EP2176592A2

EP2176592A2 - Improved fuel utilization

Info

Publication number: EP2176592A2
Application number: EP08771988A
Authority: EP
Inventors: Raymond Bryce Bushnell; Anthony Dean; Danny Robert Lewis; Marcus Dehaas
Original assignee: Vapor Fuel Technologies LLC
Current assignee: Vapor Fuel Technologies LLC
Priority date: 2007-07-02
Filing date: 2008-06-26
Publication date: 2010-04-21
Also published as: CN101802501A; WO2009006177A3; BRPI0812991A2; AU2008270608A1; JP2010532445A; WO2009006177A2; US20080032245A1

Abstract

Embodiments of the present invention provide a fuel supply system for combustion engines, whereby the temperatures of an oxidizer and fuel may be increased so that the temperatures approach but do not achieve an auto-ignition temperature for the fuel charge. The fuel charge may result in substantial improvements in fuel efficiency.

Description

IMPROVED FUEL UTILIZATION

Related Applications The present application is related to and claims priority to U.S.

Provisional Application no. 60/947,623 filed on July 2, 2007, and U.S. Non- Provisional Application No. 11/871 ,743 filed on October 12, 2007.

Technical Field Embodiments of the present invention relate to the field of providing vaporized or liquid fuel to engines, and more particularly to vapor and liquid fuel systems where various parameters of the fuel mixture may be varied to increase the efficiency of a given fuel charge.

Background and Brief Description

Vaporizing fuel prior to its entrance into the cylinder can lead to improved performance, particularly with respect to substantially improved fuel economy. Applicants have discussed the advantages and various inventions surrounding vapor fuel systems in many of their current patents and pending applications (See, U.S. Patent Nos. 6,681 ,749; 6,907,866; 6,966,308; 7,028,675; and Application Numbers 11/465,792 and 11/421 ,698). While some of these patents and applications teach advantages of running an engine "lean" (i.e., at an air to fuel ratio of greater than about 15 to 1 ), they also teach improving fuel economy in conventional systems that are designed to operate at current stoichiometric conditions, such as an air to fuel ratio around 14.7 to 1.

More recently, systems have been focused on increasing the temperature of a fuel charge once it enters the combustion chamber to a point where the mixture of air and fuel spontaneously ignite. The low end temperature at which typical grade gasoline begins to ignite, in such a manner, is around 500° F. Most systems are achieving this necessary temperature through increased compression ratios. Examples of such systems include Controlled Auto Ignition (CAI) and Homogeneous Charge Combustion Ignition (HCCI). These systems have disadvantages and are not well suited for dealing with transients, such as periods of acceleration or deceleration. One of the disadvantages that may stem from the wide ranges and diversity of temperatures required for the spontaneous ignition of a given fuel charge (e.g. 500°-1100° F). For example, these systems attempt to ignite the entire charge at one moment in time. Because of this, their temperatures are generally elevated towards the higher end of the temperature range. This wide range of ignition temperatures combined with elevated ignition temperatures may allow a fuel charge to prematurely ignite, for example before the piston reaches top dead center, and may result in a decrease in efficiency and possible engine damage. Conversely, ignition temperatures that are not elevated may contribute to an environment conducive to longer combustion durations, where components having lower ignition temperatures ignite first and then propagate, like a forest fire, through the components requiring higher ignition temperatures.

Additionally, various ones of these systems may also require substantially steady state conditions to function efficiently. For example, in an HCCI mode, there is no sparking device to trigger the combustion event. Rather, combustion is dependent solely upon the conditions within the cylinder, i.e., temperature, pressure, air-to-fuel ratio ("AFR"), fuel state, and exhaust gas recirculation ("EGR"). These conditions are typically varied to control when auto-ignition, and consequently, combustion occurs. If there is a rapid change in any one of these conditions, for example during periods of rapidly increasing loads, then the combustion event becomes unpredictable. As an example, when an engine increases its revolutions per minute

("RPMs") there is less time for the fuel charge to change states within the cylinder. This effectively reduces the likelihood of matching the density of the fuel with the density of the induced air, thereby resulting in an AFR mismatch. This density mismatch may lead to premature ignition, possible engine damage, and unacceptable emissions.

Applicants have developed techniques to improve combustion such that fuel economy may be improved in both vapor and liquid charged systems. In various embodiments, the fuel (liquid or vapor) and air may be independently heated and the densities of each controlled. Upon mixing the air and fuel, an air to fuel ratio of 14.7-1 may be maintained at elevated temperatures prior to entrance into a combustion chamber or within the combustion chamber. In various embodiments, elevating the pre- combustion temperature so that it approaches, but does not achieve, an auto-ignition temperature for a given fuel charge may result in more efficient combustion and a system that is better able to handle transitions. Such may be attributable to several factors including the homogeneity of the fuel charge, increased flame speed, increased in cylinder temperature, and/or the multiple flame fronts encountered. In further embodiments, fuel economy may be improved by altering various other parameters which allow for better control of the combustion of the fuel charge. Such parameters may improve efficiency by also increasing the flame speed and decreasing the combustion duration.

Brief Description of the Drawings

Embodiments of the present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings.

