WO2009057027A1

WO2009057027A1 - Fuel system for improved fuel efficiency utilizing glycols in a spark ignition engine

Info

Publication number: WO2009057027A1
Application number: PCT/IB2008/054408
Authority: WO
Inventors: Daniel Stedman Connor
Original assignee: The Procter & Gamble Company
Priority date: 2007-10-31
Filing date: 2008-10-24
Publication date: 2009-05-07
Also published as: US20090107031A1

Abstract

A fuel system for improved fuel efficiency which can be contained in a single fuel source, such as a fuel tank of a vehicle, having a gasoline phase comprising gasoline or gasohol; and an anti-knock phase comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; such that the anti-knock agent phase is substantially immiscible with the gasoline phase.

Description

Fuel System for Improved Fuel Efficiency Utilizing Glycols in a Spark Ignition Engine

FIELD OF THE INVENTION

A fuel system for improved fuel efficiency which can be contained in a single fuel source, such as a fuel tank of a vehicle, having a gasoline phase comprises gasoline or gasohol; and an anti-knock phase comprising an anti-knock agent comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; such that the anti-knock agent phase is substantially immiscible with the gasoline phase.

BACKGROUND OF THE INVENTION

This invention relates to spark ignition gasoline engines utilizing an antiknock agent which is immiscible with gasoline to improve engine efficiency while being stored in the same containment area/volume or tank of a vehicle.

It is known that the efficiency of gasoline engines can be increased by high compression ratio operation and particularly by engine downsizing. The use of techniques to increase engine efficiency, however, is limited by the onset of engine knock. Knock is the undesired detonation of fuel and can severely damage an engine. If knock can be prevented, then engine efficiency may be increased by up to twenty- five percent.

Octane number represents the resistance of a fuel to knocking but the use of higher octane gasoline only modestly alleviates the tendency to knock. For example, the difference between regular and premium gasoline (octane number of 95) is typically six octane numbers. It is known to replace a portion of gasoline with small amounts of ethanol added at the fuel distributor blending rack. Ethanol has a blending octane number of 110 (see J. B. Heywood, "Internal Combustion Engine Fundamentals," McGraw Hill, 1988, p. 477) and is also attractive because it is a renewable energy, biomas s -derived fuel.

Using a fuel system to deliver mixed octane fuels which are kept separated in two tanks or in one tank separated by a diaphragm and then mixed before injection into an engine is discussed in US 2005/0252489 Al.

It is known that restricting the use of ethanol to the relatively small fraction of time in an engine operating cycle, preferably injecting the ethanol directing into an engine cyclinder separately from gasoline when it is needed to prevent knock in a higher load regime and by minimizing ethanol use only at these times. See US 2006/0102145, US 2006/0102146.

However, the proposed use of two separate tanks in a vehicle is a recognized challenge whether consumers will mind filling up with two fuels in two different fuel tanks. Boston Globe, April 22, 2007, Third Edition, O'Brien, Keith, "Fill 'er up. But with what? - In the fevered search for the fuel of tomorrow, a team of MIT scientists has a surprising solution that just might be the most realistic one of all." Additional proposed solutions include the use of onboard separation methods of ethanol from a gasoline such as fractional distillation or membrane separation. See US 2006/0102136. Gasoline and anhydrous ethanol are miscible in any ratio, i.e., they can be mixed without occurrence of a separate liquid phase. When a certain amount of water is present, however, a separate liquid layer will occur. The occurrence of a separate liquid phase in gasohol is perceived as harmful even though the phase behavior of gasoline-ethanol-water mixtures is totally different from gasoline- water mixtures. See WO06/137725.

There still exists a problem of how to deliver two components to a gasoline engine in a consumer friendly manner that requires little to no change in customary habits. The present invention relates to a fuel having a gasoline phase and an anti-knock phase wherein the two phases are immiscible when held in a defined volume such as a fuel tank.

SUMMARY OF THE INVENTION

The present invention relates to a fuel system comprising gasoline phase comprises gasoline or gasohol; and an anti-knock phase comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; wherein the anti-knock agent phase is substantially immiscible with the gasoline phase.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of the fuel management systems discussed herein.

Fig. 2 is a graph of an engine cylinder pressure as a function of crank angle for a three bar manifold pressure.

