WO2016069455A1

WO2016069455A1 - System and method of low grade heat utilization for a waste heat recovery system

Info

Publication number: WO2016069455A1
Application number: PCT/US2015/057329
Authority: WO
Inventors: Timothy C. Ernst; James A. Zigan
Original assignee: Cummins, Inc.
Priority date: 2014-10-27
Filing date: 2015-10-26
Publication date: 2016-05-06

Abstract

A waste heat recovery system comprising a pump fluidically coupled to an engine and configured to pump a coolant through the engine. A cooling circuit includes a radiator structured to cool the coolant, and a coolant boiler. The coolant boiler is fluidically coupled to the engine and the radiator and configured to extract heat from the coolant to heat a working fluid. A thermostat is fluidically coupled to the engine and the pump. The thermostat is configured to direct the coolant towards the cooling circuit (radiator and coolant boiler) when the engine reaches a predetermined temperature. The waste heat recovery system also includes a coolant control valve. The coolant control valve is in fluidic communication with the engine, the radiator and the coolant boiler. The coolant control valve is structured to selectively redirect heated coolant received from the engine towards the radiator or the coolant boiler.

Description

SYSTEM AND METHOD OF LOW GRADE HEAT UTILIZATION FOR A

WASTE HEAT RECOVERY SYSTEM

Statement of Government Interest

[0001] This invention was made with government support under "Exhaust Energy

Recovery" Program Award Number DE-EE0003403 awarded by the Department of Energy (DOE). The government has certain rights in the invention.

Cross-reference to Related Applications

[0002] The present application claims priority to and benefit of U.S. Provisional Patent Application No. 62/068,900, filed October 27, 2014 and entitled "System and Method of Low Grade Heat Utilization for a Waste Heat Recovery System", the entire disclosure of which is incorporated herein by reference.

Technical Field

[0003] The present disclosure relates generally to waste heat recovery systems for use with internal combustion engines.

Background

[0004] A waste heat recovery system to recover heat generated by an engine that would otherwise be lost through cooling and heat rejection provides a means to improve engine efficiency. Heat is generally recovered from sources of high temperature, for example, the exhaust gas produced by the internal combustion (IC) engine, or compressed intake gas. Such high grade waste heat recovery systems include components which are configured to extract the heat from the high temperature source. These components can include exhaust gas

recirculation (EGR) boilers, pre charge air coolers (pre-CAC), exhaust system heat exchangers, or other components configured to extract heat from the high grade source of heat.

[0005] Furthermore, conventional waste heat recovery systems are focused on high grade waste heat recovery, for example, waste heat recovery from the exhaust gas and/or the compressed intake gas. The coolant employed in conventional IC engines for cooling the engine provides a source of low grade heat, for example, having a peak temperature which is substantially lower than a peak temperature of the high grade heat source. Conventional waste heat recovery systems are not configured to recover this low grade heat which is generally lost to the environment.

Summary

[0006] Embodiments described herein relate generally to waste heat recovery systems for use with IC engines, and in particular to low grade waste heat recovery systems.

[0007] In a first set of embodiments, a waste heat recovery system comprises a pump fluidically coupled to an engine and configured to pump a coolant through the engine. A cooling circuit includes a radiator structured to cool the coolant, and a coolant boiler. The coolant boiler is fluidically coupled to the engine and the radiator and configured to extract heat from the coolant to heat a working fluid. A thermostat is fluidically coupled to the engine, the cooling circuit, and the pump. The thermostat is configured to direct the coolant towards the cooling circuit when the engine reaches a predetermined temperature. The waste heat recovery system also includes a coolant control valve. The coolant control valve is in fluidic

communication with the engine, the radiator and the coolant boiler. The coolant control valve is structured to selectively redirect the heated coolant received from the thermostat to the radiator or the coolant boiler.

[0008] In particular embodiments, the coolant control valve redirects the heated coolant towards the coolant boiler when the engine is running at a low load or a mid load. The coolant control valve may redirect the heated coolant towards the radiator when the engine is running at a high load. The coolant boiler may be fluidically coupled to a high grade heat portion of the waste heat recovery system which is configured to extract waste heat from an exhaust gas. In such embodiments, the coolant boiler is configured to receive preheated working fluid from the high grade heat portion of the waste heat recovery system, continue preheating and evaporate the working fluid and communicate the evaporated working fluid back to the high grade heat portion of the waste heat recovery system for additional evaporation and superheating. [0009] In another set of embodiments, a waste heat recovery system comprises a pump fluidly coupled to an engine and configured to pump a coolant through the engine. The waste heat recovery system also includes a cooling circuit including a radiator and a coolant boiler. The radiator is structured to cool the coolant. The coolant boiler is fluidly coupled to the engine and the radiator. The coolant boiler is configured to extract heat from the coolant to heat a working fluid. A thermostat is fluidly coupled to the engine and the pump. The thermostat is configured to direct the coolant towards the cooling circuit when the engine reaches a predetermined temperature. A coolant control valve is positioned in the cooling circuit upstream of the radiator. The coolant control valve is structured to selectively allow a portion of heated coolant received from the engine to flow to the radiator.

[0010] In yet another set of embodiments, a method for recovering waste heat using a waste heat recovery system which includes a pump fluidly coupled to an engine for pumping a coolant, a cooling circuit including a coolant boiler and a radiator, a thermostat fluidly coupled to the engine and the pump, and a coolant control valve comprises initializing the engine is provided. If an engine temperature is below a predetermined temperature threshold, a coolant flow of the coolant is directed within the engine via the thermostat. In response to the coolant temperature exceeding the predetermined temperature threshold, the coolant flow is redirected towards the coolant circuit via the thermostat. The coolant flow is redirected towards at least one of the coolant boiler or the radiator via the coolant control valve.

