WO2014053167A1

WO2014053167A1 - Hydrogen flushed prechamber

Info

Publication number: WO2014053167A1
Application number: PCT/EP2012/069439
Authority: WO
Inventors: Michele SCHILIRÒ
Original assignee: Caterpillar Energy Solutions GmbH
Current assignee: Caterpillar Energy Solutions GmbH
Priority date: 2012-10-02
Filing date: 2012-10-02
Publication date: 2014-04-10
Anticipated expiration: 2015-04-02
Also published as: CN104718359A; EP2904230A1

Description

Hydrogen flushed prechamber

The present invention relates to an Otto gas engine and a procedure for running a spark-ignited Otto gas engine having an exhaust gas duct and a cylinder head, said cylinder head having at least one prechamber spark plug and a gas supply channel, said gas supply channel being connected to the prechamber for flushing the prechamber with hydrogen and having a thermal reformer for generating hydrogen the prechamber is provided with.

WO 96/02742 A discloses an ignition device for internal combustion engines, and more particularly hydrogen assisted jet ignition (HAJI) devices for improving combustion efficiency. It shows (Fig. 1) an arrangement, whereby the hydrogen gas is introduced into a prechamber having an outlet orifice by a small valve operated by a valve driver and the mixture ignited by a miniature spark plug. Further, it shows (Fig. 4) an experimental ignition device which has been subjected to testing using a high speed, single cylinder CFR engine burning methanol fuel. The ignition device comprises a body having a cylindrical portion, within which a throat insert has an outlet orifice received to define a prechamber. The cylindrical portion threadably engages an adaptor, which in turn threadably engages the spark plug opening in the cylinder head of the engine. A gasket seals a hydrogen gas injector in an injector opening formed in the body. A spark plug receiving opening in the body re^¬ ceives a spark plug, the electrodes of which project into the prechamber. It further shows (Fig. 3) a schematic of the prechamber, in which the hydrogen is generated by a reforming catalyst, the rate of reformation and thus the amount of hydrogen produced being controlled by the cata- lyst bed temperature, which here is illustrated by means of electrical heating means under control of an engine management computer.

DE 2 056 131 A discloses a procedure for running a petrol driven spark ignited Otto engine in which a prechamber of a spark plug is additionally provided with hydrogen to in^¬ crease the rate of combustion. It further discloses a cata^¬ lytic generating of hydrogen out of hydrocarbons using the temperature of the exhaust gas.

US 4, 140, 090 B discloses the use of hydrogen for the pre- combustion chamber to provide an absolutely clean combustion without unburned hydrocarbons.

The object of the invention is to configure and arrange a combustion procedure for a Otto gas engine in such a manner that an efficient supply of hydrogen together with a higher efficiency of the engine is achieved.

According to the invention, the aforesaid object is achieved in that said reformer is supplied with water, and converts water (H20) into hydrogen (H2) according to the following reactions::

Rl: MO_red + H20 «-» M0_OX + H2, (separation) R2: MO_ox «-» MO_red + 02, (regeneration) and in that the reformer is connected to at least a part of the exhaust gas duct for supplying the reformer with heat and in that there are additional heating means, said heating means being powered by a part of the gas the engine is powered with in order to achieve the following exothermic oxidation reaction:

R3: CH4 + 02 «-» 2H₂0 + C0₂, (oxidation) or

R3' : C_nH_m + ₍n/2)02 <<->> _{m/2)H2 + _nC0, (partial oxidation) whereby the heating means are thermodynamically coupled to the reformer for additionally temperature increase of the reformer .

