US3640255A

US3640255A - Carburetor adjusting method

Info

Publication number: US3640255A
Application number: US86930A
Authority: US
Inventors: Frederick L Voelz
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1970-11-04
Filing date: 1970-11-04
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: CA958612A

Abstract

A method for optimizing the performance of an internal combustion engine carburetor to minimize the amounts of carbon monoxide and hydrocarbons in the engine exhaust gases while still providing for an efficiently operating engine is disclosed. The method involves adjusting the air-fuel mixture to the carburetor so as to minimize the amount of hydrocarbons in the engine exhaust gases.

Description

United States Patent Voelz 5] Feb.8,1972

[54] CARBURETOR ADJUSTING METHOD [72] Inventor: Frederick L. Voelz, Orland Park, Ill.

[73] Assignee: Atlantic Richfield Company, New York,

[22] Filed: Nov. 4, 1970 [21] Appl. No.: 86,930

[52 U.S.Cl. ..123/119n 511 lnt.Cl ...F02m3/00 [5s fieldofSeai-ch ..123/119 OTHER PUBLICATIONS Internal Combustion Engines by Gill, Smith, & Ziurys Lincoln 1968 Shop Manual Supp. Lincoln Mercury Div. Ford Motor Co. (pp. 10-9, 1040, 10-1 I) The Automobile & Air Pollution Part ll U.S. Dept. of Comm. 12-67 (pp. 36, 37. 38 & 39)

Primary Examiner-Laurence M. Goodridge Attorney-Robert J. Mawhinney and Thomas J. Clough [57] ABSTRACT 10 Claims, No Drawings CARBURETOR ADJUSTING METHOD This invention relates to a method for reducing air pollution from intemal'combustion engines. More particularly, this invention relates to a method for optimizing the operation of the carburetor of an internal combustion engine'so as to achieve both a smooth, efficient running engine and a minimum amount of harmful engine exhaust emissions.

The internal combustion engine manufactures useful power by the explosive combustion of fuel, normally of the hydrocarbon type, such as natural gas, gasoline, kerosene, diesel fuel, etc., and oxygen, normally taken from the air; Prior to combustion, the fuel and oxygen are intimately mixed in controlled amounts. This mixing occurs in a carburetor. The carburetor normally is equipped with at least one idle mixture screw the position of which can be adjusted (e.g., by turning the screw in or out) to vary the air-fuel ratio (by varying the amount of either fuel or air) to the engine combustion chambers. In an important sense, the operational efficiency of the internal combustion engine depends on the carburetor being properly adjusted. If the engine receives an air-fuel mixture overly lean in fuel, the engine will run rough due to not being able to sustain combustion in one or more of the cylinders, i.e.', one or more of the cylinders will miss. On the other hand, if the engine receives a mixture overly rich in fuel, the engine will be wasteful, uneconomical and tend to develop excessive harmful deposits.

Many methods for adjusting carburetors have sought to control the air-fuel ratio at the value specified by the engine manufacturer. These methods, and in fact the manufacturerset air-fuel ratios, have, as a primary goal, the smooth operation of the engine. None of these methods seek to adjust the carburetor so as to give a smooth, efficient running engine which emits a minimum amount of air pollutants, such as carbon monoxide and hydrocarbons. in fact, engines may emit larger amounts of these pollutants after having the air-fuel ratio adjusted to the manufacturer-set value than before the adjustment. This is disadvantageous since internal combustion engine exhaust emissions, such as from automobiles, trucks and other transportation means, contribute significantly to the airpollution problem.

Therefore, one of the objects of the present invention is to provide an improved method for optimim'ng the operation of an internal combustion engine carburetor. Other objects and advantages of the present invention will become apparent hereinafter. v

The present invention comprises a method for optimizing the operation at idle of an internal combustion engine carburetor, equipped with at least one idle mixture screw the position of which may be adjusted (e.g., turned) to vary the airfuel ratio to the engine combustion chambers. In one embodiment, the present invention is a method which comprises:

i. analyzing for the hydrocarbon concentration of the exhaust gases from the engineequipped with the carburetor 7. setting the position of the idle mixture screws so that the corresponding air-fuel ratio provides an engine exhaust gas hydrocarbon concentration within a range from zero to about 50 p.p.m. above the minimum hydrocarbon conoentration observed in steps l), 3) and (6).

