Abstract:
A method and apparatus for determining the propensity of fuel materials to leave deposits in compression ignition engines is disclosed. The apparatus consists of a closed chamber fitted with conduits to supply fuel composition, air, and other test fluids to its interior, and arranged to contain or substantially contain a substrate. Substrate is placed in the chamber to provide interaction between a fluid passing through and the substrate. Substrate may be a monolithic machined element or a collection of discrete bodies. The chamber conduits are connected to at least two metering devices, one controlling fuel and one air flow, whereby the substrate is exposed to measured quantities of fuel compositions and air. Heating devices are in thermal communication with the substrate and the source of air provided to the chamber, thus providing a method of controlling the temperature of the substrate and air flowing through the chamber. The propensity of a fuel composition to form deposits in an engine is determined by alternatively dispersing fuel composition and hot air upon the heated substrate then determining the mass of the deposits left on the substrate.

Description:
CROSS REFERENCE PATENTS 
     FIELD OF INVENTION 
     The present invention relates to a bench top scale device for testing the potential of compression ignition engine fuel compositions which form deposits on engine components during engine operation; and a method for testing said fuel compositions that yields data measuring the propensity of said fuel compositions to form deposits that negatively effect engine operation; said data correlating directly with results obtained in testing said fuel compositions in engines operating under in use conditions. 
     BACKGROUND OF THE INVENTION 
     During operation the hot surfaces within an internal combustion engine are exposed to many fluids, both liquid and gaseous, which may undergo thermal breakdown resulting in the formation of deposits on the surfaces of these components, thus compromising engine function. Examples of the fluids which an engine component might be exposed to are fuel compositions, lubricating fluids, and combustion byproducts. Those skilled in the art are aware of the methods and apparatus generally employed for screening fuel compositions for their tendency to form deposits that can compromise engine functionality. Because of the limited ability of bench top scale apparatus and methods to duplicate the conditions encountered in an operating engine, ultimately fuel compositions are tested in a running engine, under simulated “real world” operating conditions to determine how well these fuel compositions perform in terms of suppressing the formation of engine deposits or removing engine deposits once formed. Such tests are expensive, and because of the cost of the equipment and the duration of the test, the use of test engines to determine fuel and other fluid performance is prohibitively costly to do a broadly based “screening” type of study. 
     Traditionally, bench top scale testing equipment and methods utilized to “screen” fuel compositions for their propensity to form disadvantageous deposits have been based on the notion that simple thermal degradation of fuel compositions can be correlated to the performance of these fuel compositions when they contact “real world” components in “real world” engines operating under “real world” conditions. For this reason, most of the apparatus utilized in such screening tests employ some scheme in which fluids or vapors of the fuel composition are contacted with a substrate and then heated, generally under steady state conditions. However, it is well known in the art that simple static heating of a fuel composition and observation of the amount of deposits thereby formed correlates poorly, if at all, with performance of such fuel compositions in engines operating under real world or simulated real world conditions. Those skilled in the art understand that many factors in addition to thermal conditions within the engine environment influence the formation of engine deposits. These factors include the nature of the fuel composition, the type of material from which an engine part is made and its surface finish, the thermal history of the surface during its exposure to the fuel composition, and the presence of other fluids (such as coolant, engine exhaust, or lubricant vapors) admixed with the fuel composition during contact with the engine part&#39;s surface. Additionally construction features of the engine components such as fine passageways, orifices, or sharp edges can also contribute significantly to variations in the rate of deposit formation and its impact on engine functionality. 
     To illustrate this point, an example from the prior art of fuel testing apparatus may be cited. In U.S. Pat. No. 3,059,467 to Meguerian et. al. an apparatus is described in which a metered continuous flow of liquid fuel is passed along an inclined heated conduit along with a stream of air, the heated region being either of uniform temperature or a gradient temperature over the length of the conduit, and the heating being either steady state or increasing throughout the determination. After a period of time during which fuel and air are passed through the apparatus, the conduit is removed from the apparatus and weighed, the weight being compared to its weight prior to exposure to the fuel composition to determine the amount of deposits left by decomposition of the fuel. The results obtained using this method were compared with results of two different “real world engine” tests. These data showed that for a given fuel composition and set of test conditions repeatability of the apparatus was poor. In several identical tests the apparatus yielded deposit weights wherein the highest recorded was 135% of the lowest recorded. 
     A series of Chevorlet ISD engine tests were run using different fuel compositions and compared with those same fuel composition run in the subject apparatus. Data derived from the engine tests showed that a fuel that failed the test deposited 334% greater weight of deposits than a fuel that passed the test. Tests conducted on those same two fuel compositions using the subject apparatus and method of Meguerian et. al. gave results wherein the failing fuel composition produced deposits only 149% heavier than those of the passing fuel composition. Comparison of the data obtained from the repeatability tests with those of the data obtained from the passing and failing fuel tests indicates that the testing method of Meguerian may not give a good indication of the propensity of a fuel composition to form deposits in situations where deposit formation is dependent upon factors other than the raw chemical propensity of a fuel composition to thermally decompose. As the deposit formation is increasingly dependent upon factors other than mean operating temperature, testing equipment based upon simple thermal decomposition of fuel compositions correlates less well with the results obtained from the same fuel composition employed in an operating engine test. 
     Operating conditions also contribute to variations in deposit formation within engines. For example an engine running under constant load will form deposits at a different rate than one which is subjected to cycles of acceleration and deceleration under varying load and coast conditions. 
