Internal combustion engine operable in PCCI mode with post-ignition injection and method of operation

#1. Field of the Invention

#The present invention is directed to an improved internal combustion engine for increasing fuel efficiency while reducing exhaust emissions and a method of operating such an engine. In particular, the present invention is directed to such an engine operable in a premixed charge compression ignition mode.

#2. Description of Related Art

#FIG. 1 is a schematic diagram a single cylinder of an internal combustion engine in accordance with one embodiment of the present invention.

#FIG. 2 is a schematic diagram a single cylinder of an internal combustion engine in accordance with another embodiment of the present invention.

#FIG. 3 is a graph showing combustion chamber pressure characteristics of a prior art internal combustion engine operating in a conventional PCCI mode.

#The present invention as described in further detail herein below provides an improved internal combustion engine operable in a premixed charge compression ignition mode as well as a method of operating such an engine that improves fuel efficiency while reducing exhaust emissions which may be harmful to the environment. In this regard, it should be initially noted that the present invention may be applied to various different types of internal combustion engines that combust various fuels including (but not limited to) natural gas, gasoline, diesel, naphtha, propane, and/or other fuels. In addition, as previously described, premixed charge compression ignition (hereinafter “PCCI”) refers to any engine or combustion process in which: 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, thus including homogeneous charge compression ignition (HCCI) engines. It should be noted that the term PCCI as used herein does not exclude the use of ignition timing mechanisms such as pilot injections and spark ignition to precisely time the start of combustion of a premixed charge where the vast majority of the premixed charge will burn by compression ignition without the presence of a self-sustaining propagating flame front such as in a spark ignited engine. This allows a PCCI engine to combust a mixture that is too lean to support a self-sustaining flame front thereby allowing a premixed charge leaner than is possible in a spark ignited engine. Thus, such use of ignition timing mechanisms may be applied to the present invention as well.

#FIG. 1 generally illustrates an example PCCI internal combustion engine 10 to which one embodiment of the present invention may be applied. As illustrated, the internal combustion engine 10 includes an engine body 12 with a piston assembly 14 reciprocally mounted therein. The piston assembly 14 forms a combustion chamber 16 in the engine body 12 in a manner well known in the art. The internal combustion engine 10 also includes an intake system 18 for delivering intake air to the combustion chamber 16 through an intake valve 20. It should be noted that although only one cylinder is illustrated in FIG. 1, the present invention may be utilized in internal combustion engines of various configurations including engines having any number of cylinders, for example, a four, five, six, eight, ten, twelve, or sixteen cylinders, etc.

#In accordance with the illustrated embodiment of the present invention, the internal combustion engine 10 includes a mixing device such as port fuel injector 22 that is adapted to mix intake air and a first fuel 23 upstream of the combustion chamber 16 to thereby provide premixed charge of air and the first fuel 23 to the combustion chamber 16. In the preferred embodiment of the present invention, the equivalence ratio of the premixed charge of air and the first fuel 23 may be leaner than 0.5. Of course, in other embodiments, other richer equivalence ratios such as 1.0 or even mixtures richer than stoichiometric may also be used. In addition, in the illustrated embodiment, the first fuel 23 is natural gas but in other embodiments, the first fuel 23 may be gasoline or other types of fuels or blends thereof as well. In addition, it should also be noted that other mixing devices may be used instead of the port fuel injector 16 such as a carburetor or a throttle body injector which are well known in the art. This premixed charge of air and the first fuel 23 is provided into the combustion chamber 16 and as the piston assembly compresses the premixed charge, the premixed charge is ignited due to the increased pressure and temperature in the combustion chamber 16 in a PCCI combustion event.