Patent Application
20100228466
1. Field of the Invention
This invention relates to the improved performance and reduced emissions from internal combustion (IC) engines during cold temperature, and light and moderate load operation. It involves increasing the time available for in-cylinder physical and chemical processes under certain conditions, increasing the rates of these processes and increasing cylinder-out temperatures to improve performance of exhaust emission control devices.
2. Description of Prior Art
IC engines convert fuel chemical energy into useful mechanical energy. They have long been recognized as low cost, flexible, and robust power-plants for a broad spectrum of applications. Over the past 25 years, automotive scientists and engineers worldwide have made major advances in the use of IC engines for transportation.
In IC engines, fuel and air are mixed, and ignited and allowed to burn in a combustion chamber in a cylinder. The resulting elevated as pressure causes a piston located within the cylinder to move. The linear motion of the piston is typically convened to rotary motion of the engine output shaft by means of a slider crank mechanism although other mechanisms, such as a Scotch Yoke, may be utilized. The products of combustion are subsequently discharged from the cylinder and the cycle is repeated.
Most IC engines manufactured today use cycles that comprise four strokes or processes: 1) the intake stroke where air or an air-fuel mixture is admitted into the engine cylinder via one or more intake valves, 2) the compression stroke where the engine cylinder is sealed and the air or air-fuel mixture is compressed as a result of the motion of a piston, 3) the power or expansion stroke where an air-fuel mixture is burned and the high pressure resulting from the combustion acts to move the piston and to produce work, and 4) the exhaust stroke where the products of combustion are expelled from the cylinder via at least one open exhaust valve.
Most IC engine powerplants in use today are either spark ignition (SI) engines or compression ignition (CI) engines. In conventional SI (CSI) engines, fuel is typically added to air outside the cylinder and the resulting fuel-air mixture is ignited with a spark plug after being compressed in the cylinder. In CI engines, fuel is typically injected into the compression heated air in the cylinder late in the compression process which then spontaneously auto-ignites. CI engines operate primarily with a lean overall air-fuel ratio, while CSI engines typically utilize a stoichiometric air-fuel mixture. In some SI engines, at least some of the fuel is injected into the cylinder. Such injection spark ignition (ISI) engines, where fuel is injected into the cylinder, may operate with a lean or stoichiometric overall air-fuel ratio. In some IC engines, exhaust gas recirculation (EGR), where some of the exhaust gas is returned to the intake, is used to reduce certain emissions.
Present day transportation IC engines exhibit very high combustion efficiency and produce exceptionally low pollution levels during normal operating conditions. Combustion efficiency is the fraction of the fuel energy supplied to an engine cylinder that is released by combustion. Under normal operating conditions, combustion efficiency is typically in excess of 98%. However, in certain situations, IC engines suffer from poor combustion, high emissions and degraded performance. For example, during start-up, especially when the engine is cold (cold-start), both SI and CI engines are susceptible to erratic operation, such as misfire, and high emissions. Under such conditions, combustion efficiency can be as low as zero. Also, during operation at light and moderate loads, even fully warmed up engines, that operate with leaner than stoichiometric air-fuel ratios, suffer from relatively cool exhaust. This is problematic when emission control equipment, such as particulate traps, are used. Such devices require periodically elevated exhaust gas temperatures to operate properly.
Under normal circumstances, the fuel and air charge in CSI engines is well mixed by the time ignition occurs. It is a stoichiometric, combustible mixture with very few, if any, rich or lean pockets. Ignition typically occurs as the piston approaches the end of the compression stroke commonly called the top center (TC) position. Common fuels used in CSI engines include gasoline, alcohol, and alcohol-gasoline blends. Recently there has been increasing interest in the use of natural gas and even hydrogen.
