Patent Publication Number: US-2009223117-A1

Title: Low toxicity fuel and lubricant for two-stroke engines

Description:
The present invention relates to a low toxicity fuel and lubricant package for two-stroke internal combustion engines and in particular, but not exclusively, for high performance two-stroke engines, for example for racing and recreational vehicles. The invention also relates to a lubricant for use as a component of a fuel and lubricant package for two-stroke engines. 
     The two-stroke engine has considerable merit in a wide range of applications. These include motor sport (in particular, karting), motocross, outboard engines, mopeds, motor scooters, chainsaws and snow-mobiles. The advantages include low weight, mechanical simplicity, low cost and low noise as compared to four-stroke engines of a similar power when used in motorsport applications. 
     Basic two-stroke engines have emissions that are high in unburned fuel, and when they operate at low power settings these engines will often “four-stroke” as a direct result of inadequate scavenging. This form of misfiring will result in substantial proportions of the unburned fuel being discharged in the exhaust. These hydrocarbon (HC) emissions are toxic and cause serious pollution problems. 
     Gasoline direct injection delivers major improvements in both fuel consumption and in hydrocarbon emissions, when applied to two-stroke engines. However, engines used in karting and in many other sectors that use the two-stroke cycle cannot justify expensive direct injection technologies and still use some form of carburettor. Further, some two-stroke engines used in competition operate at over 14,000 rpm and at present the application of reliable direct injection technology at such high engine speeds seems impractical. 
     The real weakness therefore of the basic two-stroke engine, when it is fuelled by carburation and crankcase scavenging, is the high level of toxic exhaust emissions. The problem results from the fact that some of the unburned hydrocarbon fuel manages to escape by “short circuiting” via the open exhaust port during the scavenge phase. This is the period when the products of combustion are leaving the cylinder and the fresh charge of fuel and air is being introduced via the transfer ports. 
     An objective of the invention is to provide a fuel and lubricant package that can reduce the toxicity of the emissions from “basic” two-stroke engines, whenever fuel and lubricant is supplied to the engine as a pre-mixed fuel and lubricant package. A further objective is to provide a fuel and a lubricant for use with two-stroke engines, where separate supply tanks are used for the fuel and the lubricant, but where the lubricant is still used on a “total loss” basis. One other objective is to provide a fuel and lubricant package with low toxicity to minimise the health risks associated with the handling of fuels and lubricants in the recreational sector. 
     According to the present invention there is provided a fuel and lubricant for two-stroke engines, including a fuel component that is based on ethanol and includes 2-25% volatile hydrocarbon fractions, and a lubricant component which is based on an oil that is soluble in ethanol. 
     Because ethanol is relatively non-toxic, the release of unburned fuel in the exhaust gases does not give rise to significant health risks. The inclusion of a lubricant that is soluble in ethanol makes the fuel and lubricant mixture suitable for use in two-stroke engines. Although some volatile hydrocarbon fractions are frequently required for cold starting, the quantity is sufficiently low to avoid causing significant health risks. 
     Advantageously, the fuel component includes 75-98% ethanol, preferably 85-95% ethanol. 
     Advantageously, the ethanol and hydrocarbon is blended for high octane and low toxicity. 
     Advantageously, the fuel component includes 3-15% volatile hydrocarbon fractions. 
     Advantageously, the volatile hydrocarbon fractions are selected from the group comprising pentane, iso-pentane, butane, iso-butane, propane and combinations thereof. These fractions have low toxicity and appear to be promising candidates for this application. Any other hydrocarbon offering low toxicity, good volatility and high octane rating and flame speed may also be suitable. 
     Advantageously, the fuel component includes one or more additives selected from a range that includes corrosion inhibitors, combustion enhancers, solubility aids and cold starting promoters. 
     Optionally, the fuel component may include 1-20% water, preferably 3-10% water. The inclusion of water reduces the combustion temperature and so lowers the production of NOx. 
     Advantageously, the lubricant component is based on a non-mineral oil. This further reduces the presence of unburned hydrocarbons in the exhaust gases. By the term “based on” we mean that the non-mineral oil comprises the major part of the oil present in the lubricant: i.e at least 50%, preferably at least 80%, and more preferably at least 90% of the lubricant. In certain circumstances, the lubricant component may include small quantities of other oils. 
     Advantageously, the lubricant component is based on a vegetable oil or an equivalent low toxicity synthetic oil. Preferably, the lubricant component is based on castor oil. We have found that the combination of an ethanol based fuel and a castor oil based lubricant is particularly effective. Alternatively, the lubricant component may be based on jojoba oil or an equivalent low toxicity synthetic oil. 
