DE102008005036A1 - Internal combustion engine, has heat recovery device comprising conveying unit for compressing liquid working medium to large extent, where mixture of water with ethanol, and methanol is used as working medium - Google Patents

Abstract

The engine (1) has a heat recovery device (2) with a conveying unit (3) for compressing a liquid working medium. A heat exchanger (4) evaporates the medium by performing heat transfer of a heat medium to the working medium. An expansion device expands the working medium and extracts mechanical energy. A condenser condenses the working medium, where the conveying unit, exchanger, expansion device and the condenser are interconnected to a circuit (CR) in which the working medium is circulatable. A mixture of water with ethanol and/or methanol is used as the working medium.

Description

The The invention relates to an internal combustion engine with a heat recovery device, the one conveyor unit for the compression of an at least largely liquid working medium, a heat exchangers for evaporation of the working medium, an expansion device for Expansion of the working medium and a condenser for condensation of the working medium. The expansion device is a mechanical one Work removable. The conveyor unit, the heat exchanger, the Expansion device and the condensation device are one Circuit interconnected in which the working medium is circulated.

today Internal combustion engines have an efficiency of up to 40 percent up. The losses are predominantly as heat to a coolant and as exhaust heat issued.

in the Prior art, various methods and devices exist, by means of those from the exhaust heat and / or the coolant heat electrical and / or mechanical energy is recovered.

Out SAE paper 2007-01-0543 entitled: "Waste Heat Recovery of Heavy-Duty Diesel Engines by Rankine Cycle Part II: Working Fluids for WHR-ORC "by Ho Teng, Gerhard Regner and Chris Howland are using an internal combustion engine a heat recovery device known with which energy from an exhaust heat of an internal combustion engine can be won. The heat recovery device includes a conveyor unit in the form of a pump, several heat exchangers, an expansion device in the form of a turbine and a capacitor. The said elements of the heat recovery device are connected to a circuit in which a working medium is feasible. The internal combustion engine allows a conversion of thermal Energy in a mechanical work by means of a so-called Rankine process. Operational the internal combustion engine is in a heat exchanger exhaust heat to Transfer working medium, so that the working medium evaporates. The vaporous working medium is then the Expander supplied and relax there to a lower pressure. From thermodynamic View is flowing through the expansion device reduces a total enthalpy of the vapor, wherein the enthalpy difference of the expansion device in the form of mechanical work is removable. The vaporous working medium is subsequently fed to the capacitor device and condensed there. about the conveyor unit the working fluid becomes more fluid Phase again to the heat exchanger directed. As a working medium in the document are different organic and inorganic media discussed. At the heart of the The influence of the working media on the thermodynamic is considered Efficiency of the internal combustion engine.

Of the Invention is based on the object, an internal combustion engine with heat recovery device specified, which is characterized by a special operational safety.

The Task is by an internal combustion engine with the features of claim 1. In this case, the working medium is a mixture of water with ethanol and / or Methanol provided. Thus, a working medium is provided, which is in a wide temperature range in the liquid phase. A Risk of icing at low temperatures and / or a Decomposition at high temperatures is thus reduced, so that improved operational safety of the internal combustion engine is.

In an embodiment of the invention is a mixing ratio of Working fluid to a in the heat recovery device adapted during operation peak temperature. This is the result Risk of decomposition at high operating temperatures below reduced all operating conditions of the internal combustion engine.

In In a further embodiment of the invention, the water is at least added so much ethanol and / or methanol that the working medium in a resting state of the internal combustion engine at lowest expected ambient temperatures at least largely in the liquid phase is present. This is in particular a risk of freezing the Reduced working medium at low ambient temperatures, so that the operational safety of the internal combustion engine continues is improved.

One embodiment The invention will be explained in more detail below with reference to a drawing.

It shows 1 schematically a circuit diagram of a heat recovery device of an internal combustion engine according to the invention.

The heat recovery device comprises a delivery unit in the form of a pump 1 , a heat exchanger 2 , an expansion device in the form of a turbine 3 and a capacitor 4 , which are connected to a circuit CR, in which circuit CR a working fluid A _L1 , A _L2 , A _D1 , A _{D2 is} circulatable. The heat recovery device is suitable for performing a Rankine cycle.

