WO2011004344A1

WO2011004344A1 - Device for hydrogen enrichment of the fuel of internal combustion engine fed by ammonia, during the start-up and during the steady state

Info

Publication number: WO2011004344A1
Application number: PCT/IB2010/053145
Authority: WO
Inventors: Alessandro Tampucci; Paolo Bert
Original assignee: Acta S.P.A.
Priority date: 2009-07-10
Filing date: 2010-07-09
Publication date: 2011-01-13
Also published as: ITFI20090155A1

Abstract

The invention describes a system for optimizing performance of an internal combustion engine fuelled with ammonia, by adding hydrogen as a combustion promoter in both start-up that throughout the march.

Description

DEVICE FOR HYDROGEN ENRICHMENT OF THE FUEL OF INTERNAL COMBUSTION ENGINE FED BY AMMONIA, DURING THE START-UP AND DURING THE STEADY STATE Field of the invention

The invention relates to the field of apparatus for hydrogen co-feeding of internal combustion engines fueled with ammonia.

State of the Art

The direct use of ammonia as a fuel in internal combustion engines requires the development of methodologies that accelerate the burning, especially during the start-up, where the engine temperature is not enough to enable prompt and efficient combustion. One of such methods, described in U.S. 2,140,254, provides the addition of hydrogen which, requiring very low ignition energy, promotes the ignition of ammonia itself.

Hydrogen concentration in the final fuel is a critical factor for the optimal running of an ammonia combustion engine. The minimum concentration for an engine operating at 1200 rpm on average ranges from 0.8 to 4 wt%.

In the last years even the mixing of hydrogen to fossil fuels like gas, oil or diesel has been studied, in order to increase the burn rate. Consequent to the addition of hydrogen it had been obtained an increase of the output power, a dramatic reduction of emissions and a significant reduction of fuel consumption.

Furthermore in diesel engines fueled with ammonia, hydrogen helps to reduce the air-fuel ratio required for combustion, thereby allowing the use of "poor" mixtures and thus reducing emissions. The idea of an internal combustion engine fueled by ammonia/hydrogen mixtures is described also in patent WO2008/150901. In this case, however, there is no indication either on the source of hydrogen nor on the possibility of generating the necessary hydrogen directly on board.

Hydrogen can be produced from multiple sources such as fossil fuels (by reforming reaction), thermal cracking of ammonia or electrolytically. One of the cheapest source of hydrogen is water. The generation of hydrogen by thermal cracking in an internal combustion engine is particularly convenient because, during the steady state phase, exhaust gases heat the catalyst that allows the dissociation of ammonia into hydrogen and nitrogen. On the other hand, the production of hydrogen by water electrolysis is among the used methods, the one that allows to obtain high purity gases and, if the energy source for electrolysis arises from renewable sources, with low environmental impact.

The commercially available electrolysers for hydrogen production have different structures depending on the amount and on the purity of the hydrogen required. Industrial scale electrolysers consist of two half-cells containing the electrodes (made by steel disks, for the simplest set-up), divided by a porous septum within circulates the electrolyte (alkali electrolysers usually use KOH) and which does not allow a defined physical separation of the hydrogen and the oxygen produced. The gases are only polarized by the current to the electrodes. Therefore if the production of hydrogen - directly compressed in the electrolyser - is required, a perfect balance of the pressure of the two gases is necessary and a perfectly constant current flow must be maintained, to prevent the formation of an explosive mixture (and the resulting explosion). These conditions do not exist in a vehicle because the flows of current alternator are variable and the balance of gas pressures is problematic.

Electrolyzers for hydrogen production to be used in ammonia internal combustion engines are described in patent WO2009/024185, filed by the same Applicant. In that case, however, due to the operating conditions of the system, which requires a periodic reversal of polarity of the electrodes, mixtures of hydrogen to nitrogen 3:1 are obtained, requiring more volume for hydrogen storage. Further disadvantages of the device described in the above mentioned patent are due to the formation of wet gas containing traces of electrolytes, such as potassium hydroxide, which could damage the mechanical components usually made by aluminum. In addition, in the condition described in that patent, in order to supply the hydrogen needed in the engine start-up, the presence of auxiliary batteries is essential, to provide the energy required by the electrolysis reaction and an induction time sufficient to produce the minimum hydrogen to start the combustion reaction of ammonia.

An alternative system for hydrogen production, working also on-board, is the thermal cracking of ammonia, thereby obtaining nitrogen/hydrogen mixtures (composition 1 :3 vol/vol), as described in Patent US7,037,484 and IT FI2008A000210. However, this reaction takes place when the temperature of the catalyst bed is higher than 400 ⁰C, but to obtain high conversions at least 500 ⁰C are needed. Again, also in this case we find in the start-up phase the same problems observed in the case of hydrogen production by electrolysis: the heating of the catalytic bed requires auxiliary batteries for a period of time long enough to reach the threshold required by the thermal reaction. Moreover, this method is not suitable for the production of compressed hydrogen and then hydrogen cannot be stored in pressurized tank, to be used during start-up.

