Patent Application
20050279093
1. Field of the Invention
The present invention relates generally to supercharged internal combustion engines. Specifically, the present invention is directed to a turbocharged-intercooled engine, which may be a homogeneous charge spark ignition (SI) type, a heterogeneous charge compression ignition (diesel) type, a heterogeneous charge (direct-injection) spark ignition type, or homogeneous charge compression ignition (HCCI) type.
2. Description of the Related Art
H. R. Ricardo stated, “The piston engine is eminently suitable to deal with relatively small volumes at high pressure and temperature and the turbine, by virtue of its high mechanical efficiency and large flow areas, to deal with large volumes at low pressures. Clearly, the logical development is to combine the two in series to form a compound unit.” (Smith 1955: 279-280). He envisaged the possibility of an engineering system, not as a modification of the piston engine, but as a new rational whole with the compelling logic of resulting mechanical (gas exchanging) advantage and thermodynamic advantage.
Existing turbocharged engines, both diesel engines and SI gasoline engines, apply turbo-charging by modifying naturally-aspirated piston engines. They produce the desired power boosting as expected. However, the power boosting in the case of SI gasoline engines is curtailed by knock limits, and, in the case of diesel engines, by mechanical and thermal load limits. Furthermore, the efficiency of turbocharged SI engines suffers as a result of measures that are necessary for knock avoidance.
Engine operating pressure and temperature approach these limits at high speed and torque load, as a result of excessive energy in the exhaust charge under these operating conditions. In the case of gasoline engines operating under these operating conditions, waste-gates are pressure-activated (pneumatically) according to a set intake-manifold pressure limit to bypass the excess exhaust charge from a turbocharger turbine in order to prevent engines from exceeding the knock limit. In the case of diesels, both waste-gate and fuel rate control are used to safeguard engines from exceeding the mechanical and thermal load limits.
A pressure-relief valve on the intake side of the engine has been used as an alternative to a waste-gate. A further refinement of the pressure-relief valve concept was presented in U.S. Pat. No. 6,158,217 (Wang). The new solution, using an apparatus referred to in Wang as a cryo-cooler unit, does more than absorb the excess charge-exhaust energy. It utilizes the excess charge-exhaust energy at high speed and high load operation to supply the compressed charge-air to the engine intake manifold at desired low temperatures. The delivery of the compressed charge-air to the engine intake manifold at low temperatures represents a better solution to matching a turbocharger with a piston-engine than the forced matching of a piston-engine turbocharger system operating with a waste-gate. However, the solution based on the cryo-cooler is conceived as a refinement to the relief valve, pressure-activated at the narrow range of high speed and torque load. According to Wang, during low speed/load operation the bypass valve opens to one path alone and directs all compressed and intercooled air to the intake manifold. During high speed/load operation, when exhaust charge with excessive enthalpy is available to drive the turbine, the bypass valve opens to both paths. The ability of such a cooler to provide intake charge of low temperature hints at a possibility that this cooler may be used as a part of engine system operation under a broad range of speeds and loads, providing the internal-combustion engine with charge-air at a preferred temperature.
The classical idea (the Carnot-Otto-Diesel paradigm) that the theoretical thermal efficiency of combustion engines increases with the engine operating temperature monotonically is rejected by two recent developments: (1) a paper, “Reflections On Heat Engines: The Operational Analysis Of Isothermal Combustion,” AES-Vol. 27/HTD-Vol. 228, Thermodynamics and the Design, Analysis, and Improvement of Energy Systems, pp. 315-327, ASME (1992); and (2) a promising engine technology, which uses a new combustion process, homogeneous charge compression ignition, leading to low temperature spontaneous flameless combustion. Both, the theoretical and the other real technology development, demonstrate that combustion engine performance improves with engine operating temperature up to a point. Once that peak-temperature point is reached, engine operation is optimized by keeping operating temperatures from exceeding that peak-temperature range.
