GB2463641A

GB2463641A - Making use of the waste heat from an internal combustion engine

Info

Publication number: GB2463641A
Application number: GB0816799A
Authority: GB
Inventors: Andrew Stephen Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-09-13
Filing date: 2008-09-13
Publication date: 2010-03-24
Also published as: GB0816799D0

Abstract

In order to use energy that is otherwise lost as waste heat from an i.c. engine, a heat engine 4 is provided to extract heat from the engine block 3 and/or exhaust system 2 of the i.c. engine 1 and convert the extracted heat into useful work by driving an impeller 12 located in an upstream part of the exhaust gas conduit 2 of the i.c. engine 1. The impeller 12 creates a partial vacuum at an outlet of the i.c. engine, thus removing hot gases more quickly and increasing the mechanical efficiency of the engine. The heat engine 4 may include a heat exchanger 5 that transfers heat energy to a liquid circulating in a closed-loop path within the heat engine 4. The liquid expands to a gas at an evaporator 7 driving a turbine 8 that provides power at an output A to which a circulation pump 13 and the impeller 12 are connected. An intake air compressor C may also be driven from the output A; excess compressed air may be stored in an accumulator 22.

Description

Internal Combustion Engine

BACKGROUND

a. Field of the Invention

The invention relates to an apparatus and method for making use of the waste heat from an internal combustion engine.

b. Related Art The amount of useful power developed by an internal combustion engine depends on the overall efficiency of the engine. Typical internal combustion engines have a low efficiency, with only about 20 % of the chemical energy from the fuel converted to useful mechanical energy, which can be used, for example, to move a vehicle.

There are three ways to characterise the efficiency of an internal combustion engine. Volumetric efficiency is the ratio of the amount of fuel and air that enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Volumetric efficiency may be increased to greater than 100 % by compressing the intake air, for example by the use of a turbocharger or supercharger. Thermal efficiency is the percentage of energy from the combustion process that is converted to mechanical work. Generally, thermal efficiency is about 25 %. Mechanical efficiency is concerned with the amount of energy lost through friction in various parts of the engine and through pumping losses, as work is required to move air and exhaust gases into and out of the combustion cylinders respectively.

In total, about 80 % of the energy from the combusted fuel is lost as heat energy.

Most of the heat energy is carried away by the exhaust gases, while some is removed by the circulation of a coolant fluid and dissipated in a radiator.

There are a number of systems being developed that have as their aim the goal of recovering some of this lost heat energy, especially in the exhaust system, for example by using an additional steam heat engine. A number of companies are developing co-generation engines based on the Rankine cycle, for use particularly in hybrid vehicles.

in these systems, the heat energy from the exhaust gasses and the coolant system is used as the external heat source in a heat exchanger. Water, contained within a closed-loop system, is converted to steam and this is used to drive a turbine or similar, The steam is then passed through a condenser and water is returned to the heat exchanger.

The power output from these Rankine cycle engines has been used in a number of ways. In one example, the steam has been used to drive a generator, which produces a current used to charge the hybrid vehicle's battery. In a second example, the additional power from the heat engine has been used to run some auxiliary systems in the vehicle, for example air conditioning, which usually draw power away from the main drive system.

Unfortunately, none of these systems improve the original efficiency of the internal combustion engine or increase its power output.

Another common way that energy contained in the exhaust gases is utilised is in the form of a turbocharger. This can increase the power output of the engine, however, it has several disadvantages including turbo lag leading to a lack of responsiveness, limited boost range, as the turbocharger requires the engine to be running above a certain engine speed, and the creation of back-pressure in the exhaust system. Furthermore, the use of a turbocharger, by increasing the air pressure at the inlet manifold, increases the fuel usage of the engine.

It is an object of the present invention to provide an apparatus and method that address these issues.

SUMMARY OF THE INVENTION

According to the invention, there is provided a system for generating a vacuum pressure in an exhaust of an internal combustion engine, comprising: -a heat engine for extracting heat from said internal combustion engine and for converting said heat into useful work at an output of the heat engine; -an impeller, the output of the heat engine being operatively arranged to drive the impeller when heat is being extracted from said internal combustion engine; and -an exhaust gas conduit including an upstream portion for conveying exhaust gas from said internal combustion engine; wherein the impeller when driven is arranged to generate a vacuum pressure in a portion of the exhaust gas conduit upstream of the impeller.