Fig. 3 is a graph of charge temperature as a function of crank angle for a three bar manifold pressure. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a fuel system for improved fuel efficiency which can be contained in a single fuel source, such as a fuel tank of a vehicle, having a gasoline phase comprises gasoline or gasohol; and an anti-knock phase comprising an anti-knock phase comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; such that the anti-knock agent phase is substantially immiscible with the gasoline phase.

With reference first to FIG. 1, a fuel management system (10) includes a gasoline engine (20) having at least one combustion chamber, such as an engine cylinder, a fuel processor system (30), a knock sensor (40), a manifold (50) or port area, a combustion chamber injector (130) and a single fuel source (60). The fuel processor system (30) controls the direct injection of an antiknock agent from a combustion chamber injector (130) that is fluidly connected to a single fuel source (60). The single fuel source (60) contains gasoline or gasohol (collectively or individually referred to herein as gasoline). The fuel management system (10) also affects the delivery of gasoline from the single fuel source (60) into manifold (50) or a port area. The fuel management system (10) also communicates with other components of the system (10) as discussed further below. The single fuel source (60) comprises at least two level detection devices (90, 100) for the gasoline (gasoline phase) and the anti-knock agent (anti-knock agent phase), the level detection devices individually indicate the levels (empty, full, or some fraction) of the gasoline and the anti-knock agent in the single fuel source (60). The level detection devices (90, 100) are in communication with the fuel processor system (30) and can individually transmit information regarding the level of gasoline and/or anti-knock agent. This information can be used for informing the vehicle user and may be used to inform other devices such as a gasoline pump at a gas station. In one embodiment, the anti-knock agent phase is dispensed into the single fuel source independently of the gasoline phase. In one embodiment, the anti-knock agent phase and the gasoline phase are dispensed into the single fuel source in a vehicle at the same time.

The single fuel source (60) further comprises at least two feeds to the gasoline engine (20), the first feed for the gasoline (gasoline feed [HO]) and a second feed for the anti-knock agent (anti-knock feed [120]). The gasoline feed (110) is located such that gasoline in a gasoline layer is able to be fluidly conveyed from the single fuel source (60) into the manifold (50), without the anti-knock agent being fluidly conveyed by the gasoline feed (110). The anti-knock feed (120) is located such that the anti-knock agent in an anti-knock layer is able to be fluidly conveyed from a single fuel source (60) to the combustion chamber injector (130) without the gasoline being fluidly conveyed by the anti-knock feed (120).

The amount of anti-knock agent injected is dictated either by a predetermined correlation between octane number enhancement and fraction of fuel that is provided by anti-knock agent or by a control system that uses a signal from the knock sensor (40) as an input to the fuel management system (10). In both situations, the fuel management system (10) will deliver the amount of anti-knock agent to a combustion chamber such as an engine cylinder to preventing knock while minimizing the amount of anti-knock agent needed. In one embodiment, the anti-knock agent phase is injected into an engine cylinder independent of the gasoline phase. In one embodiment, the anti-knock agent phase is injected into an engine cylinder after injection of the gasoline phase into an engine cylinder. The anti-knock agent is directly injected from the combustion chamber injector (130) into the gasoline engine (20) via a combustion chamber such as an engine cylinder. Using a signal from a knock sensor to determine when and how much anti-knock agent must be used at various times in a drive cycle to prevent knock, the fuel management system (10) can be employed to minimize the amount of anti-knock agent that is consumed over the drive cycle. If sufficient anti-knock agent is available in the market, the fuel management system (10) can also be used to employ more antiknock agent than would be needed to prevent knock.