Figure 1 illustrates a block diagram in accordance with various embodiments of the present invention;

Figure 2 illustrates a graphical representation of a relationship between diluting an amount of fuel and the need for improved combustion in accordance with various embodiments of the present invention;

Figure 3 illustrates graphical representations of the various combustion durations with respect to top dead center of various combustion events; Figure 4 illustrates graphical representations of the in-cylinder pressures ("ICP") of the various combustion events illustrated in Figure 3, respectively; Figure 5 illustrates a flow diagram depicting a combustion operation in accordance with various embodiments of the present invention; and

Figure 6 illustrates a flow diagram depicting a combustion operation in accordance with various embodiments of the present invention.

Detailed Description of Embodiments In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments in accordance with the present invention is defined by the appended claims and their equivalents.

Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments of the present invention; however, the order of description should not be construed to imply that these operations are order dependent. The description may use perspective-based descriptions such as up/down, back/front, and top/bottom. Such descriptions are merely used to facilitate the discussion and are not intended to restrict the application of embodiments of the present invention.

The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, "connected" may be used to indicate that two or more elements are in direct physical or electrical contact with each other. "Coupled" may mean that two or more elements are in direct physical or electrical contact. However, "coupled" may also mean that two or more elements are not in direct contact with each other, but yet still cooperate or interact with each other. For the purposes of the description, a phrase in the form "A/B" means A or B. For the purposes of the description, a phrase in the form "A and/or B" means "(A), (B), or (A and B)". For the purposes of the description, a phrase in the form "at least one of A, B, and C" means "(A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C)". For the purposes of the description, a phrase in the form "(A)B" means "(B) or (AB)" that is, A is an optional element.

The description may use the phrases "in an embodiment," or "in embodiments," which may each refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," and the like, as used with respect to embodiments of the present invention, are synonymous.

In various embodiments, fuel efficiency may be improved by causing the fuel charge to be more homogeneous in nature, i.e., the vapor makeup of a given charge has a higher concentration of like components, and correspondingly, more similar ignition temperatures. It has been found that as the fuel vapors become more homogeneous in nature their combustion duration becomes more uniform and, consequently, it becomes easier to find and maintain an optimal temperature for increasing the overall efficiency of the system. Increasing the temperature of the fuel charge to the optimal temperature may, for instance, increase the effective flame speed. By optimizing the temperature of a fuel charge and the timing of a spark assist to initiate ignition of a particular fuel charge, the combustion duration may be more efficient, i.e., a shorter and more uniform combustion duration closer to TDC and at a more optimal crank angle. In various embodiments a variety of fuels may be utilized, including but not limited to, ethanol based fuels, fossil fuels including their derivatives, and hybrid fuels. The invention is not to be limited in this regard.

In various embodiments, efficiency may be improved for fuel charges having a range of ignition temperatures by initiating a chain reaction within the combustion cylinder. For example, given a fuel charge having a range of components, combustion may be initiated via a spark which ignites a portion of the fuel charge and creates a flame front. The flame front and combustion of a portion of the fuel charge may increase the temperature and pressure inside the combustion chamber causing components having lower ignition temperatures to auto-ignite. This auto-ignition may create more flame fronts and consequently further increase the temperature and pressure within the cylinder. The further increases of temperature and pressure may then ignite the components having higher ignition temperatures. This chain reaction may continue until substantially all of the charge has been cooperatively combusted. In various embodiments, as the fuel charge becomes more homogeneous the number of steps in the chain reaction may decrease and resultantly may decrease the combustion duration, which in turn may allow better optimization of the timing and other parameters. In various other embodiments, such a chain reaction may be instigated without the use of a spark, for instance by inducting EGR into the combustion cylinder. Combustion duration generally refers to the period of time it takes for a given fuel charge to combust. Alternatively, and for the purpose of this explanation, flame speed generally refers to the rate at which the fuel is burned. Theoretically, for maximum efficiency, all of the fuel would burn at exactly the same moment. For example, if the entire fuel charge had a spontaneous ignition temperature of 500° F, when that temperature is reached in the combustion chamber all of the fuel would substantially instantaneously ignite thereby transferring the maximum amount of energy possible for that given fuel charge. This, however, is not realistic as fuel contains various components which necessitate different ignition temperatures, and consequently, ignition at different times, i.e., a longer combustion duration. For instance, in current systems, the various components in a charge vary greatly which can cause the ignition temperature of such a charge to vary, often times, by several hundred degrees. Thus to burn a charge having such greatly varied ignition temperatures, more flame fronts are encountered and a significant amount of energy is expended over a longer period of time which in turn decreases fuel efficiency. In various embodiments, improving the homogeneity of the feed stream such that there is a significantly reduced range of ignition temperatures within a given fuel charge, thereby reducing flame fronts and allowing for a more optimal temperature and timing, substantially improves fuel efficiency. In various embodiments, the vapor and/or liquid fuel, prior to being mixed with air or another oxidizer, may be separated into generally like components so that the fuel charge is more homogeneous. Such homogeneity can improve the combustion duration in the situations where the temperature is below or at the temperature required for auto ignition of the similar components in the combustion chamber. In various embodiments, liquid fuel may be viewed as being comprised of fractions that may vaporize at different temperatures. This vaporization can be achieved, for example, by initial heating of liquid fuel at a first temperature (e.g. 70° F) and subsequently increasing the temperature as the differing fractions of the liquid fuel are vaporized and/or decreased vaporization of the fuel is detected. Referred to herein as fractionation, applicants have learned that generally sequentially supplying fractions of vapors to the combustion chamber will improve efficiency by allowing a more predictable and uniform combustion duration which may be adjustably triggered to maximize the energy transfer.