During the last few decades there has been a dramatic reduction in tail pipe emission of unburned hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx) from vehicles powered with CSI engines. Key to this reduction has been the development, use and continued improvement of the three-way catalytic converter (TWC). The TWC has proven to be exceptionally effective under most operating conditions. It is external to the engine and acts on the exhaust gases after they leave the cylinder through the exhaust valve. When the TWC reaches normal operating temperature, it is capable of removing substantially all of the HC, CO & NOx pollutants produced by the SI engine so long as the engine is operated at a stoichiometric overall air-fuel ratio.
However, the TWC is ineffective at low temperatures, such as during cold-start. Under these conditions, the TWC does not appreciably reduce cylinder-out emissions before they leave the exhaust pipe. Therefore, whatever is produced in the cylinder largely escapes into the atmosphere. As a result, the bulk of HC and CO emissions from an SI engine powered vehicle with a TWC are typically produced during approximately the first 60 seconds of operation. This is largely because it takes approximately 60 seconds for the TWC to reach operational temperatures. Various types of auxiliary catalyst heaters have been tested in the laboratory to accelerate this warm-up process, but have not achieved widespread use due to drawbacks such as high cost, excessive electrical load and adverse fuel economy impact.
When the engine is cold, not only is the TWC ineffective, but the chemical processes in the cylinder are also sub-optimal and produce high amounts of emissions. Typically, the time available for evaporation and mixing before ignition must occur in SI engines is very limited. At cold temperatures, slower evaporation rates hamper proper mixture formation in the cylinder. As a result, even if the overall fuel and air mixture supplied to an engine is stoichiometric, the mixture can become stratified so that very lean and very rich pockets are produced. Such lean pockets are typically difficult to ignite. If a lean pocket happens to be located in the region of the spark plug at the time it discharges, misfire may result. Even if the mixture is successfully ignited, the temperature and local stoichiometry in the vicinity of the ignition site may be such that the flame cannot be sustained, still resulting in partial or complete misfire.
Misfire frequently leads to high concentrations of HC or CO in the exhaust, excessive cyclic engine torque variability and a cool exhaust temperature. To reduce the likelihood of such problems, engine designers frequently resort to over-fueling the engine during cold-start. The overall equivalence ratio of the mixture is made richer which reduces the chances of misfire and reduces cyclic variability. However, the richer overall stoichiometry exacerbates the HC and CO emissions. Consequently, large amounts of unburned or partially burned fuel are expelled from the cylinder during the exhaust process under such conditions. Poorly combusted mixtures are necessarily cooler. The problem is therefore compounded by the fact that the high emissions cannot be eliminated by the cold TWC. This results in a vicious cycle where the TWC in turn is not warmed up quickly because of the cool exhaust temperatures.
In 4-cycle injection engines such as CI and ISI engines, the bulk of the fuel is typically injected into the cylinder during the intake or compression strokes although some fuel may be added to the air before it is inducted into the cylinder. In some injection engines, fuel is injected into a separate chamber, called a pre-chamber, that is in communication with the cylinder. The fuel injection into the cylinder occurs during the intake or compression processes in the form of a single or multiple injection pulses. Under normal operating conditions, the fuel rapidly atomizes, evaporates and mixes with the gases in the cylinder. In CI engines the mixture typically auto-ignites without the intervention of a spark device when it is injected into the compression heated gases in the cylinder. CI engines typically use diesel fuel and operate under leaner than stoichiometric overall equivalence ratios at all times. In ISI engines, a spark source is typically used and the engines may operate under overall lean or stoichiometric conditions.
Ignition in IC engines may occur by means other than a spark plug, such as homogeneous charge compression ignition (HCCI). HCCI is an ignition process whereby an air-fuel charge is allowed to simultaneously auto-ignite throughout the entire combustion chamber. Examples of an HCCI implementation are disclosed in U.S. Pat. Nos. 5,535,716, 7,343,902 and 7,461,627 that are incorporated herein by reference in their entirety.
TWC's are typically lot used with IC engines that operate primarily at other than stoichiometric conditions. However, cold-start is a problem in lean operating injection engines, such as CI and ISI engines, as well. As in CSI engines, start up under cold ambient conditions in injection engines can lead to partial or total misfire due to poor fuel evaporation, mixing, ignition and combustion. As a result, rough operation and excessive emissions may result. In CI engines, these difficulties can sometimes be diminished but not eliminated by the use of glow plugs.