Direct injection substantially increases the benefits of anti-knock agent addition and decreases the required amount of anti-knock agent. Recent advances in fuel injector and electronic control technology allows for tightly controlled amounts of fuel at high pressures injected directly into an engine cylinder in very short time frames rather than traditional fuel injection into the manifold (50). A combustion chamber injector (130) is provided for direct injection of the anti-knock agent into a combustion chamber, such as an engine cylinder of the gasoline engine (20) and a fuel processor system (30) controls injection of the anti-knock agent into the cylinder to control knock. The injection of the antiknock agent can be initiated by a signal from a knock sensor (40), initiated when the engine torque is above a selected value or fraction of the maximum torque where the value or fraction of the maximum torque is a function of the engine speed or initiated upon an increase in pressure on an accelerator pedal of a vehicle or a rate of change in position of the accelerator pedal of the vehicle. The combustion chamber injector (130) injects the anti-knock agent after inlet valve/valves are closed in the combustion chamber, such as an engine cylinder. In one embodiment the injector (20) injects the anti-knock agent tangentially into the combustion chamber or the engine cylinder, preferably at the upper portion of the combustion chamber or upper portion of the engine cylinder.

In the case of anti-knock agent direct injection the charge is directly cooled. 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. In the embodiment of FIG. 1 gasoline is vaporized in the inlet manifold or port injection and does not contribute much to cylinder charge cooling. The high heat of vaporization of the anti-knock agent with its direct injection late in the cycle gives the desired impact of knock suppression. The temperature decrease of the air in the cylinder increases with the amount of oxygen in the anti-knock agent (in terms of the O:C ratio of the antiknock molecule(s)). It is also useful to compare ratios of the heat of vaporization to the heat of combustion, a measure of the potential effects when used as anti-knock agents. This parameter gives a measure of the amount of evaporative cooling for a given level of torque.

Thus when variable anti-knock agent is employed, the fuel processor system (30) needs to adjust the amounts of air, gasoline and anti-knock agent such that the air/fuel ratio is stochiometric. The additional control is needed because, if the air/fuel ratio determined by the fuel processor system (30) were not corrected during the injection of anti-knock agent, the mixture would no longer be stoichiometric. Preferably the fuel processor system (30) can choose the ratio of the anti-knock agent and gasoline.

The octane enhancement effect as discussed herein refers primarily to the decrease in the engine octane requirement rather than an increase in octane of the fuel itself. Relatively precise determinations of the actual amount of octane enhancement from given amounts of direct anti-knock agent injection can be obtained from laboratory and vehicle tests in addition to detailed calculations. These correlations can be used by the fuel processor system (30). Direct injection of gasoline results in approximately a five octane number decrease in the octane number required by the engine, as discussed by J. Stokes, T. H. Lake and R. J. Osborne, "A Gasoline Engine Concept for Improved Fuel Economy— The Lean Boost System," SAE paper 2000-01-2902. Thus the contribution is about five octane numbers per 30K drop in charge temperature. Without being bound by theory, it is believed that the anti-knock agent can decrease the charge temperature, which decreases the octane number required by the engine due to the drop in temperature.

The optimum timing of the injection of anti-knock agent for best mixing and a near homogeneous charge is soon after the inlet valve closes, provided that the charge is sufficiently warm for antiknock agent vaporization. If, on the other hand, a non-uniform mixture is desired in order to minimize anti-knock agent requirements and improve ignition stability, then the injection should occur later than in the case where the best achievable mixing is the goal.

It is important to inject the anti-knock agent relatively quickly, and at velocities which minimize any cylinder wall wetting, which as described below could result in the removal of the lubrication oils from the cylinder liner.

FIG. 2. shows the pressure (a) and the temperature (b) of the cylinder charge as a function of crank angle, for a manifold pressure of 3 bar and a value of β=0.4. For exemplification only, two values of ethanol fractions are chosen, one that results in autoignition, and produces engine knock (0.82 ethanol fraction by fuel energy), and the other one without autoignition, i.e., no knock (0.83 ethanol fraction). Autoignition is a threshold phenomenon, and in this case occurs between ethanol fractions of 0.82 and 0.83. The occurrence of knock at a given value of torque depends upon engine speed. For an ethanol energy fraction of 0.83, the pressure and temperature rise at 360° (top dead center) is due largely to the compression of the air/fuel mixture by the piston. When the ethanol energy fraction is reduced to 0.82, the temperature and pressure spikes as a result of autoignition. Although the autoignition in FIG. 2 occurs substantially after 360 crank angle degrees, the autoignition timing is very sensitive to the autoignition temperature (5 crank angle degrees change in autoignition timing for a change in the initial temperature of 1 K, or a change in the ethanol energy fraction of 1%). In one embodiment, the anti-knock agent is injected into an engine cylinder at about 280 to about 330 degrees crank angle.

