Reducing agent supply method for SCR system of ammonia engine

Abstract

A reducing agent supply method for an SCR system of an ammonia engine. For a high-pressure direct injection ammonia engine, an ammonia injector in a cylinder is used during an initial stage of engine exhaust or scavenging, and when the temperature in the cylinder is lower than the kindling point of ammonia, the ammonia injector is used to inject a reducing agent required by an SCR system. The method can be used in both an ammonia engine and an ammonia / diesel dual-fuel engine. For the ammonia / diesel dual-fuel engine, the method can be used in both a diesel mode and an ammonia mode. According to the method, ammonia used as the reducing agent of the SCR system can be fully mixed with exhaust gas in the cylinder, thereby facilitating thorough denitration reaction in the presence of an SCR catalyst, enhancing the denitration efficiency of the SCR system and reducing ammonia slip. For the ammonia / diesel dual-fuel engine, in the diesel mode, the ammonia injector still needs to work due to operation of the SCR system, thereby avoiding the dry burning problem caused when the ammonia injector does not work in the diesel mode.

Description

A method for supplying reducing agent to an ammonia engine SCR system Technical Field

[0001] The invention relates to a reducing agent supply method for an ammonia engine SCR system, belonging to the technical field of engine equipment. Background Art

[0002] Selective catalytic reduction (SCR) system is used to solve the problem of engine nitrogen oxides (NO x ) emission post-treatment technology, which requires the use of urea solution or ammonia as a reducing agent to reduce NO x Reacts to reduce engine NO x Emissions. The SCR system usually has a separate reductant supply system, and the reductant spray gun is set on the exhaust pipe upstream of the SCR reactor, and the reductant is sprayed into the exhaust gas by the reductant spray gun. For the SCR system of the ammonia engine, ammonia is used as fuel and can also be used as a reductant for the SCR system. Ammonia engines use ammonia as fuel. For high-pressure direct injection ammonia engines, ammonia injectors are provided on the cylinders for ammonia fuel injection. Near the top dead center of the piston, the ammonia fuel injector sprays ammonia into the cylinder. After the ammonia fuel is ignited, the cylinder performs work. For ammonia / diesel dual-fuel engines, the ammonia injector will dry burn in the diesel mode due to non-operation, which will affect the life of the ammonia injector.

[0003] Summary of the Invention

[0004] The technical problem to be solved by the present invention is: how to control the reducing agent supply of the SCR system of an ammonia engine to reduce the impact of dry burning on the ammonia injector in diesel mode.

[0005] In order to solve the above technical problems, the present invention provides a method for supplying a reducing agent to an ammonia engine SCR system, comprising the following steps:

[0006] Step 1): Based on the exhaust flow rate of ammonia engine, NO x Emission concentration, NH3 emission concentration, ammonia nitrogen ratio, calculate the reducing agent supply amount SCRnh3 required by the SCR system under various engine loads: SCRnh3 = Mexh × (α × Vnox - Vnh3) / 1000000 / 1.293 / 22.4 × 17;

[0007] Wherein, SCRnh3: the reducing agent supply required by the SCR system, g / s;

[0008] Mexh: engine exhaust flow, g / s;

[0009] α: ammonia nitrogen ratio, α value ranges from 0.8 to 1.0;

[0010] Vnox: NO xEmission concentration, ppm;

[0011] Vnh3: NH3 emission concentration, ppm;

[0012] Step 2): The ammonia injector must meet the ammonia fuel injection quantity requirement in ammonia mode. However, the ammonia injection quantity used as an SCR reductant is much smaller than the ammonia fuel injection quantity. Therefore, it is necessary to check whether the minimum continuous stable injection quantity Q of the ammonia injector can meet the reductant supply quantity M required per cylinder per working cycle.

