Fuel management system for variable ethanol octane enhancement of gasoline engines

Abstract

Fuel management system for efficient operation of a spark ignition gasoline engine. Injectors inject an anti-knock agent such as ethanol directly into a cylinder of the engine. A fuel management microprocessor system controls injection of the anti-knock agent so as to control knock and minimize that amount of the anti-knock agent that is used in a drive cycle. It is preferred that the anti-knock agent is ethanol. The use of ethanol can be further minimized by injection in a non-uniform manner within a cylinder. The ethanol injection suppresses knock so that higher compression ratio and/or engine downsizing from increased turbocharging or supercharging can be used to increase the efficiency or the engine.

Claims

1. A fuel management system for a spark ignition engine which utilizes port fuel injection and also utilizes direct fuel injection; and where there is a first torque range where direct injection and port injection are both used at the same value of torque throughout the first torque range and where in at least part of the first torque range as torque is increased the amount of fuel that is directly injected is changed so as to obtain knock-free operation and the amount of directly injected fuel used to provide knock-free operation is minimized.

2. The fuel management system of claim 1 where as torque is increased the fraction of fuel that is directly injected is increased to the value that prevents knock.

3. The fuel management system of claim 1 where active control using a knock detector is used to change the amount of fuel that is directly injected as torque is increased.

4. The fuel management system of claim 1 or 2 where open loop control using a lookup table is also used to change the amount of fuel that is directly injected as torque is increased.

5. The fuel management system of claim 4 where a predetermined correlation between knock resistance and fraction of fuel provided by direct injection is employed.

6. The fuel management system of claim 1 where if torque is increased beyond the highest value of torque in the first range of torque, direct injection alone would be required for knock-free operation.

7. The fuel management system of claim 1 where only port fuel injection is used in a second range of torque.

8. The fuel management system of claim 7 where as the torque increases beyond the highest value of torque in the second range of torque, the engine operates in the first range of torque.

9. The fuel management system of claim 7 where as the torque increased beyond the highest value in the second range of torque, the engine operates in the first range of torque; and where if the torque were to be increased beyond the highest value in the first range of torque, direct injection alone would be required for knock-free operation.

10. The fuel management system of claim 7 where the highest torque in the second torque range is the highest torque at which knock-free operation can be obtained with port fuel injection alone.

11. The fuel management system of claim 7 where when spark retard is employed to enable operation with port fuel injection alone where it would not otherwise be used and where the spark retard is controlled by sensed information.

12. The fuel management system of claim 7 where spark retard is employed so that port fuel injection alone can be used where it would not otherwise be used.

13. The fuel management system of claim 1 where spark retard is used to reduce the fraction of fuel that is provided by direct injection.

14. The fuel management system of claim 1 where the amount of directly injected fuel is minimized throughout the first torque range.

15. The fuel management system of claim 1 where the amount of directly injected fuel is minimized from zero torque to the highest torque in the first torque range.

16. The fuel management system of claim 1 where there is third torque range where the highest torque is the highest torque in the first torque range of the operation and where within the third torque range as torque is increased the fraction of fuel provided by direct injection is changed to the value needed to prevent knock.

17. The fuel management system of claim 9 or 16 where the engine is turbocharged.

18. The fuel management system of claim 16 where the amount of direct injection is minimized.

19. A fuel management system for a turbocharged spark ignition engine which utilizes port fuel injection and also utilizes direct fuel injection; and where there is a first range of torque throughout which direct injection and port injection are used at the same value of torque; and wherein as torque is increased the fraction of fuel that is directly injected is increased to a value that prevents knock; and where there is a second range of torque where only port fuel injection is used; and where when torque exceeds the highest torque in the second range of torque the engine operates in the first range of torque.

20. The fuel management system of claim 19 where the second torque range starts at zero torque.

21. The fuel management system of claim 19 or 20 where the highest value of torque in the second region of torque is the highest value of torque at which direct injection is not needed to prevent knock.

22. A spark ignition engine where port fuel injection and direct injection are used and the fraction of fuel provided by direct injection is increased so as to prevent knock that would otherwise occur; and where spark retard is employed to enable reduction of the amount of direct injection that would otherwise be employed.

23. The spark ignition engine of claim 22 where the engine is operated with port fuel injection alone at values of torque where port fuel injection alone would not otherwise be employed.

24. The spark ignition engine of claim 22 or 23 where the spark retard is controlled by detection of knock and by information from another sensed parameter.

25. The spark ignition engine of claim 22 or 23 where without the application of the spark retard the engine is operated with direct injection alone.

26. The spark ignition engine of claim 22 or 23 where without the application of the spark retard the engine is operated with both port fuel injection and direct injection at the same value of torque.

27. The spark ignition engine of claim 22 where without the employment of the spark retard the fraction of fuel provided by direct injection increases with increasing torque.