[0011] It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

Brief Description of Drawings

[0012] The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several im lementations in accordance with the disclosure and are therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

[0013] FIG. 1 is a schematic block diagram of a waste heat recovery system, according to an embodiment.

[0014] FIG. 2 is a schematic block diagram of another embodiment of a waste heat recovery system.

[0015] FIG. 3 is a schematic flow diagram of an example method of recovering waste heat using a waste heat recovery system.

[0016] Reference is made to the accompanying drawings throughout the following detailed description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.

Detailed Description of Various Embodiments

[0017] Embodiments described herein relate generally to waste heat recovery systems for use with IC engines, and in particular to low grade waste heat recovery systems. Embodiments of the waste heat recovery system described herein for extracting heat from the coolant can provide several benefits including, for example: (1) extracting heat from the coolant which is otherwise lost to the environment for preheating and evaporating the working fluid; (2) selectively controlling the flow of coolant to either a coolant boiler or a radiator; and (3) preheating and evaporating a working fluid used in conjunction with high grade waste heat thereby increasing the power output of the waste heat recovery system. [0018] FIG. 1 shows a schematic block diagram of a waste heat recovery system 100 according to an embodiment. The waste heat recovery system 100 includes a pump 112 in fluidic communication with an engine 1 10, a radiator 130, a coolant boiler 140 which is fluidically coupled to a high grade heat portion 150 of the waste heat recovery system 100, a thermostat 114, and a coolant control valve 120. The system 100 is configured to selectively recover heat from the coolant, which is a low grade heat source, based on an operating condition of the engine 110, as described herein.

[0019] The engine 110 can include an IC engine, for example, a diesel engine, a gasoline engine, a natural gas engine, a positive displacement engine, a rotary engine, or any other suitable engine, which converts a fuel (e.g., diesel, gasoline, natural gas, biodiesel, ethanol any combination thereof or any other suitable fuel) into mechanical energy. The conversion produces heat which heats up an engine block or otherwise housing of the engine 110. To cool the engine 110, a coolant is pumped through the engine block or otherwise housing of the engine 110. The coolant can have a sufficient heat capacity to extract a substantial portion of the heat from the engine 110. The coolant can include any suitable coolant, for example, a coolant suitable for use with a diesel engine. Such coolants can include water, ethylene glycol (e.g., as an antifreeze agent), water and ethylene glycol mixture, oils, or any other suitable coolant. Furthermore, the coolant can include additives such as corrosion inhibitors, antifoam agents, dyes, and/or other additives. Suitable additives can include phosphates, silicates, borates, carboxylates, any other suitable additive or a combination thereof.

[0020] The radiator 130 is configured to receive the heated coolant from the engine 110 and is further structured to cool the coolant. The cooled coolant can then be communicated back to the engine 110. The radiator 130 can include any suitable radiator, for example, an air cooled radiator. Blowers or fans can be used and configured to force air through the radiator 130 to cool the coolant flowing through the radiator 130.

[0021] The pump 112 is fluidically coupled to the engine 110 and configured to pump a coolant through the engine 110, for example, through an engine block or otherwise housing of the engine 110 to cool the engine 110. Furthermore, the pump 112 is fluidically coupled to the radiator 130 to receive the cooled coolant from the radiator 130. [0022] A thermostat 114 is fluidically coupled to the engine 110 and the pump 112. The thermostat 114 is configured to direct the coolant towards the cooling circuit which includes the radiator 130 and the coolant boiler 140 as described herein only when the engine 110 has reached a predetermined temperature. For example, the thermostat 114 can include a temperature activated valve. When a temperature of the engine 110 is below a predetermined engine temperature threshold, for example, at ambient temperature on engine 110 startup, the valve of the thermostat 114 is closed, blocking any flow of the coolant to the cooling circuit and routing coolant flow back into the engine itself. This allows the engine 110 to warm up rapidly. Once the engine 110 reaches or exceeds the predetermined engine temperature threshold (e.g., an operating temperature of about 200 degrees Fahrenheit), the valve of the thermostat 114 opens allowing the coolant to flow from the engine 110 to the cooling circuit (radiator and/or coolant heat exchanger).

[0023] The coolant boiler 140 is fluidically coupled to the engine 110 and the radiator 130 and configured to extract heat from the coolant to heat a working fluid. The coolant boiler 140 can include any suitable heat exchanger which can extract heat from coolant and communicate the heat to a working fluid. The temperature of the coolant can be sufficient to preheat the working fluid and, for example, cause the working fluid to change phase (e.g., evaporate). The coolant boiler 140 is also fluidically coupled to the high grade heat portion of the waste heat recovery system, 150 and configured to receive preheated working fluid from the high grade heat portion 150 of the waste heat recovery system 100, evaporate the working fluid and communicate the evaporated working fluid back to the high grade heat portion 150 of the waste heat recovery system 100.