In a preferred embodiment, the heat engine includes a circulating liquid, a heat exchanger to transfer heat energy extracted from the internal combustion engine to the circulating liquid, an evaporator, in which the liquid is converted to a gas, a turbine arranged to be driven by said gas, and a condenser, in which the gas is converted to a liquid.

Usually, the heat engine is a closed loop system and it may be advantageous to use the output of the heat engine to work a pump to circulate the liquid around the closed-loop path through the heat engine. It may not be necessary to operate the pump when insufficient heat is being extracted from the engine, therefore, a clutch may be provided between the output of the heat engine and the pump to control the circulation of liquid under different temperature conditions.

According to the invention, there is also provided an internal combustion engine, comprising: -an engine block comprising at least one combustion cylinder; -an exhaust port for allowing exhaust gasses to escape from the or each cylinder; -an exhaust gas conduit for conveying said exhaust gasses from said combustion cylinder(s); and -a system for generating a vacuum pressure in said exhaust gas conduit.

In a preferred embodiment, the heat engine extracts heat from various parts of the internal combustion engine; however, it may be desirable to remove heat exclusively from exhaust gases in the exhaust gas conduit, or from the engine block of the internal combustion engine.

The output from the heat engine may also be arranged to drive a compressor to increase the pressure of air supplied to the combustion cylinders.

To aid in regulating the flow of compressed air produced by the compressor, it is preferable to provide a throttle valve, between an output of the compressor and an inlet of the combustion cylinder(s), an air accumulator for storing air under pressure, and a pressure valve means downstream of the output from the compressor and upstream of an air inlet to said combustion chamber(s) for admitting and releasing air from the accumulator. The pressure valve means is arranged to admit air to the air accumulator when the air compressor is providing an excess of compressed air and arranged to release air from the air accumulator when the air compressor is providing a deficit of compressed air, according to desired engine operational characteristics. For safety reasons, the air accumulator may additionally have a pressure relief valve for venting to atmosphere excess stored air.

Also according to the invention, there is provided a method for generating a vacuum pressure in an exhaust gas conduit of an internal combustion engine, comprising the steps of: -extracting heat from said internal combustion engine using a heat engine and converting said heat into useful work that is then used to drive an impeller; and -using the driven impeller to generate a vacuum pressure in a portion of the exhaust gas conduit upstream of the impeller.

Furthermore, according to the invention, there is provided a method for operating an internal combustion engine, including one or more combustion cylinders, in which heat is extracted from said internal combustion engine using a heat engine and said heat is converted into useful work, and in which said work is used to: -drive an impeller to generate a vacuum pressure in a portion of an exhaust gas conduit upstream of the impeller; -operate a pump to circulate liquid around a closed-loop path through the heat engine; and -drive a compressor to increase the pressure of air supplied to said combustion cylinder(s).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: Figure lisa schematic diagram of one embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 shows a schematic of an internal combustion engine I according to a preferred embodiment of the invention. In use, heat is generated by combustion within an engine block 3 most of which is, in general, is carried away by the exhaust gases through an exhaust system 2, while some of the heat is removed by the circulation of a coolant fluid, especially around the engine block 3, to be dissipated in a radiator (not shown).

In the invention, a heat engine 4 is provided to extract heat from the engine block 3 and/or exhaust system 2 and convert the extracted heat to useful work, which is then used to increase the power output of the internal combustion engine. In a preferred embodiment, the heat engine 4 inc(udes a heat exchanger 5 that transfers the heat energy from the exhaust gases flowing through an exhaust gas conduit in the exhaust system 2 and from the coolant in the engine block 3, to a circulating liquid within the heat engine 4. The heat exchanger 5 may be of any

suitable type.

The circulating liquid flows around a closed-loop path in the heat engine 4. Liquid passes from the heat exchanger to an evaporator 7 where the hot liquid expands to form a gas. This gas drives a turbine 8 that provides a power output A 9 from the heat engine 4. The vapour that has passed through the turbine 8 is then condensed in a condenser 11 and the cold liquid is returned to the heat exchanger 5.

