Thursday, 5 June 2014

THERMAL MICROINJECTOR by mosesdhilipkumar

                            THERMAL MICRO INJECTOR 

                           Today, the major problem which troubles the engineers is controlling the emissions from an automobile with out sacrificing its efficiency. The one way to solve the problem is utilizing the alternate fuels which will be an Eco friendly. But the main disadvantage is the power output from such alternate fuels is less compared to the conventional fuels such as petrol and diesel. So through this paper we present the various advanced technologies of fuel injection which will be an Eco friendly as well as an efficient one.

This paper reports a new application of a thermal micro injector for fuel injection. The paper estimates the ejected velocity of the diesel fuel droplet, and the minimum temperature for bubble formation. The effective fuel spray penetration using the thermal micro injector is explained elaborately. Analysis of the temperature profile evolution and activation curve between water and diesel fuel is helpful for optimization of the micro injector design. The micro injector is fabricated using combined surface and bulk micro machining. Also we have discussed some advantages of the micro injector over the conventional fuel injector 
The fuel injection system is the heart of the internal combustion engine. The function of the injector is to provide fuel to the engine chamber. The fuel will be atomized into small droplets, and begin to evaporate as it moves away from the nozzle and mixes with hot air. The fuel-air ratio is not uniform across the engine chamber because of the complexity of the mixing process. The fuel injection system mainly deals with the atomization step for a typical combustion engine sequence that consists of
                                    1. Atomization,
                                   2. Vaporization,
                                   3. Air entrainment,
                                   4. Ignition, and
                                   5. Combustion.
The typical nozzle diameter for a diesel fuel injector lies between 200 µm and 1000 µm, while the ratio of the length to diameter of the nozzle ranges from 2 to 8. The fuel injection pressure is usually very high (20-170 MPa). Also, the temperature in the cylinder at the time of injection is about 1000 K . The diameter    of a typical diesel fuel droplet with a back pressure of 39.3 MPa (5700 psi) ranges from 10 µm to 100 µm, with the average about 51 µm (0.002 in)


The operating principle of micro injector is similar to that of commercial thermal inkjet print heads. The thermal jet technique uses thermal energy to grow bubbles inside a chamber, functioning as a pump to eject droplets. Fig. 2 illustrates the droplet ejection sequence of a typical thermal jet. The jet uses an electric current pulse to boil liquid inside the micro chamber. The expanding bubble pressurizes the chamber and ejects a column of liquid through a nozzle. The liquid column further breaks into a sequence of droplets through the interaction between surface tension and inertial force.

After the liquid column is separated from the nozzle, the chamber is refilled by liquid from the manifold via the capillary force. The size of a fuel droplet highly depends on the shape and size of the micro nozzle. A monolithic silicon micro injector has been fabricated using MEMS technologies and successfully demonstrated the ability of single-droplet ejection with water and ink as working fluids. 

thank you for your support by moses dhilip kumar.BE

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