Such curves may be compiled via a computer model combining physical models of the anti-knock agent vaporization effects and the effects of piston motion of the anti-knock agentl/gasoline/air mixtures with a state of the art calculational code for combustion kinetics. An example for the calculational code for combustion kinetics may be the engine module in the CHEMKIN 4.0 code [R. J. Kee, F. M. Rupley, J. A. Miller, M. E. Coltrin, J. F. Grcar, E. Meeks, H. K. Moffat, A. E. Lutz, G. Dixon-Lewis, M. D. Smooke, J. Warnatz, G. H. Evans, R. S. Larson, R. E. Mitchell, L. R. Petzold, W. C. Reynolds, M. Caracotsios, W. E. Stewart, P. Glarborg, C. Wang, O. Adigun, W. G. Houf, C. P. Chou, S. F. Miller, P. Ho, and D. J. Young, CHEMKIN Release 4.0, Reaction Design, Inc. , San Diego, Calif. (2004)]. This model uses chemical rates information based upon the Primary Reference gasoline Fuel (PRF) mechanism from Curran et al. [Curran, H. J., Gaffuri, P., Pitz, W. J., and Westbrook, C. K. "A Comprehensive Modeling Study of iso-Octane Oxidation," Combustion and Flame 129:253-280 (2002) to represent onset of autoignition.

Because of the large heat of vaporization of the anti-knock agent, there could be enough charge cooling with early injection so that the rate of vaporization of anti-knock agent is substantially decreased. By injecting the anti-knock agent into the hot end gases in the cylinder, which is the case with injection after the inlet valve has closed, the temperature at the end of full vaporization of the anti-knock agent is substantially increased with respect to early injection, increasing the evaporation rate and minimizing wall wetting.

Injection after the valve has closed may require that a modest fraction of the gasoline (e.g. 25%) be port injected in order to achieve the desired combustion stability. A tumble-like or swirl motion can be introduced to achieve the desired combustion stability. Tangential injection is believed to achieve a swirl motion of the anti-knock agent within the cylinder.

It is preferred that anti-knock agent 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 anti-knock agent can be achieved by stratifying the end gases and the anti-knock agent. A swirl motion (from tangential injection) is not affected much by the compression stroke and thus survives better than tumble-like motion that drives turbulence towards top-dead-center and then dissipates. The instantaneous anti-knock agent injection requirement and total anti-knock agent 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. Gasoline/Gasohol Phase

As used herein "gasoline" refers to a mixture of hydrocarbons boiling in the approximate range of

4O⁰C to 21O⁰C and that can be used as fuel for internal combustion engines (e.g., motor gasoline as defined by ASTM Specifications D-439-89) . Gasoline may contain substances of various natures, which are added in relatively small amounts, to serve a particular purpose, such as to increase the octane number, biocides, antifungals, anticorrosion agents or other benefit agents.

As used herein "gasohol" refers to a mixture of gasoline and an alcohol, typically ethanol (see

ASTM D-4814-91). The ethanol content is froml to 85 volume %. Typically the ethanol content is from 5 to 10 volume %. Ethanol is typically fermented from grain (corn, wheat, barley, oats, sugar beets, cane sugar etc.) in a fermentation process. In the future, ethanol may be produced from biomass such as switch grass, waste wood, fibers and other carbohydrates. The ethanol is blended into gasoline in various quantities. Octane of gasoline or gasohol may be measured according to

ASTM Method D2700.

Gasoline is utilized in the discussion herein to encompass both gasoline and gasohol as defined herein for ease in communication and is not intended to limit the discussion to solely gasoline.

As used herein, the term "immiscible" regarding the gasoline phase and the anti-knock agent phase refers to the amount of one phase which may be present in the other phase. As used herein, the term

"substantially immiscible" means the gasoline phase comprises less than 0.1 vol% of the anti-knock agent, preferably less than 0.05 vol% of the anti-knock agent in the gasoline phase. Similarly, the anti-knock agent phase comprises less than 10 vol% of gasoline, preferably less than 5 vol% of the gasoline phase in the anti-knock agent.

As used herein, the term "fuel" means any combustible materials including the gasoline, gasohol, anti-knock agents such as the glycol anti-knock agent and second anti-knock agent.

