DE102022121521A1 - METHOD OF OPERATING A HYDROGEN COMBUSTION ENGINE - Google Patents

Abstract

Method for operating a hydrogen internal combustion engine, with the steps of detecting (S101) a sudden change in load of the hydrogen internal combustion engine; calculating (S102) an amount of water based on the load jump; and adding (S103) the amount of water to a hydrogen combustion mixture to compensate for fuel-rich operation of the hydrogen internal combustion engine.

Description

The invention relates to a method for operating a hydrogen internal combustion engine and a hydrogen internal combustion engine.

Nowadays it is becoming more and more important to replace fossil fuels such as petrol and diesel with more environmentally friendly fuels. In practice, this is already being achieved with biofuels such as fuels that contain bioethanol. But even operation with such biofuels cannot significantly reduce the emission of exhaust gases such as CO ₂ . In addition, some internal combustion engines have to be adapted to work optimally with the new fuel. Therefore, there is increasing interest in hydrogen as a fuel in automobiles. Theoretically, the combustion of hydrogen with oxygen only produces water as a waste product.

In comparison to other gaseous fuels, however, hydrogen has a high tendency towards knocking combustion. This is due to the fact that hydrogen engines tend to ignite prematurely due to their low minimum ignition energy. Because pre-ignition can significantly advance combustion, peak pressures can increase and the likelihood and severity of knock increases. A so-called "mega knock" due to pre-ignition restricts the operating limits and can cause major damage to the power unit.

The pamphlet U.S. 2012/260886 A1 relates, for example, to an internally cooled piston internal combustion engine for conventional fuels.

It is the technical object of the invention to reduce the emission of nitrogen oxides from a hydrogen internal combustion engine.

The method according to the invention serves to operate a hydrogen internal combustion engine and comprises the steps of detecting a sudden change in load of the hydrogen internal combustion engine; calculating an amount of water based on the load jump; and adding the amount of water to a hydrogen combustion mixture to compensate for fuel-rich operation of the hydrogen internal combustion engine. By adding the amount of water in a targeted manner when there is a sudden change in load, the technical advantage is achieved, for example, that the emission of NO _x emissions is reduced. In addition, abnormalities in combustion such as premature ignition and knocking can be prevented.

The amount of water can be determined using physical or empirical models based on predicted engine behavior. This achieves the technical advantage, for example, that the required amount of water is provided at the right time. Accurate, reliable and realistic calculations can be carried out by using physical or empirical models. Using this, the amount of water required can be easily calculated, so that the size of the required water tank can be determined in advance. Thereby, unnecessary waste of space in designing the vehicle can be avoided and weight can also be saved. Another technical advantage is that the exact determination of the amount of water also increases the efficiency of the engine, since neither too much nor too little water is introduced.

Before injecting water, an amount of water may be determined based on an operating timing and/or an emissions target. This achieves the technical advantage, for example, that the required amount of water is available at the right time to be injected. If too little water is injected, or if the injection is too late or too early, the knocking operation cannot be prevented. If too much water is injected, the hydrogen combustion mixture can no longer ignite because it is too diluted.

In a technically advantageous embodiment of the method, an expected drop in the lambda value when the load changes is calculated. This achieves the technical advantage, for example, that exact calculations of the amount of water can be carried out.

In a further technically advantageous embodiment of the method, the amount of water is calculated on the basis of the expected drop in the lambda value.

This achieves the technical advantage, for example, that the amount of water can be precisely determined.

In a further technically advantageous embodiment of the method, the amount of water is injected into the combustion chamber. The injection can take place via a direct injection. This achieves the technical advantage, for example, that the evaporation of the water takes place directly in the combustion chamber, so that the hydrogen combustion mixture is cooled and diluted. This prevents premature ignition and also reduces _NOx emissions.

In a further technically advantageous embodiment of the method, the quantity of water is supplied to the hydrogen combustion mixture before it enters the combustion chamber. The amount of water can be added to the hydrogen combustion mixture via a port injector. This achieves the technical advantage, for example, that fewer connections have to be attached to the combustion chamber. This increases the pressure resistance and stability of the combustion chamber.

In a further technically advantageous embodiment of the method, the quantity of water is injected via a multi-hole injector. This injection is called spray targeting. This achieves the technical advantage, for example, that the water is introduced in finely divided form and can therefore evaporate more quickly. This prevents premature ignition early enough and also reduces NOx emissions.

In a further technically advantageous embodiment of the method, the lambda limit is lowered. This achieves the technical advantage, for example, that a better load response is achieved.

In a further technically advantageous embodiment of the method, the sudden change in load is determined on the basis of a torque requirement. This achieves the technical advantage, for example, that the sudden change in load can be determined in a simple manner and with a short time delay.