Note that in step (7) it may be unnecessary to readjust the position of the idle mixture screws if the last idle mixture screw adjustment in step (6) results in an increase in hydrocarbon concentration of about 50 p.p.m. or less. In this situation the last idle mixture screw position set in step (6) gives aproper carburetor adjustment according to the method 7 of the present invention and this modification of the method is expressly included in the scope of the present invention.

In order to insure a smooth, efficiently running engine while maintaining substantial pollution control benefitsfrom the present invention, it is preferred to adjust the carburetor to feed a slightly rich (rather than a slightly lean) air-fuel mixture to the engine. Therefore, in a preferred embodiment of the present invention, step (7) of the above method involves adjusting the position of the idle mixture screws so that the corresponding air-fuel ratio contains a maximum proportion of fuel'and provides an exhaust gas hydrocarbon concentration a range from zero to about p.p.m. above the miniminh hydrocarbon concentration observed in steps (l), (3) and (6). In a more preferred embodiment of the present invention, step (7) involves adjusting the position of the idle mixture screws so that the corresponding airfuel ratio provides the minimum exhaust gas hydrocarbon concentration observed in' steps (I), (3) and (6). Due to hydrocarbon analysis lirnitations and/or the characteristics of the particular carburetor being optimized, more than one air-fuel ratio may provide at engine exhaust gas having the same minimum hydrocarbon concentration observed in steps (1 (3) and (6). Therefore, in the most preferred embodiment of the present invention, step (7) comprises adjusting the idle mixture screws so that the corresponding air-fuel ratio contains a minimum proportion of fuel and provides the minimum exhaust gas hydrocarbon concentration observed in steps l (3) and (6 In practicing the method of the present invention, it is possible I that the first two (or more) exhaust gas analyses will show the being optimized, the exhaust gases being sampled while the engine is operated at essentially constant conditions on the idle carburetion circuit at normal engine operating temperatures;

2. adjusting the position of the idle mixture screws by a small increment to change the air-fuel ratio;

3. repeating step l with the air-fuel ratio being changed as in step (2).

4. adjusting the position of the idle mixture screws by a small increment to change the air-fuel ratio in the direction of decreasing hydrocarbon concentration, said direction of decreasing hydrocarbon concentration being determined by comparing the hydrocarbon concentrations obtained in steps l and (3 repeating step (1 with the air-fuel ratio being changed as in step (4);

tained in the immediately preceding analysis; and

same hydrocarbon concentration. in this instance, it is necessary to further adjust the idle rnixture screws by a small more ment and again analyze the exhaust gases in order to determine the direction of decreasing hydrocarbon concentration. This modification is expressly included in the scope of the present invention as outlined in step 1 to (7) above.

In' order that the minimum exhaust gas hydrocarbon concentration obtainable be approximated by practicing the method of the present invention, it is necessary that the position of the idle mixture screws be adjusted in small increments. In most cases, this means that the idle mixture screws are adjusted, i.e., turned, less than about one-half turn (e.g., one-fourth turn); preferably less than about one-fourth turn (e.g., one-eighth turn); and more preferably less than about one-eighth turn (e.g., one-sixteenth turn) between exhaust gas hydrocarbon analyses. Of course, while practicing the method repeating steps (4) and (5) at least until an analysis shows of the present invention it is possible, and may even be preferred, to adjust the position of the idle mixture screws by different sized small increments. For example, as you ap' preach the minimum exhaust gas hydrocarbon concentration, the idle mixture screw adjustment between analyses may be made smaller in order to fine tune the carburetor.