The purpose of this invention is to provide an apparatus that can be used also on- board, for feeding a combustion engine with fuel mixtures enriched with hydrogen.

Summary of the invention

The current invention solves the above mentioned problems with a system for optimizing the performances of an internal combustion engine fueled with ammonia, by adding hydrogen as a combustion promoter in both start-up and throughout the steady state phase.

The aim of this invention is an apparatus for co-feeding hydrogen internal combustion engines, fueled with ammonia, said apparatus comprising:

- a catalytic device for the production of hydrogen by thermal cracking of ammonia;

- a device for the electrolytic production of directly pressurized hydrogen, dry and free of contaminants, acids and bases, and

- a tank containing pressurized hydrogen. Brief description of figures

FIG. 1. shows the functional diagram of an internal combustion engine powered by hydrogen-ammonia mixtures, in the start-up phase. FIG. 2. shows the block diagram of an internal combustion engine powered by hydrogen-ammonia mixtures, during the steady state phase.

FIG. 3. shows the block diagram of an internal combustion engine powered by hydrogen-ammonia mixtures in the charging tank of hydrogen by electrolysis of water, during the steady state phase.

Detailed description of the invention.

Said apparatus includes two devices for the production of hydrogen to be co-fed to the engine: a device that generates hydrogen electrolytically and a device that generates hydrogen by ammonia cracking.

The apparatus of this invention preferably employs an innovative electrolyser 11 for which the same Applicant filed simultaneously the patent application PCT/IB2010/053142, such innovative electrolyser allows the production of hydrogen directly pressurized from alkaline solutions, and contains at least of one electrolytic cell in which:

- two half-cells, anodic and cathodic, separated by an anion exchange membrane whose surface in contact with the cathodic half-cell is a membrane-electrode assembly, and

- alkaline solution is present only in the anodic half-cell.

The electrolyser 11 may be formed by a single cell or a stack of the electrolytic cells.

In the electrolytic cells of electrolyser 11 , in order to allow an intimate contact between the membrane and the cathodic electrode, it is preferable that the cathode consists of electrocatalysts cathode deposited directly onto the ion exchange membrane, thereby obtaining a assembled device membrane-electrode (MEA).

In the anodic half-cell of the electrolyser 11 the electrocatalysts can be deposited on suitable conductive media, such as various kinds of wire mesh and texture, or as alternative directly on the ionic exchange membrane.

In the electrolyser 11 , the alkaline solution is placed exclusively in the anode half- cell. Due to its hydrophilicity, such anion-exchange membrane is completely soaked with water, up to the surface layer in contact with the cathodic half-cell. Such amount of water is adequate for the formation of hydrogen at a rate that allows only the electrolysis reaction without the evaporation of water. In this way the hydrogen produced has high purity and is dry. The OH^" ions formed during the cathodic half-reaction migrate through the membrane towards the other half-cell, ensuring the conditions for electrolytic equilibrium.

Such electrolytic device, due to an anion exchange membrane suitably catalyzed, produces dry hydrogen pressurized to 100 bar, which is stored in a pressure tank. Thanks to the innovative electrolyser described above, hydrogen can be directly stored in a pressure tank, dry and free of contaminants, acidic or basic, which would lead to the corrosion of metallic components of the engine.

Preferably the catalytic device is a gas-gas heat exchanger whose cells crossed by the ammonia flow are coated with a catalyst suitable to promote the cracking of ammonia, and heated by exhaust gases; said heat exchanger is thus actually a heat exchanger/reactor 23.

In the apparatus of the present invention, during the startup of the engine 20 the combustion of ammonia is efficiently promoted by the co-feeding of ammonia and hydrogen from the tank 16, containing pressurized hydrogen.

In the device of the invention the engine exhaust fumes pass through the heat exchanger/reactor which then heats up; when it reaches the temperature of 450 ⁰C, the start-up shall be considered complete and the steady state phase begins. In this phase the exchanger/reactor is hot enough to produce hydrogen by thermal cracking of ammonia; the mixture hydrogen/nitrogen thus produced is co-fed with ammonia to the engine. At the end of the start-up phase the co-feeding of hydrogen from the container 16 is interrupted.

During the steady state phase electrolysis is done by the electrolyser 11 , and preferably the electrolyser is electrically powered by the on-board electric generator 21 connected to the internal combustion engine (20).

Preferably, the electrolyser 11 is fed with the water contained in the tank 12 and preferably to prevent the refill, water is obtained by the condensation of exhaust fumes, consisting only of nitrogen gas and water vapor. The hydrogen produced is conveyed to a tank 16, pressurized directly by the electrolyser itself without any need of auxiliary compressors (up to a maximum pressure of 100 bar) and then used during the following engine startup. Thus, since a supply of pressurized hydrogen is already available, the engine startup can be instantaneous, without downtime and without any auxiliary power sources.

The system of the invention therefore preferably includes a condenser 26 where the exhaust gases are conveyed through the valve 25 and a container 12 for collecting the water condensed from the condenser 26.