In a further technically advantageous embodiment of the method, the amount of water is recovered from the exhaust gas of the hydrogen internal combustion engine. By adding the amount of water to the hydrogen combustion mixture in a targeted manner, the exhaust gases also contain high water concentrations, which in turn lower the temperature of the exhaust gases. A high water content and low flue gas temperatures make the recovery of water from the flue gas viable. This achieves the technical advantage, for example, that the water tank for the water injection can be kept small. Saving space is advantageous in motor vehicles, since this allows the storage space of a vehicle to be increased in a simple manner and the weight is also kept low.

The hydrogen internal combustion engine according to the invention, with a detection device for detecting a load jump of the hydrogen internal combustion engine; an electronic control unit for calculating an amount of water based on the load jump; and a feed device for adding the quantity of water to a hydrogen combustion mixture in order to compensate for fuel-rich operation of the hydrogen internal combustion engine, achieves the same technical advantages as the method. The sudden changes in load are detected, for example, by the control unit.

• 1 eine graphische Darstellung verschiedener Verbrennungsabläufe beim Betrieb eines Wasserstoff-Verbrennungsmotors;
• 2 eine schematische Darstellung einer Brennkammer eines Wasserstoff-Verbrennungsmotors in zwei Ausführungsformen;
• 3 ein Blockdiagram eines Verfahrens zum Betreiben eines Wasserstoff-Verbrennungsmotors;
• 4 eine graphische Darstellung des Einflusses einer zugegebenen Wassermenge auf verschiedene Betriebsparameter; und
• 5 eine graphische Darstellung des Einflusses einer zugebenen Wassermenge auf weitere Betriebsparameter.

Exemplary embodiments of the invention are explained in more detail with reference to the following figures. show:

• 1 a graphical representation of various combustion processes when operating a hydrogen internal combustion engine;
• 2 a schematic representation of a combustion chamber of a hydrogen internal combustion engine in two embodiments;
• 3 a block diagram of a method for operating a hydrogen internal combustion engine;
• 4 a graphical representation of the influence of an added amount of water on various operating parameters; and
• 5 a graphical representation of the influence of an added amount of water on other operating parameters.

1 shows a graphical representation of various combustion processes when operating a hydrogen internal combustion engine. Here, the cylinder pressure (Cylinder Pressure) is compared to the crank angle (Crank Angle) α. The crank angle α describes the angle of the crankshaft in relation to the top dead center of the piston. The curves shown are curve 105 of regular combustion, curve 107 of knocking combustion, curve 109 of the so-called “mega knock” and curve 111 of non-knocking combustion, which results from early ignition 111 .

The resulting pressures are higher in the two curves 107 and 109 of knocking combustion and in curve 111 of non-knocking combustion after premature ignition than in regular combustion. Hydrogen internal combustion engines tend to ignite prematurely due to the low minimum ignition energy of hydrogen. As pre-ignition advances combustion, peak pressures increase and knock probability and magnitude increases.

The highest pressures occur during knocking in the so-called "Mega Knock". The "mega knock" is often preceded by premature ignition. The "Mega Knock" 109 severely limits the operating limits of a hydrogen internal combustion engine and causes major damage to the power unit. The inventive method is achieves the technical advantage that such anomalies are effectively prevented during combustion. The "mega knock" occurs particularly when the engine is enriched, ie when there is a fuel-rich combustion mixture.

2a and 2 B show a schematic representation of the combustion chamber 200 of a hydrogen internal combustion engine in two embodiments. In 2a the hydrogen combustion mixture is mixed with water via a port injector 201 outside of the combustion chamber 200, ie before it is fed into the combustion chamber 200. In 2 B hydrogen or water is injected directly into the combustion chamber 200 via a direct injection 203 . This direct injection 203 can also be a port injector, but other ways of introducing water, such as a nebulizer, are also conceivable. In both embodiments, the hydrogen combustion mixture mixed with water is then ignited via a spark plug 205, so that the piston 207 is then in turn driven by the ignited hydrogen combustion mixture.

By introducing water into the premixed hydrogen combustion mixture, combustion anomalies such as pre-ignition and knocking can be prevented. On the one hand, the introduction of water dilutes the filling of the combustion chamber, i.e. the hydrogen combustion mixture required for combustion. This has the technical advantage that premature ignition is effectively prevented.

