Patent Application
20080060621
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring to
The elements and operation of a fuel injector as described thus far are well known in the prior art.
As discussed hereinabove, it is desirable in an internal combustion engine that the fuel being injected as a liquid for atomization and combustion be at a temperature at or above the flash point temperature for the fuel. This may require heating of fuel such as alcohol-based fuels from an ambient temperature as low as about −30° C. to as high as +120° C. at system fuel pressure, ethanol having a flashpoint of about +77° C. at ambient barometric pressure. The present invention provides a means to accomplish heating of a liquid fuel resident in chamber 36.
Referring now to
Heater element 46 may be formed, within the scope of the invention, by wrapping a cylindrical resistance heater wire (not shown) around substrate 44. However, such an embodiment has disadvantages because a cylindrical wire provides only line contact with substrate 44 and therefore provides relatively poor heat transfer into barrel 14. In an aspect of the invention, heater element 46 comprises a thick film of a ceramic resistance material, applied to wall 15 in any suitable circuit pattern having terminals at each end. The circuit pattern may be, for example, a helical strip with terminals at each end. A typical application process requires coating and/or printing of a plurality of layers followed by firing in a kiln, as is known in the art. Electrical leads 48 are attached to the ends of helical heater element 46 for supply of electricity through element 46 in known fashion.
Preferably, the ceramic material of heater element 46 has a positive temperature coefficient of electrical resistance such that resistance increases as temperature of the element increases. The advantage of a PTC heater element is that it is self-regulating: when current flows through the element, causing a temperature increase, the resistance increases, reducing the current, resulting in an equilibrium of temperature and current. As the element is dynamically cooled, as by passage of cool fuel into chamber 36, the heater is thereby cooled and automatically responds to generate more heat. If fuel flow through chamber 36 stops, as at engine shutdown, the heater element returns to its equilibrium temperature and current which preferably is above the vaporization point of the fuel. Thus, by proper selection of the thickness, width, and helix pitch of the film; thickness of the barrel wall; length of heater element; and heater element driving voltage, a fuel injector in accordance with the invention may be fabricated which automatically keeps a specific fuel such as alcohol heated above the fuel vaporization point even during periods of engine shutdown, permitting rapid and reliable starting of an alcohol-fueled engine even in cold climates. In severe conditions, it may be desirable to provide a thermally insulative jacket 50 over heater element 46 as a part of heater assembly 40. Of course, a heater assembly in accordance with the invention may be dynamically controlled by feedback or open control as desired.
Wall 15 of barrel portion 14 is desirably as thin as is safely practical for a port fuel injector, which may experience internal fuel pressures exceeding 100 bar. The thinner the barrel wall, the more rapid is the thermal response within chamber 36. For a stainless steel barrel, a currently preferred thickness is about 0.7 mm, which exhibits a thermal lag of about 0.7 second between heating on the outside and an equivalent temperature on the inside. It is understood that the barrel may be formed of a suitable material other than metal such as, for example, plastic or ceramic, in order to achieve the desired thermal response.
Referring now to
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