[0024] As shown in FIG. 1, the coolant is structured to allow the coolant to flow

therethrough in a first direction, for example left to right along a longitudinal axis of the coolant boiler 140 as shown in FIG. 1. Furthermore, the working fluid of the high grade heat portion

150 of the waste heat recovery system 100 flows through the coolant boiler 140 in a second direction which is opposite the first direction, for example from right to left. In other embodiments, the coolant boiler 140 and/or the high grade heat portion 150 can be structured so that first direction is the same as the second direction i.e., the coolant and the working fluid flow through the coolant boiler 140 parallel to each other in the same direction. [0025] The high grade heat portion 150 of the waste heat recovery system 100 is configured to extract heat from a high grade heat source such as, an exhaust gas (e.g., diesel exhaust gas) from the engine 110, or a compressed intake gas communicated into the engine 110. The high grade heat source has a substantially higher peak temperature (e.g., in the range of about 550 degrees Fahrenheit to about 1,300 degrees Fahrenheit) than a peak temperature of the coolant (e.g., in the range of about 180 degrees Fahrenheit to about 230 degrees Fahrenheit).

[0026] The working fluid can include any suitable working fluid which can extract heat from the high grade heat source and change phase, for example, vaporize. The working fluid can include, for example, Genetron^® R-245fa from Honeywell, low-GWP alternatives of existing refrigerant based working fluids, Therminol^®, Dowtherm J™ from Dow Chemical Co., Fluorinol^® from American Nickeloid, toluene, dodecane, isododecane, methylundecane, neopentane, neopentane, octane, water/methanol mixtures, ethanol steam, and other fluids suitable for the anticipated temperature ranges and for the materials used in the various described devices and systems.

[0027] The high grade heat portion 150 of the waste heat recovery system 100 can include an exhaust gas recirculation boiler 152. The exhaust gas recirculation boiler 152 is configured to extract heat from the high grade heat source and heat the working fluid such that working fluid preheats and superheats. The vaporized working fluid is communicated to an energy conversion device 154 configured to perform additional work or transfer energy to another device or system. The energy conversion device 154 can include, for example, a turbine, piston, scroll, screw, or other type of expander devices that moves (e.g., rotates) as a result of expanding working fluid vapor to provide additional work.

[0028] The additional work can be fed into the engine's driveline to supplement the engine's power either mechanically or electrically (e.g., by turning a generator), or it can be used to drive a generator and power electrical devices, parasitics or a storage battery (not shown). Alternatively, the energy conversion device 154 can be used to transfer energy from one system to another system (e.g., to transfer heat energy from waste heat recovery system 100 to a fluid for a heating system). [0029] The high grade heat portion 150 of the waste heat recovery system 100 also includes a recuperator 156 configured to receive the expanded working fluid from the energy conversion device 154 and communicate at least a portion of the preheated working fluid to the coolant boiler 140. The recuperator 156 is fluidically coupled to an elevated receiver 158 and a valve manifold 159. A condenser 162 and a sub-cooler 163 are also fluidically coupled to the recuperator 156. The condenser 162 and sub-cooler 163 can be configured to receive the working fluid from the recuperator 156 and/or the valve manifold 159, and condense the working fluid into a liquid phase. A feed pump 155 is fluidically coupled to the sub-cooler 163 and the valve manifold 159, and configured to pump the working fluid through the high grade heat portion 150 of the waste heat recovery system 100 liquid circuit. A filter 157 (or otherwise a drier) is disposed downstream of the feed pump 155 and upstream of the valve manifold 159. The filter 157 is structured to remove particulates or contaminants from the working fluid.

[0030] Vaporization of the working fluid by the coolant boiler 140 can reduce the amount of energy required by the exhaust gas recirculation boiler 152 to heat the working fluid such that it completes phase change and superheats. For example, the working fluid can be vaporized in the coolant boiler 140 and the exhaust gas recirculation boiler 152 can be used only to superheat the vaporized working fluid. This may increase the power output of the waste heat recovery system 100 and/or allow superheating of the working fluid to even higher temperatures thereby, increasing the amount of work that can be extracted by the energy conversion device 154 from the working fluid. The heat extracted from the coolant boiler 140 however, may be

substantially less than the heat extracted from the coolant by the radiator 130. Thus, running the coolant continuously through the coolant boiler 140 can result in slow rise in temperature of the coolant flowing through the engine 110 until the coolant temperature is insufficient to cool the engine 110, for example, at high load conditions (e.g., during acceleration).

[0031] As shown in FIG. 1, the system 100 also includes the coolant control valve 120. The coolant control valve 120 is in fluidic communication with the engine 110, the radiator 130, and the coolant boiler 140. The coolant control valve 120 is structured to selectively redirect the heated coolant received from the engine 110 to the radiator 130 or the coolant boiler 140. For example, the coolant control valve 120 can include an active thermostat (e.g., a temperature activated valve), or any other active valve. In various embodiments, the coolant control valve 120 includes a three way valve.

[0032] In one embodiment, the coolant control valve 120 is configured to redirect the flow of the heated coolant towards the coolant boiler 140 when the engine 110 is running at low loads (e.g., idling), or mid loads (e.g., vehicle cruise condition on a level road). In such instances, the heated coolant is used by the coolant boiler 140 to extract heat and preheat and vaporize the working fluid. As described herein, the coolant temperature can continue to rise gradually but can still be at a low enough temperature to cool the engine 110 running under low load or mid load conditions.

[0033] In another embodiment, the coolant control valve 120 is configured to redirect the flow of the heated coolant towards the radiator 130 when the engine 110 is running at a high load (e.g., accelerating or in a hill climb condition). In such instances, the engine 110 produces more heat relative to low load and mid load conditions thereby, requiring more heat transfer from the coolant to cool the engine 110. The coolant can thus, be communicated to the radiator 130 to rapidly cool the coolant such that the coolant can efficiently cool the engine 110.