The aforesaid object is also achieved by a procedure in that said thermal reformer converts water into hydrogen ac^¬ cording to the following reactions::

Rl: MOred + H20 «-» MOox + H2,

R2: MOox <<->> MOred + 02,

and in that the reformer is supplied with heat from at least a part of the exhaust gas stream and in that there are additionally heating means, said heating means being powered by a part of the gas the engine is powered with in order to achieve the following exothermic oxidation reac^¬ tion :

R3: CH4 + 02 «-» 2H₂0 + C02, or R3' : C_nH_ra + _(n/2)02 «-» _(m/2)H2 + _nCO,

whereby the heating means are thermodynamically coupled to the reformer and are additional heating the reformer. Due to the fact that the reformer is being supplied with addi^¬ tional heat by the heating means, particularly process R2 is supplied with extra heat to regenerate the catalyst and discharge H2.

Gas engines are provided with natural gas, which contains at least Methane, Ethane or Propane. The exhaust gas of such gas engines is nearly free of carbon particles. One reason for having carbon particles in the exhaust gas is the gas-air-mixture in the spark plug prechamber. If the prechamber of the spark plug is flushed, it is supplied with gas, e.g. natural gas or methane, which is the gas the engine is supplied with, too. The prechamber is charged ad^¬ ditionally with air due to the upward stroke of the piston. The gas mixture in the prechamber is relatively rich (lamb^¬ da < 1) for this carbon particulate matter is generated which makes the usage of the exhaust gas energy more difficult. Beside this, the environmental compatibility is doubtful .

As hydrogen is free of carbon, no carbon particulate matter is generated by/with flushing the prechamber.

The hydrogen produced is injected into the prechamber and thus mixed at least in part to the gas mixture in the combustion chamber. The hydrogen increases the rate of combustion and thus the efficiency of the engine. Though the efficiency asset results in part from the methane for the oxidation reaction R3, R3' there is energy recharged with hydrogen, produced by using exhaust gas energy.

The efficiency of the H2 production by a chemical reaction is not subject to restrictions like a thermo dynamic cyclic process. Therefore, the thermal exhaust energy used in this chemical process is reformed with a much better degree of efficiency, which leads to a better degree of efficiency overall .

Moreover, recharging this produced hydrogen leads to a reduction of nitrogen oxide (NO_x) and formaldehyde, i.e. methanal (CH₂0) emissions, because the added hydrogen has a catalytic effect on the combustion. For this, the efficiency of the engine is increased, too.

It can also be an advantage having at least one compressor for loading a combustion chamber with an air-gas-mixture, whereby at least one compressor is motor-driven, for example electrically. In addition to the energy of reaction R3, R3' the exhaust gas turbine of the turbo charger could be replaced and the air compressor could be driven by electricity or fluids. This allows the exhaust gas to keep more of its thermal energy, i.e. higher exhaust gas temperatures of about 550 °C to 600 °C, which are 100 °C to 150 °C higher as in case of an exhaust gas turbine. These temperatures are used for the reactions Rl and R2. In this case, the de^¬ gree of efficiency raises up to about 53 %.

Another increase in the rate of combustion is achieved with a mixing section in which hydrogen is mixed with air, said mixing section being connected to the injector.

Especially stationary engines which are integrated in a co- generation process are supplied with natural gas, for which a addition of hydrogen is advantageous, especially in view of generating a higher rate of combustion. It can also be advantageous if the prechamber is flushed with a hydrogen- air mixture having a ratio λ (Lambda) as following: 1,3 <= λ <= 2,5. With a ratio exceeding one (λ = 1) the rate of combustion within the prechamber is growing up to a point at which the ratio is λ > 1,5.

Advantageously, the ratio λ is in a range of 1,3 to 3,5.

It can also be advantageous if for the main combustion the engine is powered with gas that contains predominantly oth^¬ er proportions than hydrogen. In this case, the additional generation of hydrogen brings both advantages, less carbon particulate matter in the exhaust gas and a higher rate of combustion . Other advantages and details of the invention are explained in the claims and in the description as well as shown in the figures, in which:

Figure 1 shows a schematic diagram of a supply chain of an engine generator unit with a H2 reformer;

Figure 2 shows a schematic diagram similar to figure 1 with an electrically driven compressor; Figure 3 shows a schematic diagram of the cylinder head with combustion chamber.

