DE102013007337A1 - Heat engine with high thermal efficiency - Google Patents

Abstract

The invention relates to a heat engine with high thermal efficiency, in which water (1) flows as working fluid from the storage tank (2) via an injection line (3) to the injection pump (4), in which it continues to the injection valve (5) under high pressure ) the expansion machine (6) is pressed. On the way to the injection valve, heat (7) is added to the water in the injection line up to the overheating area without the water being able to evaporate. The externally controlled injection valve opens at the TDC point of the piston (8) so that the heated water sprays into the cylinder space (9) that is being formed. When the upper cylinder space is enlarged, the injected water is isenthalpically transformed into steam and expands adiabatically after the end of injection until the outlet valve (10) opens, through which it is expelled. The exclusive heat absorption via the water means that the heat absorption takes place in a small volume and thus the working fluid has a high heat density w = Q / V (kJ / m3).

Description

The heat engine is a modified steam engine that also heats water as a working fluid via external heat input and has features of a diesel engine. The difference to the steam engine is that the heat absorption of the working fluid in the heat engine takes place in a smaller volume than in the steam engine and thus allows a higher efficiency.

This type of heat absorption is achieved by the fact that the water despite high temperatures has no possibility for evaporation and sprayed in liquid form into the cylinder and turns into steam, which then performs mechanical work.

The heat absorption of the working fluid relative to the volume available to it is referred to in this patent specification as a heat density and treated in more detail as a result of this description.

The type of injection is similar to a common-rail diesel engine, ie with a high-pressure accumulator whose heat transfer medium is oil.

To 1 the water flows through the heat engine ( 1 ) from the reservoir ( 2 ) via an injection line ( 3 ) to the injection pump ( 4 ), where it continues under pending high pressure up to the injection valve ( 5 ) of the expansion machine ( 6 ) is pressed. On the way to the injection valve the water in the injection line is heated up to the overheating area ( 7 ) added without the water can evaporate. The externally controlled injection valve opens in the TDC point of the piston ( 8th ), so that the heated water in the forming cylinder chamber ( 9 ) splashes. When the upper cylinder space is enlarged, the injected water turns isenthalp to steam and expands adiabatically after the end of the injection until the exhaust valve opens ( 10 ) through which it is ejected.

Although the injection time is shorter depending on the piston stroke and the injection mass is larger than that of the diesel engine, this is not problematic because the working fluid does not have to be finely atomized and does not require time to burn.

A quantity of heat in a water which is superfluous in the superheated area generates a quantity of steam having a specific enthalpy which is greater for the same amount of heat and enthalpy than for conventional generation of steam. This means a higher efficiency.

The idea that injecting the water in the cylinder chamber filled with compressed air just like the oil in the diesel engine is thermodynamically meaningless, since the water would turn into steam during injection and this would take the space available to him, what a throttling would come soon and reduce the conversion into mechanical energy. The term of the heat density listed in this invention application as a prerequisite for high efficiency would thus not be met. Another advantage over the steam engine is the small amount of water to be heated for the operation of the heat engine.

• Punkt 1: Einspritzbeginn des Wassers in den Zylinder
• Punkt 1 nach 2: Isotherme Einspritzung (Isenthalpe)
• Punkt 2: Einspritzende
• Punkt 2 nach 3: Adiabate Expansion (Isentrope)
• Punkt 3: Öffnungsbeginn Auslass-Ventil
• Punkt 3 nach 4: Ausstoß des Dampfes
• Punkt 4: Schließen des Auslassventils

The functioning of the heat engine is after 4 :

• Point 1: start of injection of water into the cylinder
• Point 1 to 2: Isothermal injection (Isenthalpe)
• Point 2: Injection end
• Point 2 to 3: Adiabatic Expansion (Isentrope)
• Point 3: Start of opening outlet valve
• Point 3 to 4: expulsion of the steam
• Item 4: Close the exhaust valve

To evaluate thermodynamic processes of heat engines, the term "heat density" is used, which is used in this patent application.