It is preferred to practice the present invention with a carbure'tor which initially provides an overly rich air-fuel mixture. One reason for this is because an engine operating on an overly rich air-fuel mixture will run smoothly and, therefore, provide an exhaust gas having a consistent hydrocarbon concentration, whereas an engine operating on a lean air-fuel mixture tends to have uneven fuel combustion and provides an exha'iist gas having an inconsistent (i.e., nonreproducible hydrocarbon concentration. Also, since the exhaust gas hydrocai'bon concentration is generally less sensitive to changes in idle mixture screw position with an overly rich airfuel mixture, approaching the minimum hydrocarbon concentration from the rich side is more convenient than from the lean" side. If the carburetor is known to initially provide an overly rich air-fuel mixture, it is preferred that step (2) of the method as outlined above comprise adjusting the position of the idle mixture screws by a small increment to increase the air-fuel ratio (i.e., reduce the fuel proportion or increase the air proportion of the air-fuel mixture).

Engine operation with an overly rich air-fuel mixture can be assured by increasing the fuel proportion beyond that needed to give a smooth running engine. This may be done in many ways. For example, one may adjust the air-fuel ratio to the manufacturer-set value and then increase the fuel proportion (or reduce the air proportion). Altemately, one may lightly seat the idle mixture screws (i.e., seal off completely the fuel or air to the engine without applying excessive force to the idle mixture screws which might cause permanent damage to the carburetor) and then turn open the idle mixture screws to a point which, from experience, is known to give an overly rich air-fuel mixture. This latter method is preferred since lightly seating the idle mixture screws tends to cause certain carburetor deposits to be jarred loose, thus providing a cleaner carburetor which when adjusted will maintain this proper adjustment for a substantial period of time.

While practicing the method of this invention, the engine choke system, if any, should be completely open so that this system does not restrict the flow of air to the engine. A completely open choke system can be obtained by operating the engine for a sufficient length of time to achieve normal operating temperature. Of course, the choke system can also be manually disengaged from the engine so that it will not interfere with the testing procedure. However, the engine should be run at normal operating temperatures when the carburetor is being adjusted. Generally, normal operating temperatures for internal combustion engines are from about 170 to about 240 F. (engine block temperature).

In order to achieve maximum benefit from the invention, i.e., a proper carburetor adjustment for a reasonably long period of time, it may be necessary to perform certain maintenance on the engine prior to adjusting the carburetor. In particular, it is preferred to adjust a carburetor that is free of deposits and/or other contaminants that might cause fuel or air blockages and thus disrupt the carburetor adjustment. Various components of the air and fuel intake systems, e.g., carburetor air filter element, positive crankcase ventilation system (if any), etc., as well as the carburetor itself can be inspected and maintenance performed if necessary prior to making the carburetor adjustment.

Any carburetor which is used to provide a mixture of fuel and combustion air to an internal combustion engine is capable of being adjusted according to the method of the present invention. These carburetors may have one or a plurality (e.g., two, four) of mixing chambers or jets.

In order to practice this invention, the internal combustion engine equipped with the carburetor to be adjusted is operated on the idle carburetion circuit. Idle carburetion circuit operation is normally achieved at engine speeds from about 400 rpm. to about 1,100 rpm. The engine operated in the practice of this invention may be the engine normally equipped with the carburetor to be adjusted, or it may be any other internal combustion engine capable of employing this carburetor to provide a controlled fuel-air mixture. For convenience, speed and accuracy of adjustment, it is preferred that the test engine be the engine normally equipped with the carburetor to be adjusted. The engine idle speed is preferably set according to the manufacturer's specification both before and after the carburetor adjustment. Included among the internal combustion engines used in the practice of this invention are those engines operated in association with transportation means such as automobiles, trucks, etc. Internal combustion engines not associated with transportation means can, of course, also be used in the practice of this invention. Engines which are used and/or designed for testing purposes are also suitable. In fact, any internal combustion engine, including two-cycle engines, four-cycle engines, rotary piston driven engines and turbine engines, which uses a carburetor to provide a air-fuel mixture can be utilized in the practice of the present invention.