     In general, for bench top scale testing equipment to mimic conditions, and thus more accurately gauge the propensity of fuel materials to form deposits which lead to impairment of engine operation, they must incorporate features which permit cycling through various temperature conditions and conditions of fuel composition loading on the surface, as well as the ability to introduce other fluids into the testing apparatus under the conditions in which they would contact a surface in an operating engine. Additionally, testing apparatus must be designed so that channels and other surface features that appear within an engine are mimicked in the testing apparatus. Finally, for any apparatus to test the propensity of a fuel composition to leave deposits within an engine, it must address the problems associated with variations in surface composition and finish of the substrate upon which deposits are left within the testing apparatus, as well as provide a means of reproducibly providing a substrate surface of accurately measured surface area and finish, one of the keys to reproducible test results. Presently, this factor is either largely ignored, or is addressed through the requirement of requiring an expensively custom machined and finished substrate, resulting in elevated costs associated with testing apparatus. Due to the expense of such substrates, practitioners typically resort to cleaning the substrate after use, which preclude preservation of samples and often leaves the quality of the resulting surface finish in doubt from the perspective of a reproducible surface. 
     Accuracy of devices employing gravimetric measurement of deposits left on a substrate surface also suffers when low surface area substrates are employed from the standpoint that minimal catalytic surface/volume of fuel leads to small amounts of deposits being formed (thus the range of weight change in the substrate for various fuel compositions is small), and the surface area to weight ratio is low, making it difficult to accurately measure the weight change. 
     Additional factors, such as non-uniform distribution of fuel compositions within the test apparatus, and fuel puddling within the test apparatus can also effect the reproducibility of test data. 
     Operating conditions are of utmost importance when testing fuel compositions intended to be burned in diesel engines. This is particularly true when concerned with the tendency of diesel fuel compositions to leave deposits within fuel injectors. Unlike spark ignition engines, compression ignition engines have fuel delivery components exposed to combustion chamber temperatures, and during operation under “motoring” conditions (engine operating under coasting or braking conditions), very high temperature gas is forced into the injectors, resulting in degradation of fuel residue left in the injector. For this reason, an apparatus used to examine the tendency of diesel fuel compositions to degrade and leave deposits must permit tests to be conducted at temperatures near the flash point of the fuel composition. This requires testing equipment that is designed to address the safety issues associated with such high temperature testing. Additionally, automating the testing equipment affords the ability to conduct tests in which the conditions within the testing apparatus are cyclic rather than static, giving a testing regime which more nearly matches the environment found in an operating engine. 
     U.S. Pat. No. 5,693,874 to De La Cruz discloses a test apparatus designed to simulate the conditions of the intake manifold in a gasoline engine employing port fuel injection, and the attendant conditions in which an intake valve in such a gasoline engine operates. The design is unsuitable to testing diesel fuels because of the low surface area to weight ratio of the test specimen and the absence of safety devices that would permit high temperature soak cycles. 
     U.S. Pat. No. 3,438,248 to Taylor et. al. discloses a device wherein the thermal decomposition of bulk fuel flow over metallic test strips may be examined. Taylor is directed at studying the conditions most commonly found in nearly empty fuel tanks of aircraft traveling at supersonic speeds. This device does not closely approximate the conditions found in an operating diesel engine and does not incorporate safety features necessary to conduct such tests at temperatures which approach the conditions found in an operating diesel engine. 
     U.S. Pat. No. 3,318,667 to Fabuss et. al. discloses a device designed to duplicate the results of the ASTM-CRC fuel coker test apparatus while using a drastically lower volume of fuel material in the test. Fabuss is directed at studying the thermal decomposition of fuel compositions under conditions of bulk liquid fuel flow such as would be found in the systems supplying fuel to the engines of high performance aircraft. It is not suited to studying decomposition of residue under conditions simulating those in the combustion chamber of an operating diesel engine because it relies on liquid fuel flowing through the apparatus to perform the test. This also precludes testing under conditions in which the test surfaces are exposed to gases and vapors having the chemical characteristics of other fluids such as lubricant or exhaust gas during the test. 
     U.S. Pat. No. 3,059,467 to Meguerian et. al. discloses an apparatus in which liquid fuel is passed along a heated conduit, the conduit being subjected to gravimetric analysis before and after exposure to the fuel. The conduit has a low surface area to mass ratio which can negatively effect the sensitivity of test data to the propensity of a fuel to form engine deposits. As with other such apparatus used to study the thermal degradation of liquid fuel streams, this device is also unsuited to simulating the conditions to which components in the combustion chamber of a diesel engine are exposed. 
     The present invention provides a method in which a highly reproducible low cost surface mimicks the structural morphology typically found within engines. Additionally it provides an apparatus in which the operating extremes typically found in operating diesel engines may be duplicated while maintaining a safe working environment. Additionally it provides a method of automatically determining the propensity of diesel fuel materials to form deposits within diesel engines that has good correlation with tests performed in running diesel engines. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide a bench scale apparatus in which diesel fuel compositions may be examined for their propensity to leave deposits in diesel engines under operating conditions. 
     Another aspect of the present invention is to provide a method of using the apparatus to test the propensity of diesel fuels to leave deposits in operating diesel engines. 
     Another aspect of the present invention is to provide a method of utilizing low cost materials in the testing apparatus that give a highly reproducible substrate upon which deposits are formed during the test. 
