Patent Publication Number: US-2007119390-A1

Title: System and method for operating an internal combustion engine

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to internal combustion engines, and more particularly to method of operating an internal combustion engine in response to engine loads.  
     BACKGROUND  
      In a reciprocating internal combustion engine, a mixture of air and fuel is generally combusted within a cylinder in order to convert chemical energy into thermal energy. The high-pressure gases resulting from this combustion expand against a piston that is adapted to reciprocate within the cylinder and drive a rotating crankshaft. Thus, the chemical energy of the fuel is ultimately converted into mechanical energy that may be used to power an automobile or any other mechanism  
      One of the challenges associated with such an engine is appropriately timing the start of combustion during the engine cycle. This is particularly true for spark-ignited (SI) engines, which control the start of combustion by appropriately timing a spark plug that ignites an air-fuel mixture within the cylinder. The spark plug is often timed such that the start of combustion occurs when the piston is positioned near the top, or head, of the cylinder during the end of its reciprocal movement.  
      However, during the compression stroke of the piston, the increased pressure within the cylinder raises the temperature of the air-fuel mixture. If the temperature is raised high enough, the mixture will uncontrollably detonate or self-ignite without the use of a spark plug. The result is a phenomenon known as engine “knock” or “ping,” which generates pulses of extremely high pressure throughout the engine. In some cases the piston will still be moving towards the cylinder head when self-ignition occurs. As such, the piston cannot simply reverse its motion to ease the build-up of pressure in the cylinder and the engine may become permanently damaged.  
      In order to limit the temperature and pressure of the air-fuel mixture at the end of the compression stroke, the static compression ratio of an SI engine is typically kept within a particular range of values. For example, the ability of a fuel to resist self-ignition is generally determined by its anti-knock index (AKI), which is commonly referred to as the octane number (ON) or octane rating of the fuel. Most gasoline fuels for automobiles have octane numbers ranging from 87 to 93. In order to avoid self-ignition with these “pump fuels,” the static compression ratios of SI engines are typically kept between approximately 8:1 and approximately 11:1.  
      Some SI engines may experience knock despite these relatively low static compression ratios. For example, many high performance and racing engines are equipped with a supercharger or turbocharger to increase the net power output of the engine. These forced induction systems compress the air supplied to the cylinder so that a greater amount of the air-fuel mixture can be combusted during each engine cycle. Thus, supercharges and turbochargers provide the engine with an “effective” compression ratio, which is basically the sum of the static compression ratio plus the additional compression resulting from the forced induction.  
      The effective increase in compression ratio raises the temperature and pressure within the cylinder to levels unsuitable for regular pump fuels (87 to 93 ON). A higher octane fuel must therefore be readily available to prevent engine knock during peak operating conditions. More specifically, the octane number of the fuel supplied to the engine at peak operating conditions must be sufficient to resist self-ignition at the pressures and temperatures associated with the peak conditions.  
      One approach to addressing this problem is to inject alcohol into the manifold of the engine when the effective compression ratio increases. Alcohol fuels, such as methanol and ethanol, are generally capable of withstanding higher compression ratios because of their relatively high heats of vaporization (h fg ). In other words, alcohol fuels generally have higher rates of evaporative cooling than conventional pump fuels and thus are more effective at cooling the charge and cylinder walls within the combustion chamber. Water injection has also been used in internal combustion engines for substantially the same reasons.  
      While injecting alcohol may suffice for some applications, there are many drawbacks associated with such fuels. In particular, alcohol fuels only offer a limited increase in compression ratio. Both methanol and ethanol have octane numbers of approximately 100, which is generally not sufficient to prevent self-ignition under the pressures and temperatures experienced by racing engines. Additionally, alcohol fuels only have about half of the energy content as conventional gasoline fuels. This means that almost twice as much alcohol must be burned to give the same energy input to the engine as gasoline. Unless the storage tank for the alcohol injection system is relatively large, the duration over which an engine will be able to operate at high compression ratios without refilling the tank may be limited. Furthermore, alcohol fuels may be more corrosive than gasoline on fuel lines, storage tanks, gaskets, and other metal engine parts. These and other disadvantages are the primary reasons why alcohol fuels have not been used as the main source vehicle fuel in most countries.  