Though not essential, in various embodiments, fractionation may help to decrease the combustion duration by reducing the variation of ignition temperatures within a fuel charge. For example, while various standard ignition engines may utilize a fuel charge having ignition temperatures which may vary between 500° - 1100 ⁰F, fractionation may produce a first fraction of vapor in which the ignition temperatures may vary between approximately 500⁰F - 700 ⁰F, and a second fraction in which the ignition temperatures may vary between approximately 700° - 1100 ⁰F. In various embodiments, the more homogeneous bands may be narrower or wider. Therefore, when the fuel charge is ignited, the "forest fire" effect mentioned earlier may be reduced, i.e., the combustion duration is decreased. With the combustion duration decreased, in various embodiments, the timing of the spark may be adjusted to place the shortened combustion duration substantially just past TDC. This also improves thermal efficiency of the system, as the thermal losses associated with combustion across different ignition temperatures (which occur in systems having wide ranging spontaneous ignition temperatures (e.g. from 500° F to 1100° F)), are reduced.

Heating the fuel and vapor, however, may alter the density of the fuel vapors. Therefore, to maintain a balance the oxidizer may also be heated to alter its density. The heating of the oxidizer may, in various embodiments, work to maintain an AFR that is compliant with emissions standards and/or maintain currently accepted AFR. This AFR, in various embodiments, may be controlled during operation by a density balance control strategy and implemented by a controller. In various embodiments, the density balance control strategy may control the varying densities of both the oxidizer and the fuel vapors by the use of sensors upstream from the combustion event. These sensors may monitor, for example, oxygen, temperature, hydrocarbons, and/or vapor density. Through this monitoring, the sensors may control the heating and/or mixing events, for both the oxidizer and the fuel vapors, to maintain a 14.7 to 1 AFR. By maintaining this ratio, the quantity of the fuel charge may be varied, i.e., diluted relative to the cylinder volume, to achieve efficiency as well as allowing for adjustments to constantly changing combustion strength. In various embodiments, sensors may also or alternatively be employed downstream from the combustion event, and adjustments may be made based on emissions content.

In various other embodiments, it has also been found that increasing the temperature of both the fuel and the oxidizer may generate additional benefits for combustion engines. Applicants have discovered that as the vaporized fuel that is being conveyed to the engine's combustion chamber is mixed with air, condensation may appear. This can happen, for example, as a result of the air having a temperature below that of the liquid fuel vaporization temperature. As the air is mixed with the fuel vapors to achieve the desired air-to-fuel ratio, the cooler temperature of the air reduces the temperature of the vaporized fuel and returns it to liquid form, i.e., it condenses. This condensation may alter the combustion characteristics and/or homogeneity of the fuel charge, thus decreasing efficiency and/or flame speed. Accordingly, in various embodiments, the temperature of the air, vapor, and/or the mixture may be elevated to a point above that required for vaporization so the fuels will remain in vaporized form, homogenously mixed to a desired ratio, and substantially devoid of condensation. Such heat treatment, i.e., the creation of a higher temperature, vapor/air mixture may help achieve improved performance.

Further such heating of the air supply, vaporized fuel, and/or air- vaporized fuel mixture may also further enhance the flame speed of the fuel/air mixture and shorten the combustion duration. This in turn can extend the "lean limit" (i.e., the highest air-to-fuel ratio where the engine can perform satisfactorily, without excessive loss of power, misfire, and/or unacceptable hydrocarbon emissions). This extension of the lean limit may have several advantages, including, but not limited to: (1 ) improving fuel economy and (2) decreasing the amount of NOx produced. This pre-heating may also help to achieve some of the benefits that improve engine performance, including not only preventing condensing of the fuel, but also increasing the flame speed. In various embodiments, the Exhaust Gas Recirculation ("EGR") amount may be increased, which in turn may increase efficiency and fuel economy. EGR, effectively, recirculates a portion of the engine's exhaust (which can be over 1000F) back to the engine cylinders. Mixing the incoming fuel charge with EGR serves to help raise the temperature of the charge in the combustion chamber to thereby increase the flame speed and decrease the combustion duration. It also fills the volume of the chamber with inert gases, mostly nitrogen, carbon dioxide, and steam which not only reduces the amount of fuel charge used while being diluted to match the load requirements, but it allows the air to fuel mixture to remain at a desired stoichiometric ratio (e.g. about 14.7 to 1 ). In one embodiment, the EGR may be between 15% and 30%.