     Another aspect of the present invention is to provide a bench top scale apparatus in which diesel fuel compositions may be safely tested at the extreme operating conditions typically experienced in an operating diesel engine. 
     Yet another aspect of the present invention is to provide an apparatus in which testing of diesel fuel compositions is completely automated, requiring technician input only to set up the testing conditions and retrieve the substrate at the end of the test period. 
     An additional aspect of the present invention is to provide a method of utilizing a low cost substrate that leads to improvement in the sensitivity of gravimetric measurement of deposits formed during tests carried out to determine the propensity of a diesel fuel composition to leave deposits in a running engine, accomplished by increasing the surface area to mass ratio of the substrate employed over that conventionally used in fuel testing apparatus. 
     A further aspect of the present invention is to provide an apparatus in which the parameters of fuel loading and thermal excursion may be adjusted dynamically over a broad range, permitting testing to be carried out under conditions which closely mimic those experienced in an operating diesel engine. 
     Yet another aspect of the present invention is to provide an apparatus in which the conditions experienced within an operating diesel engine are further mimicked through the ability to entrain vapors and gasses that mimic other fluids such as lubricating oil and coolant encountered in an operating diesel engine. 
     An additional aspect of the present invention is to incorporate fire suppression equipment and a method of automatically actuating the fire suppression equipment during a determination carried out in the testing apparatus. 
     Another aspect of the present invention is to provide an apparatus and a method of using the apparatus to study the propensity of diesel fuel compositions to leave deposits deleterious to the operation of diesel engines which has a high degree of correlation between test data derived from the apparatus and the results observed in operating diesel engines. 
     Other aspects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown, since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
     FIG. 1 is a schematic block diagram of the arrangement and connectivity of the elements of the testing apparatus and the control and sensor lines utilized by the automatic control device in the preferred embodiment. 
     FIG. 2 is a cross sectional representation of the structure of the best mode testing chamber indicated as block element  103  in FIG.  1 . 
     FIG. 3 is a side view of the best mode embodiment testing chamber of FIG. 2 with preferred flange seal half installed. 
     FIG. 4 is a cross sectional schematic diagram of the FIG. 3 flange sealed testing chamber assembled to a conduit plate and containing ball bearing substrate. 
     FIG. 5 a  is a cutaway top plan view showing machining detail of the best mode conduit plate, represented schematically in FIG. 4 as element  405 . 
     FIG. 5 b  is a side plan sectional view along axis  5 B of FIG. 5 a.    
     FIG. 5 c  is a side plan sectional view along axis  5 C of FIG. 5 a.    
     FIG. 6 a  is a spiral substrate member, an alternative substrate embodiment. 
     FIG. 6 b  is a top plan view of FIG. 6 a.    
     FIG. 6 c  is a side plan view sectional view along axis  6 C of FIG. 6 b.    
     FIG. 7 a  is a cutaway view of an alternative embodiment testing chamber with spiral substrate member therewithin. 
     FIG. 7 b  is a top plan view of FIG. 7 a.    
     FIG. 8 is a block diagram of the steps carried out in using subject apparatus to determine the propensity of a fuel composition to leave deposits. 
     FIG. 9 is a graph illustrating deposit formation as a function of the addition of a typical anti-deposit additive. 
     FIG. 10 is a schematic illustrating integration of the electrical control and sensor signals for employing a digital computer to control the testing apparatus. 
     FIG. 11 is a graph illustrating correlation between engine tests and the deposit formation observed in the bench scale deposit testing apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The general scheme of the experimental apparatus may be seen as system  1000  in FIG.  1 . With reference to FIG. 1, the system  1000  consists of chamber  101  in which air is heated. Chamber  101  is connected via conduits  133  and  102  to testing chamber  103 , which in use contains substrate  104  upon which fuel deposits are formed. Conduit  105  provides a means of conducting various fluids into testing chamber  103 , in particular fuel compositions delivered by fuel flow controller  121 , and a variety of gas from flow controller  107 ,  108 , and  109 . Fuel flow controller  121  also meters fuel onto substrate  104  during testing 
     Testing chamber  103  is in thermal communication with heater  106 , which is used for heating the testing chamber surfaces and the substrate therein. 
     Flow controller devices  107 ,  108  and  109  may be employed to control the conduct of inert gas, fluid simulating fluids found in the engine environment other than fuel, and/or fire suppressing gas into chamber  103  via conduit  105  during testing. Inert gas or fire suppressing gas passed into testing chamber  103  during a high temperature thermal excursion within chamber  103  in the course of testing a fuel composition or in the event of a fire or explosion occurring within chamber  103  during testing forms an inert gas blanket which acts to suppress fire and explosions. 
     One skilled in the art will appreciate that there are numerous types of valves and fluid flow control devices which may be employed to control the fluids passing into and out of chambers  101  and  103 . For control of air and other gases passing into chamber  103 , examples of suitable control devices which are familiar in the art include, but are not limited to, ball valves, diaphragm valves, needle valves, gate valves, and bellows valves, rotometer type volume flow meters, and mass flow controllers. It is contemplated that different embodiments could employ each device alone or in a combination with other devices such that one device is used to control volume or mass flow and another is used to provide positive shut off or redirect flow. Thus, with reference to FIG. 1, flow control devices  120 ,  122  and  123  may be a simple shut off valve such as a diaphragm valve, a combination of a fixed orifice and a shut off valve, a variable orifice valve such as a needle valve, alone or in combination with a shut off valve, and the various valves may be manually or automatically actuated. In an alternate embodiment, flow control device  120  may be a proportioning type apparatus such as are well known in the art that divide the inlet flow between two outlet legs, one of which is an exhaust or recycle leg, the other being connected to inlet conduit  102  and thence into testing chamber  103 . 
