Internal-combustion engines – Combustion chamber means combined with air-fuel mixture... – Having a single combustible mixture inlet combined with...
Reexamination Certificate
2000-02-18
2001-10-09
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means combined with air-fuel mixture...
Having a single combustible mixture inlet combined with...
C123S14500A, C123S532000, C123S534000
Reexamination Certificate
active
06298825
ABSTRACT:
BACKGROUND OF THE INVENTION
Reciprocating gas engines, which are operated with combustion gases having a high energy content, can be operated either according to the Otto method or also according to the so-called diesel-gas method. In both cases, a mixture of air and combustion gas is sucked in and compressed. With the Otto method, ignition occurs through spark-over between the electrodes of a spark plug. With the diesel gas method, ignition occurs via a so-called pilot injection, meaning a metered amount of a self-igniting, liquid ignition fuel, as a rule diesel fuel, is injected with high pressure into the compressed combustion gas-air-mixture to initiate the combustion. This injected ignition fuel self-ignites and thus forms a multitude of spatially distributed ignition sources. The energy released as a result of the injected ignition fuel is considerably higher than the spark energy from a spark plug. This method has advantages with respect to the maintenance costs and the idle times since the spark plugs are subjected to high wear owing to the increase in ignition energy, which decreases the service life drastically.
With a gas engine operating according to the Otto method, full use is made of the special advantage of a considerably lower pollutant emission, particularly of nitrogen oxides, as compared to the gasoline engines or the diesel engines. With a gas engine operating according to the diesel method, the pollutant emission is increased, relative to the “pure” gas engine operating according to the Otto method, because of the fuel injected for the ignition. Until now, the diesel gas method could therefore be used only for very large stationary gas engines with a volume of 20,000 cm
3
and more per cylinder. This is due to the fact that the additional discharge of pollutants caused by the ignition fuel could only be kept low for large engines of this type, relative to the total pollutant discharge of the gas engine. The problem results from the injection process being controlled by the rotational movement of a camshaft and a specified cam profile, so that start and end of the injection and thus also the amount injected with a specified injection fuel admission pressure are not influenced, even though they depend on the speed.
German Patent A-44 19 429 discloses a method for operating a self-igniting, mixture-compressing gas engine, which uses an ignition gas in place of a liquid ignition fuel. It is advantageous to use as ignition gas the same combustion gas that is also used to operate the gas engine in the form of a combustion gas-air-mixture. With the known method a small antechamber is assigned to each cylinder that forms the main combustion chamber. The ignition gas is injected into the antechamber with a pressure that is higher than the compression pressure in the main combustion chamber. The advantage of this method is that only one type of combustion fuel is required, so that a reduction of the emission values can be achieved, particularly for nitrogen oxides. The disadvantage of this method is that it requires an involved engine design resulting from the use of antechambers.
SUMMARY OF THE INVENTION
It is the object of the invention to create an ignition process for gas engines, which simplifies the structural expenditure as well as the engine operation.
This object is solved according to the invention with an ignition method for a multi-cylinder reciprocating gas engine. To initiate an operating cycle, a compressed and essentially homogeneous combustion gas-air-mixture that is not self-igniting and is contained in the respective cylinder space to be fired is ignited according to this method by directly injecting a small amount of combustion gas as ignition gas onto a hot surface. The start of the injection can be specified by way of an engine control unit and in dependence on the crankshaft position. With this method, the combustion gas-air-mixture is initially compressed inside the respective cylinder and is present in homogeneous form near the end of the compression lift. However, as a lean mixture it does not meet the self-ignition requirements due to the mixing ratio. For the ignition, the small amount of combustion gas is injected at the end of the compression lift as ignition gas directly and under pressure into the combustion chamber. It is advisable to use as ignition gas the same combustion gas that is also used in the combustion gas-air-mixture, preferably without an essential amount of mixed-in air. The direct injection of the ignition gas causes practically a point-type enrichment of the mixture in the injection region, through which the self-ignition conditions are adjusted over a narrowly defined range.
In order to determine the ignition location inside the combustion chamber and also shorten the ignition delay, the ignition gas is injected via an ignition aid in the form of a hot surface, which surface has a temperature that is clearly above the combustion chamber surface temperatures. This hot surface can be provided, for example, in the form of an incandescent body that projects into the combustion chamber and is connected with a source for providing heat energy. The source can be a current source, for example, with which the required surface temperature of the incandescent body is maintained during the start-up phase of the engine. Following a corresponding operating time, however, the incandescent body has a sufficiently high temperature level, so that the current source can be turned off. However, other structural parts in the cylinder chamber can also serve as hot surface, e.g. projections or the like.
The start of the fuel conversion is respectively controlled by the release of the amount of ignition gas to be injected, so that it is possible to control the combustion process in the same way as the ignition moment of a spark ignition.
The ignition method according to the invention can be used advantageously in particular for methane-containing gases having a low energy content, the so-called lean gases, because the ignition energy made available is high, owing to the targeted and locally fixed self-ignition. Thus, a secure ignition is ensured even with energy-poor gases, but also with lean combustion gas-air-mixtures. Lean gases of this type can be obtained, for example, from coke gas, blast furnace gas or even converter gas in the steel-producing industry, but also as pyrolysis gas from the incineration of waste products.
It is possible in principle to use a central combustion gas source under high pressure to inject the ignition gas with a correspondingly high pressure directly into the individual cylinder chamber to be fired, in the manner of a common-rail injection system known from standard diesel engines. However, one advantageous embodiment of the invention provides that the ignition gas be metered in from an ignition gas accumulator that is assigned respectively to one cylinder and by way of a controllable ignition valve. In that case, the ignition gas accumulator is connected on the one hand to a combustion gas supply and, on the other hand, to a cylinder chamber. The ignition gas accumulator can be admitted by way of a valve arrangement with the maximum combustion chamber pressure by using operating gases from the cylinder chamber. This arrangement has the advantage that a relatively small-volume ignition gas accumulator can be charged at a pressure of approximately 4 to 8 bar by using the pressure generator for the combustion gas supply, which is normally available anyway for charging the gas engines. This pressure is not sufficient to inject the ignition gas amount counter to the compression pressure into the respective cylinder chamber. As soon as the ignition gas accumulator is filled with ignition gas, the ignition gas accumulator is connected to a cylinder that has just been fired. Thus, the ignition gas content in the ignition gas accumulator is compressed with the maximum operating cycle pressure by feeding in a small amount of the operating gas from the fired cylinder chamber. This operating pressure is with certaint
Hupperich Patrick
Umierski Markus
Argenbright Tony M.
FEV Motorentechnik GmbH
Kunitz Norman N.
Venable
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