Internal-combustion engines – Charge forming device – Gaseous fuel and air mixer
Reexamination Certificate
1996-11-07
2001-03-06
Kwon, John T. (Department: 3747)
Internal-combustion engines
Charge forming device
Gaseous fuel and air mixer
Reexamination Certificate
active
06196204
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for forming a turbulent fuel-air mixture in the combustion chamber of each cylinder of an internal combustion engine controlled with valve timing, as well as to a device for implementing this method.
BACKGROUND INFORMATION
The operation of internal combustion engines using gaseous fuels requires properly adapted devices and mixing methods for forming a fuel-air mixture, as well as for supplying this mixture to the combustion chamber in the cylinders of the internal combustion engine. The gaseous fuel is mixed for the most part upstream from the combustion chamber in the area of the air intake passages and then flows during the intake stroke into the combustion chamber(s) of the internal combustion engine. The European Patent 309 044 B1 already discloses a mixture and regulating device of this type, which is arranged in the engine air-intake line. Air and gaseous fuel are thereby mixed in a so-called venturi tube, and this fuel-air mixture then flows, as is generally known, into the engine. As is apparent from this known device, it is relatively expensive and difficult to regulate the mixture ratio, and there is no guarantee of a thorough and uniform intermixing of air and gaseous fuel. The result is uneven combustion of the mixture in the combustion chamber of the engine, so that no optimal energy utilization is possible and undesirable pollutants are formed. To ensure an effective combustion of the gas-air mixture in the combustion chamber, additional measures are, therefore, needed to generate a turbulent flow of the mixture, the aim being to achieve a thorough intermixing and rapid combustion. As is known, additional turbulence is generated when the mixture stream flows at the end of the intake passage through the annular gap between the valve and the valve seat at the cylinder head, through which means a conical mixture spray is formed. It is also known to increase turbulence by applying a rotational energy to the mixture stream flowing into the cylinder by shaping the intake passage accordingly or by installing interior components upstream from the intake valve. Furthermore, a so-called squish effect is produced in the cylinders of present-day engines in that as the piston approaches the top dead center between the piston and the cylinder head, a narrower and narrower gap is formed, so that the mixture is squeezed out of this gap into a central combustion chamber recess. This also has the effect of intensifying turbulence. The disadvantage associated with all of these known measures for increasing turbulence in the combustion chamber is that the intensity of the turbulence varies more or less in proportion to the engine speed. This is because the velocity of the air, gas, and mixture flows changes in response to variations in engine speeds. Therefore, at low speeds, the turbulence is weak and, accordingly, combustion is poor. This effect becomes especially pronounced when natural gas is used as fuel and/or when a lean mixture is used. However, at high speeds, the flow velocities are so high that it is more difficult to ignite the mixture. At high speeds, that is at high flow velocities, an intensive vortex flow through the intake valve also results in a considerable loss of pressure, so that cylinder charging and, thus, power output are diminished. To compensate for these disadvantages, compromises have to be made, for the most part, when working the internal combustion engines that use gaseous fuels, or additional complicated and expensive measures have to be resorted to.
SUMMARY OF THE INVENTION
The object of the present invention is to conceive of a method and a device, which when applied to internal combustion engines that use gaseous fuels, such as natural gas or liquefied petroleum gas, will generate a high turbulence of the mixture in the combustion chamber. The intensity of the turbulence should be as constant as possible, independently of the engine speed, the intention being to use simple means.
The supplying of the gaseous fuel should permit an efficient and simple controlling and regulating of the mixture formation, as well as of the engine function. Furthermore, it should be possible to use gaseous fuels in conventional engines with very little adaptation, and the elements required for supplying the gaseous fuel should be protected from excessive stresses, e.g. from thermal and compressive stresses, and have a correspondingly long service life.
The means for achieving the object in accordance with the present invention yields advantages in that the gaseous fuel and the air are not mixed until after (downstream from) the intake valve in the combustion chamber of each cylinder. Gaseous fuel is introduced via a valve-timed gas nozzle, which is arranged in the area of the intake passage, i.e., outside of the hot combustion chamber of the engine. Therefore, the thermal stresses of the gas nozzle are able to be kept within acceptable limits, so that correspondingly high service lives can be expected. The pressure under which the gaseous fuel is normally stored is high enough to produce a high-speed gas spray in the properly shaped gas injection nozzle. Because of the very low density of the gas compared to liquid gasoline and its compressibility, sonic velocity is reached when gaseous fuels are introduced by nozzle in the narrowest cross-section. The velocity can be increased even more in an outlet passage designed as a Laval nozzle. Thus, already at customary gas pressures of a few bar, e.g. 5 to 10 bar, a coherent gas spray with a flow velocity of 250-600 m/s can be produced. A coherent gas spray is understood to be a gas spray which essentially does not diverge and, thus, has a constant cross-section. The kinetic energy of such a gas spray is many times greater than that of a gasoline spray, given the same pressure. The kinetic energy of the fuel spray in the case of gas reaches more or less the same order of magnitude as the kinetic energy of the entire air flow through the intake valve, given a high speed. The present invention utilizes this high kinetic energy of the gas spray to produce a greatest possible turbulence in the combustion chamber. To this end, the coherent gas spray is injected through the annular gap of an open intake valve directly into the combustion chamber, where the kinetic energy being released causes the spray of gaseous fuel to mix intensively with the inducted air and to undergo vorticity.
The gas spray is injected intermittently, or rather as a pulsed spray, the instant of each injected pulse of gaseous fuel being dependent upon the opening of the annular gap at the intake valve. Therefore, the gas-injection nozzle is advantageously provided with a valve, which can be actuated, as is generally known, electromagnetically or otherwise. The fuel quantity required by the engine can be expediently regulated by modifying the time duration of the gas-spray pulse. This renders possible the application of control processes, as they are used in gasoline injection. Other advantages can result when the direction of the axis of the gas spray is selected in relation to the central axis of the combustion chamber, and the gas spray is thereby injected at an angle and/or eccentrically to the logitudinal axis of the combustion chamber. This makes it possible for an additional vortex to be generated in the combustion chamber, thus further intensifying turbulence. Additional advantages are attained in that the velocity of the injected gas spray is independent from the engine speed and, therefore, an intensive turbulence is also rendered possible in the combustion chamber given low engine speeds. As a result, one can do partially or entirely without supplementary measures for generating turbulence, so that the design and configuration, as well as the method for injecting the gaseous fuel, are simplified. If necessary, by shifting the timing of the gas pulse relative to the opening duration of the intake valve, it is also possible to inject only one portion of the quantity of gaseous fuel di
Kenyon & Kenyon
Kwon John T.
Robert & Bosch GmbH
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