On the other hand, the evaporation of the water has a cooling effect on the hydrogen combustion mixture and on the combustion chamber. The ignition timing α _IGN is the point in time at which the spark plug fires. This cools hot spots in the combustion chamber so that premature ignition can be effectively prevented. Another technical advantage of cooling the gas mixture is that it reduces the emission of _NOx compounds. The term NO _x compounds stands for a large number of nitrogen oxides, such as nitrogen monoxide NO or nitrogen dioxide NO ₂ . _NOx gases are produced from the reaction between nitrogen and oxygen, especially at high temperatures, during combustion in air. These prerequisites for the formation of _NOx compounds are present in the combustion chamber of a hydrogen internal combustion engine, since ambient air containing nitrogen is used for the combustion of hydrogen.

There are four ways to arrange the injection, namely H2 PI/H2O PI; H2DI/H2OPI; H2PI / H2ODI; or H2 DI / H2O DI (PI - Port Injection; DI - Direct Injection). Simultaneous injection is possible with the former and the latter, and can bring an advantage for special systems. The oil film can be prevented from being washed away via the nozzle geometry, for example with a multi-hole nozzle or with a coordinated injection timing.

The water injection can be into an intake manifold or direct water injection is performed. By simultaneously injecting the hydrogen combustion mixture directly into the combustion chamber 200 by means of a multi-hole injector, the lining of the combustion chamber is not abraded over time, since the water does not stay in the combustion chamber for a long time. Since the combustion chamber walls are not sprayed, the oil film is not washed away. Simultaneous injection of hydrogen and water is not required. It is beneficial to spray on the plunger when it is in the correct position.

The process occurs immediately with the ignition of the hydrogen combustion mixture. The formation of these NO _x compounds is reduced by the method according to the invention. Consequently, the process also has a positive effect on air purity.

3 shows a block diagram of the method for operating the hydrogen internal combustion engine. In the first step S101, a sudden change in load of the hydrogen internal combustion engine is detected. This load jump occurs, for example, when there is a transition from idling operation to full-load operation. In step S102, a water quantity is determined on the basis of the load jump. For this purpose, an expected drop in the lambda value can be calculated when there is a sudden change in load. The amount of water can then be calculated based on the expected drop in lambda value.

The calculation of the resulting lambda value works in a similar way to the soot limit in a diesel engine. In the event of a sudden change in load, the fuel mass is increased until a certain lambda limit is reached. In addition, however, there is still the use of a throttle valve. The position of the gas pedal then specifies the required torque, ie the required fuel mass, which, however, cannot be provided immediately because of the lack of air. The air mass that can initially be provided is increased by opening the throttle valve and can then be determined, for example, using a physical charge model. The specified minimum lambda value, which can be further reduced by the water injection, is then Adjustment of the resulting fuel mass achieved.

In step S103, the amount of water is added to a hydrogen combustion mixture in order to compensate for fuel-rich operation of the hydrogen engine. The targeted addition of water when there is a sudden change in load can reduce nitrogen oxide emissions. In addition, the lambda value can be further reduced in order to improve transient behavior. In addition, abnormal combustion of the hydrogen combustion mixture, such as premature ignition or knocking, can be prevented.

4a until 4d show the influence of the amount of water fed into the hydrogen combustion mixture on various parameters during the operation of the hydrogen internal combustion engine over time.

4a shows the speed of the hydrogen internal combustion engine over time. The speed of the hydrogen internal combustion engine is constant over time.

4b shows the time course of a change in the engine torque (engine torque) of the hydrogen internal combustion engine in Nm. The dashed curve 403 shows the torque request. The torque requirement is initially constant and then jumps to a higher value in a load jump 401 . The curve 405 is the actual torque without the addition of the amount of water. In the curve 405 of the actual torque, a time delay in comparison to the torque request during the load step 401 can be seen due to a plateau.

Curve 407 shows the actual torque after the water quantity has been supplied for sudden load change 401. No plateau can be seen in curve 407. The time lag compared to the load step 401 of the torque request decreases, so that the hydrogen internal combustion engine responds more directly. The responsiveness of the hydrogen internal combustion engine can be improved by adding the amount of water to the hydrogen combustion mixture and the desired torque demand can be reached more quickly. In the event of a sudden change in load, such as a sudden change from idling to full load, the new torque requirement can be responded to more quickly. The response behavior of the hydrogen internal combustion engine is improved by introducing the amount of water.

4c shows the associated lambda value over time. The lambda value is measured by the lambda probe. The lambda probe (λ probe) is the main sensor in the control circuit of the lambda control for catalytic exhaust gas cleaning. The aim is to minimize the emission of pollutants such as nitrogen oxides. The lambda probe compares the residual oxygen content in the exhaust gas with the oxygen content of a reference, usually the current atmospheric air. From this, the combustion air ratio λ (ratio of combustion air to fuel) can be determined and adjusted.