The object of all heat engines is that heat is converted into mechanical energy by supplying a quantity of heat to a working medium so that its pressure energy is increased to obtain mechanical energy therefrom.

The conversion of the pressure energy into mechanical energy via their degradation by a pressure gradient, which has an increase in volume of the working medium result.

On the way of increasing the volume, there is a work service. This can be taken in the form of displacement work or kinetic gas energy of the heat engine.

In order to obtain the largest possible increase in volume, it is essential that in the heat supply, the working volume is small and the pressure is high and after the volume increase, the volume is large and the pressure is small.

Thus, it is essential for the efficiency and efficiency of a heat engine that the highest possible amount of heat in the smallest possible volume of the working fluid is supplied, which is also the reason for the compression of the working fluid in the internal combustion engines.

The distribution of the heat quantity to a certain size is called energy density.

It is converted during the work process high energy density in lower energy density, so that their difference is the power of the heat engine.

To record the thermal quantities in formulas, these are assigned to the physical quantities.

The supply of the heat "Q" takes place on the working medium in the combustion chamber "V", which remains constant during the heat supply, so that the energy density of the heat is expressed by the following formula:

To convert heat into mechanical energy, the energy density of the heat must be converted to an energy density of the pressure energy.

The pressure energy is the product of pressure times volume. Pressure energy W = p · V kJ

Energy density of the pressure energy is the pressure p · V / V = p kN / m ²

Thus, the heat density as well as the pressure is a state variable and independent of the path of change of state.

If a quantity of heat "Q" is supplied to the working medium with the mass "m", its temperature "T" rises by the temperature increase "ΔT".

Equivalently, at the initial pressure "po", the total pressure "p" increases by the heat input due to the pressure increase "pw". p = po + pw ΔT = Q / m · cv K

After the general gas equation is (T + ΔT) = p × V / m × Rs K

The equation for the temperature increase is used in the general gas equation T + Q / m * cv = p * V / m * Rs K

After dissolution after printing results: p = Rs * T * m / V + Q * Rs / V * cv kN / m ²

The first summand gives the pressure before the beginning of the heat supply, while the second summand is divided into two factors after the heat supply.

First factor: Q / V kJ / m ³ = w Energy density of heat

On the mass of a kg is related with
q kJ / kg
vm ³ / kg w = q / v kJ / m ³ Second factor: Rs / cv kJ / kg · k / kJ / kg · K = A Dimensionless conversion factor of the heat density in pressure p = po + w · A

The conversion factor is thus:

In thermodynamics, the heat input in the calculation and design of heat engines is given as the mixture heating value "HG".

This is an energy density of heat, which refers to a standard cubic meter of the working medium at stoichiometric combustion.

If the physical data of the standard cubic meter and the mixture heating value are entered in the formula for the pressure calculation, then w = HG kJ / m ³ Rs = 0.287 kJ / kg · K cv = 0.912 kJ / kg · K χ = 1.4 A = Rs / cv = 0.287 / 0.912 = 0.3146 p = Rs * T * m / V + w * A kN / m ² p = 101 + HG x 0.3146 kN / m ²

Only 31.46% of the mix heating value is converted to pressure.

Otto engine

The Otto engine has a mixture calorific value of the gasoline-air mixture of
HG = 3655.07 kJ / m ³

This results in the following pressure for the uncompressed standard cubic meter of the gasoline-air mixture during combustion: p = 101 + 3655.07 x 0.3146 kN / m ² p = 1.01 + 11.49 bar p = 12.5 bar

verdichtet, damit dessen Wärmedichte erhöht wird, um dann bei der Verbrennung bei gleichem Temperaturbeginn wie beim Normkubikmeter einen höheren Druck zu erzielen. pmax = po·ε + ε·HG· Rs / cv kN/m² To increase the pressure to a maximum pressure "pmax" in the system, the working medium with its Gemischheizwert before combustion with a compression ratio

compressed so that its heat density is increased, and then to achieve a higher pressure during combustion at the same temperature start as the standard cubic meter. pmax = po · ε + ε · HG · Rs / cv kN / m ²