Because CI and lean ISI engines operate with excess air, the exhaust from even a warmed up engine may be relatively cool. This dilution, which results in depressed exhaust temperatures especially at light and moderate operating conditions, makes it difficult to operate some exhaust treatment devices. Devices such as particulate traps, that must be used to control soot emissions, rely on heat from the exhaust for regeneration. Circulating large quantities of excess air through the system also results in additional pumping losses and fouling of engine components such as filters.
This invention ameliorates these limitations of IC engines during certain operating conditions in an effective manner without disturbing their performance under normal operating conditions.
It is a primary object of this invention to improve the performance of IC engines under certain operating conditions where cold engine temperatures result in poor combustion, high emissions and low cylinder-out temperatures. Cylinder-out temperature is the mean temperature of the gas leaving the cylinder through an exhaust valve. This mean is determined by mass averaging the instantaneous exhaust temperature over the period that the valve is open. Improved performance is achieved by extending the time available for in-cylinder processes such as evaporation, mixing and combustion. The increase in time available is achieved by modifying conventional 4-stroke valve timing to include additional expansion and compression strokes between an intake stroke and any subsequent discharge of mass from the cylinder, such as a result of an exhaust stroke.
It is a further object of this invention to have at least one fuel injection event in each of at least two compression strokes in a lean injection engine, such as CI and lean ISI, which occur between an intake stroke and any subsequent discharge of mass from the cylinder. Any combustion products generated as a result of an earlier fuel injection event are retained to increase the temperature of the gas in the cylinder and accelerate physical and chemical processes during subsequent compression and expansions strokes.
It is a further object of this invention to have at least one fuel injection event in an injection engine during one compression or one expansion stroke where at least some of the combustion of the resulting fuel and air mixture occurs during a subsequent compression or expansion stroke and before cylinder contents are discharged from the cylinder.
It is a further object of this invention to expose liquid fuel in an IC engine cylinder to lowered cylinder pressures after fuel delivery to the cylinder to induce liquid fuel break up by means of bubble formation in the liquid fuel.
It is a further object of this invention to increase the cylinder-out temperature of a CI or lean ISI engine during light and moderate load operation.
It is a further object of this invention to increase the cylinder-out temperature from an IC engine cylinder before the engine has reached operating temperature such as during cold start.
It is a further object of this invention to reduce cylinder out emissions from CSI engines during certain operating conditions, such as cold start, where the engine is cold.
It is a further object of this invention to open cylinder valves in an IC engine late during the intake stroke or early during the compression stroke if the pressure in the cylinder is low compared to the pressure upstream of the valves, causing a rush of incoming gases to supplement the mass in the cylinder or enhance mixing within the cylinder.
It is a further object of this invention to enhance the regeneration of particulate traps by increasing cylinder-out temperatures at low and moderate loads in lean engines.
In today's CSI engines that use liquid fuel, the fuel is typically added to the air outside a cylinder at a point just upstream of the intake valve. Either before or after entering the cylinder through one or more valves, the fuel must evaporate and thoroughly mix with the air prior to ignition. These processes must occur very quickly, typically within 0.2 seconds or less. When the engine is cold, such as during cold start, the rate of evaporation is slowed. As a result, a substantial fraction of the fuel supplied to a cylinder can survive in liquid form in the cylinder until ignition or later. Fuel in liquid form cannot be effectively mixed with air to produce an ignitable or combustible mixture and may therefore leave the cylinder during exhaust without burning.
Under cold operating conditions, chemical reaction rates are also diminished such that even fuel that has vaporized may not ignite properly. Even fuel that is successfully vaporized and ignited may fail to burn completely in a timely fashion. Under such conditions, if the exhaust valves are opened with a conventional 4-stroke cycle timing, a substantial quantity of unburned or partially burned fuel may be expelled from the cylinder. Such exhaust gases would also not attain an elevated temperature since a substantial portion of the heating value of the fuel would not have been released. Therefore, even if the engine is fitted with a TWC, under these conditions such emissions would not be effectively eliminated because of the poor performance of an unheated converter.