      Another approach to preventing knock in a forced induction system is to convert regular octane fuel into high octane fuel by adding a racing fuel concentrate. Racing fuel concentrates are petroleum distillates (UN no. 1268) that can be mixed with pump fuel to produce a significant increase in octane number. For example, Torco® Racing Fuels produces an unleaded concentrate as part of its “Mach-1” fuel series that, when blended with a 93 octane super unleaded fuel, makes up to a 104 octane race fuel. Torco® also produces a leaded concentrate as part of its Mach-1 series that can be mixed with 100-octane low-lead aviation fuel to get up to 112 octane race fuel. The concentrates are typically blended with pump fuel within the engine&#39;s fuel tank or within a separate container and subsequently supplied to an empty fuel tank. Thus, whenever a racing fuel concentrate is used, the engine&#39;s fuel tank is filled with a high octane fuel so that the engine does not experience knock.  
      At relatively low loads, however, the effective compression ratio of the engine is substantially the same as the static compression ratio and a higher octane fuel is not needed. For example, in a supercharged engine the supercharger is driven by the engine&#39;s crankshaft. At low RPM&#39;s, the air supplied to the cylinder will not be significantly compressed and a regular octane fuel (87 to 93 ON) will be sufficient to operate the engine without experiencing knock. Any high octane fuel supplied to the engine during these low loads will not generate additional power or improve fuel economy. Therefore, the racing fuel concentrate used to make the high octane fuel is essentially wasted until the engine begins to experience the pressures and temperatures associated with higher loads (i.e., higher effective compression ratios). This waste is particularly undesirable due to the high costs associated with the racing fuel concentrate.  
     SUMMARY OF THE INVENTION  
      The present invention provides a method of operating an internal combustion engine in a manner that involves supplying amounts of racing fuel concentrate to the intake manifold of the engine on an as-needed basis. Such a method helps eliminate the wasted costs associated with the current methods of using racing fuel concentrate, as will be apparent from the description below.  
      More specifically, the method comprises supplying a primary fuel having a first octane rating to the intake manifold. For example, the primary fuel may be a gasoline “pump” fuel with an octane rating of 87. In order to bring the primary fuel to a second octane rating that is greater than the first octane rating, an amount of racing fuel concentrate is supplied to the intake manifold in response to a signal associated with the engine load. The racing fuel concentrate is a low-solubility, petroleum distillate that has been processed as premium racing fuel. For example, the racing fuel concentrate may be Torco® Mach Series Accelerator Race Fuel Concentrate.  
      The method further comprises varying the amount of the racing fuel concentrate supplied to the intake manifold in response to variance of the signal. In this manner, the engine may be designed to run on the primary fuel at relatively low engine loads without experiencing knock. When temperatures and pressures within the engine increase to levels unsuitable for the primary fuel, the racing fuel concentrate may be added to prevent self-ignition within the combustion chamber.  
      The effective compression ratio is increased as the supercharger boost or turbocharger boost is increased. Therefore, hypothetically if it is safe to use a ratio of racing fuel concentrate to gasoline at a volume ratio of 1:80 at 8 PSI boost but unsafe to run a higher boost with the same concentration of concentrate, the concentration must be increased to a hypothetical ratio of 4:80 when the boost pressure reaches 21 PSI, assuming of course that the concentrate can raise the octane level to the desired level. Therefore, in order to achieve that ratio, the amount of concentrate per 80 volume units of gasoline needs to be increased hypothetically from 1 to 4 volume units, for example. The present system varies concentration of the racing fuel additive per unit volume of gasoline, depending on the boost level and resultant effective compression ratio.  