In another embodiment, the temperature of the fuel charge may be raised or lowered by varying both the temperature of the oxidizer mixed with the fuel and/or the amount of EGR allowed into the combustion chamber. In effect, the diluted density due to the increase in temperature of the fuel charge may act as the coarse adjustment to enable a faster flame speed, while the EGR makes finer adjustments that may react to quick changes in conditions.

These temperatures, in another embodiment, may allow for increased efficiency when acceleration is needed, and consequently, the spark plugs (or other ignition source) may be employed to initiate ignition. In one embodiment, the temperature of the fuel vapor may be increased to a temperature just below that which is required to spontaneously ignite the fuel charge, a spark plug may then initiate ignition of the fuel charge just prior to or at TDC, and thus create the necessary increased pressure and temperature to substantially auto-ignite the fuel charge. The increased temperature of the fuel charge combined with the generally homogeneous nature of the fuel charge, in accordance with various embodiments, may lead to a faster flame speed, shorter combustion duration, increased efficiency, and better control.

In various other embodiments, the fractionation discussed above may apply to liquid fuel injected systems, in that the homogeneity of the fuel charge may improve efficiency. In one example embodiment, the liquid fuel may be vaporized, or separated by other methods, and condensed such that the fuel is not thoroughly mixed, but rather separated by generally like components having similar vaporization, auto ignition, condensation temperatures, and/or flame speeds. Such fractions may then be injected into the combustion chamber for combustion. The homogeneity of fuel charge allows the temperature of the fuel charge to be increased so that it approaches, but does not achieve, a substantially similar auto-ignition temperature for the entire fuel charge prior to a spark. Consequently, when the spark is initiated, the decreased combustion duration is allowed to transfer more energy closer to TDC, thereby allowing for improved efficiency.

Additionally, it has been observed that standard onboard computer systems may further enhance the benefits discussed above. For example, in standard onboard computer systems, upon periods of acceleration the amount of EGR is decreased while the timing of the spark plug is advanced. In one embodiment, the reduction of EGR necessitates that more fuel be added to the cylinder, therefore allowing for acceleration. Additionally, the advanced ignition timing causes the spark to occur sooner in the compression cycle, which may be prior to the fuel charge meeting the required ignition temperature and spontaneously combusting. Therefore, in various embodiments, the reduced EGR and the advanced ignition timing may have the effect of decreasing the temperature of the fuel charge and returning the engine to a standard spark initiated ignition mode. This would not be possible if the fuel charge operated at the increased temperatures required for auto-ignition, as is done in current systems (e.g. HCCI). In fact, it might lead to premature ignition of the fuel charge, and consequently, damage to the engine. Furthermore, even in a standard ignition mode, a fuel mixture having a decreased but higher than ambient temperature may still have the effect of decreasing the combustion duration in comparison to non-vaporized and/or non pre-heated fuel.

In an example embodiment, it may be known that vaporizing fuel at 70° F generates a more homogeneous vapor which may substantially spontaneously ignite within a known band of temperatures (e.g. 500° F - 788° F). Consequently, a vapor fuel system in accordance with various embodiments may vaporize a first fraction of gas and adjust the operating conditions to heat the vapor and/or an oxidizer so that the mixture is in a ratio of 14.7-1 and approaches a temperature of 450 ° F, a temperature which approaches but does not achieve spontaneous ignition. Accordingly, in various embodiments, an internal combustion engine having a combustion chamber may then induct the homogenous fuel charge (e.g. fractionized fuel vapors) into the combustion chamber. Thereafter a spark from a spark plug may be used to initiate ignition of the fuel charge. In such an instance, the rate at which the entire fuel charge is expended may be substantially increased thereby increasing the overall efficiency of the engine. As the combustion duration continually decreases, the timing may be changed to position the combustion closer to TDC in order to maximize the energy transfer.

In various embodiments, as thermal efficiency increases, the pressure due to combustion will increase while the duration of the combustion event will decrease. As the combustion duration decreases, the ignition timing may be adjusted to move ignition closer toward TDC, and when the fastest flame speed and shortest combustion duration is reached (e.g. at or near auto ignition), ignition may occur at or close to TDC. In various embodiments, a sensor or sensors and logic may recognize the increased pressure and, in addition to the aforementioned timing change, increase the amount of EGR so the combustion pressure can match the power that would be produced by a normal combustion. The additional EGR will act as filler and substantially dilute the quantity of fuel and air within the cylinder thereby reducing the quantity of fuel consumed, thus improving efficiency while matching the power consumed by standard methods. Moving the ignition timing to a point closer to TDC and diluting the fuel and air quantity by heating the charge, which thus changes the density, and adding EGR are critical elements to matching the power requirement, protecting the engine and improving fuel economy. Reference is made to Figure 1 , which provides a block diagram of the components of a system in accordance with embodiments of the present invention. A combustion chamber 110 may be coupled to a mixer 108 which combines heated air from air intake 104 and air heater 106 with vaporized and/or fractionated fuel from fuel tank 100 and vaporization chamber 102. Additionally, in various embodiments an exhaust system 112 may be coupled to the combustion chamber 110 and/or a mixer 108. The exhaust system 112 allows for recirculation of exhaust, i.e., Exhaust Gas Recirculation ("EGR"). In various embodiments exhaust system 112 may be coupled, directly or indirectly, to other components. The invention is not to be limited in this regard.