The curve 409 (solid line) shows the lambda value without adding the amount of water to the hydrogen combustion mixture. The profile 411 (dashed line) shows the lambda value after adding the amount of water to the hydrogen combustion mixture (dashed line 411). A comparison of the two curves 409 and 411 shows that adding the amount of water reduces the lambda value by 0.2. The lambda value can therefore be reduced by adding water, so that the transient operation is improved. The lambda limit can also be shifted to lower values for improved load behavior.

4d shows the concentration of NO _x emissions over time in ppm. Trace 413 (solid line) shows the NOx emissions without adding the amount of water to the hydrogen combustion mixture. Curve 415 (dashed line) shows the NOx emissions after adding the amount of water to the hydrogen combustion mixture.

In the event of a load jump, fuel-rich operation occurs and the associated increased NO _x emissions, since the amount of fuel supplied is increased rapidly. A comparison of the two curves 413 and 415 shows that the targeted addition of the amount of water reduces the formation of NO _x compounds. The introduction of the amount of water into the hydrogen combustion mixture causes compensation for fuel enrichment in transient operation.

From the history of 5b until 5d it can be seen that in conventional hydrogen internal combustion engines without the targeted addition of water to the hydrogen combustion mixture, a sudden load change leads to fuel-rich operation. This causes high NO _x emissions. The method according to the invention of the targeted addition of a quantity of water not only reduces the NO _x emissions, but also prevents anomalies during combustion, such as premature ignition and knocking.

5a until 5d show the influence of the added amount of water on various parameters during the combustion of a hydrogen combustion mixture in the hydrogen internal combustion engine.

5a shows the ratio of the mass flow rate ṁ _H2O of the water contained in the exhaust gas of a hydrogen internal combustion engine to the mass flow rate ṁ _H2 of the hydrogen used as a function of the relative air-fuel ratio (Rel. AFR - Relative Air Fuel Ratio). At a relative air-fuel ratio of about 1.8, combustion is better than at a ratio of 2.4. In between, the curve flattens out more and more.

5b shows the efficiency η as a function of the relative air-fuel ratio. The curve shows that the efficiency increases as the relative air-fuel ratio increases. The efficiency of the engine increases when there is sufficient air and, accordingly, oxygen.

5c shows the peak-to-peak ratio of knocking operation (KPP - Knock Peak-to-Peak) as a function of the relative air-fuel ratio. The curve with the solid line shows that the peak-to-peak ratio is constant on average during knocking operation. The curve with the dashed line shows that the peak-to-peak ratio during knocking operation increases at the maximum at higher air-fuel ratios due to the lower injected water mass. At higher air-fuel ratios, not only higher pressures but also high pressure fluctuations in the combustion chamber 200 can occur. This can lead to damage to the combustion engine.

5d shows the frequency in percent of pre-ignition as a function of the relative air-fuel ratio. With an increasing relative air-fuel ratio, i.e. an increasing proportion of air and thus an increasing proportion of oxygen, the probability of premature ignition increases due to the lower injected water mass.

All of the features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the object according to the invention in order to realize their advantageous effects at the same time.

All method steps can be implemented by devices that are suitable for carrying out the respective method step. All functions performed by physical features can be a method step of a method.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US2012260886A1 [0004]

Claims (10)

Method for operating a hydrogen internal combustion engine, comprising the steps: - Detecting (S101) a sudden change in load of the hydrogen internal combustion engine; - Calculating (S102) an amount of water on the basis of the sudden change in load; and - adding (S103) the quantity of water to a hydrogen combustion mixture in order to compensate for a fuel-rich operation of the hydrogen internal combustion engine. procedure after claim 1 , whereby an expected drop in the lambda value is calculated when the load changes. procedure after claim 2 , where the amount of water is calculated based on the expected drop in lambda value. A method according to any one of the preceding claims, wherein the quantity of water is injected into the combustion chamber (200). A method according to any one of the preceding claims, wherein the quantity of water is added to the hydrogen combustion mixture prior to entering the combustor (200). Method according to one of the preceding claims, in which the injection of the quantity of water takes place via a multi-hole injector. Method according to one of the preceding claims, wherein the lambda limit is lowered. Method according to one of the preceding claims, wherein the load jump is determined on the basis of a torque requirement. A method according to any one of the preceding claims, wherein the quantity of water is recovered from the exhaust gas of the hydrogen internal combustion engine. Hydrogen internal combustion engine, with: - A detection device for detecting a load jump of the hydrogen internal combustion engine; - An electronic control unit for calculating a water quantity on the basis of the load jump; and - A feed device for adding the amount of water to a hydrogen combustion mixture in order to compensate for fuel-rich operation of the hydrogen internal combustion engine.

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