Gas engine

Details Gas engine Gas engine

1999-03-03

2001-01-30

Argenbright, Tony M. (Department: 3747)

Internal-combustion engines

Burning by highly compressed air

Oil engine air preheated

C123S406290, C123S406450, C123S435000, C123S526000

Reexamination Certificate

active

06178927

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates a gas engine, especially a diesel gas engine, with a control system for controlling and regulating the gas engine in dependence on changing limiting conditions. More specifically, the invention relates to a gas engine with a pilot control device which receives measurements of the limiting conditions, calculates output signals, and transmits the output signals to activators which activate final control elements for adjusting the engine operating point to the changed limiting conditions.
2. Description of the Related Art
Modern gas engines that operate on the lean-burn principle are able to comply with the standards for NOx emissions (e.g., those based in Germany on T A Luft) without requiring exhaust gas after treatment, even at high mean pressures. One prerequisite for meeting the standards for NOx emissions is a lean gas-air mixture, which requires a high air-fuel ratio &lgr; in the combustion chamber (lean-burn method).
The engine must therefore be kept within a narrow operating range at all limiting conditions (ambient temperature, ambient pressures, gas qualities, etc.). The operating range is limited, on the one hand, by the knocking limit or toxic emissions standards and, on the other hand, by the lean-operation limit. Moreover, the operating range depends on the output, and within the possible operating range optimum efficiency is to be attained. These physical relationships apply for diesel gas engines based on the diesel gas principle as well as to pilot injection gas engines and spark ignition gas engines, in all cases with or without prechamber ignition.
Various methods of keeping the engine in the preestablished operating range are known from the prior art. These methods include knocking control, ignition failure control, &lgr; control, and methane measurement probes.
The use of these methods is disadvantageous in that their use is limited during changes in the limiting conditions. In addition, there are essential disadvantages due to the inherent physical principles of the methods of knocking control and ignition failure control.
For example, knocking control devices do not become active until the engine is already in knocking operation. However, the operating state bordering directly on the knocking limit places engines, especially engines with high mean pressures (>16 bar), under high mechanical and thermal stresses. Generally, the limits on NOx emissions cannot be complied with during knock-controlled operation. Similarly, ignition failure recognition devices cannot respond until actual ignition failure occurs. In such an operating state, however, a considerable loss in efficiency has already taken place.
During changes in limiting conditions such, for example, as fluctuations in the amount of methane or the charging air temperature/mixture temperature before the cylinder, the adjustment of the air-fuel ratio by &lgr;-control ensures neither compliance with NOx emission standards (lean-operation limit) nor maintenance of a sufficient distance from the top limit.
Another important influence on the NOx emissions and knocking limit operating parameters is the properties of the combustible gas. Therefore, a sensor that detects the combustible gas properties may be used to control the engine operating parameters.
A prior art gas engine with a control and regulating system for controlling the gas engine in response to changes in the limiting conditions is known from the article “Influence of methane number on combustion in the spark ignition gas engine” [“
Einfluss der Methanzahl auf die Verbrennung im Gas
-
Ottomotor”
] in
Motortechnischen Zeitschift
54 (1993), pp. 350 ff. A disadvantage of the control and regulating concept described in this article is that although the described pilot control device ensures compliance with desired emission limits by controlled operation in methane ranges wherein the knocking limit has not yet been reached, the control device does not prevent the engine from reaching the knocking limit or being driven into a knocking operation state.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas engine with a control system for operating the gas engine reliably, i.e., free of knocking and ignition failure, at maximum attainable power with optimal efficiency while complying with the toxic emission limits, even during sharply changing limiting conditions.
This object is attained by the invention because the pilot control device is so embodied that, upon changes in the limiting conditions being detected by its sensors, the engine operating point is not permitted to come closer to the limits of the operating range than a defined minimum distance. In addition, the pilot control device is subordinated to a knock monitoring device in such a way that, when the operating point has reached the minimum distance from the knocking limit of the gas engine, the knock monitoring device adjusts the output of the engine or stops the engine.
The invention differs from existing solutions in that the pilot control device does not allow the gas engine to be driven at the limits of its operating range, but rather ensures that a safety distance from the limits is maintained. In addition, the pilot control device is subordinated to a knock monitoring device, so that engine damage can be avoided in circumstances that cannot be protected against via the pilot control device such as improper operation of the engine or the like.
According to the invention, the following advantages are attained: Critical operating states, such as running the engine at the knocking limit or the ignition failure limit, are avoided. As a result, thermal and mechanical stresses are kept low, operating reliability is increased and wear is reduced. Due to the flexibility of the control system, the engine can be automatically operated in a wide range of changing limiting conditions with maximum possible output, optimal efficiency and reliable compliance with toxic emission standards. The additional knock monitoring device according to the invention helps to avoid knocking damage that could occur due to parameters not monitored or not monitorable by the pilot control device.
In an especially advantageous embodiment, the knock monitoring device has a temperature sensor for measuring the combustion chamber temperature and forwarding the combustion chamber temperature to the knock monitoring device as an input signal. The knock monitoring device is embodied so as to directly generate a stop signal for the gas engine when a defined maximum combustion chamber temperature is exceeded. This measure is especially advantageous when knocking occurs suddenly and it is desirable to avoid dead times created by downstream regulating devices during which the engine could sustain damage.
In a further advantageous measure, the sensors assigned to the pilot control device include a temperature sensor that measures the charging air temperature and/or mixture temperature as an input signal of the pilot control device. This ensures that this important parameter for the output of the gas engine is detected by the pilot control device.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.


REFERENCES:
patent: 4376429 (1983-03-01), Youngblood
patent: 5224457 (1993-07-01), Arsenault et al.
patent: 5333591 (1994-08-01), Korsmeier et al.
patent: 5887566 (1999-03-01), Glauber et al.
Schiffgens et al., “Einfluss der Methanzahl auf die Verbrennung im Gas-Ottomotor” inMotortechnischen Zeitschift54, 1993 pp. 350-357.

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