With unchanged conversion factor and a compression ratio ε = 10, pmax = 101 × 10 + 10 × 3655.07 × 0.3146 kN / m ² pmax = 1010 + 11498.9 kN / m2 ^ 125.08 bar

diesel engine

In order to make a comparison of the energy conversion between the heat engine and the diesel engine, both machines are charged with the same amount of heat and the resulting pressure energy is determined, which then each represents a measure of the efficiency.

The supply of an amount of heat of Q = 1000 kJ in a standard cubic meter of air corresponds to the usual conditions of running diesel engines with constant pressure combustion.

den Wirkungsgrad mitbestimmt, wird als optimaler Kompromiss
φ = 1,77 bei einem Dichtungsverhältnis von
ε = 18 gewählt.Because with the diesel engine the injection ratio

Determining the efficiency is considered an optimal compromise
φ = 1.77 at a sealing ratio of
ε = 18 selected.

Verdichtungsarbeit von P1 nach P2 L_1-2 = 1 / χ – 1 (p₁·V₁ – p₂·V₂) L_1-2 = 1 / 1,4 – 1 (101·1 – 5790·0,0555) L_1-2 = 550 kJ Zustandspunkt P3 Q = 1000 kJ Zugeführte Wärmemenge von P2 nach P3 p₃ = 57,9 bar V₃ = V₂·φ = 0,055·1,77 = 0,0983 m³ T₃ = T₂ + ΔT ΔT = Q / m·cp = 1000 / 1,2928·1,17 = 661 K c_p = 1,17 kJ/kg K T₃ = 1528 K Volumenarbeit von P2 nach P3 L_2-3 = p₃·(V₃ – V₂) = 5790 (0,093 – 0,0555) L_2-3 = 247 kJ Zustandspunkt P4

Volumenarbeit = Expansionsarbeit von P3 nach P4 L_3-4 = 1 / χ – 1·(p₃·V₃ – p₄·V₄) L_3-4 = 1 / 1,4 – 1·(5790·0,0983 – 222·1) L_3-4 = 867 kJ Nutzarbeit = Für mechanische Energie verwertbare Druckenergie L_N = L_3-4 + L_2-3 – L_1-2 L_N = 867 + 247 – 550 L_N = 564 kJ The pv diagram after 2 shows in the points P1-P4 the respective state variables and their course.

State point P1 (state of the standard cubic meter) T ₁ = 273K p ₁ = 1.01 bar V ₁ = 1 m ³ m = 1.2928 kg ν ₁ = 0.7735 m ³ / kg State point P2

Compaction work from P1 to P2 L _1-2 = 1 / χ - 1 (p ₁ * V ₁ -p ₂ * V ₂ ) L _1-2 = 1 / 1.4 - 1 (101 x 1 - 5790 x 0.05555) L _1-2 = 550 kJ State point P3 Q = 1000 kJ Amount of heat transferred from P2 to P3 p ₃ = 57.9 bar V ₃ = V ₂ · φ = 0.055 · 1.77 = 0.0983 m ³ T ₃ = T ₂ + ΔT ΔT = Q / m × cp = 1000 / 1.2928 × 1.17 = 661K c _p = 1.17 kJ / kg K T ₃ = 1528 K Volume work from P2 to P3 L _2-3 = p ₃ * (V ₃ -V ₂ ) = 5790 (0.093-0.0555) L _2-3 = 247 kJ State point P4

Volume work = expansion work from P3 to P4 L _3-4 = 1 / χ - 1 · (p ₃ · V ₃ - p ₄ · V ₄ ) L _3-4 = 1 / 1.4 - 1 x (5790 x 0.0983 - 222 x 1) L _3-4 = 867 kJ Useful work = energy that can be used for mechanical energy L _N = L _3-4 + L _2-3 - L _1-2 L _N = 867 + 247 - 550 L _N = 564 kJ

This means that 564 kJ of 1000 kJ heat input have been converted into pressure energy, ie a thermal efficiency of η = 56.4%.

