Internal-combustion engines – Charge forming device – Heating of combustible mixture
Reexamination Certificate
1999-07-19
2001-02-13
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Charge forming device
Heating of combustible mixture
C123S558000
Reexamination Certificate
active
06186126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus and method for the utilization of the heat energy normally discarded in the exhaust of internal combustion engines (or from other sources) by converting the heat to mechanical work in a highly efficient manner either using the phase change properties of a working medium or heating a fluid that is pressurized above its critical pressure, thereby increasing the overall efficiency of the engine. The field of application is primarily in internal combustion engines for motor vehicles.
2. Prior Art
The growing utilization of automobiles greatly adds to the atmospheric presence of various pollutants including oxides of nitrogen and greenhouse gases such as carbon dioxide. Accordingly, the need exists for innovations to significantly improve the efficiency of fuel utilization for automotive powertrains.
Internal combustion engines create mechanical work from fuel energy by combusting the fuel over a thermodynamic cycle consisting typically of compression, ignition, expansion, and exhaust. Expansion is the process in which high pressures created by combustion are deployed against a piston, converting part of the released fuel energy to mechanical work. The efficiency of this process is determined in part by the thermodynamic efficiency of the cycle which, in turn, is determined in part by the final pressure and temperature to which the combusted mixture can be expanded while performing work on the moving piston. Generally speaking, the lower the pressure and temperature reached at the end of the expansion stroke, the greater the amount of work that has been extracted.
Conceptually, the work that is performed on the piston can be resolved into two components. One component is the fuel energy released by the combustion process. Another is the compression energy that is returned as the compressed mixture expands again after piston top dead center (TDC) as it naturally would, with or without combustion. When fuel is injected in a liquid state, a phase change (vaporization) occurs which consumes some of the energy present in the compressed mixture that now cannot be reclaimed in the expansion. After combustion has been initiated and expansion of the combustion products begins, the amount of energy in the cylinder available to be delivered via expansion is fixed. At this point all that remains is to expand the high temperature and pressure combustion gases to as near ambient conditions as possible considering the engine design and the properties of the combustion products. Expansion is limited by the fixed maximum volume of the cylinder, since there is only a finite volume available in which combusting gases may expand and still be performing work on the piston. Even if expansion to atmospheric pressure is achieved, the expanded gases are still at high temperature, often exceeding 1000° F. Thus, not only is potential work lost to vaporization of the fuel, but a large amount of potential work is lost as exhaust heat.
A prior art means of utilizing exhaust heat by way of heat transfer to and phase change of a working fluid in a separate system is the well known Rankine Bottoming Cycle. Water is most often used followed by condensation and recycle of the water. Other closed system working fluids may also be used. However, all such systems are costly and have relatively low energy recovery efficiency primarily because much of the energy from the exhaust gas is consumed by the phase change (evaporation) of the working fluid and this energy is mostly lost again in the condenser.
SUMMARY OF INVENTION
The present invention provides a combustion system which includes an expander (bottom-cycle device) and an internal combustion engine (hereinafter, “ICE,” also referred to herein as a “topping device”) wherein the working fluid for the expander is a suitable fuel for the ICE. The superheated fuel vapor from the expander is combusted in the ICE instead of injecting a liquid fuel, thus eliminating loss of energy to fuel vaporization. The invention also involves a method of operating such a combustion system.
The present invention uses either a vaporizable liquid, or a liquid supplied above its critical pressure, preferably a combustible liquid fuel, rather than a heated compressed gas as in prior art, as the working fluid. Thus, the exhaust heat that powers the bottoming cycle is imparted to a liquid rather than a cooled compressed gas. The high pressure vapor fed to the topping apparatus (ICE) results from a phase change from liquid to gas in a heat exchanger. This eliminates the need for compressor cooling and does not require as much handling of high pressure compressed gas. A liquid working fluid such as methanol, or other working fluid having a more favorable critical point than more traditional phase change liquids such as water (steam), could also be chosen. The working fluid can also be combusted directly in the expander, or in an optional fuel reactor, as an additional means of “hear addition” to the bottoming cycle.
In the preferred embodiments of the present invention the expander is a piston device that imparts exhaust gas heat to liquid fuel, rather than to a compressed gas, resulting in a phase change in the fuel (liquid to gas) that provides a superheated vapor which can be used as working fluid for the expander or as pre-vaporized fuel for an engine or both. The expander may employ combustion of the working fluid as an additional form of heat addition (in addition to the heat that induces the phase change and the superheating of the resulting vapor). This combustion of working fluid may take place instead of or in addition to combustion of the fluid in the ICE.
The present invention includes two different embodiments: (1) a first embodiment wherein the expansion stroke of the ICE serves as the expander and (2) a second embodiment which uses a physically separate expander device. Both embodiments utilize the ICE fuel as the primary phase change working fluid, with an option of adding some additional working fluid such as water to enhance the overall exhaust energy recovered.
As noted above, in the first embodiment the expansion stroke of the ICE also serves to expand the phase change working fluid. The phase change working fluid is introduced at the beginning of the expansion stroke of the ICE, expands and is combusted as expansion continues. Maximum useful mechanical work can be extracted with the least additional hardware and cost by this first embodiment.
In all embodiments, a fuel reactor vessel may be added after superheating to remove additional heat energy from the exhaust gases. For example, methanol fuel can be dissociated into hydrogen and carbon monoxide or further reformed in the presence of water vapor to hydrogen and carbon dioxide transforming exhaust waste heat energy into a higher state of chemical fuel energy for subsequent release during combustion.
The separate expander of the second embodiment may utilize two different modes of operation: (1) two stroke and (2) four stroke. The two stroke separate expander receives the superheated working fluid from the phase-change heat exchanger near TDC and expands the high pressure vapor producing useful work to bottom dead center (BDC). The expander then returns to TDC exhausting the working fluid to the intake of the internal combustion engine for subsequent combustion. The four stroke separate expander first receives intake air as the piston travels from TDC to BDC in the first stroke. The air is then compressed as the piston travels to TDC in the second stroke. The superheated phase change fluid is then added during the initial expansion as the piston travels to BDC in the third stroke producing useful mechanical work. Finally, the air and working fluid mixture is then compressed in the fourth stroke and transported to the intake of the ICE, optionally provided a pressurized charge to boost the ICE.
A representation of the ideal thermodynamic cycle is shown in FIG.
1
. The line ab represents the initial intake of ambient air to a cylin
Lorusso & Loud
McMahon Marguerite
The United States of America as represented by the Administrator
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