     In the preferred embodiment valves employed in flow control are electrically actuated. An alternate embodiment employs pneumatically actuated valves and an electropneumatic control device to actuate the valves upon receiving an electric signal, such as is well known in the art. In various embodiments it may also be advantageous to insure that fluid is delivered at constant pressure to flow control devices by first passing the fluid being controlled through a pressure regulating device such as a gas regulator and its equivalents such as are well known in the industry. 
     Fuel flow stop valve  121  is used to introduce a measured quantity of the fuel composition being tested into test chamber  103  via conduit  105 . Any arrangement of devices as would be familiar to one skilled in the art wherein an electrically or pneumatically actuated valve is coupled to an orifice (fixed or adjustable) and a fuel supply (either pressurized or gravity fed) may be employed. Examples of valves that may be suitably employed to this purpose are (but are not limited to) a commercially available fuel injector of either a piston pump or pintle valve type construction, pneumatically or electrically operated valves coupled to an orifice (either fixed or variable and a metering pump coupled to a control device which permits it to operate for any number of operator selected strokes in a given cycle. Any arrangement of valves, flow control devices, and pressure regulating devices that can deliver a constant volume of fuel such that it is distributed evenly over substrate  104  as long as the delivery device is actuated is contemplated as suitable for supplying measured quantities of fuel to testing chamber  103 . Such devices and control schemes are well known in the art of delivering controlled quantities of fluids. 
     The preferred embodiment of the fuel metering device in the present invention utilizes a gas pressurized fuel reservoir and an electrically actuated valve controlling flow to an orifice to introduce measured amounts of fuel into chamber  103 . Variation in the amount of fuel introduced is operator adjustable on the basis of varying the length of time during which the valve is actuated. Such an embodiment is disclosed in U.S. Pat. No. 5,693,874 to De La Cruz et. al., which is incorporated by reference herein. 
     In the preferred embodiment, flow of fuel, air, exhaust gas, and inert gas is accomplished by regulating the pressure of the supply and the size of the orifice through which the fluid passes, and the “on time” of a valve controlling passage through the appropriate conduit. Thus, a measured amount of fuel is delivered to the test chamber by supplying an appropriate signal to hold open fuel flow stop device  121  for a period of time that corresponds to the desired quantity of fuel. Flow stop devices  107 ,  108 , and  109  are similarly operated. Alternative embodiments are possible wherein the volume of the fluid is regulated by a mass flow controller or the like, eliminating a requirement for the operator to predetermine delivery rates or make orifice adjustment in the apparatus prior to conducting a test. 
     With further reference to FIG. 1, in one embodiment chamber  101  consists of outer shroud  130  which is connected to inlet conduit  132  and outlet conduit  133  and encloses heating element  131 . Heating element  131  may be of hollow tube construction through which a heated fluid is passed, such as steam or hot oil, or may be an electrical heating element, either device being well know in the art. Together shroud  130  and heating element  131  comprise a heat exchanger, and may be of any convenient configuration to provide heat transfer between the heating element and the air passed into it through inlet conduit  132 , such heat exchangers being well known in the art. The source of the air supplied to inlet conduit  132  may be derived from a compressed gas cylinder or supplied by compressor or blower using techniques which are well known in the art. The preferred embodiment of chamber  101  is disclosed in U.S. Pat. No. 5,693,874 to De La Cruz et. al., and is incorporated by reference herein. The De La Cruz patent 874 discloses a hot air supply element in which a pressure regulated stream of compressed gas is passed into a conventional tube within tube heat exchanger, such heat exchanger being well known in the art, the outlet conduit of the heat exchanger being equipped with a relief valve and the heat exchanger working fluid being set to give the desired temperature to the air stream passing thorough it. The disclosed hot air supply system is adapted to use in the present invention by interposing a pressure regulator and flow control device  120  between chamber  101  and testing chamber  103  to permit automatic control of air flow from chamber  101  into testing chamber  103 . In the preferred embodiment, flow control device  120  is a pressure regulator coupled to a manually variable orifice and an electrically actuated valve disposed in such a manner that actuating the valve open commences hot air flow, and maintains air flow until the valve is actuated to the closed position. Other embodiments are possible in which the manually variable orifice may be replaced with an electrically or pneumatically variable orifice such as are well known in the industry, or with a proportioning throttle type valve which would provide a constant flow of gas through the heat exchanger, giving a constant temperature but permitting hot air volume passing through chamber  103  to be varied. An additional embodiment is contemplated in which highly accurate swings in air temperature may be produced in which a proportioning valve is employed to mix streams of hotter and colder air to produce an air stream of the desired temperature. Using such a device would permit rapid and highly accurately controlled thermal excursions to be directed to test chamber  103  that ranged from the temperature of the cooler air stream to that of the hotter air stream. In the preferred embodiment of the hot air supply, temperature excursions are accomplished by raising the temperature of the heat exchanger working fluid or reducing the flow rate through the heat exchanger or a combination of the two. 