According to one embodiment of this invention, the intake and exhaust valves of an IC engine cylinder are timed to retain any unburned or partially burned mixture for additional compression and expansion strokes so that they may be fully burned prior to being expelled from the cylinder. Furthermore, heat released during earlier strokes is used to accelerate physical and chemical processes during subsequent strokes.
According to a further embodiment of the invention, the valves of an IC engine are timed to expose liquid fuel in the cylinder to lowered pressures to facilitate liquid fuel break up. According to the invention, the intake valves are opened and fuel and air are inducted into a cylinder where at least a portion of the fuel may be in liquid form. The intake valve or valves are then closed to seal the cylinder substantially before the piston reaches the bottom center (BC) position, so that the pressure in the cylinder drops. The earlier the valve is closed, the lower the pressure that will be achieved. The lower pressure will cause certain low boiling point portions of the fuel or dissolved air in the fuel to rapidly form bubbles. This will help break apart the liquid fuel droplets or film and the resulting smaller droplets will evaporate more readily. If necessary, at least one intake valve or exhaust valve may subsequently be opened to allow additional air or air-fuel mixture to rush into the cylinder either before or after the piston reaches the BC position. The resulting rush of gas into the cylinder may also help mix the air and the fuel within the cylinder and improve the uniformity of the mixture in the cylinder.
Late in the compression process or early in the expansion process of the SI engine, the ignition source is triggered to ignite the air-fuel mixture. The mixture may also be ignited by other means such as HCCI.
Under certain circumstances, ignition and subsequent combustion may be ineffective or partially effective leaving a substantial amount of unburned or partially burned fuel in the cylinder. Opening the exhaust valve under such condition will result in a high level of emissions being expelled from the engine. When the piston approaches the position where the exhaust valves may normally be opened in a conventional 4-stroke cycle or at any convenient point after ignition, engine or cylinder sensors may be used by onboard processors to determine the burned fraction of the mixture in the cylinder and whether the extending the cycle may be beneficial. If it is determined not to extend the cycle, the exhaust valves may be opened to discharge the contents of the cylinder. Sensors that can be used to evaluate the state of the mixture in the cylinder include pressure, luminosity, temperature, and oxygen sensors, or crankshaft acceleration detectors. Look up tables may also be used to estimate the fraction of burned mass based on engine operating and ambient conditions. The engine cylinder may then be returned to conventional 4-stroke operation for subsequent cycles. This decision may be independent of whether or not the other cylinders of a multi-cylinder engine are returned to conventional operation.
If the exhaust valve is not opened, the mixture in the cylinder will undergo an additional compression process. The temperature of the mixture in the cylinder during subsequent compressions may be higher due to retained heat from oxidation of fuel up to that point in the cycle. When the piston again approaches its TC position, the ignition source may again be triggered to ignite any still unburned fuel mixture. Any remaining fuel may also be ignited by an alternative ignition mechanism, such as HCCI.
Subsequently as the piston again approaches the end of the expansion stroke, a decision may again be made whether or not to open the exhaust valves. Alternatively if it is determined that the pressure in the cylinder is lower than the pressure upstream of the intake valve, the intake valve may be opened again to admit additional air or air and fuel,
Under warmed up operating conditions, the cylinders of a CSI engine with a TWC are normally supplied with stoichiometric mixture so that any pollutants that leave the cylinder can effectively be eliminated. However, to avoid erratic operation and misfire during cold start, CSI engines are frequently over-fueled with a fuel rich mixture. This promotes more reliable ignition and combustion events, but unfortunately results in high levels of HC and CO emissions and higher fuel consumption. In a CSI engine designed according to this invention, since the fuel, even during cold-start, can be effectively evaporated, mixed and combusted within the cylinder, over fueling is thus not necessary. The cylinder may be operated during cold-start with a stoichiometric or lean mixture. The total amount of fuel-air mixture inducted into the cylinder and thus the power produced during a cycle may be controlled by timing the opening and closing of the intake valves based on the average load requirements at a given time and the length of the cycle.