     Advantageously, the lubricant component includes one or more additives selected from a range that includes corrosion inhibitors, solubility aids and detergents. 
     Advantageously, the lubricant component is combined with the fuel component at a rate of 0.5-5.0 cc per 100 cc of the fuel component, preferably at a rate of 1-4 cc per 100 cc of the fuel component. 
     According to another aspect of the invention there is provided a lubricant for use in a fuel and lubricant as defined by any one of the preceding statements of invention, wherein the lubricant is based on an oil that is soluble in ethanol. 
     Advantageously, the lubricant is based on a non-hydrocarbon oil, preferably a vegetable oil or an equivalent low toxicity synthetic oil. The lubricant may be based on castor oil or an equivalent low toxicity synthetic oil. Alternatively, the lubricant may be based on jojoba oil or an equivalent low toxicity synthetic oil. 
     Advantageously, the lubricant includes one or more additives selected from a range that includes corrosion inhibitors, solubility aids and detergents. 
     An objective of the invention is to provide a fuel and lubricant for use in two-stroke engines in applications where very high power is the prime requisite. Such engines generally operate rich of stoichiometric to maximise power, but as a result high levels of unburned fuel will be present in the exhaust gases. Such conditions are commonplace in competition two-stroke engines. Typically, such engines run at air-fuel ratios of around 12.5:1 when using gasoline. As shown in the enclosed graph ( FIG. 1 ), this results in high levels of exhaust toxins. An objective of the invention is therefore to provide a fuel that has low toxicity in the exhaust gas. A further objective of the invention is to minimise the health risks associated with use and handling of the fuel within the competition and recreational sectors. 
     Blair (“The Basic Design of Two-Stroke Engines”, Warrendale, Pa.: Society of Automotive Engineers, 1990) conveys a picture of reasonably low CO, low NOx, but high unburned hydrocarbon emissions in respect of “basic” crankcase scavenged two-stroke engines. This poor emission picture relates largely to the discharge of unburned hydrocarbon fuels and to a lesser extent some of the lubricant. However, this picture changes completely if an environmentally friendly fuel (a gasoline replacement) and a benign bio-lubricant are used to replace the bulk of the hydrocarbons in the fuel and to replace the synthetic and semi-synthetic lubricants which are generally toxic. It should also be possible to create a “synthetic” non-toxic lubricant that is suitable for two-stroke applications when used with ethanol. Solubility is a fundamental requirement which the castor based lubricants appear to already meet. 
     Some appropriate hydrocarbons remain useful to improve cold starting characteristics, but these are only required in small proportions. The correct hydrocarbons are required for this clean fuel technology, and there is the need to select hydrocarbon fractions with low toxicity, high octane rating and appropriate volatility as the key blending requirements. 
     The main exhaust gases are carbon-dioxide, nitrogen and water vapour. These gases are relatively benign: however, the worst pollutants in the engine&#39;s exhaust are those products of incomplete combustion, namely carbon-monoxide and a range of unburned hydrocarbons. The oxides of nitrogen (NOx) are the result of atmospheric nitrogen and oxygen which will combine under conditions of high temperature and pressure. However, the emissions of NOx are generally much lower from two-stroke engines than from the four-stroke counterparts. 
     Emissions of carbon-monoxide can be minimised by good combustion chamber design and by operating with air-fuel ratios “lean” of stoichiometric (oxygen rich). Formation of NOx can be minimised by any reduction in the peak combustion temperature, and for this purpose a fuel which can absorb water can prove beneficial. Added water has the disadvantage that it will increase the risks of corrosion, but anti-corrosion additives should serve to minimise the problems. Materials used in the engine fuel system should also be selected to reduce the corrosion problems. 
     A combination of alternative fuels and lubricants is proposed as a solution to the above emission problems and to reduce the health risks associated with handling highly toxic fuels and lubricants. The initial blends proposed here provide the opportunity to retain a liquid fuel and to replace the toxic unburned fuels and lubricants which are emitted in the exhaust gases from “basic” two-stroke engines. Instead those components which have been specified have been selected for their benign nature, whilst providing the opportunity to maintain or improve octane rating and charge density. 
     A range of additives is required to address various issues such as corrosion, solubility, cold starting and a number of undesirable characteristics. It may also prove beneficial to improve luminosity of the flame with an appropriate marker-tracer. The appropriate additives will be incorporated into both the lubricant and the fuel. 
     Various embodiments of the invention will now be described by way of the following examples. 
    