[0034] In some embodiments, the coolant control valve 120 includes a temperature activated valve. In such embodiments, the coolant control valve 120 can be configured to selectively redirect the heated coolant towards the coolant boiler 140 when the temperature of the coolant is below a predetermined temperature threshold. The coolant can thus be used to preheat and evaporate the working fluid as described herein, and can experience a rise in temperature. Once the temperature of the coolant meets or exceeds the predetermined temperature threshold, the coolant control valve 120 can redirect the heated coolant towards the radiator 130 instead of or in addition to the coolant boiler 140.

[0035] In some embodiments, the coolant control valve 120 is configured to selectively redirect the coolant flow towards the radiator 130 if a vehicle speed of a vehicle which includes the waste heat recovery system 100 is less than a predetermined threshold (e.g., less than 30 mph, 25 mph, 20 mph, 15 mph or less than 10 mph). In other embodiments, the coolant control valve 120 is configured to redirect the coolant flow towards the radiator 130 if the waste heat recovery system 100 is in a faulted state. The faulted state can include, for example loss of working fluid in the coolant boiler 140, loss of coolant from the coolant boiler 140, one or more sensors (not shown) included in the waste heat recovery system 100 malfunctioning or failing and/or any other faulted state determined by any other sensor or condition of the waste heat recovery system 100.

[0036] In still other embodiments, the coolant control valve 120 is configured to selectively redirect the coolant flow towards the radiator 130 if a fan (not shown) of the engine 110 activates. This can, for example indicate that the coolant temperature is exceeding the predetermined temperature threshold or the engine 110 is getting too hot. The coolant control valve 120 then redirects the coolant towards the radiator 130 to reduce the temperature of the coolant facilitated by the fan of the engine 110.

[0037] In yet other embodiments, the coolant control valve 120 is configured to selectively redirect the coolant flow towards the radiator 130 if a user manually instructs the coolant control valve 120 to redirect coolant flow towards the radiator 130. For example, a control panel (e.g., a dashboard) of a vehicle or system which includes the waste heat recovery system 100 can include an indicator which indicates a temperature of the engine 110 and/or coolant, and/or an operating condition of the engine 110 and/or an operating condition of the waste heat recovery system 100. Based on one or more of these operating conditions, the user can manually operate the coolant control valve 120 to redirect the coolant towards the radiator 130.

[0038] In particular embodiments, the coolant control valve 120 is configured to selectively redirect coolant flow towards the radiator 130 if a condenser pressure of the condenser 162 is too high, for example exceeds a predetermined condenser pressure threshold. The

predetermined condenser pressure can, for example include a maximum allowable pressure of the working fluid within the condenser, for example in the range of 60 to 80 psia (e.g., 60, 65, 70, 75 or 80 psia inclusive of all ranges and values therebetween).

[0039] In still other embodiments, the coolant control valve 120 is configured to selectively redirect coolant flow towards the radiator 130 if an inlet temperature of the energy conversion device 154 exceeds an inlet temperature threshold, for example a maximum allowable temperature of the evaporated and/or superheated working fluid entering the energy conversion device 154. For example, the inlet temperature threshold can be in the range of 450 to 500 Fahrenheit (e.g., 450, 455, 460, 465, 470, 475, 480, 485, 490, 495 or 500 Fahrenheit inclusive of all ranges and values therebetween). In yet other embodiments, the coolant control valve 120 is configured to selectively redirect coolant flow towards the radiator 130 if an inlet pressure of the energy conversion device 154 exceeds an inlet pressure threshold, for example a maximum allowable pressure of the evaporated and/or superheated working fluid entering the energy conversion device 154. For example, the inlet pressure threshold can be in the range of 180-200 psia (e.g., 180, 185, 190, 195 or 200 psia inclusive of all ranges and values therebetween).

[0040] In various embodiments, a controller (not shown) can be communicatively coupled to the coolant control valve 120, the thermostat 114 and/or any other components included in the waste heat recovery system and configured to control the functions thereof. Such a controller can include, for example a system computer or electronic control module which can include a processor, a memory, a sensor and/or a transceiver. Instructions for operating the coolant control valve 120 in accordance with the disclosure can be stored on the memory of the controller. Such instructions can include, for example look up tables, algorithms, and/or equations for activating the coolant control valve 120 based one or more of a coolant temperature, a working fluid temperature, a load on the engine 110, a vehicle speed, an operational state of the waste heat recovery system 100 (e.g., is the waste heat recovery system in a faulted state), engine fan ON/OFF, a condenser pressure of the condenser 162, an inlet temperature and/or an inlet pressure of the energy conversion device 154. One or more of this information can be used by the controller to generate a valve operating signal for operating the coolant control valve 120 as described herein.

[0041] In various embodiments, the coolant control valve 120 is configured to split the coolant flow into a first portion and a second portion. The first portion can be directed towards the radiator 130 and the second portion can be directed towards the coolant boiler 140. The relative flow rates of the first portion and the second portion can be varied by the coolant control valve 120 based on the temperature of the coolant and/or operating conditions of the engine 110. In yet another embodiment, the coolant control valve 120 can be replaced by a flow splitter, for example, a T-connector, or a Y-connector. The flow splitter can split the coolant flow into a first portion directed towards the radiator 130 and a second portion directed towards the coolant boiler 140.

[0042] FIG. 2 is a schematic block diagram of another embodiment of a waste heat recovery system 200. The waste heat recovery system 200 includes a pump 212 in fluidic

communication with an engine 210, a radiator 230, a coolant boiler 240 which is fluidly coupled to a high grade heat portion 150 described before in detail with respect to the waste heat recovery system 100 of FIG. 1. The waste heat recovery system 200 also includes a thermostat 214, and a coolant control valve 220. The radiator 230 and the coolant boiler 240 are included in a cooling circuit for cooling the engine 210. The system 200 is configured to selectively recover heat from the coolant, which is a low grade heat source, based on an operating condition of the engine 210, as described herein.