     With reference to FIG. 1, chamber  103  may be of any convenient shape or configuration that permits good thermal contact between the walls of testing chamber  103 , heating device  106 , and substrate  104  placed within test chamber  103 . It may be that different forms of substrate  104  may find one particular shape more advantageous than another for testing chamber  103 . 
     Testing chamber  103  may be insulated or uninsulated, and it may be internally or externally heated by such devices as are well known in the art. Examples of suitable heating devices are (but are not limited to) fluid heat exchangers and electrically powered resistance heating elements. The important design elements of testing chamber  103  is that it provide a flow through design, and provide that fluids introduced into testing chamber  103  are dispersed so as to contact the surfaces of substrate  104  placed within the chamber uniformly. Additionally, testing chamber  103  should afford a tight, thermally robust seal so as to insure containment of fuel compositions and air/fuel mixtures evolved during testing. A final design requirement for testing chamber  103  is that it have an access way of sufficient dimension to permit placement and withdrawal of the substrate without disturbing any deposit layer which may have been left on the surface of the substrate in the course of a test. 
     One embodiment of the schematic element testing chamber  103  is shown with reference to FIG. 2, as cylindrical testing chamber  203 . Cylindrical testing chamber with a conical shape imparted to its outlet end  204  is the preferred form of the testing chamber of the present invention. The conical shape of the outlet is of particular advantage in suppressing the formation of fuel droplets and fuel puddles within the chamber. The presence of droplets and puddles of fuel has been found to negatively influence repeatability in sequential determinations conducted under the same testing conditions in bench top scale fuel testing apparatus. 
     The best mode of attaching testing chamber  203  into an assembled testing apparatus is shown with reference to FIG. 3, flange mounted testing chamber  303  (wherein the cylindrical section testing chamber and conical outlet  307  of testing chamber  303  is equivalent to testing chamber  203  of FIG.  2 ). Testing chamber  303  is a hollow cylinder in form, with a flange plate affixed at the inlet end and a conical internal profile at the other. In the best mode, the flange half affixed to the inlet end of the testing chamber (face  306 ) mates with a similar flange face machined into, with reference to FIG. 5 c,  face  520  of conduit plate  506 , and by any flange sealing means as are well known in the art, the testing chamber is affixed to the rest of the testing apparatus. 
     The cylindrical form of the testing chamber provides the advantage that it is an easy and cost effective shape to machine, and the cylindrical walls provide a convenient shape for the external attachment of cylindrical sections of heating elements, the testing chamber outer diameter being sized to give close contact between the chamber walls and cylindrical section electric heating element sections, such elements being well known in the art. 
     A schematic of the testing chamber charged with substrate is shown in FIG.  4 . Of particular note in the assembled testing chamber is the location of two cylindrical section electric heaters  420  placed about the external diameter of testing chamber  403 , one near the inlet and the other near the outlet. Alternatively, testing chamber  403  could have affixed to it heat exchange conduit through which a fluid is passed to heat the chamber. Additional alternative embodiments are possible in which well insulated electrically powered heating elements or conduits through which a heat exchange fluid is passed may be placed within the chamber, or testing chamber  403  could even be of hollow wall construction with a heat transfer fluid passed through it, such as is well know in the processing arts. 
     With further reference to FIG. 3, the best mode of the present invention is for one end of cylindrical test chamber  303  to be supported by one half of a conventional flange closure, either welded or of rotatable construction such as is well known in the art. In the best mode, test chamber  303  is welded to flange half  304  at location  305 . A sealing lip may be located on sealing face  308  of flange half  304 , but in the best mode, the end of cylindrical testing chamber protruding from the flange is provided with sealing lip  306  is located on the open end of testing chamber  303 . When assembled with other parts disclosed below, sealing lip  306  forms a seal suitably robust to withstand the testing conditions. Conical bottom  307  of chamber  303  has a hole bored through it and is fitted with an outlet conduit to conduct fluids from the test chamber. Many fittings are suitable and are well known in the art, but may include compression fittings, threaded fittings, small flange fittings and the like. 
     With reference to FIG. 4, testing chamber  403 , which is the equivalent to FIG. 1 testing chamber  103 , is shown sealed with a flange type sealing device. Testing chamber  403  is joined to lower flange half  405  which in turn is bolted to conduit plate  406  to effect a sealed testing chamber. With reference to FIGS. 5 a,    5   b,  and  5   c,  conduit plate  506 , which is the same as FIG. 4 conduit plate  406 , is machined of any metal capable of withstanding the conditions of the testing chamber. In the best mode plate  506  is made of mild steel, but one practiced in the art will readily understand that it may be made of stainless steel, aluminum, brass, copper, monel, titanium, and the like. Plate  506  is through bored across its thickness to form flange mounting bolt holes  501  and  502 , and flange mounting oblong bolt holes  503  and  504 . Additionally, centered in conduit plate  506  is air stream conduit inlet hole  505 , also bored through the thickness of conduit plate  506 . Further, with reference to FIG. 5 b,  face  520  of conduit plate  506  is adapted to mate, with reference to FIG. 3, to sealing surface  306  of the testing chamber. Face  521  of conduit plate  506  is machined to mate, with reference to FIG. 4, to air stream inlet conduit  407 . One skilled in the art can appreciate that numerous coupling schemes are well known, such as a flange with a knife edge sealing surface and ductile metal gasket, machined flange faces sealed with fiber gasket packing, internally or externally threaded passage way and sealant, compression fitting and the like. 
