Measuring And Analysis Of Diesel Fuel Temperature In High Pressure Pipe Heated By PTC Materials

The researchers have paid more attention to the cold starting andemissions of Diesel engine. Therefore, utilizing the heaters to preheat diesel fuelbecomes an important research area at present. PTC (positive temperature coefficient)materials are used as heaters, which have a lot of characteristics, such as simplestructure, safe and rapid heating, and stable heating temperature around its Curietemperature. If the voltage is a fixed value, the thermal power of PTC materialsrapidly changes to stabilize its temperature fluctuation. So the heaters made of thesematerials have the characteristic of self temperature regulation.In order to improve the cold starting and reduce the emissions of Diesel engine,the paper presents a new method, which is heating diesel fuel in the high pressurepipe by PTC materials to raise the temperature of diesel fuel and improve itsatomization effect. At first, a heat transfer model of PTC materials heating diesel fuelis constructed to analyze the heating effects of static and flowing diesel fuel; then thediesel fuel heating system by PTC materials is also set up to measure the temperatureof injecting oil under different heating time and pump’s rotating speed; at last, inorder to realize testing for fuel injection temperature without disassemble, a BPnetwork model is designed according to the test results.The dynamical models for both the controlled object and PTC materials arepresented by the way of the lumped parameter, and its heating effects are alsosimulated and analyzed. The calculation results show that the diesel fuel in the highpressure fuel pipe is heated by the PTC materials effectively. The PTC materials of373K Curie temperature can heat the diesel fuel from293K to371K in60s.Meanwhile, the heating law by PTC materials heating diesel fuel in the high pressurefuel pipe of engine is also summarized. Then the paper studies the heating effortswhen the pump works. A heating model of high-pressure tube was brought forward,and the pressure of tube measured at a certain Diesel engine as the computationalboundary condition. The heating effect of flowing diesel fuel is also simulated. Simulation results show that the heating efforts decline during dynamic heating.When the Curie temperature is398K and the heating length is500mm and700mm,the diesel fuel temperature at the outlet is330K and366K respectively. If the Curietemperature of PTC materials is513K and the heating length is105mm, theaverage diesel fuel temperature at the outlet is329~338K. The simulationresults also show that longer heating length would ensure the temperature of dieselfuel stable. Therefore, Curie temperature of PTC materials and the heatinglength must be balanced to achieve better test results.The diesel fuel heating system by PTC materials is also set up, which based onthe pump bench. Some measuring points are fixed at outer wall of fuel pipe andinjector. There are5points which are used to measure temperature of outer wall offuel pipe,3points are at heating zone and2points are out of the heating zone, all ofthe points are separated by a space of3.5cm. The static diesel fuel is heated by PTCmaterials at first, when the temperature of diesel fuel is constant, measure theinjection temperature under different rotating speed of pump. The test results showthat if the Curie temperature is240℃, voltage is24V, and heating zone is10.5cm, the increasing rate of temperature is faster, but the stability temperature islower at the high rotation rate, and the temperature of injecting oil rises up to15~20℃in100s. The test results also show that the temperature of outer wall of pipe canbe heated to180℃, as the fuel pump operating, the PTC materials heater changes itsresistance to control its power in order to maintain a better heating effect, and thetemperature rises along the diesel fuel flowing direction.In the real car test, it’s difficult to measure the temperature in the combustionchamber. So this paper designs a three-layer BP network model for estimating thetemperature of injecting oil. The temperature of outer wall of pipe is the inputvariable and the temperature of injecting oil is the output variable. The estimatingresults show that the model is effective and feasible, and this can realize thenondestructive testing for fuel injection temperature.