[0013] Step 3): If all the reducing agent required by the SCR system is injected and supplied by the ammonia injector of a certain cylinder, calculate the reducing agent injection amount M of the cylinder per engine working cycle: M = SCRnh3×60 / V×N / 2;

[0014] Where, N: number of engine strokes, 2 or 4;

[0015] V: engine speed, rpm;

[0016] M: Ammonia injection amount per working cycle of a cylinder of the engine, g;

[0017] Step 4): If the reducing agent required by the SCR system is supplied by injection from all cylinder ammonia injectors, calculate the reducing agent injection amount Mi of each cylinder per working cycle of the engine: Mi = M / n;

[0018] Wherein, Mi: the amount of ammonia injected per cylinder per working cycle of the engine, g;

[0019] n: number of engine cylinders;

[0020] Step 5): Determine the minimum continuous stable injection time t of the ammonia injector;

[0021] Step 6): Determine the minimum continuous stable injection flow rate q of the ammonia injector;

[0022] Step 7): Determine the minimum continuous stable injection amount Q of the ammonia injector: Q = q × t;

[0023] Where, Q: minimum continuous stable injection quantity of the injector, g;

[0024] q: minimum continuous stable injection flow rate of ammonia injector, g / s;

[0025] t: minimum continuous stable injection time of ammonia injector, s;

[0026] Step 8): Control the state of injecting the reducing agent according to the minimum continuous stable injection amount Q of the ammonia injector:

[0027] If Q>M, it means that the ammonia injector cannot meet the injection demand of the reducing agent supply amount M, and the ammonia injector cannot be used for the reducing agent injection of the SCR system;

[0028] If Mi<Q≤M, it means that the ammonia injector can meet the requirement that the SCR reducing agent is injected by one or several cylinders in each working cycle; then when the SCR is running, one or several cylinders can be fixedly used to inject the reducing agent;

[0029] If Q≤Mi, it means that the ammonia injector can meet the SCR reducing agent requirement of injecting reducing agent in each cylinder and each working cycle; then the reducing agent is injected in each cylinder and each working cycle when the SCR is running;

[0030] Step 9): Determine the reducing agent injection timing: After the exhaust or scavenging phase begins, when the cylinder temperature is lower than the auto-ignition point of ammonia, the ammonia injector injects ammonia into the cylinder to be used as a reducing agent for denitrification in the SCR system;

[0031] Step 10): Determine the ammonia injector continuous injection time T: T = M / q; or T = Mi / q;

[0032] Where, T: ammonia injector injection duration, s.

[0033] Preferably, the minimum continuous stable injection time t of the ammonia injector determined in step 5) is a factory setting.

[0034] Preferably, the method for determining the minimum continuous stable injection flow rate q of the ammonia injector in step 6) is: Q = 1000A × (2P × ρ) ^ (1 / 2)

[0035] Where A: effective flow area of ​​ammonia injector nozzle, m 2 , the value is factory setting;

[0036] P: the difference between ammonia injection pressure and cylinder pressure, Pa;

[0037] ρ: density of liquid ammonia, kg / m 3 .

[0038] Preferably, the autoignition point in step 9) is 649°C.

[0039] Preferably, in order to avoid the dry burning problem of the ammonia injector, in addition to using one or several cylinders to inject the reducing agent, the following strategy is also adopted: replace different ammonia injectors in the same cylinder or the ammonia injectors of other cylinders to rotate the injection of the reducing agent at regular intervals.

[0040] More preferably, the switching order of the ammonia injectors between the cylinders is opposite to the engine firing order.

[0041] For high-pressure direct injection ammonia engines, the ammonia injector in the cylinder is used to inject the reducing agent required by the SCR system during the exhaust or scavenging stage of the engine, when the temperature in the cylinder is lower than the auto-ignition point of ammonia. This method can be used for ammonia engines as well as for ammonia / diesel dual-fuel engines. For ammonia / diesel dual-fuel engines, this method can be used in diesel mode as well as in ammonia mode. The advantage of the present invention is that the ammonia used as the reducing agent of the SCR system can be fully mixed with the exhaust gas in the cylinder, which is beneficial to the full denitration reaction of the SCR catalyst, improving the denitration efficiency of the SCR system and reducing the amount of ammonia slip. For ammonia / diesel dual-fuel engines, the ammonia injector still needs to work in diesel mode due to the operation of the SCR system, which can avoid the dry burning problem caused by the non-operation of the ammonia injector in diesel mode.