     With reference to FIG. 4, the preferred method of attaching the testing chamber to the testing apparatus and sealing the testing chamber is with a flange and metal gasket mating surface between test chamber  403  and the lower face of conduit plate  406 , with heated air stream conduit  407  welded to the upper face of conduit plate  406  in such a manner that it is coaxial with through bored hole  408 , hole  408  being identical with FIG. 5 a  through bored hole  505 . 
     With reference to FIGS. 5 a,    5   b,  and  5   c,  conduit plate  506  additionally contains four lateral passageways,  507 ,  508 ,  509 , and  510 . These passageways are blind bored laterally parallel with the plate faces, starting at the edge of conduit plate  506  and terminating before they encroach on through bore passageway  505 . They are spaced equidistant about the perimeter of the plate and normal to the plate edge. As is shown in FIG. 5 b,  four blind holes exemplified by hole  511  are bored through the test chamber mounting face  520  of conduit plate  506  such that a right angle conduit is defined, one for each lateral passageway. Grooves, concentric with through bored hole  505  and machined into face  520  could be used instead of blind holes such as  511  for each passageway. 
     With reference to FIG. 4, other embodiments of the assembly defined by the junction of testing chamber  403 , conduit plate  406 , and heated air inlet conduit  407  are possible. Both testing chamber  403  and heated air stream conduit  407  could be fixed to flange plates which mate to a double sided conduit plate  406  by flange and gasket coupling arrangement, such as is well known in the art. Alternatively, conduit passageways  409 , 410 , 411 , and  412  which pass through conduit plate  406  could be effected by boring blind holes  411  and  410  through face  430  of conduit plate  406  to intersect the lateral blind passageways, thus effecting the same number of conduit inlets to the testing chamber but requiring fewer lateral blind passageways to be machined into conduit plate  406 . 
     Finally, with reference to FIG. 5 a,  in an alternative embodiment, lateral passageways  507 ,  508 ,  509 , and  510  may be through bored to intersect hot air stream conduit  505 , requiring no blind holes exemplified by blind hole  511  to effect passageway into the testing chamber. 
     It will be appreciated by one skilled in the art that there are many other arrangements of passageways, holes, and fastenings which could be used to effect a testing chamber that could be sealed and have gas inlets and outlets which are well known in the art and would equally serve the purpose of containing a substrate in a controlled atmosphere. 
     Other embodiments are possible in which any number of conduits are affixed directly to conduit plate  406  and/or testing chamber  403  and/or heated air stream conduit  407 . 
     With further reference to FIG. 4, testing chamber is shown to contain substrate  413  retained at the bottom of said chamber with a perforated or mesh plate  404 . In the best mode of the present invention, testing chamber  403  is a hollow cylinder having a conical tapering outlet end which is fitted at the conical end with a plate containing through punched holes of a size sufficient to permit fluids to pass from testing chamber  403  and retain packing material  413  within testing chamber  403  under conditions of full volume flow of test fluids. 
     With further reference to FIG. 4, substrate  413  may be made in any convenient shape and in any material which mimics the catalytic surface of metals found in the engine environment. The best mode substrate material is grade 25 ¼″ hardened stainless steel ball bearings. It will be apparent to one familiar with the art that any ball bearing with a surface finish of grade 25 or better may be employed. The use of ball bearings offers several advantages over other substrates in that they are inexpensive, have very consistent surface finish bearing to bearing, yielding a substrate surface that is highly reproducible from test to test and ball bearings have a large surface area to mass ratio improving the sensitivity of gravimetric measurement of the amount of deposits formed. 
     It will be appreciated by one skilled in the art that the packing arrangement of the ball bearings comprising the substrate may be altered by varying the diameter of cylindrical chamber  403  such that successive layers of substrate may be placed exactly on top of each other or associated in varying degrees of interstitial arrangement, such as is well known to those in the art of packing arrangements of regular solids. Using these well known packing principles varying size voids may be created within chamber  403  which may be used to model different sizes of fine passageways in internal combustion engines. It will be appreciated by one skilled in the art that similar results in creating different sizes of passageways may be achieved using varying mixtures of spherical substrate having 2 or more different diameters within a chamber of a given size. 
     A further feature which will be apparent by referring to FIG. 4 is the placement of temperature sensing devices  421  and  422 , which in the best mode is thermally coupled to the exterior wall of cylindrical chamber  403  via stud  423  welded to the exterior side wall of testing chamber  403 , although alternate equally suitable mounting arrangements are well known in the art. In the preferred embodiment the temperature sensing elements are thermocouples. Thermocouple  421  is employed to monitor the temperature of the packing material while thermocouple  422  is employed to sense an over temperature condition within chamber  403  during a test. It will be appreciated by one skilled in the art that any arrangement of temperature sensing devices which maintains thermal contact with substrate material  413  may be used. By way of example, but not intended to be limiting, in a different embodiment, a temperature sensing device resides within chamber  403  in direct thermal contact with the substrate, electrical contact being provided by feed through electrodes inserted in conduit plate  406 , such feed through devices being well known in the art. 
     Temperature sensing devices are also not limited to thermocouples, but any device suitable to the temperature range of the test may be employed, such as devices based upon a resistance element or upon fluid expansion, such devices being well known in the art. 