      Various systems for implementing such a method are also provided herein. In several of the systems, the signal associated with the engine load is the air pressure of the engine manifold. These systems are particularly suited for engines having a forced induction system, such as a turbocharger or supercharger, that increases the effective compression ratio of the engine as the load increases. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.  
       FIG. 1  is a schematic view of a system for operating an internal combustion engine;  
       FIG. 2  is a schematic view of an alternative system that incorporates an electronic control unit for operating an internal combustion engine;  
       FIG. 3  is a schematic view of a further system for operating an internal combustion engine, the system incorporating a flow valve;  
       FIG. 4A  is a cross-sectional view of showing the flow valve of  FIG. 3  in a closed position; and  
       FIG. 4B  is a cross-sectional view showing the flow valve of  FIG. 3  in an open position. 
    
    
     DETAILED DESCRIPTION  
       FIGS. 1-3  illustrate various systems for operating an internal combustion engine. Each of the systems may be used to implement one or more methods according to the invention. More specifically, each of the systems enables racing fuel concentrate to be supplied to the engine on an as-needed basis. Although only three systems are shown and described herein, those skilled in the art will appreciate from the following description that other systems and arrangements may be used to implement methods according to the invention.  
      As a preliminary matter, the term “racing fuel concentrate” refers to a petroleum distillate (UN no. 1268) for premium racing fuels. In other words, the term refers to a product made from crude oil that has been distilled in a refinery and processed in a manner consistent with the production of racing fuels. One example of such a product is Torco® Mach Series Accelerator Race Fuel Concentrate. Racing fuel concentrates typically have a solubility in water of less than approximately 25 percent by volume, and in some cases, may even have a solubility of approximately nil. Racing fuel concentrates also have a specific gravity at 60 degrees Fahrenheit of less than approximately 0.79, and more preferably, a specific gravity between approximately 0.74 and approximately 0.76.  
      The most important property of racing fuel concentrates, however, relates to their ability to increase the octane rating (anti-knock index) of pump fuels when mixed therewith. Only a small amount of racing fuel concentrate is needed to significantly raise the octane number of gasoline. For example, when 80 parts of 93-octane gasoline is mixed with one part of Torco® Mach-1 Unleaded Race Fuel Concentrate, the octane number of the gas increases to 97. When 80 parts of 93-octane gasoline is mixed with two parts of Torco® Mach-1 Unleaded Race Fuel Concentrate, the octane number of the gas increases to 104. And finally, when 80 parts of 93-octane gasoline is mixed with four parts of Torco® Mach-1 Unleaded Race Fuel Concentrate, the octane number of the gas increases to 107. In order to produce such increases, the octane rating of the racing fuel concentrate itself must be greater than 120.  
      As mentioned above,  FIG. 1  shows one example of a system  10  for supplying racing fuel concentrate to an engine on an as-needed basis. The system  10  includes a fuel pump  20 , a supply or tank  22  of racing fuel concentrate, a pressure regulator  24 , and one or more fuel injectors  26 . The fuel pump  20  is activated by a switch  32  once the engine experiences a certain load. For example, in an engine with a forced induction system, the switch  32  may be designed to activate the fuel pump  20  when the air pressure in the manifold of the engine reaches a predetermined “set point.” The activated pump then delivers racing fuel concentrate from the supply  22  to the fuel injectors  26  via fuel lines  34 . The pressure regulator  24  and a return fuel line  36  regulate the pressure of the racing fuel concentrate delivered to the fuel injectors  26 , which ultimately discharge the concentrate into the intake manifold of the engine.  
      The system  10  shown in  FIG. 1  is designed to supplement the engine&#39;s normal fuel supply system (not shown). In other words, a primary fuel having a first octane rating, such as 93-octane gasoline, is supplied to the intake manifold of the engine by separate fuel injectors (not shown). The engine may in fact be designed to run entirely upon the primary fuel under low and normal load conditions. For example, consider a supercharged, or “boosted,” engine having an 8:1 static compression ratio. Such an engine is generally capable of operating solely on the 93-octane gasoline until approximately 8 lbs. of “boost,” or positive air pressure, are added to the manifold. The amount of boost in a supercharged engine is associated with the engine load because the output of the engine drives the supercharger.  