[0043] The engine 210 can include an IC engine, for example, a diesel engine, a gasoline engine, a natural gas engine, a positive displacement engine, a rotary engine, or any other suitable engine, which converts a fuel (e.g., diesel, gasoline, natural gas, biodiesel, ethanol any combination thereof or any other suitable fuel) into mechanical energy. The engine 210 is substantially similar to the engine 110 included in the waste heat recovery system 100 and therefore, not described in further detail herein.

[0044] A coolant flows through the coolant circuit and is communicated through the engine 210 to cool the engine. The coolant can have a sufficient heat capacity to extract a substantial portion of the heat from the engine 210. The coolant can include any suitable coolant as described before with respect to the waste heat recovery system 100.

[0045] The radiator 230 is configured to receive the heated coolant from the engine 210 and is further structured to cool the coolant. The radiator 230 is substantially similar to the radiator 130 described before with respect to the waste heat recovery system 100. The pump 212 is fluidly coupled to the engine 210 and configured to pump a coolant through the engine 210, for example, through an engine block or otherwise housing of the engine 210 to cool the engine 110. Furthermore, the pump 212 is fluidly coupled to the radiator 230 to receive the cooled coolant from the radiator 230. A thermostat 214 is fluidly coupled to the engine 210 and the pump 212. The pump 212 and the thermostat 214 are substantially similar in structure and function to the pump 112 and the thermostat 214 included in the waste heat recovery system 100 and therefore, not described in further detail herein.

[0046] The coolant boiler 240 is fluidly coupled to the engine 210 and the radiator 230 and configured to extract heat from the coolant to heat a working fluid. The coolant boiler 240 is substantially similar to the coolant boiler 140 described with respect to the waste heat recovery system 100. The coolant boiler 240 is also fluidly coupled to the high grade heat portion 150 and configured to receive preheated working fluid from the high grade heat portion 150, evaporate the working fluid and communicate the evaporated working fluid back to the high grade heat portion 150.

[0047] As shown in FIG. 2, the coolant boiler 240 is structured to allow the coolant to flow therethrough in a first direction, for example left to right along a longitudinal axis of the coolant boiler 240. Furthermore, the working fluid of the high grade heat portion 150 flows through the coolant boiler 240 in a second direction which is opposite the first direction, for example from right to left within the coolant boiler 240.

[0048] In other embodiments, the coolant boiler 240 is structured to allowed the coolant to flow in the same direction as the working fluid, for example also from right to left along the longitudinal axis of the coolant boiler 240 parallel to the working fluid. Directing the coolant flow and the working fluid flows parallel to each other in the same direction can provide various benefits. For example, in some instances a saturation temperature of the working fluid can change with working fluid pressure. In such instances, the pressure difference across the coolant boiler 240 can cause an outlet temperature of the working fluid at an outlet of the coolant boiler 240 to be lower than an inlet temperature of the working fluid at an inlet of the coolant boiler 240, for example during a 2-phase scenario (i.e., a portion of the working fluid is in liquid phase and another portion of the working fluid is in vapor phase).

[0049] This can, for example, arise if the inlet pressure of the working fluid entering the coolant boiler 240 is higher than an outlet pressure of the working fluid exiting the coolant boiler 240. This can cause "pinch-point" issues in the coolant boiler 240. The pinch-point is the location of the minimum temperature delta between the working fluid and the coolant throughout the length of the heat exchanger. Due to the pressure drop of the working fluid as it flows through the coolant boiler 240, if the inlet and outlet of the working fluid side is at or near 2-phase conditions, then the inlet can be at higher temperature than the outlet which can cause the "pinch-point" to be at or near the inlet of the working fluid side. In such instances it is beneficial for the highest temperature coolant on the coolant side to coincide with that portion of the heat exchanger, which can be achieved by flowing the coolant and the working fluid in the same direction within the coolant boiler 240 in a parallel flow arrangement.

[0050] Vaporization of the working fluid by the coolant boiler 240 can reduce the amount of energy required by the exhaust gas recirculation boiler 152 to heat the working fluid such that it completes phase change and superheats. For example, the working fluid can be vaporized in the coolant boiler 240 and the exhaust gas recirculation boiler 152 can be used only to superheat the vaporized working fluid. This may increase the efficiency of the high grade heat portion 150 and/or allow superheating of the working fluid to even higher temperatures thereby, increasing the amount of work that can be extracted by the energy conversion device 154 from the working fluid. The heat extracted from the coolant boiler 240 however, may be substantially less than the heat extracted from the coolant by the radiator 230. Thus, running the coolant continuously through the coolant boiler 240 can result in slow rise in temperature of the coolant flowing through the engine 210 until the coolant temperature is insufficient to cool the engine 210, for example, at high load conditions (e.g., during acceleration or hill climb conditions).