In various embodiments, the air (or other oxidizer) mixed with the fuel vapor may be heated by a dedicated heat source (e.g. heating coils disposed within the air flow) or via passive heating from engine or other vehicle components. Further, the air may be heated (e.g. by the engine) prior to air intake 104. In one embodiment a heat source 106 may control the temperature of the air flow and elevate the temperature of the air supply as deemed necessary based on the content of the emissions and/or vaporization temperature of the fractionated fuel vapors. In various embodiments, the air inflow may be controllably elevated in temperature from, for example, a range of about 60° F to 80° F to a temperature of about 100° F to 120° F, or higher. Again, the temperature of the air supply may vary depending on the emission content and/or the temperature required for vaporizing and mixing with the instant fraction of fuel, and may be controlled based thereon. In various embodiments, the air and/or oxidizer may be controllably heated in order to maintain a desired oxidizer-to-fuel ratio. In various other embodiments, the intake air need not be heated. In various embodiments, the liquid fuel in fuel tank 100 may be vaporized in vaporization chamber 102. The vaporization chamber 102 may include a number of heating sources (not shown) to controllably heat the liquid fuel including but not limited to engine component proximity, engine fluids, electrical circuits, independent heating devices, and/or heated air from intake 104 or air heater 106. In various embodiments, the vaporization chamber 102 may vaporize the fuel by fractionation, i.e., heating the fuel in increments so as to improve the homogeneous nature of the fuel vapors. More specifically, in one embodiment, fuel may be transferred from fuel tank 100 to vaporization chamber 102. The fuel may occupy the lower half of the tank, and a heating element and temperature sensor (not shown) may be set to incrementally increase the temperature settings for heating the fuel in the vaporization chamber 102 thereby causing fractionation of the fuel. As mentioned previously, the fractionized fuel is more homogeneous in nature which improves the combustion duration, and consequently, efficiency. In various embodiments, a sensor may monitor various characteristics of the created vapor, and control the further vaporization of the fuel to maintain a desired mixture density and/or homogeneity range. In one embodiment, the air heater 106 may be coupled to the vaporization chamber 102 to facilitate conveyance of the fuel vapors to the mixing chamber 108 and subsequently to the combustion chamber 110. While the air-fuel mixture is being conveyed, however, as previously discussed, there may be the possibility that a part of the mixture may condense to liquid form prior to entering the mixing chamber 108 and/or the combustion chamber 110. In one embodiment, to prevent condensation from taking place, the air heater 106 may establish a temperature of the air at or above the temperature of the of the fractionated fuel vapors. In another embodiment, the fuel vapors carried by the heated air to the mixer 108 may be heated again to a temperature above that which the fractionated fuel was vaporized. This may help to improve burning efficiency as well as prevent condensation in the mixing chamber itself. In various embodiments the mixer 108 may combine the heated intake air and the heated fractionated fuel to form a fuel charge. This mixture may be controlled, by a controller (not shown), in order to maintain a desired oxidizer-to-fuel ratio.

In one embodiment, after the fuel vapors and/or fuel charge have been passed to the combustion chamber 110, a spark plug (not shown) may perform a spark to substantially ignite the fuel charge. The timing of the spark may be adjusted, by a controller, so combustion of a fuel charge may occur after and/or at an optimal crank angle. In other embodiments, the adjustment of the spark may be based on at least the characteristics of the fuel charge/fuel vapors.

After combustion, the exhaust may then be transferred to an exhaust system 112. The exhaust system, in various embodiments, may dispose of the exhaust or recirculate the exhaust gas back to the combustion chamber 110 or the air vapor mixture that is to be combusted. In one embodiment, Exhaust Gas Recirculation ("EGR") may be used to improve efficiency and fuel economy. In various other embodiments, the amount of EGR that is circulated may be determined and controlled by onboard computers and a series of valves (not shown). The optimal percentage of EGR varies and is limited by the fuel characteristics such as the fuel charge's auto-ignition temperature, and the amount of fuel required for various load conditions. Additionally, in other embodiments, the EGR may be circulated to the mixer 108 to increase the temperature of the fuel and/or oxidizer prior to the fuel charge entering the combustion chamber 110. In various embodiments, one or more sensors may be disposed in the feed stream for the combustion chamber 110, and adapted to sense a characteristic of the fuel charge, such as hydrocarbon content, temperature, density, ignition temperature, air to fuel ratio, etc. The sensors may be coupled to an onboard computer, which may in turn adjust various parameters to improve the combustion of the particular charge. For example, if the amount of hydrocarbons in the sensed fuel charge is out of balance, which could result in an incorrect ignition, the amount of EGR may be increased or decreased, the timing may be advanced or retarded, and/or the temperature of the fuel charge may be otherwise increased or decreased. In another example, the density or the temperature of the charge could be sensed and corrected as desired in order to achieve more optimal combustion at normal stoichiometric conditions.

Figure 2 is a graph illustrating a relationship between diluting an amount of fuel to be combusted in a cylinder and the need for more efficient combustion of the fuel to maintain an acceptable level of performance. In various embodiments this may be achieved by adjusting the combustion of the diluted fuel charge based on various characteristics of the fuel charge.