28. The spark ignition engine of claim 22 where there is a first torque range throughout which port fuel injection and direct injection are used at the same torque and wherein the fraction of fuel provided by direct injection increases with increasing torque in such a way as to enable knock-free operation and where there is a second torque range where only port fuel injection is used and where when the torque exceeds the highest torque in this range, the engine operates in the first torque range.

29. The spark ignition engine of claim 28 where the engine operates in the second torque range between zero torque and the highest torque in the second torque range.

30. The spark ignition engine of claim 22 where spark retard is used to reduce the amount of direct injection to zero from what it would otherwise have been.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of one embodiment of the invention disclosed herein.

(2) FIG. 2 is a graph of the drop in temperature within a cylinder as a function of the fraction of energy provided by ethanol.

(3) FIG. 3 is a schematic illustration of the stratification of cooler ethanol charge using direct injection and swirl motion for achieving thermal stratification.

(4) FIG. 4 is a schematic illustration showing ethanol stratified in an inlet manifold.

(5) FIG. 5 is a block diagram of an embodiment of the invention in which the fuel management microprocessor is used to control a turbocharger and spark retard based upon the amount of ethanol in a fuel tank.

DETAILED DESCRIPTION

(6) With reference first to FIG. 1, a spark ignition gasoline engine 10 includes a knock sensor 12 and a fuel management microprocessor system 14. The fuel management microprocessor system 14 controls the direct injection of an antiknock agent such as ethanol from an ethanol tank 16. The fuel management microprocessor system 14 also controls the delivery of gasoline from a gasoline tank 18 into engine manifold 20. A turbocharger 22 is provided to improve the torque and power density of the engine 10. The amount of ethanol injection is dictated either by a predetermined correlation between octane number enhancement and fraction of fuel that is provided by ethanol in an open loop system or by a closed loop control system that uses a signal from the knock sensor 12 as an input to the fuel management 125 microprocessor 14. In both situations, the fuel management processor 14 will minimize the amount of ethanol added to a cylinder while still preventing knock. It is also contemplated that the fuel management microprocessor system 14 could provide a combination of open and closed loop control.

(7) As show in FIG. 1 it is preferred that ethanol be directly injected into the engine 10. Direct injection substantially increases the benefits of ethanol addition and decreases the required amount of ethanol. Recent advances in fuel injector and electronic control technology allows fuel injection directly into a spark ignition engine rather than into the manifold 20. Because ethanol has a high heat of vaporization there will be substantial cooling when it is directly injected into 135 the engine 10. This cooling effect further increases knock resistance by a considerable amount. In the embodiment of FIG. 1 port fuel injection of the gasoline in which the gasoline is injected into the manifold rather than directly injected into the cylinder is preferred because it is advantageous in obtaining good air/fuel mixing and combustion stability that are difficult to obtain with direct injection.

(8) Ethanol has a heat of vaporization of 840 kJ/kg, while the heat of vaporization of gasoline is about 350 kJ/kg. The attractiveness of ethanol increases when compared with gasoline on an energy basis, since the lower heating value of ethanol is 26.9 MJ/kg while for gasoline it is about 44 MJ/kg. Thus, the heat of vaporization per Joule of combustion energy is 0.031 for ethanol and 0.008 for gasoline. That is, for equal amounts of energy the required heat of vaporization of ethanol is about four times higher than that of gasoline. The ratio of the heat of vaporization per unit air required for stoichiometric combustion is about 94 kJ/kg of air for ethanol and 24 kJ/kg of air for gasoline, or a factor of four smaller. Thus, the net effect of cooling the air charge is about four times lower for gasoline than for ethanol (for stoichiometric mixtures wherein the amount of air contains oxygen that is just sufficient to combust all of the fuel).

(9) In the case of ethanol direct injection according to one aspect of the invention, the charge is directly cooled. The amount of cooling due to direct injection of ethanol is shown in FIG. 2. It is assumed that the air/fuel mixture is stoichiometric without exhaust gas recirculation (EGR), and that gasoline makes up the rest of the fuel. It is further assumed that only the ethanol contributes to charge cooling. Gasoline is vaporized in the inlet manifold and does not contribute to cylinder charge cooling. The direct ethanol injection provides about 13 C. of cooling for each 10% of the fuel energy provided by ethanol. (It is also possible to use direct injection of gasoline as well as direct injection of ethanol. However, under certain conditions there can be combustion stability issues.

(10) The temperature decrement because of the vaporization energy of the ethanol decreases with lean operation and with EGR, as the thermal capacity of the cylinder charge increases. If the engine operates at twice the stoichiometric air/fuel ratio, the numbers indicated in FIG. 2 decrease by about a factor of 2 (the contribution of the ethanol itself and the gasoline is relatively modest). Similarly, for a 20% EGR rate, the cooling effect of the ethanol decreases by about 25%.

