Method for starting and operating an internal combustion engine

Details Method for starting and operating an internal combustion engine Method for starting and operating an internal combustion engine

2000-03-27

2003-08-05

Solis, Erick (Department: 3747)

Internal-combustion engines

Precombustion and main combustion chambers in series

With ignition means particularly positioned relative to...

C123S261000, C123S267000, C123S277000, C123S0270GE, C123S526000

Reexamination Certificate

active

06601560

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improved method for operating an internal combustion engine, in particular to an improved method for starting an internal combustion engine, and to an internal combustion engine adapted to operate under such a method.
BACKGROUND OF THE INVENTION
Internal combustion engines find use in a wide range of applications. One particular application is the stationary internal combustion engine, used as a source of power at sites, such as oil well heads and drilling operations. It is in this application that internal combustion engines powered by gaseous hydrocarbons, in particular natural gas, have become prominent.
Typically, such engines operate using fuels, such as diesel, which are ignited under compressive conditions generated within the cylinders of the engine, or using fuels, such as gasoline or natural gas, which require the provision of an ignition source. Commonly, the source for the ignition in the latter type of engine is a spark generated in the combustion of the engine, most commonly by means of a spark plug. In order to improve the durability and rating of the spark-ignited engines, the so-called “pilot ignited” engines have been developed. In the pilot ignited engines, a small volume of a liquid fuel having a suitably high cetane number is injected directly into the combustion chamber. The volume of fuel so injected is typically about 5 percent of the total fuel volume. The pilot ignited engines have found acceptance in the industry as a result of the aforementioned improvements. In addition, these engines offer the ability to change the fuel composition during the running of the engine and to switch, for example, from natural gas to diesel operation, without modification or shutting down of the engine. These engines are referred to as “dual fuel” or “gas diesel” engines.
Examples of dual fuel engines are disclosed in U.S. Pat. Nos. 4,603,674, 4,463,734, and 4,527,516. In each of these documents, an internal combustion engine is disclosed, which can operate on a mixture of fuels introduced directly into the combustion chamber of the engines.
As a result of concerns regarding emissions from internal combustion engines, a system was developed, in which the engine is provided with a so-called “auto-ignition chamber” or “torch cell”. In such an arrangement, the engine is provided with a pre-combustion chamber in communication with the combustion chamber of the engine. A combustible fuel mixture is introduced into the pre-combustion chamber and ignited therein. The thus ignited fuel mixture is then allowed to enter the combustion chamber, where it ignites the main fuel/air mixture. An engine of this configuration is able to operate using a lean fuel mixture, which in turn results in a reduction in the emissions from the engine. Examples of such engines are as follows.
U.S. Pat. No. 4,306,526 discloses an internal combustion engine and a method for its operation. The engine is a turbocharged, two cycle engine and is operated on a lean fuel/air mixture. A jet cell ignition device is provided to ensure uniform and complete combustion of the fuel mixture. U.S. Pat. No. 4,966,103 discloses a combustion system for an internal combustion engine. The engine is a dual fuel engine operating on a mixed gas-liquid fuel and comprises a torch cell comprising an auto-ignition chamber in which a fuel having a sufficiently high cetane rating is caused to ignite. This in turn ignites the charge of fuel and air in the main combustion chamber of the engine.
A number of other torch-ignition systems are also known. U.S. Pat. No. 4,127,095 discloses a torch-ignition internal combustion engine provided with a main and pre-combustion chamber, in communication with each other through a torch aperture. The electrodes of a spark plug are disposed within the pre-combustion chamber. During operation, a lean air-fuel mixture is introduced into the main combustion chamber, from where a portion enters the pre-combustion chamber under the action of the compression stroke of the engine. The combustible mixture in the pre-combustion chamber is ignited by the spark plug, the flames from which propagate through the torch aperture into the main combustion chamber and thereby act as an ignition source for the main portion of the fuel mixture.
A modified version of this torch-ignition system is disclosed in U.S. Pat. No. 5,947,076. This patent describes and internal combustion engine having a main combustion chamber and a pre-combustion chamber, as in U.S. Pat. No. 4,127,095. The pre-combustion chamber is again provided with a spark plug. However, in the embodiment of U.S. Pat. No. 5,947,076 the electrode of the spark plug is located within a further chamber, a so-called “plug combustion chamber”, intended to protect the electrode of the spark plug from turbulence within the main and pre-combustion chambers.
U.S. Pat. No. 5,293,851 addresses the issue of providing an improved internal combustion engine, in particular engines operating with gas as a fuel. One issue that can arise with such engines is problems with starting the engine, in particular from cold. Typically, in order to improve the starting of the engine, it was known to add a certain amount of diesel fuel to the gas fuel during the start-up phase, until the engine could be run on gas alone. In order to reduce this problem, U.S. Pat. No. 5,293,851 provided the internal combustion engine with a torch cell having a pre-combustion chamber provided with a glow plug. In operation, a combustible fuel mixture, typically and air-gas mixture, is introduced into the main combustion chamber of the engine. During the compression stroke of the engine, a portion of the compressed mixture is forced into the pre-combustion chamber of the torch cell. At or about the same time, a liquid fuel, typically diesel, is injected directly into the pre-combustion chamber so as to contact the glow plug. The action of the glow plug is to ignite the liquid fuel, which in turn ignites the gaseous fuel within the pre-combustion chamber. The flame front leaves the pre-combustion chamber and enters the main combustion chamber and ignites the main fuel mixture. The engine of U.S. Pat. No. 5,293,851 is capable of operating under reduced compression ratios, in turn allowing it to accommodate fuels having a lower octane rating than can be accommodated by the higher compression ratios of the more conventional torch-ignited engines.
The engine of U.S. Pat. No. 5,293,851 has been found to work very well and provide a range of advantages. However, some difficulty has been encountered with the operation of the engine under certain conditions. In particular, it has been found that starting the engine can be troublesome, especially when the engine is cold. It has been found that the walls of the pre-combustion chamber, when cold, act as a sizeable heat sink and impair the combustion characteristics of the engine, leading to poor starting performance. In addition, it has been found that, under certain conditions, the glow plug can provide a source for pre-ignition of the air-fuel mixture. This in turn leads to poor running characteristics of the engine and, if allowed to persist, can lead to extensive damage to the engine components.
Accordingly, there is a need for an internal combustion engine arrangement which provides all the advantages of the engine of U.S. Pat. No. 5,293,851, but which does not suffer from the aforementioned drawbacks.
SUMMARY OF THE INVENTION
Surprisingly, it has been found that the running problems of the engine of U.S. Pat. No. 5,293,851 are significantly improved if a spark ignition system is provided for the combustible fuel mixture in the main combustion chamber, in addition to the torch-cell ignition system. Under difficult running conditions, such as cold starting, the spark ignition is used to supplement the torch-cell ignition system and achieve efficient operation of the engine.
Accordingly, the present invention provides a method for operating an internal combustion engine, which engine comprises

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