In various embodiments, dilution of a fuel charge may result from vaporizing an amount of fuel and/or mixing the fuel with a heated oxidizer. For example, as an amount of fuel changes phase from a liquid to a gas its density will be reduced. Mixing the fuel with a heated oxidizer may also or additionally reduce the fuel's density. In various embodiments, the fuel and/or oxidizer may be diluted in order to maintain a desired oxidizer-to-fuel ratio, such as for example, about 14.7-to-1. This may allow for the optimization of power and fuel economy while avoiding known NOX issues if a standard catalytic converter is used. With the fuel and/or oxidizer having reduced densities, due to their increased temperatures, the result may be less fuel and oxidizer, by weight, required to fill the combustion cylinder. In this manner, less fuel may be consumed thereby increasing efficiency.

In various embodiments, another effect of the increased temperatures of the fuel and/or oxidizer may be a shorter and more efficient combustion duration. Improved combustion duration may allow a diluted fuel charge to provide acceptable levels of performance by combusting the diluted fuel at an optimized crank angle (e.g. 3 to 15 degrees past TDC). In this manner, increasing the temperature of the fuel and/or oxidizer may not only serve to dilute the fuel charge, but also provide a mechanism for increasing the efficiency of a combustion event to maintain an acceptable performance level. As previously mentioned, in various other embodiments, EGR may also be used to dilute and increase the temperature of a fuel charge.

As shown in Figure 2, a performance line 204 is illustrated. This may represent an acceptable level of performance for a given fuel charge. At line 212, a fuel charge may be diluted by any of the methods previously discussed. At line 212, because the fuel charge has been diluted, there is a need for increased efficient combustion of the fuel charge to produce the desired amount of performance. Similarly, at line 208 a fuel charge is represented as being further diluted with respect to line 212. Therefore, to maintain the same level of performance with respect to line 212, a further increase in temperature and/or efficient combustion may also be needed. Consequently, figure 2 illustrates that as a fuel charge becomes further diluted, there is a need for a more efficient combustion of the diluted fuel charge to maintain a desired level of performance. As illustrated, line 208 produces the same performance with less fuel being utilized. This relationship is more fully described with reference to Figures 3 and 4.

It should be understood that Figure 2 is provided only for the purpose of demonstrating a general relationship between fuel dilution and a need for efficient combustion of the diluted fuel. Figure 2 is not intended to be an exact representation of the illustrated relationship as those of skill in the art will readily recognize. It is merely provided for ease of understanding. Furthermore, the figure may only illustrate a portion of the relationship. Referring now to Figures 3 and 4, a series of graphs 1 -4 illustrate the effect of increased flame speed on the time required to completely combust (combustion duration) an identical quantity of fuel. Graphs 5-8 of Figure 4 illustrate the corresponding in cylinder pressure ("ICP") of the combustion events in Figure 3, respectively.

Referring first to Graph 1 , a typical, slower flame propagation event is illustrated. The flame front begins at the spark plug and continues until the fuel has been combusted or the next cycle begins. The combustion lasts well past the optimal crank angle (e.g. 45-50 degrees past TDC). Because the combustion duration is long, i.e., the fuel is still combusting as the piston moves away from TDC, the ICP is also relatively low as seen in graph 5 of figure 4.

Referring now to Graph 2, a more ideal combustion event is illustrated. Graph 2, demonstrates a nearly spontaneous ignition, or auto- ignition, of the same quantity of fuel as combusted in graph 1. As shown, the combustion duration is much faster, i.e., the entire quantity of fuel is consumed faster. This fast combustion duration places most of the combustion just passed TDC. This leads to an increase in pressure at TDC as seen in Figure 4, graph 6. In comparing graph 6 with graph 5, it can be seen that as the combustion duration is decreased and the timing optimized at TDC, the same amount of fuel creates a greater amount of pressure over a smaller change in crank angle, and consequently, the engine power is increased.

Graphs 3 and 4 illustrate a spark assisted auto-ignition as discussed above with reference to various embodiments. In the graphs, the conditions within the cylinder are very close to those needed to support auto-ignition when the spark plug ignites prior to TDC. In graph 3, the resulting flame front quickly raises the temperature and pressure to a point where the remaining fuel substantially auto-ignites. In graph 4 the combustion event requires more fuel be burned as a result of the flame in order to achieve the conditions required to support auto-ignition, increased pressure and temperature. Graph 4 is therefore, not as efficient as graph 3. This becomes apparent when comparing the ICPs, graphs 8 and 7. Because the combustion duration of graph 4 is slightly longer than that of graph 3, the ICP of graph 8 is slightly less than that of graph 7, and consequently, slightly less efficient. While graph 8 is slightly less efficient than graph 7, it can be seen that both Graphs 8 and 7 have ICPs greater than that of graph 5, the slow flame propagation event.

The increases of ICP in graphs 6, 7, and 8, relative to graph 5, illustrate an increase in efficiency that may be possible. More specifically, in graphs 6, 7, and 8, the fuel may be diluted to match the ICP of graph 5. This translates into less fuel accomplishing the same amount of work as the typical flame propagation event.

