Internal-combustion engines – Burning by highly compressed air – Oil engine air preheated
Reexamination Certificate
2002-04-09
2004-01-13
Kwon, John (Department: 3747)
Internal-combustion engines
Burning by highly compressed air
Oil engine air preheated
C123S0270GE, C123S526000, C123S299000
Reexamination Certificate
active
06675748
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for dual fuel injection into the combustion chamber of an internal combustion engine. More specifically, the present invention relates to a dual fuel injection method suitable for application in the internal combustion engine of a car, truck, bus, locomotive, ship or other engine-powered forms of transportation, as well as in stationary applications, such as engines related to energy production and industrial applications.
BACKGROUND OF THE INVENTION
Due to the benefits of converting diesel-stroke engines so that they operate burning gaseous fuels has resulted in many recent developments in this area of engine technology. Many gaseous fuels, such as natural gas or hydrogen, by way of example, are clean burning fuels (relative to diesel), which means that when an engine substitutes such gaseous fuels for diesel fuel, the engine can, depending on a number of variables including the gaseous fuel chosen, operate with reduced emission levels of particulate matter (PM), hydrocarbons and nitrogen oxides (NO
x
).
A known method that allows diesel engines to operate using gaseous fuels utilizes a second fuel as well as the gaseous fuel. For the purposes of this discussion natural gas will constitute the gaseous fuel, however, other gaseous fuels such as hydrogen, methane, ethane, propane, lighter flammable hydrocarbon derivatives, etc. will also operate as gaseous fuels. Generally, natural gas is mixed with the intake air prior to the introduction of the air
atural gas mixture into the engine cylinder (a process known in the field involved here as fumigation). A homogeneous air
atural gas mixture is thus introduced into the piston cylinder during the intake stroke. During the compression stroke, the pressure and temperature of the homogeneous mixture is increased. Near the end of the compression stroke, a small quantity of pilot diesel fuel is employed to ignite the air
atural gas mixture. The advantage of employing a homogeneous mixture of air and gas is that the combustion fuel to air ratio (F/A ratio) can be controlled so as to burn in a lean homogeneous manner and achieve lower NOx emissions and lower particulate matter, compared to equivalent diesel-fuelled engines.
Note also that the homogeneous mixture of fuel and air can also be ignited by a spark or hot surface. Rather than the ignition of pilot fuel, a spark or hot surface can be employed to cause the homogeneous mixture to ignite, optimally near top dead center at the commencement of the power stroke.
This method of gaseous combustion, namely, employing a fumigated fuel, has a number of disadvantages. The first main disadvantage is encountered at high load engine operating conditions, when the elevated temperature and pressure in the piston cylinder during the compression stroke makes the air
atural gas mixture susceptible to “excessive knocking”. Knocking is an uncontrolled combustion process resulting in a very high rate of heat release. Knocking is characterized, in most instances, by relatively rapid fluctuations in combustion chamber pressure. Excessive knocking is associated with conditions where the rapid heat release rate causes excessive combustion chamber pressure that is large enough to damage engine components. Excessive knocking can also cause engine damage through excessive heat release resulting in thermal damage to engine components, such as, by way of example, the piston crown.
A few measures for reducing the risk of excessive knocking include lowering the compression ratio of the engine or limiting the power and torque output, but these measures cause a corresponding reduction in the engine's cycle efficiency (that is, not as much power is available from each piston stroke). A “knock limit” is designated and defined as that set of conditions within the cylinder at which excessive knock can occur as described above. Ultimately, fumigated fuel is knock limited and, as such, is unable to meet load demands beyond a certain level dictated by the knock limit.
For the purposes of this application, “fumigated fuel” or “fumigated gaseous fuel” will be a fuel (generally gaseous) and oxygen mix. Fumigated fuel is a fuel/oxygen mix where the fuel has been mixed with oxygen by the time the piston has reached top dead center immediately prior to both combustion and the piston power stroke. The oxygen would generally be provided as a constituent of intake air; however, it could be provided in some other manner. The fumigated fuel can be mixed with oxygen in the combustion chamber or in the intake manifold (or intake conduit) or partially mixed within both the intake manifold and combustion chamber. For the purposes of this discussion, the fumigated fuel will generally be substantially homogeneous, however, it can also be stratified to some extent.
The second main disadvantage of a homogeneous mixture of fuel and air is that, under low load engine operating conditions, the mixture of fuel and air becomes too lean to support stable combustion via flame propagation and results in incomplete combustion or misfiring. The intake air flow can be throttled to maintain a F/A ratio above a flammability limit, however, such throttling adversely affects the engine efficiency. As will be discussed further below, the flammability limit is defined as the condition limits with the engine under which the F/A ratio will begin to support a flame propagation combustion event.
Third, during start-up it is important that the fumigated fuel, introduced into the cylinder be ignited. However, as is well known in the field involved here, an initial injection of fumigated fuel and, in some cases, a pilot fuel, into the cylinder does not necessarily cause the engine to start on each attempt. When this occurs, a highly flammable mixture can flood the cylinder as well as the exhaust system. This could cause an uncontrolled combustion event when engine ignition is next attempted.
Recently, a different type of dual fuel combustion engine, herein referred to as a high pressure direct injection gas engine, has become known in the field involved here. Similar to the conventional dual fuel method described above, high pressure direct injection gas engines burn a large quantity of gaseous fuel, yielding an improvement over diesel-fuelled engines by reducing the emission levels of NO
x
and particulate matter. In addition, high pressure direct injection gas engines have been demonstrated to achieve the same combustion efficiency, power and torque output as state-of-the-art diesel-fuelled engines. The operational principle underlying high pressure direct injection gas engines is that two fuels are injected under pressure into the chamber near the end of the compression stroke. According to one method, a small quantity of “pilot fuel” (typically diesel) is injected into the cylinder immediately followed by a more substantial quantity of gaseous fuel. The pilot fuel readily ignites at the pressure and temperature within the cylinder at the end of the compression stroke, and the combustion of the pilot fuel initiates the combustion of the gaseous fuel that might otherwise be difficult to ignite. Known high pressure direct injection gas engines have no fumigated fuel. As a result, the directly injected gas operates in a “diffusion combustion” mode, rather than a premixed combustion mode. In a diffusion combustion mode typical of homogeneous fuel combustion, the bulk of the combustion is believed to occur in a local near-stoichiometric reaction zone, where the temperature and resulting NO
x
formation are relatively high (compared to the temperature and resulting NO
x
formation caused by a lean burn premixed combustion).
In U.S. Pat. No. 5,365,902 (hereinafter referred to as the '902 patent), a method and apparatus for dual fuel injection is disclosed, which combines some of the advantages of diffusion combustion and premixed combustion with flame propagation. According to the '902 patent, the engine load conditions are detected, and under low load conditions, the pilot fuel is in
Ancimer Richard
Tanin Konstantin
Kwon John
McAndrews Held & Malloy Ltd.
Westport Research Inc.
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