Figures 1-3 schematically represent one of the realizations of the apparatus of the present invention and its operating principle in the three different phases of run: the startup of the internal combustion engine (Fig. 1 ), the steady state phase including the co-feeding of hydrogen from the exchanger reactor (Fig. 2) and the production of hydrogen by electrolysis while running in steady state (Fig. 3).

During the startup of the engine (Figure 1 ) the hydrogen, stored in the tank 16 up to a maximum pressure of 100 bar, passes through a flow-meter 18 and is fed to the internal combustion engine 20. In parallel, the ammonia stored as pressurized liquid (8-9 bars) in the tank 28 passes through a check valve 29 and an expansion valve 30, and flow into the internal combustion engine 20. Here ammonia combines with the hydrogen and produces the combustion process.

Exhaust gases from the combustion process (consisting of water vapor and nitrogen gas at about 600 ⁰C) pass through a gas-gas heat exchanger 23 of suitable length and geometry (such as but not limited type of honey-comb) in order to raise the temperature up to the value required from the ammonia thermal cracking (not less than 450 ⁰C, preferably above 500 ⁰C). The heat exchanger cells through which ammonia is flown are coated with a layer of catalyst active for the thermal cracking reaction. After passing through the heat exchanger, the exhaust gases are expelled into the atmosphere.

The steady state phase starts as soon as the heat exchanger/reactor 23 has reached the temperature required for ammonia thermal cracking reaction.

The temperature of the heat exchanger 23 is monitored by a temperature probe 22 associated with the temperature control valve 19. When the temperature of the heat exchanger 23 has reached at least 450 ⁰C, the valve 19 stops the supply of hydrogen from the tank 16. At this stage the valve 24 divides the stream of ammonia from the tank 28, flowing a part directly to the internal combustion engine 20 and a part to the heat exchanger/reactor 23. The thermal cracking reaction has place in the exchanger 23, providing the hydrogen necessary to promote the ammonia combustion reaction (that is mixed with the nitrogen obtained as co- product). The ratio of the two ammonia streams should be enough to provide a final composition Hydrogen (arising from cracked ammonia)/ammonia (flown directly from the tank) comprised between 0.5 and 4 wt% of hydrogen.

A further phase for the device of this invention is the refill of the auxiliary hydrogen tank, by water electrolysis (Figure 3). This phase occurs during the steady state of the vehicle and does not require batteries or auxiliary power sources to generate electrolysis. The water for the electrolyser is obtained by condensation of exhaust combustion gases of the engine, consisting only of nitrogen gas and water. It is known that any nitrogen oxides formed react further with ammonia, forming in their turn as products nitrogen and water. Instead of expelling them directly into the atmosphere, the valve 25 flow them to a condenser 26. The condensed water is fed through a pump 27 to tank 12, while the nitrogen gas is discharged into the atmosphere. The tank 12 has a level control 31 which, when he amount of water is enough, acts on the valve 25 and blocks the flow. The water collected is fed through a pump 13 to the anode compartment of the electrolyser 11. The electrolyser is electrically powered by the electric alternator 21 connected to the motor 20. The hydrogen produced is fed into the pressurized tank 16, flowing through the valve 14. When the pressure control 17 indicates the maximum operating pressure required for the following start-up phase of the engine, the associated valve 15 blocks the additional flow of hydrogen into the tank 16.

Claims

1. An apparatus for hydrogen co-feeding to an internal combustion engine, fuelled by ammonia, said apparatus comprising:

- a catalytic device for the production of hydrogen by means of thermal cracking of ammonia;

- an electrolytic device for the production of directly pressurized dry hydrogen, lacking any acidic or alkaline contaminant;

- a vessel containing pressurized hydrogen.

2. Apparatus according to claim 1 wherein said electrolytic device is an electrolyzer (1 1 ) for hydrogen production from alkaline solution and said electrolyzer comprises at least one electrolytic cell wherein:

- the two half-cells, anodic and cathodic, are separated by an anionic exchange membrane whose surface in contact with the cathodic half-cell is a membrane-electrode assembly, and

- the alkaline solution is contained exclusively in the anodic half-cell.

3. Apparatus according to any one of the claims 1-2 wherein the electrolytic device is consisting of a single cell or a stack of electrolytic cells.

4. Apparatus according to any one of the claims 1-3 wherein the catalytic device is an exchanger/reactor (23) whose channels crossed by the ammonia stream are coated by a catalyst active for ammonia cracking promotion

5. Apparatus according to any one of the claims 1-4 in which the electrolytic devices is electrically fed by the electric generator (21 ) connected to the internal combustion engine (20).

6. Apparatus according to any one of the claims 1-5 further comprising a vessel (12) for the water to be fed to the electrolyzer (1 1 ).

7. Apparatus according to any one of the claims 1-6 further comprising a condenser (26) in which the exhaust fumes are driven through by means of a valve (25), and a vessel (12) that collects the condensed water obtained from condenser (26).