      By the time the supercharger adds approximately 8 lbs. of boost, the effective compression ratio of the engine is approximately 12.4:1. At higher loads the engine will begin experiencing pressures and temperatures that would ordinarily cause the 93-octane fuel to self-ignite. The system  10  prevents this problem by supplying the racing fuel concentrate to the intake manifold to appropriately increase the octane rating of the 93-octane fuel. Thus, for the purposes of this example, the “set point” for the switch  32  is approximately 8 lbs. of boost. As loads continue to increase beyond the set point, the pressure regulator will be referenced to adjust the flow of racing fuel concentrate to the fuel injectors  26 . Such an arrangement allows the amount of racing fuel concentrate supplied to the intake manifold to be instantaneously adjusted in response to variance of the engine load.  
      In the example shown in  FIG. 2 , the system  10 ′ further includes an electronic control unit (ECU)  50  to monitor engine load conditions. For example, the electronic control unit  50  may be used to monitor the manifold air pressure (i.e., boost), revolutions-per-minute (RPM), or other signals associated with engine load. This information is processed by the electronic control unit  50  to generate injection command pulses that are communicated to the fuel injectors  26 . Thus, the electronic control unit  50  may be used to adjust the injection time of the fuel injectors  26 , and thus the amount of racing fuel concentrate supplied to the manifold, in response to signals associated with the engine load.  
      In the example shown in  FIG. 3 , the system  10 ′ further includes a flow valve  70  to control the amount of fuel delivered by the fuel injectors  26 . As shown in  FIGS. 4A and 4B , the flow valve  70  comprises a housing  72  that has a first chamber  74  communicating with the manifold air pressure ( FIG. 4B ) and a second chamber  76  adapted to receive the racing fuel concentrate through an intake passage  80 . A diaphragm  84  positioned in the first chamber  74  is operatively connected to a needle  88  extending through the second chamber  76 . The needle  88  has a tapered portion  92  that contacts a seat  96  within the second chamber  76  such that the second chamber  76  is divided into first and second portions  98 ,  100 . This arrangement prevents racing fuel concentrate from flowing through the second chamber  76  and into an outtake passage  104 .  
      The diaphragm  84  is adapted to move in response to the manifold air pressure of the engine. However, a spring  108  associated with the needle  88  is adapted to resist such movement. Thus, when the manifold air pressure exceeds the resistance of the spring  108 , the diaphragm  84  and needle  88  will move downwardly to create an opening between the seat  96  and tapered portion  92  ( FIG. 4B ). Racing fuel concentrate can then flow from the intake passage  80 , through the second chamber  76 , and into the outtake passage  104 , where it is ultimately delivered to the fuel injectors  26  ( FIG. 3 ). If the manifold air pressure continues to increase, the tapered portion  92  will move further away from the seat  96  so that a greater amount of racing fuel concentrate may be delivered to the fuel injectors  26 .  
      In each of the examples discussed above, racing fuel concentrate is delivered to the intake manifold of an engine only when it is necessary to increase the octane rating of the primary fuel and prevent engine knock. In order to further ensure that the engine will not be damaged by knock, the systems shown in  FIGS. 1-3  may incorporate various safety features. For example, after the fuel pump  20  has been activated, a pressure switch (not shown) may be used to monitor the pressure of the racing fuel concentrate delivered to the fuel injectors  26 . The pressure switch is adapted to be activated when the system reaches a minimum pressure set point. If this event does not occur within a predetermined time delay after the pump has been activated, a rev-limiter (not shown) will automatically limit the RPM&#39;s of the engine. Thus, the pressure switch ensures that sufficient racing fuel concentrate is discharged into the manifold before the engine begins to experience conditions that would otherwise lead to knock.  
      While the invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, the invention may apply to naturally aspired engines in addition to engines having forced induction systems. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicants&#39; general inventive concept.