     Although the preferred embodiment of the present invention utilizes ball bearings as a substrate within the testing chamber, as detailed above, an alternative embodiment of the substrate may be understood by reference to FIGS. 6 a,    6   b,  and  6   c  wherein the spherical ball substrate is replaced with a hollow cylindrical substrate  601  which has had the exterior surface cut in a plurality of spiral grooves  602 , and which is dimensioned such that it fits snuggly, with reference to FIG. 4, within testing chamber  403 . When such a substrate is employed, cylindrical section heaters  420  are not employed and support plate  404  is not required. 
     With reference to FIG. 6 c,  a further feature of substrate  601  is that it is axially through bored such that it has a hollow center,  603 , which is dimensioned such that it snugly accommodates an electrical cartridge style heater, such heaters being well known in the art. 
     With reference to FIG. 7 a,  the spiral type packing  701 , which is the equivalent of spiral packing  601  of FIGS. 6 a,    6   b,  and  6   c,  is inserted into test chamber  703  (dimensioned so that the external fins of spiral packing  701  fit snuggly against the interior walls of testing chamber  703 , testing chamber  703  being the equivalent of chamber  403  of FIG.  4 . It will be appreciated by examining FIG. 7 a  that fluid passed into the top of testing chamber  703  will be forced along the spiral grooves of spiral packing  701 . It will further be appreciated that because it is hollow to accommodate a cartridge heater the ratio of spiral packing  701  surface area to it&#39;s weight is greater than that of a similarly sized solid machined piece, thereby improving the accuracy of gravimetric measurement of deposits left on the surface of spiral packing  701  over similar deposits left on solid shapes of similar design. 
     It will be appreciated from inspection of FIG. 7 a  that when spiral substrate  701  is employed instead of ball bearings, cartridge heater  702  passes through, with reference to FIG. 5, through bored hole  505  in the center of conduit plate  506 . Conduit plate  704  is identical to conduit plate  506  of FIG. 5, and has the same bored through holes and passage ways as conduit plate  506 . With reference to FIG. 7 a,  when spiral substrate  701  is used the heated air stream conducted into the testing chamber through one of the radial passageways (exemplified by passageways  706  and  705 ) bored into conduit plate  701  instead of through central hole  707  as was described for a ball bearing substrate embodiment. 
     It will be appreciated by one skilled in the art that many other forms of substrate may be employed in a suitably designed chamber, such as random shapes, sands, nodules, and coils of material having similar composition and surface finish to the engine components which they model. The only requirements is that they pack in such a manner that passageways are uniformly distributed through the substrate mass, and that they are in sufficient thermal communication with each other and the walls of the test chamber in which they reside that their temperature may be adequately monitored and controlled via the testing chamber heating system and temperature sensing devices associated with the testing chamber as described in detail above. 
     In the preferred embodiment of the present invention the testing apparatus, and therefore the conduct of a test, is controlled automatically by electrically actuated flow control and temperature control devices driven by a computer or industrial controller/timer such as are well known in the art. FIG. 1 indicates which devices are controlled and which are monitored by indicating control or monitor line connection to the various schematic elements. Thus, with reference to FIG. 1, the monitoring lines are shown as heated air heat exchanger temperature monitoring line  141 , substrate temperature monitoring line  142 , and over temperature monitoring line  143 . Temperature sensing devices  144  and  145  may be thermocouples as discussed hereinabove in connection with FIG. 4, thermocouples  421  and  422 . Control lines shown in FIG. 1 are testing gas control lines  153 ,  154 ,  155 , and  156 ; heated air flow control line  151 , substrate heater control line  150 , and air heater control line  152 . The temperature monitoring lines are connected to an automatic controller which receives information from the associated temperature sensitive element, such as are well known in the art, and, using the associated device control line (also connected to the automatic controller) alters the power supplied to the related device to adjust the output according to an operator selected set point. Thus, sensor line  141  transmits signals proportional to the temperature of the air stream passing out of the chamber  101  and the controller adjusts the temperature of the air stream passing out of chamber  101  according to an operator selected set point via control line  152 . In like manner, temperature sensor line  142  sends a signal to the controller proportional to the temperature of the substrate within testing chamber  103  and adjusts power accordingly to heater  106  via control line  150 . In the same fashion, temperature sensor line  143  also sends a signal proportional to the temperature of the substrate within testing chamber  103  and if an operator selected maximum is exceeded the controller shuts off power to heater  106 , discontinues fuel dosing by interrupting power to fuel flow controller  121  via control line  153 , and actuates the fire suppression system, opening flow control device  109  via control line  155 . 
     Furthermore, in the preferred embodiment, in addition to controlling the heaters and flow control devices which vary testing conditions, the controller employed has the capacity to control the timing of fuel dosing/soaking and hot air bake cycle automatically, according to values set by the operator prior to running a determination. Additionally, in the preferred embodiment, the controller contains a testing cycle clock to control the duration of the test, such duration being adjustable by the operator. 
     With Reference to FIG. 10, the best mode contemplated for control and timing of operations such as the opening and closing of valves and control of temperature and flow control in the various devices employed in the subject apparatus is contemplated to be by digital computer fitted with the appropriate interface boards, such as will be familiar to one skilled in the art. By way of example, although not limited to be limiting, a Pentium Corporation OptomuxR System may be fitted to any digital computer of the PC designation to effect the required control of the appratus. It will be apparent to one skilled in the art that any of the numerous other systems designed to collect analog signals and convert them into a format compatible with a digital computer, and to receive digital signals from a digital computer and convert them into signals suitable for actuating control devices may also be employed. It will also be apparent to one skilled in the art that, even though more difficult to implement, control may be achieved by using one or more stand alone programmable controllers such as is exemplified by a Square D products Class 8005 Model 50 Programmable Controller. 