A pump D 13 is connected to the output A of the heat engine 4. The pump D drives the liquid around the heat engine 4 allowing a greater amount of heat energy to be transferred from the engine to the liquid in a given time. Therefore, the addition of this pump D in the closed-loop path can be used to improve the efficiency of the heat engine at higher operating temperatures. However, at lower operating temperatures, for example when the engine is first started, it is not desirable or necessary to pump the liquid at an increased rate. Therefore, a clutch is provided between the output A of the heat engine 4 and the pump D so that the pump 13 may be disconnected at low temperatures and the speed of the pump may be increased as the operating temperature increases. An engine temperature sensor (not shown) may be used to measure the temperature of the engine, and the system may be arranged to use the clutch 10 to activate and control the speed of the pump according to the measured engine temperature.

The output A of the heat engine 4 is also connected to an impeller B. This impeller B forms part of a vacuum pump 12 or similar and is located in an -.7-upstream portion 6 of the exhaust gas conduit 2, between the engine block 3 and the location of the heat exchanger 5. The vacuum pump 12 may be located in an exhaust manifold 15. The vacuum pump 12 creates a partial vacuum at an exhaust port or outlet of the combustion cylinders (not shown). The application of the vacuum pressure helps to draw the hot gases out of the combustion cylinder when the exhaust valve of the cylinder opens. In addition to removing the hot gases from the cylinders more quickly, the partial vacuum also helps to draw the piston up the cylinder, so that less work is done by the engine on the exhaust stroke, increasing the mechanical efficiency of the engine.

The output A of the heat engine is also connected to a compressor C 17 positioned on an inlet side of the engine block 3. The compressor C compresses intake air 19 thereby increasing the mass flow of air into the combustion cylinders, and increasing the volumetric efficiency of the engine and its power output. Any suitable compressor may be used. An intercooler may also be used to cool the compressed air and increase its density.

The flow of this compressed air into the combustion cylinders is controlled by a throttle valve VB 20. When less power is required from the internal combustion engine, the throttle valve 20 is closed to restrict the amount of air that is supplied to the combustion cylinders. When the throttle valve is at least partially closed, there may be excess compressed air being supplied by the compressor C 17 that is not entering the combustion cylinders. An air accumulator 22 is used to store this excess air, under pressure, when it is not required by the engine. Pressure valve means VA 24 controls the flow of air into and out of the air accumulator 22.

When the throttle valve V8 20 closes, the pressure valve means VA 24 opens to allow compressed air from the compressor 17 to enter the air accumulator 22.

When the throttle valve VB 20 opens to increase the air supplied to the cylinders, the pressure valve means VA 24 opens to allow air flow in the opposite direction, such that compressed air from the air accumulator 22 supplements the air, from the compressor 17, entering the combustion cylinders. This is of particular advantage when the engine is operating at lower temperatures, as less heat is extracted by the heat engine, reducing the power output to the compressor. The air supplied from the accumulator 22 will be cooled in the expansion process, and this can be mixed with compressed air from the compressor 17 in or to help cool the compressed air.

The pressure valve means VA 24 may be of any suitable design that permits the flow of compressed air in two different directions. The pressure valve means VA 24 may consist of two distinct pressure valves.

In a preferred embodiment, the air accumulator pressure valve means VA 24 is upstream of the throttle valve VB 20, such that the throttle valve can further act to control the flow of air from the air accumulator 22 to the combustion cylinders.

Also provided on the air accumulator 22 is a pressure relief valve V 26 that prevents an unsafe pressure building up in the air accumulator, by venting excess air to atmosphere.

The combination of the compressor C 17 on the inlet side of the engine block 3 and the vacuum pump 12 on the outlet side of the engine block has a synergistic effect. As the compressor C 17 increases the density of the air entering the combustion cylinders, there must necessarily be an increased mass of gas exiting the combustion cylinder during the exhaust stroke, compared to a naturally-aspirated engine. The vacuum pump 12 helps to remove these exhaust gases at a faster rate. This arrangement means that both the mechanical and volumetric efficiencies of an internal combustion engine are increased, increasing the useful power output of the engine.

Therefore, the invention provides a convenient and economical solution to problem of how to utilise the large percentage of energy that is otherwise lost through in waste heat and by the exhaust system in order to increase the efficiency and power output of the internal combustion engine.