The compelling logic in mechanical and thermodynamic advantages that Ricardo hinted at should be modified as follows. While high intake charge pressure due to turbocharging brings about high power output, this increase in high intake charge pressure should be accompanied with an optimal intake charge temperature, which is not necessarily a monotonic function of pressure. In fact, the optimal intake charge temperature may change in an opposite direction to pressure, once the engine operating temperature reaches the peak-temperature range.
Accordingly, the present invention is made to solve the above-mentioned problems and limitations in the prior art. The present invention provides a supercharged intercooled engine utilizing the turbo-cool principle and methods for operating the same. It is an object of the invention to provide for the simultaneous controlling of both load and speed control and conditioning of intake air in such engines so as to provide superior engine operation. It is a further object of the invention to provide a first operation control unit primarily for speed control, a second operation control unit primarily for conditioning intake air, and an operation control means for controlling a start-of-combustion. It is another object of this invention to provide a method for operating an internal combustion engine including the steps of simultaneously controlling load-and-speed and condition of intake air temperature through the combined application of a first operation control unit, primarily for load-and-speed control, and a second operational control unit, primarily for intake air conditioning. It is also an object of this invention to provide an engine management method for optimally controlling engine operation through the use of an engine management mapping-algorithm.
The present invention is applicable to both spark ignition and diesel engine types and therefore has multiple embodiments to recognize the different methods of engine load controls unique to the engine type and which will not be changed by the present invention. The spark-ignition (SI) engine load is controlled by changing intake-manifold pressure (thus, charge-air mass flow) brought about through varying the throttle-butterfly opening. The intake air of diesel engines is not throttled; the fuel quantity (fuel rate) alone is used for the diesel engine's load control. The direct-injection SI engine load control is similar to the diesel engine during its heterogeneous-charge operation mode and similar to the SI engine during its homogeneous-charge operation mode.
The present invention, turbo-cool, introduces a new application of the cryo-cooler, which was itself a refinement of the pressure relief valve concept as a replacement of the waste-gate. The cryo-cooler was conceived to operate under load/speed conditions that would have necessitated waste-gate operation and its operation leads to low temperature intake air. The turbo-cooling principle integrates this temperature lowering function of the cryo-cooler with the temperature regulation function. An actively controlled flow-control-valve controls engine operation under broad loads and speeds. In the prior art, the “cryo-cooler” served as means of handling excess charge exhaust energy with a passively controlled relief valve, pressure-activated under high speed/load operation only. In acknowledging its new application as an active temperature regulation, the cryo-cooler is hereinafter referred to as a turbo-cooler and the flow-control-valve is hereby referred to as a turbo-cooler valve.
The present invention employs a first operation control unit to primarily address load/speed control and a secondary control unit to address conditioning intake air temperature. The active control-use of turbo-cooler valve towards engine operation control operates in the following way: the turbo-cooler, primarily for conditioning intake air temperature, is used in combination with a primary load/speed control to simultaneously control engine load/speed and intake air temperature at optimal values over a broad range of loads and speeds.
The optimum setting of turbo-cooler valve for each given throttle butterfly setting in the SI engine model is determined by testing. Correspondingly, the optimum setting of turbo-cooler valve for each given fuel rate setting in the diesel engine is also determined by testing. The combined application of the primary load/speed control and the primary intake air temperature control allows the engine of the present invention to operate at each steady-state speed and load with intake air in a “sweet spot” of charge-air temperature and pressure, producing unsurpassed performance in thermal efficiency and power.
Significant gains in both thermal efficiency and power density (extraordinary gain in the case of SI engines) of the proposed engine technology form a powerful combination with superior synergistic potential in fuel economy improvement for automotive use, producing unsurpassed performance at reasonable cost.
The capability to simultaneously control engine load/speed and intake air temperature at optimal values over a broad range of loads and speeds has an additional application. One of the most promising engine technologies that has emerged over the past few years is called the homogeneous charge compression ignition (HCCI) engine. The combustion process for the HCCI engine is fundamentally different from SI or diesel combustion in the form of spontaneous flameless combustion. The low temperature spontaneous flameless combustion produces very low NOx and particulate matter (PM) emissions combined with high, diesel-like efficiency under ideal conditions. This combination of low emissions and high efficiency explains the excitement generated by the prospect of HCCI.