The schematic diagram in Figure 1 shows the supply chain of a spark-ignited gas engine 1 with an air-gas mixture and the exhaust system of the spark-ignited gas engine 1.

Starting from a gas mixer 11 at which the ambient air is mixed with the combustion gas, an air-gas duct 12 is conducted via a compressor 8 and an air-gas mixture cooler 13 to the gas engine 1 or to a combustion chamber 1.1 of the gas engine 1. A throttle valve 14 that is controlled based on the output of the gas engine 1 is provided in this air- gas duct 12 immediately upstream of the gas engine 1.

The gas engine 1 comprises an exhaust gas duct 6 in which an exhaust gas turbine 15 is provided downstream from the gas engine 1 that is used to drive the above-mentioned compressor 8. After passing through the exhaust gas tur^¬ bine 15, the exhaust gas is conducted through a reformer 5 where it dissipates heat to the reformer 5 or the first reactor 5.1 or the second reactor 5.2, respectively. The exhaust gas passes the reformer 5 in parallel via two separate exhaust gas streams that are coupled or controlled, respectively, via a valve 16 for exhaust gas, and associat^¬ ed with the respective reactor 5.1, 5.2. The valve 16 for exhaust gas is followed by a heat exchanger or superheater 17, respectively, and a downstream evaporator 18 for the water circuit 19 described below. An exhaust gas heat ex^¬ changer 20 is provided downstream before the exhaust gas is carried off to the exhaust system not shown here.

A water circuit or water duct 19 is provided for supplying the reformer 5 with water for producing hydrogen. First, the water carried in it is preheated by a heat exchanger for water 19.1 coupled to the air-gas duct 12, wherein the heat is taken from the compressed exhaust gas-air mixture. Then the water is heated in the evaporator 18 mentioned above, and the vapor is overheated accordingly in the down^¬ stream superheater 17 before it is returned to one of the two reactors 5.1, 5.2 of the reformer 5 via a respective valve for water 21. The hydrogen that is produced during reformation is fed to a prechamber 2.1 of the spark plug 2 via a hydrogen duct 22 and a condenser 22.1. In addition, a mixing section 9 may be provided in which ambient air is admixed to the hydrogen to obtain a lean hydrogen-air mix^¬ ture. The oxygen generated during hydrogen generation is carried off into the environment via a waste gate 5.3.

In order to achieve the temperatures required in the respective reactor 5.1, 5.2 or in the reformer 5, respectively, the respective reactor 5.1, 5.2 additionally comprises heating means 7.1, 7.2 that are also supplied with the air- gas mixture fed to the gas engine 1. For this purpose, the air-gas duct 12 comprises an air-gas valve 12.1 via which the required air-gas mixture is supplied via another air- gas valve 23 to the respective reactor 5.1, 5.2 or the re^¬ spective heating means 7.1, 7.2. The C02 exhaust gas that is produced when operating the respective heating means 7.1, 7.2 is carried off via a waste gate 5.3.

In addition, the gas engine 1 comprises a cooling cir^¬ cuit 24 with an engine heat exchanger 24.1 for cooling the gas engine 1. The cooling circuit 24 is also connected to an oil cooling exchanger 25.

The measure described above for the reformer 5 considerably improves the efficiency of a gas engine 1-generator 26 unit . According to the functional diagram shown in Figure 2, the compressor 8 is driven by an electric motor 10. The exhaust gas turbine 15 as shown in Figure 1 is eliminated. The ex^¬ haust gas, when it enters the reformer 5, has a temperature that is 100°C to 150°C higher. This higher temperature serves improved operation of the reformer 5 or the respective reactor 5.1, 5.2 such that the heating means 7.1, 7.2 can generate less heating output.

According to Figure 3, the gas engine 1 comprises a cylinder head 3 with a spark plug 2 arranged in a pre^¬ chamber 2.1. The prechamber spark plug 2 or the pre^¬ chamber 2.1, respectively, is supplied with hydrogen via an injector 4. By flushing the prechamber 2.1 with hydrogen, a highly ignitable gas mixture is produced there such that combustion in the combustion chamber 1.1 of the gas chamber is fast and almost free of carbon particles.