The hydrocarbon concentration of the exhaust gases may be analyzed for in any conventional manner known to the art. Ineluded among these conventional analytical methods are: gas chromatography, mass spectrometry, and infrared spectrometry. Because of the speed and accuracy of the final analysis, it is preferred to utilize infrared spectrometry in the practice of the present invention. In particular, the use of nondispersive infrared (NDIR) analyzers is preferred in the practice of this invention. These infrared analyzers operate on the known principle that hydrocarbons absorb infrared energy having a specific wavelength. When infrared energy is sent through a stream of engine exhaust gas, a certain amount of energy is absorbed by the hydrocarbons in the gas stream. The amount of absorbed energy has a direct relationship to the volume concentration of hydrocarbon in the exhaust gas. By comparing, normally using electronic means, the amount of infrared energy of the wavelength absorbed by hydrocarbons remaining with the original amount of infrared energy of this wavelength, it is possible to determine the amount of hydrocarbon in the exhaust gas. This type of infrared analyzer can be packaged as a relatively portable instrument. This analyzer mobility is an additional reason for prefem'ng infrared spectrometry for analyzing the engine exhaust gases for hydrocarbon concentration.

When adjusting carburetors of internal combustion engines that are associated with automobiles and other motor vehicles, it is preferred to sample the engine exhaust gases for hydrocarbon analysis from the exhaust system effluent, i.e., tailpipe effluent. Since the engine exhaust system, (i.e., mufiler, tailpipe, etc.) is subject to great wear, the possibility of gas leaks exists. Therefore, in order to insure the accuracy of the tailpipe effluent hydrocarbon analysis, it is preferred that if the tailpipe effluent is used as a source of exhaust gas samples, the engine exhaust system be tested for gas leaks at some point during the practice of this invention. It is preferred that the leak testing take place prior to any carburetor adjusting taking place.

The exhaust system leak testing can be accomplished in any conventional manner, for example, visual inspection of the exhaust system. However, the preferred method of leak testing is to analyze the tailpipe effluent for oxygen concentration. It is well known that the exhaust gases from a conventional fourcycle internal combustion engine (standard automobile engine) contain about 1 to about 4 percent by volume of oxygen. Any significant deviation, for example, by at least about 3 percent by volume from the upper limit of this range, indicates a leak in the engine exhaust system. Exhaust gases from engines which are equipped with air injection emission control devices normally contain between about 7 to about 20 percent by volume of oxygen and, therefore, may be deemed insensitive to the oxygen analysis" method of testing for air leaks. The oxygen concentration can be determined by any conventional method, such as amperometric methods, magnetic susceptibility methods, mass spectrometry and gas chromatography. The preferred methods of oxygen analysis are the amperometric methods.

The following procedure may be used in the practice of the present invention to optimize the performance of a single barrel carburetor. This type of carburetor has only one idle mixture screw which can be turned, for example, counterclockwise to allow more fuel to flow to the engine and, conversely, clockwise to reduce the amount of fuel to the engine. While practicing the present invention, the engine is operated at essentially constant conditions on the idle carburetion circuit at normal operating temperatures. The idle mixture screw may be lightly seated and then adjusted so as to provide an overly rich air-fuel mixture to the engine. At this point, the engine exhaust gases are analyzed for hydrocarbon content and the concentration is noted and recorded. Next, the idle mixture screw is turned clockwise by a small increment, for example, onewfourth turn, to reduce the amount of fuel to the engine and the exhaust gases are again analyzed for hydrocarbon concentration. The steps of clockwise adjustment of the idle mixture screw and analysis of the engine exhaust gases are re- 5 ficient running and the amounts of carbon monoxide and hydrocarbon emitted in the engine exhaust gases are minimized.

The same general procedure can be followed in adjusting carburetors having a plurality of barrels (e.g., two, four) according to the method of the present invention. Carburetors with two or four barrels each have two primary passages or jets. Each primary jet has its own idle mixture screw. One additional factor that must be considered in adjusting these multiple barrel carburetors is that it is important that each of the idle mixture screws be balanced, so that the same amount of fuel enters each mixing chamber. To insure proper balance, each idle mixture screw is set at the same relative position. One method of insuring that the idle mixture screws are in the same relative position is to turn each screw so that it becomes lightly seated against the body of the carburetor. Each screw is then turned in the opposite direction a set number of turns. This procedure may be followed for each idle mixture screw in turn in order to avoid causing the engine to stop from complete lack of fuel (this will occur if all the idle mixture screws are lightly seated at the same time). Not only does this procedure balance the idle mixture screws, but also it may help to free the carburetor jets of deposits and other dirt. When making adjustments to the screw positions, each screw should be moved the same amount. The same criterion for a minimum emissions adjustment applies to the multiple barrel carburetors as to the single barrel carburetors.