Currently, the promise and the excitement are tempered only by the considerable challenges HCCI faces. The most crucial ones among them is the control of the start-of-combustion (SOC) due to the “spontaneous” nature of combustion-ignition. Methods, such as exhaust gas recirculation (EGR) and ignition-assistance, are available for promoting HCCI ignition (making SOC earlier) at low engine loads. It is more difficult to delay HCCI ignition (which becomes necessary at middle and high engine loads under turbocharging conditions) to produce ideal HCCI combustion at high loads. Methods, including conditioning of the intake charge that are used in laboratory experiments for controlling SOC, are impractical for mobile applications. Turbo-cool is a technology for conditioning of intake charge for mobile applications, and is ideally suited for solving the latter SOC control problem for HCCI engines at middle and high engine loads.
The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted to keep the subject matter of the present invention clear.
A supercharged intercooled engine in accordance with turbo-cooling principle is depicted in
Air stream 13 enters a turbo-cooler 50, wherein air stream 13 is divided into two paths: air stream of the first path exiting as charge-air 15, and air stream of the second path exiting as air discharge stream 26.
The details of turbo-cooler are depicted in
The second air stream 21 is in communication with the inlet of a turbine expander 53 of an expander/suction-compressor unit 52. Air stream 21 undergoes an expansion cooling process in turbine expander 53 from P2 to P3. The exit pressure P3 from expander 53 is determined by the power balance between turbine expander 53 and suction compressor 55 of the expander/suction-compressor unit 52. The energy expended in operating turbine expander 53 reduces the temperature of second air stream 21 from T2 to T3. This air stream leaving turbine expander 53 at T3 (denoted by reference numeral 23) is thereupon passed through a water separator 141 (now denoted by reference numeral 24) and then conveyed to the heat exchanger 57, wherein heat transfer takes place from first air stream of charge-air to the second air stream. The second air stream exits the heat exchanger 57 at a temperature T4 and a pressure P4, which is only slightly lowered than P3, as air stream 25. The first air stream of charge-air exits the heat exchanger 57, as air stream 15, at a pressure P5, which is only slightly lower than P2, and at a temperature T5. (In the case diesel engines, first air stream exiting heat exchanger 57 will be denoted as air stream 16 at T6 and P6, see explanation below.)
The heat exchange 57 may be either a cross flow heat exchanger or a rotary heat exchanger. For the rotary heat exchanger, the rotating matrix of the heat exchanger is in contact alternatively with colder second air stream (24 to 25) and with warmer first air stream (14 to 15) potentially making the water separator 141 unnecessary.
The conditioning of air intake, as performed by the turbo-cooler may be carried out by other types of conditioning apparatus and methods. The methods for conditioning of air intake may include the use of a refrigeration unit mechanically powered by a crankshaft of the engine; and may include the use of an injector of water or liquids having a low boiling temperature.
The second air stream 25 is in communication with the inlet of a suction-compressor 55 of the expander/suction-compressor unit 52. Air stream 25 undergoes compression in compressor 55, powered by expander 53, from pressure P4, which is less than atmospheric, to P7, which is equal to the atmospheric P0, discharging as air stream 26. The same compression process of compressor 55 increases the temperature of second air stream from T4 to T7. Air discharging stream 26 into atmosphere at T7, which is moderately above ambient air temperature, represents only a moderate loss of available energy.
Referring back to
In the case of diesel engines, there is no throttle butterfly. The first air stream exiting from heat exchanger 57 is the charge-air, which enters directly the inlet-manifold means 60 of internal combustion engine cylinder 70 as charge-air stream 16 (i.e., for diesel engines, P5=P6=PC and T5=T6=TC).
