Patent Application
20090050084
1. Field of the Invention
The present invention relates to a spark-ignited gas engine with a number of cylinders, wherein on each cylinder a mechanical fuel feed valve for direct feeding of gaseous fuel into the cylinder and a fuel line opening into the cylinder are provided and the fuel line can be closed by the mechanical fuel feed valve in the direction of the cylinder. The invention also relates to a method for controlling such a gas engine and a method for converting a gas engine to such a gas engine.
2. The Prior Art
In spark-ignited gas engines, e.g., large-volume gas engines operated with natural gas in natural gas extraction and transport or in the chemical industry, the gaseous fuel (natural gas, liquefied gas, hydrogen, etc.) is metered at low pressure directly into the cylinders when a mechanical fuel feed valve is opened. When the fuel feed valve is open, gaseous fuel flows through the mechanical fuel feed valve, then through the fuel line and into the cylinder. Because of the low pressure the gas feed takes place at low cylinder pressure, e.g., during the initial compression phase. The fuel feed into the cylinder is discontinued once the fuel feed valve is closed again. The mechanical fuel feed valve is generally controlled by a camshaft and therefore opens for a predetermined crank angle range or a period of time as a function of the speed. Since this determines the opening time, the mount of fuel amount fed to the cylinder depends largely on the prevailing pressure in the fuel line. In order to control such a gas engine, for example when the load varies, the pressure in the fuel line must consequently be controlled. However, such control is expensive and under certain conditions causes irregular combustion and unstable and unreliable operation of the gas engine, which in turn can lead to operational and mechanical problems. Another problem of such mechanical control of a two-stroke gas engine is that unburnt fuel from the cylinder can flow into the intake manifold and/or exhaust pipe when the speed of the gas engine is reduced, which can lead to dangerous explosions in the intake manifold or exhaust pipe, high hydrocarbon emissions and higher fuel consumption. In addition, mixture is consequently forced back into the gas system t, leading to poor metering accuracy and thus misfiring.
In order to avoid these problems, individually controlled gas valves, e.g., hydraulically and/or electromagnetically controlled valves which inject a predeterminable gas amount into the cylinder during the intake stroke, can be employed instead of the mechanical fuel feed valves. However, in order to be able to feed sufficient fuel into the cylinder despite the very short injection times and the small available opening cross sections, fuel at high pressure is required in these systems, which increases expenditures. Such a gas valve results is disclosed in AT 413 136 B, for example.
It is likewise possible in four-stroke engines to feed the gaseous fuel directly into the intake line in which the mixing of air and gaseous fuel then takes place. However, ignitable mixture is then present in the intake manifold, which can lead to undesirable backfiring.
A spontaneously igniting gas engine is disclosed in from JP 08-028 268 A, where through a controlled valve a defined gas amount is introduced into an auxiliary combustion chamber. At the end of the compression phase a mechanical valve is opened so that hot compressed air is able to flow into the auxiliary combustion chamber through which the gas mixture present in the auxiliary combustion chamber is ignited. The ignited gas mixture then expands into the cylinder and brings about the power stroke. However, nothing with regard to metering of gaseous fuel directly into the cylinder of a spark-ignited gas engine may be deduced from JP 08-028 268 A.
It is an object of the invention to provide a spark-ignited gas engine and a method for controlling such a gas engine which allows accurate, flexible metering of gaseous fuel into the cylinder and hence accurate, flexible control of the gas engine.
This object is achieved for the gas engine according to the invention in that a controlled valve is arranged in the fuel line upstream of the fuel feed valve so that in the fuel line between the fuel feed valve and the controlled valve a defined intermediate volume is created and gaseous fuel can be fed via the controlled valve into the intermediate volume. This object is achieved for the method according to the invention in that a controlled valve is arranged in the fuel line upstream of the fuel feed valve so that a defined intermediate volume is created in the fuel line between the fuel feed valve and controlled valve, and in that the amount of fuel fed into the cylinder is set by feeding a defined amount of fuel into the intermediate volume through the controlled valve. With the invention it is possible to admit a defined amount of gaseous fuel into each individual cylinder of the gas engine, thus allowing accurate, flexible control of the gas engine. In addition, the contribution of the individual cylinders to the total output of the gas engine can be easily adjusted. The invention enables gaseous fuel to be fed at a constant pressure to the cylinder for a certain time (or crank angle), thus enabling accurate setting of the amount of fuel for each cylinder to achieve uniform combustion and stable operation of the gas engine. Moreover, no fuel or less fuel can be supplied to one cylinder or a plurality of cylinders by the individual and independent feeding of each cylinder, which, particularly in the partial load range, allows stable operation of the engine which is optimized in terms of pollutant emissions.
