternative fuels for internal combustion engines.However,when methanol and diesel are mixed as fuel,the engine has the problem of difficulty in cold start.Based on the unique self-control characteristics of PTC materials,this paper proposes to install PTC as a heating element on the fuel injector,so as to make the fuel temperature rise in a short time.The geometric model of the fuel injector is established by using Gambit.PTC thermistors are installed on the outside of the needle valve body,and the injector is meshed,and the mesh quality is checked.Fluent is used to correlate the injector model,fuel physical properties,PTC materials and boundary conditions,etc.The parameters were set,and simulations were carried out to study the influence of different fuel blending ratio,ambient temperature,fuel flow,PTC Curie temperature and terminal voltage on the heating effect of the fuel injector.The Curie temperature of the PTC heating element used in this article is 333 K and 423 K,and the terminal voltage is 12 V,24V and 36 V respectively.The fuel is divided into M0,M10,M20,M30,M40 according to the methanol blending ratio,and the ambient temperature is263 K,268K,273 K,278K,the fuel flow rate adopts 0.0001kg/s,0.0003kg/s,0.0005kg/s,0.0007kg/s,the calculation of 50 S for each working condition.The simulation results show that:(1)Both PTC components with Curie temperature of 423 K and 333 K can effectively heat the fuel,and the average outlet temperature of the fuel rises significantly.In each working condition,the average outlet temperature of the injector has the same changing trend,which first rises rapidly,then slows down and finally becomes stable.However,when other conditions are the same,the average temperature at the injector outlet of PTC based on the Curie temperature of 423 K is higher and the rising speed is faster.Therefore,PTC thermistor with the Curie temperature of 423 K has more advantages in view of the requirements of the fuel temperature rising in a short time.(2)When other conditions are the same,the average temperature of the fuel outlet increases with the increase of the ambient temperature,but because the PTC thermistor will quickly heat the injector until it is near the Curie temperature,the difference in the average temperature of the fuel outlet is very small;(3)When other conditions are the same,the fuel flow will affect the heating effect of the PTC on the fuel,and the average temperature of the fuel outlet will decrease with the increase of the fuel flow;(4)When other conditions are the same,after adding methanol to diesel,the average temperature of the injector outlet will decrease with the increase of methanol content in the fuel;but because the proportion of methanol is not large,and the PTC has a better heating effect on the injector,The temperature difference between the fuels is not large;(5)When other conditions are the same,the average temperature of the injector outlet increases with the increase of the PTC terminal voltage.Therefore,it can be considered to use a voltage regulator to adjust the voltage of the PTC at low temperatures to ensure that the fuel temperature rises rapidly in a short time.In summary,the method of using PTC to heat the injector can be considered to improve the engine cold-start,and a voltage regulator can be used to regulate the voltage of the PTC to ensure that the fuel temperature rises rapidly in a short time at low environment temperature. |
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