These graphs are not intended to be exact illustrations of the occurrences but rather a general illustration of the effect of various combustion durations/ flame speeds. Referring now to Figure 5, a flow diagram of a combustion operation

500 is illustrated in accordance with various embodiments of the present invention. The operation may begin at block 502, and progress to block 504 where the temperature of the fuel charge is adjusted. In various embodiments, adjusting the temperature of the fuel charge may comprise heating both an oxidizer component and/or a fuel component prior to inducting the fuel charge into the combustion chamber. In various embodiments, this heating may be accomplished by combining exhaust-gas- recirculation with the oxidizer and/or fuel component.

At block 506, in accordance with various embodiments, adjustments to the temperature and/or amounts of oxidizer and/or fuel may be monitored and controlled to maintain a desired oxidizer-to-fuel ratio. If the desired ratio is not achieved, the operation may return to block 504 for further adjusting of the fuel charge. In various embodiments the fuel component may be fractionated prior to being heated, or the fuel component may be fractionated and then condensed back into liquid form. In such a manner the fuel charge may include a liquid fuel component or a vapor fuel component. In various embodiments, after the desired oxidizer-to-fuel ratio is achieved, the operation may continue to block 508 where the fuel charge is inducted into the combustion chamber. Once inside the combustion chamber, the timing of the combustion event may be adjusted to substantially auto-ignite the fuel charge based at least on characteristics of the fuel charge 510. In various embodiments the characteristics of the fuel charge may include the homogeneity of the fuel charge, the temperature of the fuel charge, the combustion duration and/or flame speed of the fuel charge. These characteristics may allow the timing of the initiation of the combustion event to be adjusted so that the fuel charge substantially auto- ignites after a piston reaches top-dead-center in the combustion chamber.

In various embodiments, after the timing of the combustion event has been adjusted to maximize efficiency, the operation may initiate the combustion event in block 512. The initiating of the combustion event, in one embodiment, comprises initiating a spark to substantially auto-ignite the fuel charge. The operation may then end at block 514.

Referring now to Figure 6, a flow diagram of a combustion operation 600, in accordance with various embodiments, is illustrated. The operation may begin at block 602 and proceed to block 604 where a decision is made as to whether the combustion engine is operating in a first mode of operation or a second mode of operation. If the combustion engine is operating in a first mode of operation, the method may continue to block 606 where an amount of preheated fuel is inducted into a combustion chamber. In various embodiments, the amount of preheated fuel may be mixed with an oxidizer and have an oxidizer-to-fuel ratio of approximately 14.7-1. Subsequently, at block 608, an amount of exhaust-gas-recirculation is combined with the amount of preheated fuel. At block 616, the amount of fuel may be ignited. In various embodiments this may be due to the increase in temperature provided by the EGR, or in other embodiments a spark may be used in combination with EGR to ignite the fuel. The timing of the combining of the exhaust-gas-recirculation may be adjusted based at least on characteristics of the amount of preheated fuel. In other embodiments, a spark may be used in conjunction with the amount of exhaust-gas-recirculation to substantially ignite the amount of preheated fuel, as stated above. In such a manner, the first mode of operation may include the spontaneous ignition of a fuel charge. The method may then loop back to decision block 604 where it may be decided, once again, whether a first mode operation or a second mode of operation is desired.

If a second mode of operation is desired, the method may continue to block 610 where an increased amount of preheated fuel is inducted into the combustion chamber. The increased amount of fuel may be needed, in various embodiments, for increased loads, such as during periods of acceleration. After the increased amount of fuel is inducted into the combustion chamber, the method may continue to block 612 where a decreased amount of exhaust-gas-recirculation is combined with the increased amount of preheated fuel. In various embodiments, the combination of an increased amount of preheated fuel and a decreased amount of exhaust-gas-recirculation may substantially reduce the occurrence of a spontaneous ignition, e.g., the decreased amount of exhaust-gas-recirculation may be incapable of substantially igniting the increased amount of preheated fuel. The method may then continue to block 614 where a spark may be performed to substantially ignite the fuel charge. In various embodiments, the spark may be advanced to occur sooner in a compression cycle. In one embodiment the advancement of the spark may be controlled by standard onboard computer systems. After ignition of the fuel charge, the method may loop back to decision block 604. Therefore, in various embodiments, a method of operating an internal combustion engine comprises; creating a generally homogenous vapor or liquid fuel stream (e.g. by fractionizing the fuel); mixing the fuel vapors with heated air to increase the temperature of the air fuel mixture; inducting the air fuel mixture into a combustion chamber; and combusting the air fuel mixture to generate energy has been shown and described. Embodiments may maintain the pre-combustion temperature of the mixture at or near the auto-ignition temperature of a given charge, as well as improve overall efficiency by increasing the flame speed and reducing the overall combustion duration. Coupled with being able to control the timing of the combustion further improves efficiency and the ability of the system to respond to transient conditions. Although certain embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that embodiments in accordance with the present invention may be implemented in a very wide variety of ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments in accordance with the present invention be limited only by the claims and the equivalents thereof.