(11) The octane enhancement effect can be estimated from the data in FIG. 2. Direct injection of gasoline results in approximately a five octane number decrease in the octane number required by the engine, as discussed by Stokes, et al. Thus the contribution is about five octane numbers per 30K drop in charge temperature. As ethanol can decrease the charge temperature by about 120K, then the decrease in octane number required by the engine due to the drop in temperature, for 100% ethanol, is twenty octane numbers. Thus, when 100% of the fuel is provided by ethanol, the octane number enhancement is approximately thirty-five octane numbers with a twenty octane number enhancement coming from direct injection cooling and a fifteen octane number enhancement coming from the octane number of ethanol. From the above considerations, it can be projected that even if the octane enhancement from direct cooling is significantly lower, a total octane number enhancement of at least 4 octane numbers should be achievable for every 20% of the total fuel energy that is provided by ethanol.

(12) Alternatively the ethanol and gasoline can be mixed together and then port injected through a single injector per cylinder, thereby decreasing the number of injectors that would be used. However, the air charge cooling benefit from ethanol would be lost.

(13) Alternatively the ethanol and gasoline can be mixed together and then port fuel injected using a single injector per cylinder, thereby decreasing the number of injectors that would be used. However, the substantial air charge cooling benefit from ethanol would be lost. The volume of fuel between the mixing point and the port fuel injector should be minimized in order to meet the demanding dynamic octane-enhancement requirements of the engine.

(14) Relatively precise determinations of the actual amount of octane enhancement from given amounts of direct ethanol injection can be obtained from laboratory and vehicle tests in addition to detailed calculations. These correlations can be used by the fuel management microprocessor system 14.

(15) An additional benefit of using ethanol for octane enhancement is the ability to use it in a mixture with water. Such a mixture can eliminate the need for the costly and energy consuming water removal step in producing pure ethanol that must be employed when ethanol is added to gasoline at a refinery. Moreover, the water provides an additional cooling (due to vaporization) that further increases engine knock resistance. In contrast the present use of ethanol as an additive to gasoline at the refinery requires that the water be removed from the ethanol.

(16) Since unlike gasoline, ethanol is not a good lubricant and the ethanol fuel injector can stick and not open, it is desirable to add a lubricant to the ethanol. The lubricant will also denature the ethanol and make it unattractive for human consumption.

(17) Further decreases in the required ethanol for a given amount of octane enhancement can be achieved with stratification (non-uniform deposition) of the ethanol addition. Direct injection can be used to place the ethanol near the walls of the cylinder where the need for knock reduction is greatest. The direct injection may be used in combination with swirl. This stratification of the ethanol in the engine further reduces the amount of ethanol needed to obtain a given amount of octane enhancement. Because only the ethanol is directly injected and because it is stratified both by the injection process and by thermal centrifugation, the ignition stability issues associated with gasoline direct injection (GDI) can be avoided.

(18) It is preferred that ethanol be added to those regions that make up the end-gas and are prone to auto-ignition. These regions are near the walls of the cylinder. Since the end-gas contains on the order of 25% of the fuel, substantial decrements in the required amounts of ethanol can be achieved by stratifying the ethanol.

(19) In the case of the engine 10 having substantial organized motion (such as swirl), the cooling will result in forces that thermally stratify the discharge (centrifugal separation of the regions at different density due to different temperatures). The effect of ethanol addition is to increase gas density since the temperature is decreased. With swirl the ethanol mixture will automatically move to the zone where the end-gas is, and thus increase the anti-knock effectiveness of the injected ethanol. The swirl motion is not affected much by the compression stroke and thus survives better than tumble-like motion that drives turbulence towards top-dead-center (TDC) and then dissipates. It should be pointed out that relatively modest swirls result in large separating (centrifugal) forces. A 3 m/s swirl motion in a 5 cm radius cylinder generates accelerations of about 200 m/s.sup.2, or about 20 g's.

(20) FIG. 3 illustrates ethanol direct injection and swirl motion for achieving thermal stratification. Ethanol is predominantly on an outside region which is the end-gas region. FIG. 4 illustrates a possible stratification of the ethanol in an inlet manifold with swirl motion and thermal centrifugation maintaining stratification in the cylinder. In this case of port injection of ethanol, however, the advantage of substantial charge cooling may be lost.

(21) With reference again to FIG. 2, the effect of ethanol addition all the way up to 100% ethanol injection is shown. At the point that the engine is 100% direct ethanol injected, there may be issues of engine stability when operating with only stratified ethanol injection that need to be addressed. In the case of stratified operation it may also be advantageous to stratify the injection of gasoline in order to provide a relatively uniform equivalence ratio across the cylinder (and therefore lower concentrations of gasoline in the regions where the ethanol is injected). This situation can be achieved, as indicated in FIG. 4, by placing fuel in the region of the inlet manifold that is void of ethanol.

