Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
2001-07-11
2003-07-29
McCall, Eric S. (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
Reexamination Certificate
active
06598468
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an apparatus and methods for determining the start of combustion in an internal combustion engine.
2. Description of Related Art
Relatively recently, because of the increased regulatory pressure for fuel efficient and low emissions vehicles, some engine designers have directed their efforts to one type of an internal combustion engine which utilizes premixed charge compression ignition (PCCI). Researchers have used various other names in referencing PCCI combustion including homogeneous charge compression ignition (HCCI) as well as others such as “ATAC” which stands for “Active Thermo-Atmosphere Combustion.” (SAE Technical Paper No. 790501, Feb. 26-Mar. 2, 1979), “TS” which stands for “Toyota-Soken” (SAE Technical Paper No. 790840, Sep. 10-13, 1979), and “CIHC” which stands for “compression-ignited homogeneous charge” (SAE Paper No. 830264, 1983). All of these terms are hereinafter collectively referred to as PCCI.
Generally, conventional internal combustion engines are either a diesel or a spark ignited engine, each, to a large extent, controlling the start of combustion (SOC) which has been found to be critical in both efficiency and emissions of internal combustion engines. Initially, it should be understood that SOC refers to combustion phasing where the energy of the fuel is released. In this regard, SOC is commonly referred to as the point in time or crank angle at which a charge within the cylinder begins to ignite or rapidly combusts. The diesel engine controls the SOC by the timing of fuel injection while a spark ignited engine controls the SOC by the spark timing. The major advantage that a spark-ignited natural gas or gasoline engine has over a diesel engine is its ability to achieve extremely low NOx and particulate emissions levels. The major advantage that diesel engines have over premixed charge spark ignited engines is in its higher thermal efficiency. One key reason for the higher efficiency of diesel engines is its ability to use higher compression ratios than premixed charge spark ignited engines since the compression ratio in premixed charge spark ignited engine must 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 controlled 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.
Unlike these conventional internal combustion engines, engines operating on PCCI principles rely on autoignition of a relatively well premixed fuel/air mixture to initiate combustion. More specifically, in PCCI engines, the fuel and air are mixed in the intake port or in the cylinder, long before ignition occurs. The extent of the mixture may be varied depending on the combustion characteristics desired. Some engines may be 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. Thus, PCCI combustion event is characterized in that: 1) the majority of the fuel is sufficiently premixed with the air to form a combustible mixture throughout the charge at the time of ignition; and 2) ignition is initiated by compression ignition. In addition, PCCI combustion is also preferably 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. Because 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 engine, it has recently been the subject of extensive research and development.
It has been recognized by the applicants of the present invention that the key to producing a commercially viable PCCI engine lies in the control of the combustion history of subsequent or future combustion events in such a manner so as to result in extremely low nitrous oxide (NOx) emissions combined with very good overall efficiency, combustion noise control and with acceptable cylinder pressure. The combustion history may include the time at which combustion occurs (start of combustion), the rate of combustion (heat release rate), the duration of combustion and/or the completeness of combustion. Applicants have determined that the combustion history, and especially the start of combustion (SOC), is sensitive to, and varies depending on, a variety of factors including changes in load and ambient conditions.
In addition, it has also been found by the present applicants that for efficient, low emission PCCI combustion, it is important to have the phasing of combustion or SOC occur properly at an appropriate crank angle during the engine cycle. If combustion starts too early, cylinder pressures will be excessively high and efficiency will suffer. If combustion starts too late, then combustion will be incomplete resulting in poor HC emissions, poor efficiency, high carbon monoxide (CO) emissions, and poor stability. It has further been found that the timing of the start of combustion (SOC) and the combustion rate (therefore combustion duration) in a PCCI engine primarily depend on various combustion history values such as the temperature history; the pressure history; fuel autoignition properties (e.g. octane/methane rating or activation energy); and trapped cylinder charge air composition (oxygen content, EGR, humidity, equivalence ratio etc.).
A premixed charge compression ignition engine with optimal combustion control with various control features for controlling SOC and the combustion rate is disclosed in the patent application Ser. No. 08/916,437 filed on Aug. 22, 1997, currently assigned to the Assignee of the present invention. This application has also been published as International Patent Application No. PCTUS97/14815. As disclosed in the '437 application, it has been found that active control is desirable to maintain the SOC and duration of combustion at the desired location of the crank shaft and at the desired duration, respectively, to achieve effective, efficient PCCI combustion with high efficiency and low NOx emissions.
More specifically, the '437 application discloses a PCCI engine co
Brackney Larry J
Zigan James A
zur Loye Axel O
Brackett, Jr. Tim L.
Cummins Inc.
McCall Eric S.
Nixon & Peabody LLP
Song Daniel S.
LandOfFree
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