Internal combustion engine

Details Internal combustion engine Internal combustion engine

2002-07-30

2004-09-14

Argenbright, Tony M. (Department: 3747)

Internal-combustion engines

Two-cycle

Pump and cylinder adjacent

Reexamination Certificate

active

06789514

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an internal combustion engine, and more particularly to a decoupled internal combustion engine whereby the mixing and compressing of air and fuel occurs within a first cylinder and the combusting and exhausting occurs within a second cylinder.
BACKGROUND OF THE INVENTION
The engine development process has often involved making decisions between competing engine characteristics, including fuel efficiency, power output, physical size, emission characteristics, reliability, and durability to name a few. In particular, emission characteristics are one criteria that are often evaluated by organizations like the Environmental Protection Agency (EPA). For instance, if some emission levels, such as nitrous oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) or particulate matter are too high for an engine, the engine may require expensive exhaust treatments such as a catalytic converter. In other instances, the engine might not be certified for operation or sale if it has poor emissions characteristics. As a result, engine emissions should be carefully considered during the engine development process. Some issues surrounding engine development regarding emissions characteristics are described below.
Carbon monoxide and NOx emissions (including both NO and NO
2
) are formed during combustion. Carbon monoxide generally results when combustion occurs with an air and fuel mixture that has more fuel than the stochiometric reaction requires (also known as a “rich” mixture). To address carbon monoxide concerns, most engines attempt to operate with stochiometric or lean (less fuel than stochiometric) air and fuel mixtures. However, some pockets of fuel rich zones will typically still exist in the air and fuel mixtures of conventional engines. These pockets can result in carbon monoxide production. Conversely, NOx emissions are high when the air and fuel mixtures are lean or near stochiometric values. Techniques used to address NOx formation include the recirculation of exhaust gases into fresh air and fuel mixtures.
Among other causes, Hydrocarbon (HC) emissions can result from incomplete combustion or unburned fuel passing through a power cylinder during a period of intake and exhaust valve overlap. Cylinders of conventional engines often provide areas where it is difficult to sustain combustion, such as in the crevices between a piston and a cylinder wall. Additionally, most fuel injection systems cannot provide fuel that is completely evaporated before combustion begins. Fuel may also cling to the walls of a cylinder after it has been injected, forming a wet sheet of fuel that does not burn. This often leads to incomplete combustion in at least portions of a combustion chamber resulting in hydrocarbon emissions. Hydrocarbon emissions are often worse when an engine is first started, as the engines are typically cold and complete evaporation of fuel is difficult to support.
Both in diesel and spark-ignition engines, the ratio of the fuel to air is not the same throughout the cylinder—thus not stochiometric—due in part to poor mixing. Some part of the fuel/air mixture is fuel rich and some part is oxygen rich (i.e., lean). The crown of the piston (i.e., the top of the piston), the injection angle, and valve size and location, etc. are varied to control the flow of injected fuel/air mixture, but the problem still persists. This non-stochiometric ratio may limit the maximum compression ratio of the engine, which controls the flame propagation speed and the combustion chemistry.
Another problem of conventional four-stroke spark-ignition engines is the knocking of the engine. This knocking problem limits the maximum compression ratio of conventional IC engines and thus, the power efficiency of the engines. This limiting compression ratio, in turn, determines the volume of the cylinder that still contains the hot combustion product when the piston is at the highest position of its compression stroke. Knocking is a result of self-ignition or auto-ignition. To prevent knocking, the most desirable combustion process in the power cylinder of spark-ignition IC engines is the one where a flame sheet propagates from the ignition point outward at a high compression ratio. Because of the expansion of the gas behind the flame front, the unburned fuel vapor and air experiences high pressure and temperature before the flame front reaches the unburned region. When the pressure and temperature of the unburned fuel-vapor/air mixture are high enough, the mixture can self-ignite (i.e., auto-ignition), causing a rapid rise in pressure, which induces vibration of the cylinder walls and audible knocks. This process is accelerated when there is enough time for sufficient auto-ignition precursors to form. Two mechanisms control “knocking”: the formation of precursors and the temperature rise that accelerate the flame propagation rate. At high engine speeds knocking may not be a problem since there is less time available for the precursors to form. On the other hand, as engine speed increases, there is less heat loss from the gases so that gas temperatures will be higher. This accelerates the precursor formation rate so that less time is required to form a concentration high enough for auto-ignition to occur. As a result of these two competing effects, some engines show knocking at high speeds, whereas some at low speeds. Knocking can be severe when the fuel-vapor/air mixture is at its stochiometric ratio. This problem has been solved in current engines in two expensive ways: the use of anti-knock additives and the lowering of the compression ratio. To prevent auto-ignition, high-octane fuel—a mixture of many hydrocarbons with high-octane additives—is used in high compression engines. If knocking persists even with the use of high-octane gasoline, it is eliminated by changing the ignition time to ignite the fuel-vapor/air mixture at a lower pressure (thus at a lower compression ratio) when the piston has moved downward from its highest position. This lowers fuel efficiency.
Conventional methods of developing products, and specifically internal combustion engines, often lead to lengthy development cycles and consequently high cost due to the iterative nature of such methods. For example, an engine designer may make a modification to one component of an engine which, in turn, requires him to make many other modifications in other already designed and tested components of the engine. Making such a change may require re-evaluating the previously tested components, thereby adding cost and time to the development process.
The inventors of the present invention have found that the use of an axiomatic design approach offered a workable methodology to design an engine that addresses at least some of the above-mentioned issues. Using an axiomatic design approach can provide a process to design an engine that allows a designer to achieve an engine with the characteristics he or she wants by providing a clear description of how the designer can achieve the characteristics. Once the engine designer understands the design needs, the understanding is transformed into a minimum set of specifications, which are defined as functional requirements (FR's), that adequately describe “what the designer wants to achieve” to satisfy the design needs. The descriptor of “how the designer will achieve the needs” is articulated in the form of design parameters (DP's).
A basic postulate of the axiomatic design approach used to design the internal combustion engine described herein, is that there are fundamental axioms that govern the design process. There are two primary axioms associated with the axiomatic design approach.
The first axiom is called the independence axiom. It states that the independence of functional requirements (FR's) should be maintained, where FR's are defined as the minimum set of independent requirements that characterize the design goals. A set of FR's is the description of design goals. The independence axiom states that when there are two o

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