     In the preferred embodiment, all controllers controlling heating devices are capable of effecting the typical control schemes such as are well known in the art, examples of which are (but not limited to) simple analog response, proportional response, and pulsed signal response to an input signal condition calling for adjustment of the conditions in the testing chamber. Other embodiments are contemplated in which controllers having only simple analog or closed loop control capabilities are employed. 
     With reference to FIG. 8, the method of testing a fuel composition for its propensity to form deposits in the apparatus of the present invention is carried in a number of steps. The first step is a weighing step  80 , which requires the operator to weigh out a suitable quantity of substrate material and record its weight. 
     The next step is the charging step  81 , wherein the weighed quantity of substrate material is placed into a test. chamber so that it is in thermal communication with the test chamber and its associated heating and temperature sensing devices. In this step the chamber is sealed and purged out with inert gas. 
     Step  82 , apparatus preparation, follows. Step  82 , includes preheating the test chamber to a predetermined temperature, thereby preheating the substrate contained therein to a predetermined temperature and setting the parameters of temperature set point and cycle duration times for the various heated portions of the apparatus and cycles of the testing method. These settings control the engine conditions simulated in the testing apparatus, thus the operator must select the “on state” times of the fuel dosing and air bake cycles and the soak interval prior to the air bake cycle (cycles detailed below). Additionally, the operator must set the testing cycle clock which determines the overall duration of the test. 
     When the desired temperature is achieved in the substrate, the testing cycle is initiated. The testing cycle includes injecting measured quantities of the fuel composition under test into the test chamber (fuel dosing/soaking step  83 ) followed by a soaking period during which fuel is distributed through the substrate, and then passing preheated air through the test chamber for a selected period of time (air baking step  84 ). Thus fuel dosing/soaking step  83  is carried out by actuating, with reference to FIG. 1, fuel flow stop device  121  via control line  153  for a predetermined period of time form 0.062 seconds to 60 seconds, and then permitting the testing chamber to sit static for any selected period of time. Following that, the air bake step is carried out by actuating, with reference to FIG. 1, air flow control device  120  using control line  151  for any selected period of time between 0.62 seconds and 20 hours. At the end of the air baking step, the flow of preheated air through the testing chamber is discontinued by actuating, with reference to FIG. 1, flow stop device  120  to the closed state. 
     With reference to FIG. 8, fuel dosing/soaking step  83  and air baking step  84  are sequentially repeated while the cycle clock is running. When the testing cycle clock time has elapsed, at the completion of the air bake step in progress or pending, the testing cycle loop is exited and testing chamber purging/cool down step  85  is carried out by purging the testing chamber with nitrogen via, with reference to FIG. 1, purge gas stop flow control device  107  and control line  156 , and powering down testing chamber substrate heater  106  to facilitate cooling the testing chamber and therewith the substrate material contained in the testing chamber. Purging is continued until the testing chamber and substrate are brought to a temperature that permits convenient handling of the substrate material. 
     With reference to FIG. 8, determination step  86  is next carried out, wherein the substrate is removed from the test chamber and weighed, the pre and post test weights being compared and correlated with the results of deposit determinations obtained from tests previously conducted in running compression ignition engines. 
     In the testing method of the subject invention, gravimetric determination is the preferred manner of determining the amount of deposits which have been formed during the testing cycle, however, it will be appreciated by one skilled in the arts that alternative methods of determining the mass increase in the substrate over the course of the test, such as inertial measuring devices or the change in vibronic frequency of an oscillating substrate may be employed, such devices being familiar to those skilled in the art. 
     In an alternate embodiment, during the air bake step  84 , a predetermined flow of fluid simulating exhaust gas or lubricant vapors may be passed into the test chamber by actuating, with reference to FIG. 1, flow stop device  108  via control line  154 . In an alternative embodiment, a plethora of such conduits controlled by such flow stop devices may be employed to provide a wide range of operating parameters during a test. Additional embodiments are possible where other fluids are introduced during any phase of the testing cycle. 
     It will be appreciated by one skilled in the art that the disclosed testing apparatus may be adjusted, by virtue of its electronic control features, such that a wide range of operating conditions may be simulated by adjusting the temperature and volume of the air stream employed in air bake step  84 , the quantity of fuel employed in fuel dosing/soaking step  83 , and the temperature of the testing chamber and substrate employed during the testing cycle. Further modification of the testing method is possible in that with suitable electronic controllers, the temperature of the substrate and air used in the air bake step may be dynamically varied during the course of a testing cycle, further tailoring the testing conditions to simulate conditions found in an operating diesel engine. 
     With reference to FIG. 9, the results of tests conducted in the subject apparatus by the subject method of the instant application are presented showing the effect on deposit formation by addition of an anti-deposit additive to a fuel composition employed in the tests. With reference to FIG. 11, the results of testing in the subject invention testing apparatus are compared with the results obtained from L-10 diesel engine tests, and a close correlation between the two methods is observed. 
     Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. Accordingly, patent protection commensurate with this invention is sought as provided by law, with particular reference to the following claims.