[0051] As shown in FIG. 1, the system 200 also includes the coolant control valve 220 positioned upstream of an inlet of the radiator 230. The coolant control valve 220 is in fluidic communication with the radiator 230. The coolant control valve 220 is structured to selectively allow a portion of heated coolant received from the engine 210 to flow to the radiator 230. In other words, once the thermostat 214 allows the coolant to flow towards the coolant circuit (e.g., when the engine 210 reaches the predetermined temperature), the coolant flows through the coolant boiler 240 but the coolant control valve 220 blocks the flow of the coolant towards the radiator 230. [0052] When certain conditions are met as described herein, the coolant control valve 220 opens to allow a portion of the coolant to flow towards the radiator 230, while the remaining portion of the coolant continues to flow towards the coolant boiler 240. For example, the coolant control valve 220 can include an active thermostat (e.g., a temperature activated valve), or any other active valve. In various embodiments, the coolant control valve 220 includes a two way valve. In other embodiments, the coolant control valve 220 can include a flow splitter (e.g., a T-connector or a Y-connector) structured to allow a first portion of the coolant to flow towards the coolant boiler 240 and a second portion of the coolant to flow towards the radiator 230. In various embodiments, a controller (not shown) can be communicatively coupled to the coolant control valve 220 and configured to control the operations of the coolant control valve, as described before with respect to the waste heat recovery system 100.

[0053] In one embodiment, the coolant control valve 220 is configured to redirect the flow of the heated coolant towards the coolant boiler 240 when the engine 210 is running at low loads (e.g., idling), or mid loads (e.g., vehicle cruise condition on level road). In such instances, the heated coolant is used by the coolant boiler 240 to extract heat and preheat and vaporize the working fluid. As described herein, the coolant temperature can continue to rise gradually but can still be at a low enough temperature to cool the engine 210 running under low load or mid load conditions.

[0054] In another embodiment, the coolant control valve 220 is configured to allow the portion of the heated coolant to flow towards the radiator 230 when the engine 210 is running at a high load (e.g., accelerating or during hill climb condition). In such instances, the engine 210 produces more heat relative to low load and mid load conditions thereby, requiring more heat transfer from the coolant to cool the engine 210. The portion of the coolant can thus, be communicated to the radiator 230 to rapidly cool the coolant such that the coolant can efficiently cool the engine 210.

[0055] In some embodiments, the coolant control valve 220 includes a temperature activated valve. In such embodiments, the coolant control valve 220 can be closed to allow all of the heated coolant to flow towards the coolant boiler 240 when the temperature of the coolant is below a predetermined temperature threshold. The coolant can thus be used to preheat and evaporate the working fluid as described herein, and can experience a rise in temperature. Once the temperature of the coolant meets or exceeds the predetermined threshold, the coolant control valve 220 opens allowing a portion of the coolant to flow towards the radiator 230 in addition to the coolant boiler 240.

[0056] In some embodiments, the coolant control valve 220 is configured to selectively allow the portion of the coolant to flow towards the radiator 230 if a vehicle speed of a vehicle which includes the waste heat recovery system 200 is less than a predetermined threshold (e.g., less than 30 mph, 25 mph, 20 mph, 15 mph or less than 10 mph). In other embodiments, the coolant control valve 220 is configured to redirect the coolant flow towards radiator 230 if the waste heat recovery system 200 is in a faulted state, as described before with respect to the waste heat recovery system 100.

[0057] In still other embodiments, the coolant control valve 220 is configured to selectively redirect the coolant flow towards the radiator 230 if a fan (not shown) of the engine 210 activates, as described before with respect to the waste heat recovery system 100. In yet other embodiments, the coolant control valve 220 is configured to selectively redirect the coolant flow towards the radiator 230 if a user manually instructs the coolant control valve 220 to redirect coolant flow towards the radiator 230, as described before with respect to the waste heat recovery system 100.

[0058] In particular embodiments, the coolant control valve 220 is configured to selectively redirect coolant flow towards the radiator 230 if a condenser pressure of the condenser 262 is too high, for example exceeds a predetermined condenser pressure threshold. The

predetermined condenser pressure threshold can include, for example include a maximum allowable pressure of the working fluid within the condenser, for example in the range of 60-80 psia (e.g., 60, 65, 70, 75 or 80 psia inclusive of all ranges and values therebetween).

[0059] In still other embodiments, the coolant control valve 220 is configured to selectively redirect coolant flow towards the radiator 230 if an inlet temperature of the energy conversion device 154 exceeds an inlet temperature threshold, for example a maximum allowable temperature of the evaporated and/or superheated working fluid entering the energy conversion device 154. For example, the inlet temperature threshold can be in the range of 450-500 Fahrenheit (e.g., 450, 455, 460, 465, 470, 475, 480, 485, 490, 495 or 500 Fahrenheit inclusive of all ranges and values therebetween). In yet other embodiments, the coolant control valve 220 is configured to selectively redirect coolant flow towards the radiator 230 if an inlet pressure of the energy conversion device 154 exceeds an inlet pressure threshold, for example a maximum allowable pressure of the evaporated and/or superheated working fluid entering the energy conversion device 154. For example, the inlet pressure threshold can be in the range of 180-200 psia (e.g., 180, 185, 195 or 200 psia inclusive of all ranges and values therebetween).

[0060] FIG. 3 is a schematic flow diagram of an example method 300 of recovering waste heat using a waste heat recovery system, for example the waste heat recovery system 100 or 200 described herein. The waste heat recovery system includes a pump (e.g., the pump 112 or 212) fluidly coupled to an engine (e.g., the engine 110 or 210) for pumping a coolant. A thermostat (e.g., the thermostat 114 or 214) is fluidly coupled to the engine and the pump. The waste heat recovery system also includes a cooling circuit including a coolant boiler (e.g., the coolant boiler 140 or 240) and a radiator (e.g., the radiator 130 or 230) and a coolant control valve (e.g., the coolant control valve 120 or 220). The coolant boiler (e.g., the coolant boiler 140 or 240) can be fluidly coupled to a high grade heat portion (e.g., the high grade heat portion 150) of the waste heat recovery system.