According to a further embodiment of the invention, the intake and exhaust valves of injection engines, such as a CI or lean ISI engine, may be timed to increase utilization of air inducted into a cylinder of the engine and to increase the mean cylinder-out temperature. Air may be inducted into the cylinder of an injection engine through an open valve as the piston moves toward the BC position. The intake valve may be closed early, thus creating a vacuum in the cylinder whenever the cylinder volume is near its maximum. If the liquid fuel injected into the cylinder does not evaporate and burn completely, the pressure in the cylinder may be allowed to drop to form a vacuum as the piston moves to the BC position. The drop in pressure would cause dissolved air or high volatility portions of any remaining liquid fuel to form bubbles, thus accelerating evaporation by helping to break up fuel still in liquid form. The engine valves may be reopened if the cylinder pressure is sufficiently depressed so that additional mass may be inducted into the cylinder.
As the piston the proceeds through another compression process, the trapped mixture in the cylinder is again compressed resulting in increased pressure and temperature. If up to this point any amount of fuel has reacted with the air, the heat released and retained will augment the beating effect of the compression. Additional fuel may then be injected into the cylinder, preferably during the compression process. The fuel in such a subsequent injection may evaporate, mix and burn more rapidly because of the increased temperatures. The subsequent combustion and expansion may be followed by additional compression strokes and additional injections so long as sufficient un-reacted oxygen is available in the cylinder to satisfactorily mix and burn any additional fuel. At any time during a cycle, but preferably at a convenient point during an expansion stroke, a decision may be made based on the state of the mixture in the cylinder to open the exhaust valve and expel the products of combustion and to begin a new cycle.
The total amount of fuel injected into the cylinder during any cycle will be a function of the load requirements at a given operating condition. With multiple injections, the overall equivalence ratio in the cylinder may be increased at a given engine load such that average air usage will be lower. Consequently, the cylinder-out temperatures will be higher than if a conventional 4-stroke cycle was utilized for the same engine load. These higher exhaust temperatures will facilitate the regeneration of exhaust treatment devices, such as particulate traps.
The intake and exhaust valves of this invention may be opened and closed by variable timing mechanisms. Examples of such mechanisms are disclosed in U.S. Pat. Nos. 5,327,856; 6,532,2919; 6,568,359; 6,857,404; 7,444,969; 7,448,350; that are incorporated herein by reference in their entirety. Under certain conditions the differential pressure between the cylinder and the manifold may also be controlled to cause one or more valves to float open. Manifold boost mechanisms, such as turbochargers or super chargers, may be used to increase intake manifold pressures.
It is preferred that one or more engine operating parameters at one or more points during an engine cycle be measured. Parameters that may be measured include, for example, cylinder pressure, instantaneous torque, and fuel and air flow into the cylinder. Based on these measurements, quantities such as fraction of mass burned in the cylinder may be determined. It is further preferred that, based on such measurements and calculations, quantities such as intake or exhaust valve timing, amount or timing of fuel delivery or ignition timing be established. Types of devices that may be used to collect such information include air mass flow sensors, manifold pressure and temperature sensors, cylinder pressure and temperature sensors, engine shaft instantaneous acceleration or torque sensors, or in-cylinder flame detection sensors such as ionization sensors. Description of several such sensors and their use for engine monitoring and control are discussed in U.S. Pat. Nos. 5,337,240; 5,775,299; 5,777,216; 7,111,611; 7,472,600 and 7,529,637 which are incorporated herein by reference in their entirety. Examples of using cylinder pressure as an engine control parameter are disclosed in U.S. Pat. Nos. 4,624,229; 6,560,526; 7,290,442; and 7,440,841 that are incorporated herein by reference in their entirety. Sensors may be used individually or in sensor suits of two or more. Parameters may also be estimated based on engine data pre-stored in a look-up table.