Claims

ClaimsWhat is claimed is:

1. A method, comprising: adjusting the temperature of a fuel charge so that the temperature approaches, but does not achieve, an auto-ignition temperature; inducting the fuel charge into a combustion chamber; and initiating a combustion event to substantially auto-ignite the fuel charge.

2. The method of claim 1 , wherein the fuel charge includes an oxidizer component and a fuel component; and adjusting the temperature of the fuel charge comprises heating the oxidizer component and/or the fuel component prior to inducting the fuel charge into the combustion chamber.

3. The method of claim 2, further comprising controlling the heating of the oxidizer component and/or the fuel component to maintain a desired oxidizer-to-fuel ratio.

4. The method of claim 1 , wherein the adjusting the temperature of the fuel charge comprises increasing the temperature of the fuel charge to dilute the fuel charge.

5. The method of claim 1 , wherein the fuel charge includes a vapor fuel component.

6. The method of claim 1 , wherein initiating the combustion event comprises initiating a spark to substantially auto-ignite the fuel charge.

7. The method of claim 1 , further comprising adjusting the timing of the initiation of the combustion event to substantially auto-ignite the fuel charge at a desired crank angle based at least on characteristics of the fuel charge.

8. The method of claim 7, wherein the characteristics of the fuel charge include homogeneity, temperature, combustion duration, and/or flame speed of the fuel charge.

9. A method comprising: during a first mode of operation: inducting an amount of preheated fuel into a combustion chamber; and combining an amount of exhaust-gas-recirculation with the amount of preheated fuel to substantially ignite the amount of preheated of fuel; and during a second mode of operation: inducting an increased amount of preheated fuel into the combustion chamber; combining a decreased amount of exhaust-gas-recirculation with the increased amount of preheated fuel, the decreased amount of exhaust-gas-recirculation incapable of substantially igniting the increased amount of preheated fuel; and performing a spark to substantially ignite the increased amount of preheated fuel.

10. The method of claim 9, wherein the first mode of operation further comprises performing an initiation spark in addition to combining the amount of exhaust-gas-recirculation with the amount of preheated fuel to substantially ignite the amount of preheated fuel.

11. The method of claim 9, wherein the second mode of operation further comprises, advancing the performing of the spark to occur sooner in a compression cycle of the combustion chamber.

12. The method of claim 9, wherein the preheated fuel has been fractionated.

13. The method of claim 9, wherein the amount of preheated fuel and the increased amount of preheated fuel are both mixed with an oxidizer, and the oxidizer-to-fuel ratio is maintained at approximately 14.7-to-1.

14. A system comprising: a vaporization chamber including a heating source to vaporize fuel; an air conduit adapted to supply and mix air with the vaporized fuel; and a controller to control the mixture of air and fuel to maintain a desired carbon level in an amount of combustion exhaust.

15. The system of claim 14, wherein the controller further controls the mixture of air and fuel to maintain a desired air-to-fuel mixture.

16. The system of claim 14, wherein: the heating source is adapted to fractionate the fuel and/or increase the temperature of the fractioned fuel; the air conduit includes an air heater adapted to increase the temperature of the air; and the controller is adapted to control the increase in temperatures of the fractionated fuel and/or the intake air to maintain a desired air-to-fuel ratio.

17. The system of claim 16, further comprising: a mixer to combine the heated intake air and the heated fractionated fuel to form a fuel charge; a combustion chamber to combust the fuel charge; and a spark plug to perform a spark to substantially ignite the fuel charge, wherein the controller further controls a timing of the performance of the spark.

18 The system of claim 16, wherein the controller further controls the mixture of the heated intake air and the heated fractionated fuel to maintain an air-to-fuel ratio of the fuel charge.

19. The system of claim 16, further comprising a sensor to monitor at least one of oxygen content, temperature, ignition temperature, carbon content, air-to-fuel ratio, and/or density of the fractionated fuel and/or intake air.

20. A method of combusting a fuel charge comprising: inducting a prepared fuel charge into a combustion chamber; initiating a flame front to ignite a first portion of the prepared fuel charge to increase the temperature and pressure inside the combustion chamber; initiating auto-ignition of a second portion of the prepared fuel charge, as a result of the increase in temperature and pressure inside the combustion chamber; and initiating subsequent flame fronts and/or subsequent auto-ignitions of the remaining portions of the prepared fuel charge to cooperatively and substantially combust the fuel charge.

21. The method of claim 20 further comprising adjusting the timing of the initiating of the flame front to cooperatively and substantially combust the fuel charge at a desired crank angle.

22. The method of claim 20 wherein the prepared fuel charge is fractionated.

23. A method comprising: diluting a fuel charge to be combusted in a combustion cylinder; and adjusting the combustion of the diluted fuel charge to generate a desired power output based at least in part on characteristics of the diluted fuel charge.

24. The method of claim 23, wherein diluting the fuel charge comprises increasing the temperature of an amount of fuel and an amount of oxidizer to generate a diluted fuel charge having an oxidizer-to-fuel ratio of approximately 14.7-to-1.

25. The method of claim 23 wherein adjusting the combustion of the diluted fuel charge comprises substantially combusting the diluted fuel charge at a desired crank angle.