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
INTRODUCTION:
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)
operation
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.
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