    
     EXAMPLE 1 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 85% 
               
               
                 Pentane or iso-pentane 
                 15% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Castor Based Oil 
                 03% (i.e. 33:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     The fuel and lubricant comprises a combination of an ethanol-based fuel component mixed with a castor based lubricant component. The fuel component comprises approximately 85% ethanol and 15% pentane or iso-pentane, plus a small quantity (typically less than 1% by weight) of fuel-specific additives, which may include, for example, corrosion inhibitors, combustion enhancers and aids for cold starting. 
     The lubricant component consists of castor oil (natural or a low toxicity synthetic oil) plus a small quantity of an ethanol-specific additive package including, for example, corrosion inhibitors, additives to aid solubility and detergents to minimise the formation of lacquers and varnishes. 
     The fuel component and the lubricant component may be supplied blended together for immediate use, or they may be supplied separately for mixing prior to use. In use, the two components are blended at a fuel and lubricant ratio of approximately 33:1, by adding 3 cc of the lubricant component per 100 cc of the fuel component. 
     EXAMPLE 2 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 90% 
               
               
                 Butane or iso-butane 
                 03% 
               
               
                 Iso-pentane or pentane 
                 07% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Castor Based Oil 
                 02% (i.e. 50:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     The fuel component in this example is similar to that of Example 1, except that the quantity of ethanol has been increased to 90% and the total hydrocarbon component has been reduced to 10% (comprising 3% butane or iso-butane and 7% pentane or iso-pentane). The fuel and lubricant components are blended at a ratio of 50:1 (2 cc lubricant per 100 cc fuel). 
     EXAMPLE 3 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 95% 
               
               
                 Propane 
                 01% 
               
               
                 Butane or Iso-butane 
                 01% 
               
               
                 Iso-pentane 
                 03% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Jojoba Based Oil 
                 02.5% (i.e. 40:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     In this example, the quantity of ethanol in the fuel component has been increased to 95% and the total hydrocarbon component has been reduced to 5% (1% propane, 1% butane or iso-butane and 3% iso-pentane). The lubricant component is based on jojoba oil, plus a suitable additive package as in Example 1. The fuel and lubricant components are combined at a ratio of 40:1 (2.5 cc lubricant per 100 cc of fuel). 
     EXAMPLE 4 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 93% 
               
               
                 Propane 
                 01% 
               
               
                 Butane or iso-butane 
                 02% 
               
               
                 Iso-pentane 
                 04% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Castor Based Oil 
                 02% (i.e. 50:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     In this example, the fuel component includes 93% ethanol and 7% hydrocarbon (1% propane, 2% butane or iso-butane and 4% iso-pentane). The lubricant is based on castor oil and is combined at a fuel and lubricant ratio of 50:1 (2 cc lubricant to 100 cc of fuel). 
     EXAMPLE 5 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 85% 
               