Before entering the pump 1 is the working medium A _L1 in the liquid phase. It has a first, comparatively low temperature and a lower process pressure. In the pump 1 the liquid working medium is approximately adiabatically and isentropically compressible to an upper process pressure. After compression, the working medium has a second temperature which at least approximately corresponds to the first temperature, or slightly exceeds this (depending on the working medium used and the operating state).

Subsequently, the working medium A _{L2 is} the heat exchanger 2 fed. In the heat exchanger 2 is a heat transfer from an exhaust gas of the internal combustion engine to the working medium A _L2 feasible. The heat transfer is largely isobaric. When flowing through the heat exchanger 2 the working medium A _{L2 is} first heated substantially isobaric in the liquid phase and then evaporated isobaric and isothermal. The gaseous portion of the working medium continuously increases during evaporation until the working medium A _{D1 is} completely in gaseous phase. Subsequently, the gaseous working medium in the heat exchanger 2 largely isobarically overheated to a third temperature.

After flowing through the heat exchanger 2 is the gaseous working medium A _{D1 of} the turbine 3 be fed, in which it can be adiabatically expand at least approximately to the lower process pressure substantially adiabatic. This is the turbine 3 on a shaft, not shown, a mechanical work can be removed. During expansion, the working fluid cools to a fourth temperature.

Subsequently, the working medium A _{D2 is} the capacitor 4 fed. In the condenser 4 is a heat transfer from the working fluid A _D2 to a coolant or ambient air realized. During a flow through the condenser 4 the working medium A _{D2 is} first cooled substantially isobaric. In the course of further flow through the capacitor 4 the heat is removed from the working medium A _D2 , so that the working medium A _D2 at least approximately completely merges into a liquid phase. In the course of further flow through the capacitor 4 may be provided a further cooling of the liquid working medium A _L1 .

After flowing through the capacitor 4 is the working fluid ^A L1 again in at least largely liquid phase of the pump 1 be fed, so that the circuit CR is closed.

When Working medium is a mixture of water with ethanol and / or methanol intended. As a result, the risk of freezing of the working medium reduced at low temperatures. The danger of freezing exists in particular when the internal combustion engine is cold Ambient temperatures longer Time is not operated. For a skilful choice of mixing ratio about that but also the danger of decomposition of the working medium A reduced at high process temperatures during operation of the internal combustion engine. A decomposition threatens in particular after the flow through the heat exchanger, if the gaseous Working medium the highest Process temperature has. The mixing ratio is preferred to the conditions of use adapted to the internal combustion engine, allowing a freezing of the working fluid prevented at the expected lowest ambient temperatures is. The mixing ratio is furthermore preferably adapted to the process control in operation and in particular to a maximum transferable in the heat exchanger to the working medium Heat flow, so that in operation even at maximum heat flow decomposition of the Working medium is at least largely avoided.

Claims (3)

Internal combustion engine ( 1 ) with a heat recovery device ( 2 ), comprising: - a conveyor unit ( 3 ) for the compression of an at least largely liquid working medium (A); A heat exchanger ( 4 ) for the evaporation of the working medium (A) by a heat transfer from a heat medium (M) to the working medium (A); An expansion device ( 5 ) for expansion of the working medium (A), wherein the expansion device, a mechanical energy can be removed; A capacitor ( 6 ) for the condensation of the working medium (A), wherein the conveying unit ( 3 ), the heat exchanger ( 4 ), the expansion device ( 5 ) and the capacitor ( 6 ) are connected to a circuit (CR), in which the working fluid (A) is circulated, characterized in that a mixture of water with ethanol and / or methanol is provided as the working medium (A). Internal combustion engine according to claim 1, characterized characterized in that a mixing ratio of the working medium (A) to one in the heat recovery device In operation it is adapted to reachable peak temperature. Internal combustion engine according to one of claims 1 or 2, characterized in that the water at least as much ethanol and / or methanol is admixed that the working fluid (A) in a resting state of the internal combustion engine at lowest expected ambient temperatures, at least substantially in liquid Phase exists.