[0061] The method 300 includes initializing the engine at 302. For example, the engine 110 or 210 is initialized by inserting an air/fuel mixture into one or more cylinders of the engine 110 or 210 to start the engine 110 or 210. The engine can be started cold, i.e., the engine is started after a significant time delay from a previous engine shut down so that the engine is at ambient temperature or is close to ambient temperature (e.g., within + 10% of ambient temperature). In other embodiments, the engine is started hot, i.e., the engine is started soon after a previous engine shut down so that the engine temperature is significantly higher than ambient

temperature (e.g., greater than 200 degrees Fahrenheit).

[0062] It is determined if an engine temperature of the engine is below a predetermined engine temperature threshold at 304. For example, the waste heat recovery system 100 or 200 can include a temperature sensor to measure a temperature of the engine 110 or 210. The predetermined engine temperature threshold can correspond to any suitable temperature, for example a temperature at or above which the coolant circulating through the engine is sufficiently hot to provide useful heat energy for heating a working fluid of a high grade heat portion of the waste heat recovery system (e.g., the high grade heat portion 150), and/or is too hot to provide sufficient cooling to the engine (e.g., the engine 130 or 230).

[0063] If the engine temperature is less than the predetermined engine temperature threshold, the coolant is directed within the engine via the thermostat at 306. For example, the thermostat 114 or 214 blocks the flow of coolant towards the coolant circuit so that the coolant recirculates within the engine 110 or 210. This allows the engine 110 or 210 to heat up rapidly.

[0064] If the engine temperature exceeds the predetermined engine temperature threshold, the coolant is directed towards the coolant circuit via the thermostat at 308. For example, the thermostat 114 or 214 redirects the coolant towards the coolant boiler 140 or 240, and the radiator 130 or 230 included in the cooling circuit.

[0065] The coolant is selectively directed towards at least one of the coolant boiler or the radiator via the coolant control valve at 310. For example, the coolant control valve (e.g., the coolant control valve 120) can be configured to selectively direct the coolant flow towards either the coolant boiler (e.g., the coolant boiler 140) or the radiator (e.g., the radiator 130). In other embodiments, the coolant control valve (e.g., the coolant control valve 220) can be configured to always allow the coolant to flow towards the coolant boiler (e.g., the coolant boiler 240) but selectively allow a portion of the coolant to flow towards the radiator (e.g., the radiator 230). In still other embodiments, the coolant control valve can include a flow splitter to always allow a portion of the coolant to flow towards the radiator (e.g., the radiator 130 or 230) and another portion of the coolant to flow towards the coolant boiler (e.g., the coolant boiler 140 or 240).

[0066] In various embodiments, the coolant flow or a portion of the coolant flow is selectively redirected towards the radiator when certain conditions are met. Such conditions can include, for example a coolant temperature is above a predetermined temperature threshold, a vehicle speed is less than a predetermined threshold, the waste heat recovery system is in a faulted state, a fan of the engine (e.g., the engine 110 or 210) activates, and/or a user manually instructs the coolant control valve (e.g., the coolant control valve 120 or 220) to redirect coolant flow towards the radiator (e.g., the radiator 130 or 230), as described in detail with respect to the waste heat recovery system 100 or 200.

[0067] In particular embodiments, the coolant flow or a portion of the coolant flow is selectively redirected towards the radiator (e.g., the radiator 130 or 230) if a condenser pressure of a condenser (e.g., the condenser 162 or 262) included in a high grade heat portion of a waste heat recovery system (e.g., the high grade heat portion 150) is too high, for example exceeds a predetermined condenser pressure threshold. The predetermined condenser pressure threshold can include, for example include a maximum allowable pressure of the working fluid within the condenser (e.g., in the range of 60-80 psia).

[0068] In other embodiments, the coolant flow or a portion of the coolant flow is selectively redirected towards the radiator (e.g., the radiator 130 or 230) if an inlet temperature of an energy conversion device (e.g., the energy conversion device 154 or 254) exceeds an inlet temperature threshold, for example a maximum allowable temperature of the evaporated and/or superheated working fluid entering the energy conversion device. For example, the inlet temperature threshold can be in the range of 450-500 Fahrenheit.

[0069] In yet other embodiments, the coolant flow or a portion of the coolant flow is selectively redirected towards the radiator (e.g., the radiator 130 or 230) if an inlet pressure of the energy conversion device (e.g., the energy conversion device 154 or 254) exceeds an inlet pressure threshold, for example a maximum allowable pressure of the evaporated and/or superheated working fluid entering the energy conversion device. For example, the inlet pressure threshold can be in the range of 180-200 psia.

[0070] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, the term "a member" is intended to mean a single member or a combination of members, "a material" is intended to mean one or more materials, or a combination thereof. [0071] It should be noted that the term "example" as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples,

representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

[0072] The terms "coupled," and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

[0073] It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.

[0074] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Claims

WHAT IS CLAIMED IS:

1. A waste heat recovery system, comprising:

a pump fluidly coupled to an engine and configured to pump a coolant through the engine;

a cooling circuit including a radiator and a coolant boiler, the radiator structured to cool the coolant, the coolant boiler fluidly coupled to the engine and the radiator, the coolant boiler configured to extract heat from the coolant to heat a working fluid;

a thermostat fluidly coupled to the engine and the pump, the thermostat configured to direct the coolant towards the cooling circuit when the engine reaches a predetermined temperature; and

a coolant control valve in fluidic communication with the engine, the radiator and the coolant boiler, the coolant control valve structured to selectively redirect heated coolant received from the engine towards the radiator or the coolant boiler.