The controlled valve is designed particularly advantageously as a solenoid valve to allow simple, accurate control of the amount of fuel fed.
Particularly advantageously a certain amount of gaseous fuel is initially pre-stored in the intermediate volume by the controlled valve in that the controlled valve upstream of the fuel feed valve opens and closes before the fuel feed valve opens. When the fuel feed valve opens, a clearly defined amount of fuel (volume of the intermediate volume) is thus fed into the cylinder. Because of this, the influence of the cylinder pressure on the feeding of the fuel into the cylinder is largely eliminated. Moreover, the influence of the control and the size of the mechanical valve is also largely eliminated. In another embodiment of the invention, however, it is also possible to keep the controlled valve open only during the opening time of the fuel feed valve or to open the controlled valve upstream of the fuel feed valve but to close it only during the opening time of the fuel feed valve.
A further object of the invention lies in a simple method of converting an existing gas engine with a mechanically controlled fuel feed valve to a gas engine that can be flexibly, accurately and easily controlled. This object is achieved in that a controlled valve is inserted in the fuel line upstream of the fuel feed valve on the cylinder so that a defined intermediate volume is created between the fuel feed valve and the controlled valve.
The invention is described in the following by means of the diagrammatic, non-limiting embodiments shown in the drawings.
In
In the flow direction of the gaseous fuel upstream of the fuel feed valve 11 a controlled valve 10, e.g., a solenoid valve, is arranged in the fuel line 2 according to the invention, into which the fuel line 2 opens. Thus, a defined intermediate volume 12, which is able to accommodate a defined amount of fuel, is created between fuel feed valve 11 and controlled valve 10. Such an intermediate volume 12 can also obviously be created or enlarged by providing a separate or additional fuel chamber between fuel feed valve 11 and controlled valve 10. When the fuel feed valve 11 is opened, e.g., at the start of the compression phase, the defined amount of fuel present in the intermediate volume 12 is fed to the cylinder Z.
Here, the feeding of gaseous fuel into the cylinder Z can be controlled in different ways:
1) Fuel feed valve and controlled valve are open simultaneously
To this end the fuel feed valve 11 opens before the controlled valve 10, which is again closed before the fuel feed valve 10. However, the maximum amount of gaseous fuel that can be supplied is determined only by the size and the opening time of the controlled valve.
2) Fuel feed valve and controlled valve are partially open at the same time
The controlled valve 10 in this case opens for a defined period before the fuel feed valve 11 in order to pre-store a defined amount of fuel in the intermediate volume 12 before the fuel feed valve 11 opens. The controlled valve 10 can be closed after or simultaneously with the fuel feed valve 11. Here, a defined amount of fuel can be stored in the intermediate volume 12 before the fuel feed valve 11 opens.
3) Fuel feed valve and controlled valves open in a staggered manner
The controlled valve 10 opens when the fuel feed valve 11 is closed in order to pre-store a defined amount of fuel in the intermediate volume 12. Before the fuel feed valve 11 is opened by the cam control, the controlled valve 10 is closed. The two valves thus operate in a staggered manner relative to each other. Thus, a precisely defined amount of fuel can be fed to the cylinder Z.
In order to suitably control the controlled valve 10, a control unit 20 can be provided which has a control input C via which a control objective can be set, e.g., a certain speed, a certain output or a certain torque. The control unit 20 has a separate control output S1 . . . Sn, for each cylinder Z or for each controlled valve 10, via which the appropriate control signals are transmitted to the controlled valves 10, e.g., indicating when the valve opens and closes and which opening cross section is exposed (e.g., the stroke in the case of a solenoid valve). To this end the control unit 20 can have additional inputs such as for instance an input for the current speed n or the current torque T, crank angle signal, pressure in the fuel line PG, etc. Appropriate sensors can be arranged on the gas engine 1 for this purpose.
Although the invention is described above taking the example of a 2-stroke spark-ignited gas engine, the invention is obviously also applicable to 4-stroke engines.
An existing spark-ignited gas engine 1 with a mechanical fuel feed valve 11 can also be converted with little effort. For this purpose, it is merely required for a controlled valve 10 to be installed on each cylinder Z between the fuel line 2 and the fuel feed valve 11. To do so, the fuel line 2 is removed, the controlled valve 10 arranged upstream of the fuel feed valve 11 and the fuel line 2 connected to the controlled valve 10. If required, a separate or additional fuel chamber for creating or enlarging the intermediate volume 12 can be arranged in the flow direction upstream of the cylinder Z to create a larger intermediate volume 12.
