Internal-combustion engines – Charge forming device – Including cylinder pressure or temperature responsive means
Reexamination Certificate
1997-08-22
2001-09-11
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Including cylinder pressure or temperature responsive means
C128S098100, C128S202250, C128S126100, C128S126100, C701S101000
Reexamination Certificate
active
06286482
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a compression ignition engine arranged to internally burn a premixed charge of fuel and air using autoignition to achieve reduced emissions while maintaining the desired fuel economy.
BACKGROUND OF THE INVENTION
For well over 75 years the internal combustion engine has been mankind's primary source of motive power. It would be difficult to overstate its importance or the engineering effort expended in seeking its perfection. So mature and well understood are merely designs made up of choices among a variety of known alternatives. For example, an improved output torque curve can easily be achieved by sacrificing engine fuel economy. Emissions abatement or improved reliability can also be achieved with an increase in cost. Still other objectives can be achieved such as increased power and reduced size and/or weight but normally at a sacrifice of both fuel efficiency and low cost.
The challenge to contemporary designers has been significantly increased by the need to respond to governmentally mandated emissions abatement standards while maintaining or improving fuel efficiency. In view of the mature nature of engine design, it is extremely difficult to extract both improved engine performance and emissions abatement from further innovations of the basic engine designs commercially available today. Yet the need for such innovations has never been greater in view of the series of escalating emissions standards mandated for the future by the United States government and other countries. Attempts to meet these standards includes some designers looking for a completely new engine design.
Traditionally, there have been two primary forms of reciprocating piston or rotary internal combustion engines: diesel and spark ignition engines. While these engine types have similar architecture and mechanical workings, each has distinct operating properties which are vastly different from each other. Diesel and spark ignited engines effectively control the start of combustion (SOC) using simple, yet distinct means. The diesel engine controls the SOC by the timing of fuel injection. In a spark ignited engine, the SOC is controlled by the spark timing. As a result, there are important differences in the advantages and disadvantages of diesel and spark-ignited engines. The major advantage that a spark-ignited natural gas, or gasoline, engine has over a diesel engine is the ability to achieve extremely low NOx and particulate emissions levels. The major advantage that diesel engines have over premixed charge spark ignited engines (such as passenger car gasoline engines and lean burn natural gas engines) is higher thermal efficiency. One key reason for the higher efficiency of diesel engines is the ability to use higher compression ratios than premixed charge spark ignited engines (the compression ratio in premixed charge spark ignited engines has to be kept relatively low to avoid knock). A second key reason for the higher efficiency of diesel engines lies in the ability to control the diesel engine's power output without a throttle. This eliminates the throttling losses of premixed charge spark ignited engines and results in significantly higher efficiency at part load for diesel engines. Typical diesel engines, however, cannot achieve the very low NOx and particulate emissions levels which are possible with premixed charge spark ignited engines. Due to the mixing nature of diesel combustion a large fraction of the fuel exists at a very fuel rich equivalence ratio which is known to lead to particulate emissions. Premixed charge spark ignited engines, on the other hand, have nearly homogeneous air fuel mixtures which tend to be either lean or close to stoichiometric, resulting in very low particulate emissions. A second consideration is that the mixing controlled combustion in diesel engines occurs when the fuel and air exist at a near stoichiometric equivalence ratio which leads to high temperatures. The high temperatures, in turn, cause high NOx emissions. Lean burn premixed charge spark ignited engines, on the other hand, burn their fuel at much leaner equivalence ratios which results in significantly lower temperatures leading to much lower NOx emissions. Stoichiometric premixed charge spark ignited engines, on the other hand, have high NOx emissions due to the high flame temperatures resulting from stoichiometric combustion. However, the virtually oxygen free exhaust allows the NOx emissions to be reduced to very low levels with a three-way catalyst.
Relatively recently, some engine designers have directed their efforts to another type of engine which utilizes premixed charge compression ignition (PCCI) or homogeneous charge compression ignition (HCCI), hereinafter collectively referred to as PCCI. Engines operating on PCCI principles rely on autoignition of a relatively well premixed fuel/air mixture to initiate combustion. Importantly, the fuel and air are mixed, in the intake port or the cylinder, long before ignition occurs. The extent of the mixture may be varied depending on the combustion characteristics desired. Some engines are designed and/or operated to ensure the fuel and air are mixed into a homogeneous, or nearly homogeneous, state. Also, an engine may be specifically designed and/or operated to create a somewhat less homogeneous charge having a small degree of stratification. In both instances, the mixture exists in a premixed state well before ignition occurs and is compressed until the mixture autoignites. Importantly, PCCI combustion is characterized in that: 1) the vast majority of the fuel is sufficiently premixed with the air to form a combustible mixture throughout the charge by the time of ignition and throughout combustion; and 2) combustion is initiated by compression ignition. Unlike a diesel engine, the timing of the fuel delivery, for example the timing of injection, in a PCCI engine does not strongly affect the timing of ignition. The early delivery of fuel in a PCCI engine results in a premixed charge which is very well mixed, and preferably nearly homogeneous, thus reducing emissions, unlike the stratified charge combustion of a diesel which generates higher emissions. Preferably, PCCI combustion is characterized in that most of the mixture is significantly leaner than stoichiometric to advantageously reduce emissions, unlike the typical diesel engine cycle in which a large portion, or all, of the mixture exists in a rich state during combustion.
An engine operating on PCCI combustion principles has the potential for providing the excellent fuel economy of the diesel engine while providing NOx and particulate emissions levels that are much lower than that of current spark-ignited or diesel engine. For example, U.S. Pat. No. 4,768,481 to Wood discloses a process and engine that is intended to use a homogeneous mixture of fuel and air which is spontaneously ignited. A controlled rate of combustion is said to be obtained by adding exhaust products to the air-fuel mixture. A combustion chamber is connected to the engine cylinder and fuel gas is supplied to the chamber via a check valve. A glow plug is positioned between the combustion chamber and the cylinder. The mixture entering the combustion is heated by the glow plug and by the hot walls of the combustion chamber. The mixture ignites due to the increase in temperature and the increase in pressure resulting from compression. The Wood patent is specifically directed to a two-stroke engine, but generally mentions that the technology could be applied to a four-stroke engine. However, this reference fails to discuss how the exhaust gas recirculation and glow plug would be controlled to optimize the start of combustion and to maintain the optimal start, and duration, of combustion, as load and ambient conditions change. A practical embodiment of this engine is unlikely to be capable of effectively controlling and maintaining PCCI combustion without additional controls.
U.S. Pat. No. 5,535,716 issued to Soto et al., discloses a compression ignition type engine
Akinyemi Omowoleoia C.
Durrett Russ P.
Flynn Patrick F.
Hunter Gary L.
Moore Greg A.
Brackett, Jr. Tim L.
Cummins Engine Company, Inc.
Leedom Jr. Charles M.
Nixon & Peabody LLP
Vo Hieu T.
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