In U.S. Pat. No. 7,418,928, Fiveland discloses an engine which utilizes an extended cycle. In this engine, a dedicated valve is utilized to relieve excess pressure. Such a valve would make the cylinder head more complex and more expensive to manufacture. Such a valve would also be very difficult to fit into a cylinder head of a modern engine because of extremely limited space. In the current invention, over pressure problems described by Fiveland would be avoided by properly metering the fuel and the air inducted. Furthermore, removing the hot gases from the cylinder during a cycle would be contrary to the intent of this invention.
The intake and exhaust valves are opened with proper timing by means of variable valve actuating mechanisms 21 and 22 respectively. The actuating mechanisms may be driven electrically, hydraulically, pneumatically or mechanically or with a combination of two or more of these methods. They may control the timing or the amount of the opening of the valves.
In this embodiment, fuel is added to the air by means of a fuel injector 23 located upstream and in close proximity to the intake valve. Fuel is then carried into the cylinder with the air through an open intake valve. Fuel may also be added to the air elsewhere in the intake system by means of injectors or other fuel delivery mechanisms such as carburetors.
The cylinder may also be fitted with sensors to measure engine parameters such as pressure, temperature, ionization, and flame radiation. Such a sensor may be a freestanding transducer 24, a combination transducer combining two or more sensors, or, one that is incorporated with other components such as the spark plug. Also shown in
The cylinder-head is also fitted with a fuel injector 36 for injection of fuel into the cylinder. CI engines may also have glow-plugs (not shown) that can be used to assist in starting an engine during cold temperatures.
In IC engines built according to the invention, the intake and exhaust valves may be opened and closed at various times during the cycle. The valve actuators/controllers 40 (in
Also shown in
a-7k represent an SI engine cylinder operating according to one embodiment of the invention using a liquid fuel. During the intake process 75, the motion of the piston causes mass of air and fuel to enter the cylinder. Under certain circumstances, EGR may be added to the air before it enters the cylinder. Some of the fuel has not evaporated and is in the form of puddles 76 or droplets 77. During the intake process, the intake valve is closed before the piston reaches the BC position so that the further motion of the piston causes the formation of a vacuum in the cylinder (
An intake valve may reopen (
If the piston is again at a point where the pressure in the cylinder is sufficiently lower than the pressure upstream of the intake valve, the intake valve may again be opened to admit additional air or fuel-air mixture into the cylinder (
a-10j shows a cylinder of a CI engine undergoing an expanded cycle.
g-h show the cylinder undergoing an additional compression. Fuel may again be injected and allowed to burn in a diffusion flame as a result of auto-ignition. Combustion may also be initiated or assisted by a positive ignition source such as a spark plug (not shown).
In
In operating an engine according to this invention, at least one valve of at least one cylinder of an engine must be controllable, such that the time of opening or closing may be flexibly controlled with respect to the position of the piston, preferably as a result of an electrical signal. Flexibly controllable valves allow intake and exhaust processes to occur independently of each others at different times during the cycle and be of variable duration or lift. Fuel may be added to the air at any point upstream of a cylinder's intake valve or injected into the cylinder or a combination of the two methods. The fuel-air mixture in the combustion chamber may be ignited for example by an electric discharge device such as a spark plug, by non-homogeneous auto ignition such as in a diesel engine or by HCCI or by a combination of these methods.
The invention has been described in terms of its functional principles and several illustrative embodiments. Many variants of such embodiments will be obvious to those skilled in the art. Therefore, it should be understood that the ensuing claims are intended to cover all changes and modifications of the illustrative embodiments that fall within the literal scope of the claims and all equivalents thereof.
This Application claims the priority of U.S. Provisional Patent Application No. 61/157,456 filed Mar. 4, 2009 the entire contents of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61157456 | Mar 2009 | US |