Exiting from engine 70, the air stream of charge exhaust (now designated by reference numeral 17) passes through exhaust manifold means 80 to enter turbine 32 of turbocharger 30. A wastegate valve 131 for boost-pressure safety-relief is placed between exhaust manifold means 80 and turbine 32. Turbine 32 powers the compressor 31.
A fuel injection means 121 is located at the inlet manifold 60 for port injection for SI engines. Alternatively, fuel injection means 121 is located at engine cylinder 70 for diesel engines. For direct injection SI engines, two fuel injection means (121) are used. One fuel injection means is located at engine cylinder 70 and the other located at inlet manifold 60, the former being used during heterogeneous-charge mode and the latter during homogeneous-charge mode operation.
A more realistic, but still schematic, drawing of one version of
Referring to
The final steady-state engine operation with the desirable charge-air temperature and pressure (referred to as turbocharged engine with Turbo-Cool Charge-Air Cooling (TCAC)) is compared with the steady-state operation of a turbocharged engine with Charge-Air Cooling (CAC) and the steady-state operation of a turbocharged engine (without CAC) in
The optimum steady-state operating TC (T6) vs. operating PC (P6) relation at a given speed may be dependent on the ambient humidity, temperature and pressure. At given ambient condition, the optimum operating TC (T6) vs. operating PC (P6) relation is determined on the basis of the “optimization” of thermal efficiency under the constraint of constant charge-air pressure.
Considering SI engines first, the optimization is described as follows. Testing data of engine steady-state operations are shown schematically in
It should be noted that the throttle butterfly opening of these optimum settings of the throttle butterfly/turbo-cooler valve combination corresponds to higher than the normal opening of throttle butterfly at a given relative load condition. This amounts to a reduction in using throttling effect in the load control of SI engines. Such reduction in reliance of throttling for load control has important benefit for the part-load thermal efficiency of SI engines. This is one reason that a much greater improvement in overall thermal efficiency is expected for SI engines, narrowing the fuel economy gap between SI engines and diesel engines.
The selection (matching) of a specific turbocharger for the base piston engine affects whether, at a given engine speed, the wide open throttle (WOT) setting is reached before the knock limit, or the WOT setting coincides with the knock limit, or the knock limit is reached before the WOT setting. These three possibilities are represented in terms of steady-state operating TC (T6) vs. operating PC (P6) in
As shown in
In
A more than 30% improvement in overall thermal efficiency for SI engines is expected as a result of the following simultaneous-benefits. Referring to
Consequently, temperature of charge exhaust, as seen in a T-S diagram, will be lowered as a result of the lower entropy of the charge-air.
The same “conditioning of charge-air through turbo-cooling” raises the (knock-limited) maximum charge-air pressure to be significantly higher than an existing turbocharged SI engine. An improvement of 50% to 100% in power density over naturally-aspirated SI engines is projected.
Testing, similar to that for turbo-cool SI engine, is conducted for turbo-cool diesel engine. The optimum steady-state operating TC (T6) vs. operating PC (P6) relation at a given speed may be dependent on the ambient humidity, temperature and pressure. At given ambient condition, the optimum operating TC (T6) vs. operating PC (P6) relation is determined on the basis of the “optimization” of thermal efficiency under the constraint of constant charge-air pressure. Testing data of engine steady-state operations are shown schematically in
Thermal efficiency is measured at each specific fuel system/turbo-cooler valve setting combination corresponding to a specific TC at the given charge-air pressure, PC. Once a particular fuel system/turbo-cooler valve combination setting is determined to provide an optimum performance, the particular setting is considered to be an “optimum” setting. There are three possibilities for the “optimum” performance: thermal efficiency reaches maximum at the setting; charge-air temperature reaches a minimum at a maximum open position of the turbo-cooler valve 111 (further valve opening leads to increasing charge-air temperature); charge-air temperature reaches a minimum operating under given ambient temperature and humidity (further temperature reduction leads to frosting in the heat exchanger). These optimum settings become the basis for designing (mechanical) mechanism for the two-degree-of-freedom load control. Alternatively, data for optimum settings are stored in maps (turbo-cooler valve position vs. fuel injection rate and engine speed) and an electronic system of sensors, actuators, and electronic control unit (ECU) is developed for engine operation in accordance with the optimum setting maps. Each optimum setting provides engine with intake air in a “sweet spot” of charge-air temperature and pressure for optimum engine operation at given steady-state speed and load.