Bezugszeichenliste

gas engine

combustion chamber

spark plug, prechamber spark plug prechamber

cylinder head

inj ector

thermal reformer

reactor

waste gate of reformer

exhaust gas duct, exhaust gas stream heating means

heating means

compressor

mixing section

electric motor

gas mixer

air-gas duct

air-gas-valve

air-gas-mixture cooler

throttle valve

exhaust gas turbine

valve for exhaust gas

superheater

evaporator

water circuit, water duct

heat exchanger for water

exhaust gas heat exchanger

valve for water

hydrogen duct condenser

valve for air-gas

cooling system / circuit cooling water heat exchanger oil cooling exchanger generator ratio air_actuai/ 31 ^stoichiometric

Claims

Spark-ignited gas engine (1) having an exhaust gas duct (6) and a cylinder head (3), said cylinder

head (3) having at least one spark plug (2) with a prechamber (2.1) and an injector (4), said injector (4) being connected to the prechamber (2.1) for flushing the prechamber (2.1) with hydrogen, and having a thermal reformer (5) for generating hydrogen,

characterized in that said reformer (5) is supplied with water and converts water into hydrogen according to the following reactions::

Rl: MO_red + H20 «-» M0_OX + H2, or R2: M0_OX «-» O_red + 02,

and in that the reformer (5) is connected to at least a part of the exhaust gas duct (6) for supplying the reformer (5) with heat and in that there are additional heating means (7.1, 7.2), said heating means (7.1, 7.2) being powered by a part of the gas the engine (1) is powered with in order to achieve the following exother^¬ mic oxidation reaction:

R3: CH4 + 02 «-» 2H₂0 + C0₂, or R3' : C_nH_m + ₍n/2)02 «-» _(m/2)H2 + _nC0,

whereby the heating means (7.1, 7.

2) are thermodynami- cally coupled to the reformer (5) for additionally heating the reformer (5) .

Spark-ignited gas engine (1) according to claim 1 having a combustion chamber (1.1) and at least one compressor (8) for loading the combustion chamber (1.1) with an air-gas-mixture, whereby at least one compres^¬ sor (2) is motor-driven.

3. Spark-ignited gas engine (1) according to claim 1 or 2 having a mixing section (9), in which hydrogen is mixed with air, said mixing section (9) being connected to the in ector ( 4 ) .

4. Spark-ignited gas engine (1) according to claim 1, 2 or 3, in which the engine is stationary.

5. Procedure for running a spark-ignited gas engine (1) with a combustion chamber (1.1) generating an exhaust gas stream (6) with at least one prechamber spark plug (2), and with a thermal reformer (5), said thermal reformer (5) supplying the prechamber (2.1) with hydrogen, characterized in that

said thermal reformer (5) converts water into hydrogen according to the following reactions:

Rl: MO_red + H20 «-» M0_OX + H2,

R2: MOox «-» MO_red + 02,

and in that the reformer (5) is supplied with heat from at least a part of the exhaust gas stream and in that there are additional heating means (7.1, 7.2), said heating means (7.1, 7.2) being powered by a part of the gas the engine (1) is powered with in order to achieve the following exothermic oxidation reaction:

R3: CH4 + 02 «-» 2H₂0 + C0₂, or R3': C_nH_m + _(n/2)02 «-» _(m/2)H2 + _nC0,

whereby the heating means (7.1, 7.2) are thermodynami- cally coupled to the reformer (3) and are additionally heating the reformer (3).

6. Procedure according to claim 5, in which the prechamber is flushed with a hydrogen-air-mixture having a ratio λ of air a and hydrogen h as following:

1,3 <= λ <= 2,5. Procedure according to claim 6, in which the ratio λ is in a range of 1,3 to 3,5.

Procedure according to claim 4, in which for the main combustion the engine is powered with gas that contains predominantly other proportions than hydrogen.