(22) The ethanol used in the invention can either be contained in a separate tank from the gasoline or may be separated from a gasoline/ethanol mixture stored in one tank.

(23) The instantaneous ethanol injection requirement and total ethanol consumption over a drive cycle can be estimated from information about the drive cycle and the increase in torque (and thus increase in compression ratio. engine power density, and capability for downsizing) that is desired. A plot of the amount of operating time spent at various values of torque and engine speed in FTP and US06 drive cycles can be used. It is necessary to enhance the octane number at each point in the drive cycle where the torque is greater than permitted for knock free operation with gasoline alone. The amount of octane enhancement that is required is determined by the torque level.

(24) A rough illustrative calculation shows that only a small amount of ethanol might be needed over the drive cycle. Assume that it is desired to increase the maximum torque level by a factor of two relative to what is possible without direct injection ethanol octane enhancement. Information about the operating time for the combined FTP and US06 cycles shows that approximately only 10 percent of the time is spent at torque levels above 0.5 maximum torque and less than 1 percent of the time is spent above 0.9 maximum torque. Conservatively assuming that 100% ethanol addition is needed at maximum torque and that the energy fraction of ethanol addition that is required to prevent knock decreases linearly to zero at 50 percent of maximum torque, the energy fraction provided by ethanol is about 30 percent. During a drive cycle about 20 percent of the total fuel energy is consumed at greater than 50 percent of maximum torque since during the 10 percent of the time that the engine is operated in this regime, the amount of fuel consumed is about twice that which is consumed below 50 percent of maximum torque. The amount of ethanol energy consumed during the drive cycle is thus roughly around 6 percent (30 percent0.2) of the total fuel energy.

(25) In this case then, although 100% ethanol addition was needed at the highest value of torque, only 6% addition was needed averaged over the drive cycle. The ethanol is much more effectively used by varying the level of addition according to the needs of the drive cycle.

(26) Because of the lower heat of combustion of ethanol, the required amount of ethanol would be about 9% of the weight of the gasoline fuel or about 9% of the volume (since the densities of ethanol and gasoline are comparable). A separate tank with a capacity of about 1.8 gallons would then be required in automobiles with twenty gallon gasoline tanks. The stored ethanol content would be about 9% of that of gasoline by weight, a number not too different from present-day reformulated gasoline. Stratification of the ethanol addition could reduce this amount by more than a factor of two. An on-line ethanol distillation system might alternatively be employed but would entail elimination or reduction of the increase torque and power available from turbocharging.

(27) Because of the relatively small amount of ethanol and present lack of an ethanol fueling infrastructure, it is important that the ethanol vehicle be operable if there is no ethanol on the vehicle. The engine system can be designed such that although the torque and power benefits would be lower when ethanol is not available, the vehicle could still be operable by reducing or eliminating turbocharging capability and/or by increasing spark retard so as to avoid knock. As shown in FIG. 5, the fuel management microprocessor system 14 uses ethanol fuel level in the 295 ethanol tank 16 as an input to control the turbocharger 22 (or supercharger or spark retard, not shown). As an example, with on-demand ethanol octane enhancement, a 4-cylinder engine can produce in the range of 280 horsepower with appropriate turbocharging or supercharging but could also be drivable with an engine power of 140 horsepower without the use of ethanol according to the invention.

(28) The impact of a small amount of ethanol upon fuel efficiency through use in a higher efficiency engine can greatly increase the energy value of the ethanol. For example, gasoline consumption could be reduced by 20% due to higher efficiency engine operation from use of a high compression ratio, strongly turbocharged operation and substantial engine downsizing. The energy value of the ethanol, including its value in direct replacement of gasoline (5% of the energy of the gasoline), is thus roughly equal to 25% of the gasoline that would have been used in a less efficient engine without any ethanol. The 5% gasoline equivalent energy value of ethanol has thus been leveraged up to a 25% gasoline equivalent value. Thus, ethanol can cost roughly up to five times that of gasoline on an energy basis and still be economically attractive. The use of ethanol as disclosed herein can be a much greater value use than in other ethanol applications.

(29) Although the above discussion has featured ethanol as an exemplary anti-knock agent, the same approach can be applied to other high octane fuel and fuel additives with high vaporization energies such as methanol (with higher vaporization energy per unit fuel), and other anti-knock agents such as tertiary butyl alcohol, or ethers such as methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), or tertiary amyl methyl ether (TAME).

(30) It is recognized that modifications and variations of the invention disclosed herein will be apparent to those of ordinary skill in the art and it is intended that all such modifications and variations be included within the scope of the appended claims.