A more than 10% improvement in thermal efficiency for diesel engines is expected as a result of the following simultaneous-benefits:
Although a diesel engine having no throttle cannot benefit from “reduction in throttling loss,” it does benefit from a similar wider-setting of load control as a SI engine (in the form of fuel injection rate instead of throttle butterfly). At optimized combined-settings of fuel injection rate and turbo-cooler valve, the fuel rate is higher than the normal fuel-rate setting at the same relative load condition (see
Data maps for optimum settings for the direct-injection SI engine are generated for its heterogeneous-charge operation mode in testing similar to the diesel engine and for its homogeneous-charge operation mode in testing similar to that for the SI engine.
Referring back to
The ability of simultaneously controlling engine load/speed and intake air temperature at optimal value over a broad range of loads and speeds has an additional application. One of the most promising engine technologies that has emerged over the past few years is called the HCCI (homogeneous charge compression ignition) engine. The combustion process for the HCCI engine is fundamentally different from SI or diesel combustion in the form of spontaneous flameless combustion. The low temperature spontaneous flameless combustion produces very low NOx and particulate matter (PM) emissions combined with high, diesel-like, efficiency under ideal conditions. This combination of low emissions and high efficiency explains the excitement generated by the prospect of HCCI. Currently, the promise and the excitement are tempered only by the considerable challenges HCCI faces. The most crucial ones among them is the control of start-of-combustion (SOC) due to the “spontaneous” nature of combustion-ignition.
Without a spark plug as in the Otto, or a fuel injector as in the Diesel, HCCI SOC depends on (i) charge mixture reactivity, and (ii) the time-temperature history of the homogeneous charge mixture (i.e., HCCI SOC is a functional of time-temperature history). The objective of SOC control is to prepare the charge of a HCCI engine at a “tipping point” for spontaneous combustion at optimal SOC crank angle, producing an ideal HCCI combustion. Methods (such as EGR and ignition-assistance) are available for promoting HCCI ignition (making SOC earlier) at low engine loads. It is more difficult to delay HCCI ignition (which becomes necessary at middle and high engine loads under turbocharging conditions) to produce ideal HCCI combustion at high loads. Methods, including conditioning of intake charge that are used in laboratory experiments for controlling SOC, are impractical for mobile applications. Turbo-Cool is a technology for conditioning of intake charge for mobile applications, and is ideally suited for solving the latter SOC control problem for HCCI engines at middle and high engine loads. Testing is conducted for the turbo-cool HCCI engine to develop an engine management mapping-algorithm, in which inputs of load requirement signal, intake manifold pressure, engine speed, knock sensor signal, fuel air ratio (oxygen sensor), temperature sensor signals, and ambient conditions are processed to generate outputs of ignition timing, fuel injection rate and timing, throttle butterfly opening, valve timing and lift, and turbo-cooler valve opening wherein the turbo-cooler valve opening is selected for conditioning of intake air for achieving the objective of improving thermal efficiency and producing start-of-combustion at correct crank-angle at middle and high engine loads resulting in maximum brake torque.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing form the spirit and scope of the invention as defined in the appended claims.
This application claims priority to a provisional application entitled “Turbo-Cool: The Turbo-Cooling Principle of Internal-Combustion Engines” filed in the US Patent Office on Jul. 22, 2004 and assigned U.S. patent application Ser. No. 60/590,100 and to a provisional application entitled “The Turbo-Cooling Principle of Internal Combustion Engines” filed in the US Patent Office on Jun. 17, 2004 and assigned U.S. Pat. No. 60/580,493.
| Number | Date | Country | |
|---|---|---|---|
| 60590100 | Jul 2004 | US | |
| 60580493 | Jun 2004 | US |