The levels discussed herein may be for the anti-knock agent or the gasoline dispensed into the single fuel source (fuel tank) or it may be levels for the anti-knock agent or the gasoline before injected into the engine. As can be seen in the examples of the present application, as the anti-knock agent is dispensed into the fuel tank, it mixes with the gasoline before separating into a distinct phase.

However, gasoline may be somewhat soluble in the anti-knock layer and ethanol may be somewhat soluble in gasoline, thereby changing the volume percentages stated herein. Anti-Knock Phase

The present invention includes an anti-knock phase comprising an anti-knock phase comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; wherein the anti-knock agent phase is substantially immiscible with the gasoline phase. The anti-knock phase should comprise enough water so two distinct phases separate rapidly in the vehicle tank after the gasoline and the anti-knock phase, which mixes during dispensing through a gasoline pump nozzle. Anti-knock Agent

The present invention includes an anti-knock phase comprising an anti-knock agent comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; wherein the anti-knock agent phase is substantially immiscible with the gasoline phase. It is preferred that the anti-knock agent have a heat of vaporization that is at least twice that of gasoline or a heat of vaporization per unit of combustion energy that is at least three times that of gasoline. Glycol anti-knock subagent

The large heat of vaporization of the anti-knock agent, there could be enough charge cooling with early injection so that the rate of vaporization of anti-knock agent is substantially decreased. The glycol anti-knock subagent is selected such that the ratio of oxygen atoms present in the molecule and carbon atoms present in the molecule is from 0.3 to 1.0, preferably 0.4 to 1.0. The high heat of vaporization of the anti-knock agent with its direct injection late in the cycle gives the desired impact of knock suppression. The temperature decrease of the air in the cylinder increases with the amount of oxygen in the anti-knock agent (in terms of the O:C ratio of the anti-knock molecule(s)). It is also useful to compare ratios of the heat of vaporization to the heat of combustion, a measure of the potential effects when used as anti-knock agents. This parameter gives a measure of the amount of evaporative cooling for a given level of torque.

The glycol anti-knock subagent may be selected from glycols of natural origin, preferably glycols derived from hydrolysis of fats and oils, made by fermentation of carbohydrates to give a naturally derived glycol or by partial hydrogenation of glycols of natural origin. Alternatively, the glycol anti-knock subagent may be selected from glycol of petrochemical origin, preferably by the oxidation and hydration of olefins to give a petrochemical glycol. The glycol anti-knock subagent is selected from the group consisting of glycerol (O:C ratio of 1:1), ethylene glycol (O:C ratio of 1:1 or 1), 1,2-propylene glycol (O:C ratio of 2:3 or 0.67), 1,3- propylene glycol (O:C ratio of 2:3or 0.67), isobutylene glycol, 1,2-butanediol (O:C ratio of 1:2 or 0.5), 1,3-butanediol (O:C ratio of 1:2 or 0.5), 2,3-butanediol (O:C ratio of 1:2 or 0.5), 1,4-butanediol (O:C ratio of 1:2 or 0.5), C₅ diols (O:C ratio of 2:5 or 0.4) such as 1,2 pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,3-pentanediol, amylene diols (O:C ratio of 2:5 or 0.4), Ce diols (O:C ratio of 2:6 or 0.3) such as 1,6-hexanediol, 2,3-hexanediol and mixtures thereof. Preferably the glycol antiknock subagent is selected from glycerol, 1,2-propylene glycol, 1,3-propylene glycol and mixtures thereof.

The anti-knock agent comprises less than 40% by volume of glycol anti-knock agent by weight of the anti-knock agent, preferably comprising from about 5% by volume to about 40% by volume of glycol anti-knock agent by weight of the anti-knock agent as dispensed into the single fuel source (fuel tank).