               
                 Water 
                 06% 
               
               
                 Butane or iso-butane 
                 02% 
               
               
                 Iso-pentane 
                 07% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Jojoba Based Oil 
                 03% (i.e. 33:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     In this example, water is included in the fuel component for lower NOx emission, the fuel component comprising approximately 85% ethanol, 6% water and 9% hydrocarbon (2% butane or iso-butane and 7% iso-pentane), plus additives. The lubricant is based on jojoba oil and is combined at a fuel and lubricant ratio of 33:1 (3 cc lubricant per 100 cc of fuel). 
     EXAMPLE 6 
       
     
       
         
           
               
               
             
               
                   
               
               
                 Compound 
                 Percentage 
               
               
                   
               
             
            
               
                 Ethanol 
                 85% 
               
               
                 Butane or iso-butane 
                 02% 
               
               
                 Iso-pentane 
                 13% 
               
               
                 Plus fuel additive package 
                 100% fuel element 
               
               
                 Castor Based Oil 
                 02% (i.e. 50:1 fuel:lubricant mix) 
               
               
                 Plus ethanol specific additive package 
               
               
                   
               
            
           
         
       
     
     In this example, the fuel component includes 85% ethanol and 15% hydrocarbon (2% butane or iso-butane and 13% iso-pentane), plus additives. The lubricant is a castor based oil and is combined at a fuel and lubricant ratio of 50:1 (2 cc lubricant per 100 cc of fuel). 
     The key to this novel approach to the problems of two-stroke competition engine emissions is provided by ethanol. However, for two-stroke applications a lubricant is required which will dissolve readily in ethanol. It must burn cleanly and also be benign in the unburned form. Castor oil is a known lubricant and it also behaves as a fuel when it is injected in a finely atomised form into diesel engines. Castor oil dissolves in ethanol and in the combustion chamber it appears to burn cleanly, while unburned castor oil in the exhaust gases should be biodegradable and relatively benign. In contact with the metallic rubbing and bearing surfaces castor oil has been shown to provide excellent lubrication qualities. A castor based lubricant therefore appears attractive for these purposes. However, some alternative lubricants may also prove to be appropriate for these applications: these could include vegetable based oils of which jojoba based lubricants appear to be promising candidates. 
     An initial formulation to address the two-stroke emission problem is made up as follows: a lubricant amounting to 1-4% of a castor or vegetable oil: this is mixed into a fuel made up of between 2-20% of appropriate hydrocarbons which are selected for their low toxicity, good volatility, high flame rate and high octane rating. These hydrocarbons are likely to originate from the “front-end fractions” of the refining process: they can include the heavier hydrocarbon gases and the lighter hydrocarbon liquids. These specific hydrocarbon components will act as the cold starting aid. The composition of this hydrocarbon fraction will be varied depending on the application and the ambient temperatures within a particular market. 
     These hydrocarbon components must also be selected for solubility in ethanol. They can include hydrocarbons which are gaseous at normal temperatures such as propane and butane and those which are liquid such as pentane and iso-pentane. However, certain other hydrocarbons may also prove appropriate to meet these requirements, the emphasis being towards low toxicity and good solubility. The remainder of the fuel is ethanol: this is rated at 108 octane RON (some sources quote octane ratings of 112-120 RON for ethanol). 
     To this blend we can consider adding water up to 10% in order to achieve further NOx suppression and to avoid spark knock. Tests have indicated that water is soluble in the ethanol/hydrocarbon/castor oil blends. The flame temperature of ethanol is lower than with gasoline and the flame luminosity is also less: this will help suppress the formation of NOx. In any case NOx is not a significant problem with two-stroke engines and the use of ethanol can be expected to further reduce NOx emissions. Adding water may well limit the formation of NOx further but the trade-off is likely to be an increase in the risk of corrosion to engine and fuel systems components and the requirement for greater fuel tank capacity. 