The following example illustrates the method of the present invention. However, this illustration is not to be interpreted as a specific limitation on this invention.

EXAMPLE 1 A 1968 Oldsmobile automobile powered by 455 cubic inch displacement, eight-cylinder, four-cycle, internal combustion engine equipped with a two-barrel carburetor was chosen for formance, the carburetor was properly adjusted. Exhaust gas hydrocarbon concentrations were obtained by sampling the tailpipe effluent and analyzing for hydrocarbons by means of a portable electronic nondispersive infrared analyzer.

After each idle mixture screw adjustment and before the collection of the corresponding sample of exhaust gas for hydrocarbon analysis, the engine was run at an elevated speed (approximately 2,000 rpm.) for about 30 seconds to clear the engine exhaust system and to insure the collection of a representative sample of exhaust gas. The initial idle hydrocarbon analysis indicated that the engine exhaust gas contained 430 p.p.m. hydrocarbon. Both idle mixture screws were adjusted equally, about one-half turn to reduce the amount of fuel to the engine. A hydrocarbon analysis indicated that the exhaust gases at this point contained 380 p.p.m. hydrocarbon. The fuel proportion of the fuel-air mixture was again reduced by turning each of the idle mixture screws one-half turn and the hydrocarbon concentration of the exhaust gases was found to be 340 p.p.m. The fuel proportion was again reduced (by adjusting each screw one-half turn) and the hydrocarbon concentration was 300 p.p.m. Further fuel proportion reductions (by adjusting each screw onefourth turn) resulted in exhaust gas hydrocarbon concentrations of 290 p.p.m., 280 p.p.m., 260 p.p.m., 270 p.p.m., 290 p.p.m., 300 p.p.m., and 360 p.p.m., at which point the engine was noticeably rough in operation. The idle mixture screws were adjusted back to the point where the resulting fuel proportion gave an exhaust gas hydrocarbon concentration of 260 p.p.m.

With the exhaust gas hydrocarbon concentration at 260 p.p.m., the engine operated smoothly and efficiently. The reduction in hydrocarbon concentration from the initial analysis was p.p.m. or more than 39 percent. The initial exhaust gas carbon monoxide concentration was about 7.7 percent by volume, while the engine exhaust gas with the carburetor adjusted as above contained 1.4 percent by volume carbon monoxide. This represented a reduction of about 68 percent in exhaust gas carbon monoxide concentration.

As the above emission reduction data indicate, the present invention can result in a significant improvement in the amounts of hydrocarbon and carbon monoxide emitted from internal combustion engines. This reduction in the amount of these han'nful pollutants is achieved without sacrificing the operating efficiency of the internal combustion engine.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for minimizing the amount of hydrocarbons emitted in the exhaust gas from an internal combustion engine which utilizes a carburetor to provide an air-fuel mixture to said engine, said carburetor being equipped with at least one idle mixture screw the position of which may be adjusted to vary the air-fuel ratio of said mixture, which method com- P118881 1. seating said idle mixture screw against the body of said carburetor;

2. adjusting the position of said idle mixture screw so as to provide an overly-rich air-fuel mixture to said engine;

'3. adjusting the engine idle speed to an essentially constant speed on the idle carburetion circuit in the range from about 400 rpm. to about 1,100 r.p.m. analyzing for the hydrocarbon concentration of the exhaust gases from said engine collected while said engine is operated at essentially constant conditions on the idle carburetion circuit at normal operating temperatures;

5. adjusting the position of said idle mixture screw by a small increment to reduce the proportion of fuel in said air-fuel mixture;

6. repeating step (4) with the air-fuel ratio being as adjusted in step (5);

7. repeating steps (5) and (6) at least until an analysis shows an increase in hydrocarbon concentration over that obtained in the immediately preceding analysis; and

8. setting the position of said idle mixture screw so that the corresponding air-fuel ratio gives an exhaust gas hydrocarbon concentration within the range from zero to about 50 p.p.m. above the minimum hydrocarbon concentration observed in steps (4), (6) and (7).