Water should be present in sufficient amounts in order to effectively result in the anti-knock agent being in a distinct layer. Water comprises at least 10% by volume of the anti-knock agent as dispensed into the single fuel source (fuel tank), preferably from about 10% by volume to about 40% by volume of the anti-knock agent as dispensed into the single fuel source (fuel tank). Second anti-knock subagent

The second anti-knock subagent selected from the group of methanol, ethanol, water and mixtures thereof. In one embodiment, the second anti-knock subagent is selected as ethanol. Additional Additives

The fuel system may also comprise additional additives. These additives may include, but are not limited to anti-knock agents other than those discussed above, corrosion inhibitors, surfactants, detergents, metal deactivators, antioxidants, fuel stabilizers, and anti-freeze components. Examples of anti-knock agents other than those discussed above include lead alkyls such as tetraethyl lead and tetramethyl lead; manganese compounds such as methylcyclopentadienyl manganese tricarbonyl; and iron compounds such as ferrocene. An example of a corrosion inhibitor is SPEC-AID 8Q103 available from GE Betz, Inc. Examples

AU parts by volume - 10 mL gasohol (Hex/Tol/EtOH); 5 mL EtOH/PG/H₂O

EtOH being ethanol; PG being propylene glycol; H₂O being water; Hex being hexane; ToI being toluene. Add the mixture to a stoppered graduated cylinder and shake vigorously for 30 seconds and allow the layers to separate.

All measurements by volume

10 mL gasohol (Hex/Tol/EtOH); 5 mL EtOH/gly/H₂O

EtOH being ethanol; GIy being glycerol; H₂O being water; Hex being hexane; ToI being toluene.

Add the mixture to a stoppered graduated cylinder and shake vigorously for 30 seconds and allow the layers to separate.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm". All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

CLAIMSWhat is claimed is:

1. A fuel system comprising:

(a) gasoline phase comprises gasoline or gasohol; and

(b) an anti-knock phase comprising an anti-knock agent comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof, preferably the second anti-knock subagent is selected as ethanol; wherein the anti-knock agent phase is substantially immiscible with the gasoline phase.

2. The system of claim 1 wherein the glycol anti-knock subagent is selected such that the ratio of oxygen atoms present in the molecule and carbon atoms present in the molecule is from 0.4 to 1.0, preferably wherein the glycol anti-knock subagent is selected from the group consisting of glycerol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, isobutylene glycol, 1,2-butanediol, 1,3- butanediol, 2,3-butanediol, 1,4-butanediol, C₅ diols and mixtures thereof, more preferably wherein the glycol anti-knock subagent is selected from glycerol, 1,2-propylene glycol, 1,3-propylene glycol and mixtures thereof.

3. The system of claim 1 wherein the anti-knock subagent comprises less than 40% by volume of glycol anti-knock agent by volume of the anti-knock agent, preferably comprising from about 5% by volume to about 40% by volume of glycol anti-knock agent by volume of the anti-knock agent and wherein the second anti-knock subagent is selected as water comprising at least 10% by volume of the anti-knock agent, preferably from about 10% by volume to about 40% by volume of the antiknock agent.

4. The system of claim 1 wherein the anti-knock agent comprises glycerol, water and ethanol, preferably water comprising at least 10% by volume of the anti-knock agent, preferably water comprising from about 10% by volume to about 40% by volume of the anti -knock agent.

5. The system of claim 1 wherein the anti-knock agent comprises 1,2-propylene glycol, 1,3- propylene glycol and mixtures thereof, water and ethanol, preferably water comprising at least 10% by volume of the anti-knock agent, preferably water comprising from about 10% by volume to about 40% by volume of the anti-knock agent.

6. The system of claim 1 wherein the anti-knock agent comprises glycerol, 1,2-propylene glycol, and mixtures thereof, water and ethanol.

7. The system of claim 1 wherein the glycol anti-knock subagent is selected from glycols of natural origin, preferably glycols derived from hydrolysis of fats and oils, made by fermentation of carbohydrates to give a naturally derived glycol or by partial hydrogenation of glycols of natural origin.

8. The system of claim 1 wherein the glycol anti-knock subagent is selected from glycol of petrochemical origin, preferably by the oxidation and hydration of olefins to give a petrochemical glycol.

9. The system of claim 1 wherein the anti-knock agent phase is injected into an engine cylinder independent of the gasoline phase.

10. The system of claim 1 wherein the anti-knock agent phase is injected into an engine cylinder after injection of the gasoline phase into an engine cylinder, preferably wherein the anti-knock agent is injected into an engine cylinder at about 280 to about 330 degrees crank angle.