Claims

CLAIMS1. A system for generating a vacuum pressure in an exhaust of an internal combustion engine, comprising: -a heat engine for extracting heat from said internal combustion engine and for converting said heat into useful work at an output of the heat engine; -an impeDer, the output of the heat engine being operatively arranged to drive the impeDer when heat is being extracted from said internal combustion engine; and -an exhaust gas conduit including an upstream portion for conveying exhaust gas from said internal combustion engine; wherein the impeller when driven is arranged to generate a vacuum pressure in a portion of the exhaust gas conduit upstream of the impeller.
2. A system as claimed in Claim I in which the heat engine includes: -a circulating liquid; -a heat exchanger to transfer heat energy extracted from the internal combustion engine to the circulating liquid; -an evaporator, in which the liquid is converted to a gas; -a turbine arranged to be driven by said gas; and -a condenser, in which the gas is converted to a liquid.
3. A system as claimed in Claim 2, in which the output of the heat engine is operatively arranged to work a pump for circulating the liquid around a closed-loop path through the heat engine.
4. A system as claimed in Claim 3, in which a clutch is provided between the output of the heat engine and the pump for controlling said circulation of liquid.
5. An internal combustion engine, comprising: -an engine block comprising at least one combustion cylinder; -an exhaust port for allowing exhaust gasses to escape from the or each cylinder; -an exhaust gas conduit for conveying said exhaust gasses from said combustion cylinder(s); and -a system for generating a vacuum pressure in said exhaust gas conduit, said system being as claimed in any preceding claim.
6. An internal combustion engine as claimed in Claim 5, in which the heat engine extracts heat from exhaust gases in the exhaust gas conduit.
7. Art internal combustion engine as claimed in Claim 5 or 6, in which the heat engine extracts heat from an engine block of said internal combustion engine.
8. An internal combustion engine as claimed in any of claims 5 to 7, in which the output from the heat engine is operatively arranged to drive a compressor for increasing the pressure of air supplied to the combustion cylinder(s).
9. An internal combustion engine as claimed in Claim 8, further comprising a throttle valve, between an output of the compressor and an inlet of the combustion cylinder(s), an air accumulator for storing air under pressure, and a pressure valve means downstream of the output from the compressor and upstream of an air inlet to said combustion chamber(s) for admitting and releasing air from the accumulator, wherein the pressure valve means is arrange to admit air to the air accumulator when the air compressor is providing an excess of compressed air and arranged to release air from the air accumulator when the air compressor is providing a deficit of compressed air, according to desired engine operational characteristics.
10.An internal combustion engine as claimed in Claim 9, in which the air accumulator has a pressure relief valve for venting to atmosphere excess stored air. -11 -
11. A method for generating a vacuum pressure in an exhaust gas conduit of an internal combustion engine, comprising the steps of: -extracting heat from said internal combustion engine using a heat engine and converting said heat into useful work that is then used to drive an impeller; and -using the driven impeller to generate a vacuum pressure in a portion of the exhaust gas conduit upstream of the impeller.
12.A method as claimed in Claim 11, in which the work from the heat engine is additionally used to operate a pump to circulate liquid around a closed-loop path through the heat engine.
13.A method for operating an internal combustion engine, including one or more combustion cylinders, in which heat is extracted from said internal combustion engine using a heat engine and said heat is converted into useful work, and in which said work is used to: -drive an impeller to generate a vacuum pressure in a portion of an exhaust gas conduit upstream of the impeller; -operate a pump to circulate liquid around a closed-loop path through the heat engine; and -drive a compressor to increase the pressure of air supplied to said combustion cylinder(s).
14. A method as claimed in Claim 13, in which, when a throttle valve closes to restrict the air supplied to an inlet of the combustion cylinder(s), a pressure valve means opens to allow compressed air from the compressor to enter an air accumulator.
15. A method as claimed in Claim 14, in which when a throttle valve opens to increase the air supplied to said cylinder(s), a pressure valve means opens to allow compressed air from the air accumulator to supplement air entering the combustion cylinder(s).
16.A system substantially as herein described with reference to the accompanying drawings.
17.A method substantially as herein described with reference to the accompanying drawings.