2. The method of claim ll wherein step (8) comprises maintaining the position of the idle mixture screw as last adjusted in step (7).

3. The method of claim 1 wherein step (8) comprises setting the position of the idle mixture screws so that the corresponding air-fuel ratio contains a maximum proportion of fuel and provides an exhaust gas hydrocarbon concentration within a range from zero to about 50 p.p.m. above the minimum hydrocarbon concentration observed in steps (4), (6) and (7 4. The method of claim 1 wherein step (8) comprises setting the position of the idle mixture screws so that the corresponding air-fuel ratio provides the minimum exhaust gas hydrocarbon concentration observed in steps (4), (6) and (7).

5. The method of claim 1 wherein said small increment is less than about one-half turn.

6. The method of claim 4 wherein step (8) comprises setting the position of the idle mixture screws so that the corresponding air-fuel ratio contains a minimum proportion of fuel and provides the minimum exhaust gas hydrocarbon concentration observed in steps (4), (6) and (7).

7. The method of claim 3 wherein said exhaust gases are

Claims

1. A method for minimizing the amount of hydrocarbons emitted in the exhaust gas from an internal combustion engine which utilizes a carburetor to provide an air-fuel mixture to said engine, said carburetor being equipped with at least one idle mixture screw the position of which may be adjusted to vary the air-fuel ratio of said mixture, which method comprises: 1. seating said idle mixture screw against the body of said carburetor; 2. adjusting the position of said idle mixture screw so as to provide an overly-rich air-fuel mixture to said engine; 3. adjusting the engine idle speed to an essentially constant speed on the idle carburetion circuit in the range from about 400 r.p.m. to about 1,100 r.p.m.; 4. analyzing for the hydrocarbon concentration of the exhaust gases from said engine collected while said engine is operated at essentially constant conditions on the idle carburetion circuit at normal operating temperatures; 5. adjusting the position of said idle mixture screw by a small increment to reduce the proportion of fuel in said air-fuel mixture; 6. repeating step (4) with the air-fuel ratio being as adjusted in step (5); 7. repeating steps (5) and (6) at least until an analysis shows an increase in hydrocarbon concentration over that obtained in the immediately preceding analysis; and 8. setting the position of said idle mixture screw so that the corresponding air-fuel ratio gives an exhaust gas hydrocarbon concentration within the range from zero to about 50 p.p.m. above the minimum hydrocarbon concentration observed in steps (4), (6) and (7).

2. The method of claim 1 wherein step (8) comprises maintaining the position of the idle mixture screw as last adjusted in step (7).

3. The method of claim 1 wherein step (8) comprises setting the position of the idle mixture screws so that the corresponding air-fuel ratio contains a maximum proportion of fuel and provides an exhaust gas hydrocarbon concentration within a range from zero to about 50 p.p.m. above the minimum hydrocarbon concentration observed in steps (4), (6) and (7).

3. adjusting the engine idle speed to an essentially constant speed on the idle carburetion circuit in the range from about 400 r.p.m. to about 1,100 r.p.m.;

4. analyzing for the hydrocarbon concentration of the exhaust gases from said engine collected while said engine is operated at essentially constant conditions on the idle carburetion circuit at normal operating temperatures;

4. The method of claim 1 wherein step (8) comprises setting the position of the idle mixture screws so that the corresponding air-fuel ratio provides the minimum exhaust gas hydrocarbon concentration observed in steps (4), (6) and (7).

6. repeating step (4) with the air-fuel ratio being as adjusted in step (5);

7. The method of claim 3 wherein said exhaust gases are analyzed for hydrocarbon concentration by means of infrared spectrometry.

8. The method of claim 6 wherein said exhaust gases are analyzed for hydrocarbon concentration by means of infrared spectrometry.

9. The method of claim 7 wherein said small increment is less than about one-eighth turn.

10. The method of claim 7 wherein said essentially constant idle speed is a speed within the range of speeds recommended by the manufacturer of said engine.