     It is anticipated that in the first instance a two-stroke ethanol/hydrocarbon competition fuel will be created. This will be “designed” for blending with a lubricant package which has been optimised for this specific fuel. This fuel and lubricant mix will be used with two-stroke engines which rely upon total-loss lubrication systems. Each of the components and additives is selected to minimise the toxic risks associated with fuel handling and to minimise toxic exhaust emissions. Each fuel component is also selected to ensure solubility and compatibility with ethanol and the lubricant formulation. Ethanol is relied upon primarily to provide clean burn, the required high octane rating and lower levels of toxins in the unburned fuel in the engine&#39;s exhaust gases. 
     The ethanol specific bio-lubricants created in line with these proposals are likely to require a range of additives such as corrosion inhibitors, additives to aid solubility and detergents to minimise the formation of lacquers and varnishes. The ethanol-based fuel needs to be blended with cold starting combustion enhancers, whilst aiming to create two-stroke emissions which have low toxicity. This type of fuel blend is essential in the absence of low cost, direct injection system for high speed, and low cost two-stroke engines. 
     The single cylinder two-stroke engine has considerable advantage over comparable four-stroke engines, in terms of simplicity, power-weight ratio, vibration, durability, noise and harshness. In fact investigations show that small capacity four-stroke engines are not particularly fuel efficient, as the frictional losses associated with the valve gear begin to assume considerable proportions as the cylinder size is reduced. There is also the added friction associated with the additional inlet and exhaust strokes. This reduces the mechanical efficiency of the smaller four-stroke engines. 
     If a two-stroke fuel is made primarily of ethyl alcohol and this is mixed with a lubricant which is largely a castor based oil (or a jojoba based oil) it would seem the emissions of unburned fuel and lubricant would be largely composed of ethanol and castor oil (or jojoba oil). There are likely to be issues associated with corrosion, solubility and engine starting, all of which can be improved through the use of suitable additives to both the fuel and the lubricant. These will need to be developed so that the fuel blend and lubricant package are appropriate for a wide range of engine technologies. 
     Two-stroke engines generally have low on NOx emissions and these proposals are likely to enhance those characteristics still further. Ethanol, as a result of its high latent heat of evaporation, creates a significant reduction in the charge temperature compared with gasoline: this helps to reduce peak temperatures and NOx formation. The high latent heat of evaporation is invaluable for reducing the charge temperature and for increasing the charge density. The result is an increase in power output. The fuel also has a higher octane rating than gasolene karting fuels currently mandated by the FIA-CIK. This will permit the use of increased compression ratios leading to improved efficiency. 
     Two-stroke engines with carburettors can be sensitive to “transient spark knock” which is caused by “light end” octane deficiency. The octane rating available with ethanol provides an opportunity to avoid this undesirable condition. However, the hydrocarbon fraction also needs to be carefully selected to avoid similar “light end” octane deficiency. 
     The two-stroke piston is exposed to twice the firing pulses of its four-stroke counterpart; the exposure of the underside of the piston to lower incoming charge temperatures of the ethanol-based fuel and air mixture will assist in piston cooling. There should be similar benefits by improving the cooling of the lower parts of the cylinder bore. This is likely to prove advantageous with two-stroke engines, which are often vulnerable to overheating particularly around the exhaust ports. 
     Lower maximum and mean flame temperatures have been reported with ethanol fuel: this will help in NOx reduction and will reduce the heat load on the piston: this is particularly important with the two-stroke cycle. We have noted lower coolant temperatures on test and this is beneficial for durability and also for the avoidance of “spark knock”. The impact of ethanol on the crankcase scavenged two-stroke engine should prove beneficial; reducing the temperatures of bottom end bearings is likely to improve durability. In fact it is probable that reduced temperatures will serve to prolong the use of air cooled two-stroke engines in a wide range of applications. 
     We have already conducted initial “field trials” with some basic formulations of the fuel, with various hydrocarbons plus the lubricant; and these proved successful in a lightly modified engine. 
     The present invention provides for the creation of a high octane but significantly more benign fuel for karting and motocross, in the absence of proven low cost direct injection systems for these applications. There is also a wide range of other two-stroke engine applications for these fuel and lubricant formulations, where the basic two-stroke engine remains desirable on grounds of simplicity and cost, where the carburettor remains both difficult and uneconomic to replace, but where the toxicity of the exhaust emissions needs to be urgently addressed.