It is the respective useful work of the absorbed heat quantity of Q = 1000 kJ are examined both in the steam engine and in the heat engine, ie without consideration of the efficiency of heat transfer to the working fluid.

The comparison between the steam engine and the heat engine with their same working fluids is based on the heat density, which is set the same for both machines.

To generate superheated steam for a steam engine, a quantity of heat is needed which heats the water to boiling point, then evaporates with the heat of vaporization and then heats the steam.

The sum of these amounts of heat is given as the enthalpy of the vapor. If the steam has the superheating temperature "T" and the vapor pressure "p", then its enthalpy "h" and its specific volume "v" and thus also its heat density w = h / v kJ / m3 are fixed.

In the heat engine, a smaller amount of heat is needed to produce the same high temperature, since it is supplied directly to the working fluid in the smaller volume without conversion into steam and its heating.

In the conversion of the injected water into steam at constant temperature energy is removed from the working fluid in the form of heat of evaporation, so that this reduces the amount of heat absorbed for conversion into useful energy as in conventional steam production.

The heat absorption in the heat engine is via the specific heat capacity "c _p " and is: q = c _p · ΔT kJ / kg

Although the specific heat quantity "q" has the same dimension as the specific enthalpy "h", the amount of heat "q" is higher.

Only when the amount of heat
"Q" is converted over the heat density "w" into enthalpy, both can be compared with each other.

Steam engine according to p-v diagram in Fig. 3rd

w₁ = 72000 kJ/m³ Wärmedichte Q = 1000 kJ aufgenommene Wärmemenge

m = 0,33 kg Masse des Dampfes

Zustandspunkt P2 (Dampfeinströmende)
Zustandsdaten von P2 entsprechen P1 p₂ = p₁ T₂ = T₁ ν₂ = ν₁ w₂ = w₁ h₂ = h₁ V₂ = ν₂·m V₂ = 0,04225·0,33 V₂ = 0,0139 m³ Dampfvolumen

Zustandspunkt P3 (nach Dampfexpansion) p₃ = 1 bar ν₃ = 1,43 m3/kg h₃ = 2294 kJ/kg V₃ = m·ν₃ V₃ = 0,33·1,43 V₃ = 0,472 m³ Arbeitsgewinn durch Dampfexpansion Δh_2-3 = h₂ – h₃ Δh_2-3 = 3043 – 2294 Δh_2-3 = 749 kJ/kg L_2-3 = Δh_2-3·m L_2-3 = 749·0,33 L_2-3 = 247 kJ Volumenarbeit L_1-2 = p₂·V₂ L_1-2 = 6000·0,0139 L_1-2 = 83 kJ Nutzarbeit = Für mechanische Energie verwertbare Energie L_N = L_2-3 + L_1-2 L_N = 247 + 83 L_N = 330 kJ For comparison with the diesel engine, a steam is selected with approximately the same pressure:

State point P1 (inflowing steam at V ₁ = 0.0 m ³ ) p ₁ = 60 bar T ₁ = 623 K (350 ° C) ν ₁ = 0.04225 m ³ / kg h ₁ = 3043 kJ / kg

w ₁ = 72000 kJ / m ³ heat density Q = 1000 kJ absorbed amount of heat

m = 0.33 kg Mass of steam

State point P2 (steam inlet end)
Condition data of P2 correspond to P1 p ₂ = p ₁ T ₂ = T ₁ ν ₂ = ν ₁ w ₂ = w ₁ h ₂ = h ₁ V ₂ = ν ₂ · m V ₂ = 0.04225 x 0.33 V ₂ = 0.0139 m ³ steam volume

