Multiple operating mode engine and method of operation

#This invention relates generally to an internal combustion engine capable of operating in, and transitioning between, different operating modes including a premixed charge compression ignition mode, a diesel mode and/or spark ignition mode.

#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 is the art of internal combustion engine design that most so called “new” engine designs 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 include some designers looking for a completely new engine design.

#FIG. 1 is a schematic diagram of one embodiment of the present invention showing a single cylinder of the multi-mode engine and associated control system;

#FIG. 2 is a graph showing diesel fuel rate in terms of equivalence ratio versus a premixed gas flow rate in terms of equivalence ratio, to illustrate a continuous operating space for transitioning between modes of engine operation;

#FIG. 3 is a graph showing another dimension of the graph of FIG. 2 with intake manifold temperature versus premixed gas flow rate in terms of equivalence ratio;

#The present invention as described in further detail hereinbelow is directed to an improved internal combustion engine capable of operating in and transitioning or transferring between different operating modes to improve fuel efficiency and reduce exhaust emissions while increasing startability and load handling across a range of engine operating conditions. Specifically, the multi-mode engine of the present invention, as generally shown at 10 in FIG. 1, may be operated in a premixed charge compression ignition (PCCI) mode, a diesel mode, a spark ignition (SI) mode and a homogeneous charge dual fuel transition (HCDFT) mode. A PCCI mode of operation refers to a combustion event wherein: 1) the majority of fuel is sufficiently premixed with air to form a combustible mixture throughout the charge at the time of ignition; and 2) ignition (start of combustion) is initiated by compression ignition, which includes 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. The diesel mode as referred to herein means the conventional diesel cycle and combustion, which includes controlling the start of combustion (SOC) by the timing of the fuel injection. The spark ignited (SI) mode means the standard Otto cycle wherein the SOC is controlled by the spark timing. Importantly, it should be understood that the spark may be either electrically produced or in the form of a pilot quantity of fuel, referred to herein as liquid spark ignited (LSI). For purposes of this application, the term spark ignited or spark ignition or SI is understood to include the use of either an electric or a liquid spark. The homogeneous charge dual fuel transition (HCDFT) mode occurs when a first fuel quantity is made early in the process to form a mixture too lean to propagate a self-sustaining flame and a second fuel quantity larger than a pilot quantity (and preferably a different fuel from the first fuel) is delivered later, e.g. near top dead center. It should be initially noted that the present invention may be applied to various types of internal combustion engines that combust various fuels including, but not limited to, natural gas, gasoline, propane, hydrogen, diesel, kerosene, naphtha and/or other fuels.

#Referring to FIG. 1, there is shown an exemplary embodiment of multi-mode engine 10 capable of transferring between two or more modes of operation. Multi-mode engine 10 includes an engine body 12 with a piston assembly 14 reciprocally mounted therein. Piston assembly 14 and engine body 12 forms a combustion chamber 16 in a manner well known in the art. Multi-mode engine 10 also includes an intake system 18 for delivering intake air or a combination of intake air and fuel to combustion chamber 16 and an exhaust system 20 for removing exhaust gas from combustion chamber 16. 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, four, five, six, eight, ten, twelve or sixteen cylinders. In addition, although the present multi-mode engine is primarily discussed with reference to a four-stroke engine, the present control system and engine may be in the form of a two-stroke engine.

#Intake system 18 includes an intake manifold 20 and an intake port 22 for directing intake air or an air/fuel mixture into combustion chamber 16. Likewise, exhaust system 20 includes an exhaust port 24 for directing exhaust gas as described hereinbelow. One or more intake valves, such as intake valve 26, and one or more exhaust valves, such as exhaust valve 28, are positioned in the respective ports and moved between open and closed positions by a conventional valve control system, or a variable valve timing system, to control the flow of intake air or air/fuel mixture into, and exhaust gases out of, the cylinder, respectively. Intake system 18 may further include a throttle 30 for controlling intake manifold pressure and thus intake air, or air/fuel mixture, flow through intake system 18. Throttle 30 may also be used as an effective way of transferring between different modes of operation as discussed more fully hereinbelow. An air cooler 32 may also be provided to control the temperature of the intake air or air/fuel mixture. An air cooler bypass circuit 34 and bypass valve 36 may be provided to more effectively control the quantity of air or air/fuel mixture flow through air cooler 32 thereby permitting more control over the temperature of the intake flow. A compressor 38 may be provided along intake air system 18, upstream of intake manifold 20 and air cooler 32, for varying boost intake pressure. Compressor 38 may be driven by any conventional means, such as an exhaust gas driven turbine 40. An exhaust restriction or throttle 42 may be positioned upstream of exhaust turbine 40 to permit greater control over the combustion process, e.g. controlling the residual mass fraction to control the SOC. Although not shown, a waste gate valve may also be provided in a conventional manner to regulate the amount of exhaust gas applied to turbine 40 thereby varying the intake pressure as desired. Another important way to control intake temperature and thus SOC is by using hot exhaust gas recirculation (EGR). An EGR circuit 44 may be used to direct hot exhaust gas from upstream of turbine 40 into intake system 18. EGR circuit 44 includes an EGR control valve 46 for controlling the recirculation of exhaust gas. Exhaust system 20 may also be provided with an exhaust gas treatment device 48, such as an oxidation catalyst 48, for treating the exhaust gas. Engine 10 may also include combustion sensor 50 for sensing a combustion characteristic, such as a cylinder pressure sensor, and generating a signal corresponding to the combustion characteristic. Preferably, a cylinder pressure sensor is provided on any or all engine cylinders for sensing, on a cycle-by-cycle basis, the SOC. Of course, combustion sensor 50 may also provide other combustion data, such as combustion rate, combustion duration, crank angle at which peak cylinder pressure occurs, combustion event or heat release location and end of combustion data, any one of which may be used instead of the start of combustion data to effectively control combustion. While in the present embodiment, the sensor 50 that provides the pressure data signal is a pressure sensor, other sensors may also be used that provide a signal indicative of cylinder pressure such as through use of correlating pressure data. Such sensors include accelerometers, ion probes, optical diagnostics, strain gages, load washers, and/or fast thermocouples in or near the cylinder head, liner or piston. Also, torque or RPM sensors could be used to detect changes in engine torque and RPM associated with each combustion event. In one embodiment, the engine may also be provided with a spark plug 52 for operating in an electronic spark ignition mode.