2. The waste heat recovery system of claim 1, wherein the coolant control valve includes a three way valve.

3. The waste heat recovery system of claim 1 , wherein when the engine is running at least at one of a low load or a mid load, the coolant control valve redirects the heated coolant towards the coolant boiler.

4. The waste heat recovery system of claim 3, wherein when the engine is running at a high load, the coolant control valve redirects the coolant flow towards the radiator.

5. The waste heat recovery system of claim 1, further comprising:

a high grade heat portion configured to recover waste heat from an exhaust gas generated by the engine, a working fluid circulating through the high grade heat portion, wherein the coolant boiler is fluidly coupled to the high grade heat portion and configured to receive working fluid from the high grade heat portion of the waste heat recovery system, preheat and evaporate the working fluid and communicate the evaporated working fluid back to the high grade heat portion.

6. The waste heat recovery system of claim 4, wherein the coolant boiler is structured to allow the coolant to a flow in a first direction and the working fluid to flow in a second direction therethrough, the first direction opposite the second direction.

7. The waste heat recovery system of claim 4, wherein the coolant boiler is structured to allow the coolant to a flow in a first direction and the working fluid to flow in a second direction therethrough, the first direction the same as the second direction.

8. The waste heat recovery system of claim 1 , wherein the coolant control valve is configured to selectively redirect coolant flow towards the radiator if at least one of:

the coolant temperature is above a predetermined temperature threshold;

a vehicle speed is less than a predetermined threshold;

the waste heat recovery system is in a faulted state;

a fan of the engine activates; and

a user manually instructs the coolant control valve to redirect coolant flow towards the radiator.

9. The waste heat recovery system of claim 5, wherein the high grade heat portion of the waste heat recovery system includes:

an exhaust gas recirculation boiler fluidly coupled to the coolant boiler and structured to receive the preheated working fluid from the coolant boiler;

an energy conversion device positioned downstream of the exhaust gas recirculation boiler; and

a condenser structured to condense the evaporated working fluid into a liquid phase

10. The waste heat recovery system of claim 9, wherein the coolant control valve is configured to selectively redirect coolant flow towards the radiator if at least one of: a condenser pressure of the condenser exceeds a predetermined condenser pressure threshold;

an inlet temperature of the energy conversion device exceeds a predetermined inlet temperature threshold; and

an inlet pressure of the energy conversion device exceeds a predetermined inlet pressure threshold.

11. The waste heat recovery system of claim 9, wherein the high grade heat portion further comprises:

a recuperator structured to redirect at least a portion of the working fluid from the energy conversion device to the condenser;

an elevated receiver;

a sub-cooler;

a feed pump;

a filter; and

a valve manifold.

12. A waste heat recovery system, comprising:

a coolant control valve positioned in the cooling circuit upstream of the radiator, the coolant control valve structured to selectively allow a portion of heated coolant received from the engine to flow to the radiator.

13. The waste heat recovery system of claim 12, wherein the coolant control valve includes a two-way valve.

14. The waste heat recovery system of claim 12, wherein the coolant control valve includes a flow splitter structured to allow a first portion of the coolant to flow towards the coolant boiler and a second portion of the coolant to flow towards the radiator.

15. The waste heat recovery system of claim 12, wherein when the engine is running at least at one of a low load or a mid load, the coolant control valve redirects the heated coolant towards the coolant boiler.

16. The waste heat recovery system of claim 15, wherein when the engine is running at a high load, the coolant control valve redirects the portion of the coolant towards the radiator.

17. The waste heat recovery system of claim 12, further comprising:

18. The waste heat recovery system of claim 12, wherein the coolant control valve is configured to selectively redirect coolant flow towards the radiator if at least one of:

the coolant temperature is above a predetermined temperature threshold;

a vehicle speed is less than a predetermined threshold;

the waste heat recovery system is in a faulted state;

a fan of the engine activates; and

19. The waste heat recovery system of claim 18, wherein the high grade heat portion of the waste heat recovery system comprises:

a condenser structure to condense the evaporated working fluid into a liquid phase

20. The waste heat recovery system of claim 19, wherein the coolant control valve is configured to selectively redirect coolant flow towards the radiator if at least one of:

a condenser pressure of the condenser exceeds a predetermined condenser pressure threshold;

21. The waste heat recovery system of claim 19, wherein the high grade heat portion further comprises:

an elevated receiver;

a sub-cooler;

a feed pump;

a filter; and

a valve manifold.

22. A method for recovering waste heat using a waste heat recovery system including a pump fluidly coupled to an engine for pumping a coolant, a cooling circuit including a coolant boiler and a radiator, a thermostat fluidly coupled to the engine and the pump, and a coolant control valve, the method comprising; initializing the engine;

if an engine temperature is below a predetermined temperature threshold, directing a coolant flow of the coolant within the engine via the thermostat;

in response to the coolant temperature exceeding the predetermined temperature threshold, redirecting the coolant flow towards the coolant circuit via the thermostat; and selectively directing the coolant flow towards at least one of the coolant boiler or the radiator via the coolant control valve.

23. The method of claim 22, wherein the coolant control valve is structured to selectively redirect coolant flow towards the coolant boiler.

24. The method of claim 22, wherein the coolant control valve is structured to selectively redirect a portion of the coolant flow towards the radiator.

25. The method of claim 22, wherein the coolant flow is selectively redirected towards the radiator if at least one of:

the coolant temperature is above a predetermined temperature threshold;

a vehicle speed is less than a predetermined threshold;

the waste heat recovery system is in a faulted state;

a fan of the engine activates; and