State point P3 (after steam expansion) p ₃ = 1 bar ν ₃ = 1.43 m3 / kg h ₃ = 2294 kJ / kg V ₃ = m · ν ₃ V ₃ = 0.33 x 1.43 V ₃ = 0.472 m ³ Labor gain through steam expansion Δh _2-3 = h ₂ -h ₃ Δh _2-3 = 3043-2294 Δh _2-3 = 749 kJ / kg L _2-3 = Δh _2-3 · m L _2-3 = 749 x 0.33 L _2-3 = 247 kJ volume work L _1-2 = p ₂ .V ₂ L _1-2 = 6000 x 0.0139 L _1-2 = 83 kJ Effective work = energy usable for mechanical energy L _N = L _2-3 + L _1-2 L _N = 247 + 83 L _N = 330 kJ

This means that 330 kJ of 1000 kJ of heat supplied have been converted into useful work, ie a thermal efficiency of η = 33%.

Heat engine according to p-v diagram in Fig. 4th

• State point P1

Injection start of 623 K warm water in a volume starting from zero, in which the state variables are also zero.

• State point P2

The following data are identical to the steam of the steam engine in point 2: T ₂ = 623 K w ₂ = 72000 kJ / m ³

Thus, the specific volume and the specific enthalpy are the same as in point 2 of the steam engine. ν ₂ = 0.04225 m ³ / kg h ₂ = 3043 kJ / kg

m = 1000 / 4,2·350 m = 0,68 kg The mass of injection water:

m = 1000 / 4.2 x 350 m = 0.68 kg

This gives a vapor volume during injection: V ₂ = m · ν ₂ V ₂ = 0.68 x 0.04225 V ₂ = 0.0289 m ³

Thus, the vapor volume at a pressure of p = 60 bar and a temperature of T = 350 ° C with the same heat absorption twice as large as in a conventional steam generation.

• State point P3

Condition data correspond to those in P3 of the steam engine
Specific work profit by steam expansion is equal to that in the steam engine Δh _2-3 = 749 kJ / kg.

The volume work is eliminated in the heat engine, because the steam is formed only in the cylinder chamber.

Effective work = energy usable for mechanical energy L _N = L _2-3 L _N = Δh _2-3 · m L _N = 749 x 0.68 L _N = 509 kJ

This means that 509 kJ of 1000 kJ heat input have been converted into useful work, ie a thermal efficiency of η = 50.9%.

With equal absorbed amounts of heat with Q = 1000 kJ in the heat engine 54% more energy is converted into useful work than in the steam engine with conventional steam generation.

Value determination with changed volume V ₂ during the injection V₂ / 2 = halved volume V ₂ during injection gives: w = 100 400 kJ / m ³ L _N = 523 kJ V ₂ · 2 = double volume V ₂ during injection yields: w = 36 580 kJ / m ³ L _N = 407 kJ

Comparison of thermal efficiencies of machine types.

The total thermal efficiency results from the product of the thermal efficiency of the machine type with the efficiency of the boiler η _K = 0.85, which characterizes the heat transfer to the working fluid and is omitted in the diesel engine. Diesel engine η _th = 56.4% Steam engine η _th = 33% · η _K η _th = 26.4% Heat engine η _th = 50.9% · η _K η _th = 40.7%

Claims (2)

Heat engine with high thermal efficiency, characterized in that water is heated as a working fluid under high pressure without the possibility of evaporation into the overheating and sprayed in a piston expansion machine from the top dead center of the piston in the forming cylinder chamber and turned into steam, then to to adiabatically expand the injection, wherein a high thermal efficiency is achieved in that the small volume of heat absorption of the working fluid has a high heat density w = Q / V (kJ / m3). Heat engine with high efficiency according to claim 1, characterized in that the supply of heat to the working fluid for the piston expansion machine takes place in its supply line, which serves as an absorber tube of a parabolic trough.

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