[0042] For ammonia / diesel dual-fuel engines, the ammonia injector has a large injection flow rate. To better apply this method, if the engine cylinder head space allows, an ammonia injector with a suitable injection flow rate can be installed to more flexibly control the ammonia injection amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG1 is a schematic diagram of a cylinder of an ammonia / diesel dual-fuel engine. DETAILED DESCRIPTION

[0044] To make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0045] Example

[0046] A method for supplying a reducing agent to an ammonia engine SCR system comprises the following steps:

[0047] Step 1): Based on the exhaust flow rate of ammonia engine, NO x Emission concentration, NH3 emission concentration, ammonia nitrogen ratio, calculate the reducing agent supply amount SCRnh3 required by the SCR system under various engine loads: SCRnh3 = Mexh × (α × Vnox - Vnh3) / 1000000 / 1.293 / 22.4 × 17;

[0048] Wherein, SCRnh3: the reducing agent supply required by the SCR system, g / s;

[0049] Mexh: engine exhaust flow, g / s;

[0050] α: ammonia nitrogen ratio, α value ranges from 0.8 to 1.0;

[0051] Vnox: NO x Emission concentration, ppm;

[0052] Vnh3: NH3 emission concentration, ppm;

[0053] Step 2): The ammonia injector must meet the ammonia fuel injection quantity requirement in ammonia mode. However, the ammonia injection quantity used as an SCR reductant is much smaller than the ammonia fuel injection quantity. Therefore, it is necessary to check whether the minimum continuous stable injection quantity Q of the ammonia injector can meet the reductant supply quantity M required per cylinder per working cycle.

[0054] Step 3): If all the reducing agent required by the SCR system is injected and supplied by the ammonia injector of a certain cylinder, calculate the reducing agent injection amount M of the cylinder per engine working cycle: M = SCRnh3×60 / V×N / 2;

[0055] Where, N: number of engine strokes, 2 or 4;

[0056] V: engine speed, rpm;

[0057] M: Ammonia injection amount per working cycle of a cylinder of the engine, g;

[0058] Step 4): If the reducing agent required by the SCR system is supplied by injection from all cylinder ammonia injectors, calculate the reducing agent injection amount Mi of each cylinder per working cycle of the engine:

[0059] Mi=M / n;

[0060] Wherein, Mi: the amount of ammonia injected per cylinder per working cycle of the engine, g;

[0061] n: number of engine cylinders;

[0062] Step 5): Determine the minimum continuous stable injection time t of the ammonia injector (the value is factory setting);

[0063] Step 6): Determine the minimum continuous stable injection flow rate q of the ammonia injector: Q = 1000A × (2P × ρ) ^ (1 / 2)

[0064] Where A: effective flow area of ​​ammonia injector nozzle, m 2 , the value is factory setting;

[0065] P: the difference between ammonia injection pressure and cylinder pressure, Pa;

[0066] ρ: density of liquid ammonia, kg / m 3 ;

[0067] Step 7): Determine the minimum continuous stable injection amount Q of the ammonia injector: Q = q × t;

[0068] Where, Q: minimum continuous stable injection quantity of the injector, g;

[0069] q: minimum continuous stable injection flow rate of ammonia injector, g / s;

[0070] t: minimum continuous stable injection time of ammonia injector, s;

[0071] Step 8): Control the state of injecting the reducing agent according to the minimum continuous stable injection amount Q of the ammonia injector:

[0072] If Q>M, it means that the ammonia injector cannot meet the injection demand of the reducing agent supply amount M, and the ammonia injector cannot be used for the reducing agent injection of the SCR system;

[0073] If Mi<Q≤M, it means that the ammonia injector can meet the requirement that the SCR reducing agent is injected by one or several cylinders in each working cycle; then when the SCR is running, one or several cylinders can be fixedly used to inject the reducing agent;

[0074] If Q≤Mi, it means that the ammonia injector can meet the SCR reducing agent requirement of injecting reducing agent in each cylinder and each working cycle; then the reducing agent is injected in each cylinder and each working cycle when the SCR is running;

[0075] Step 9): Determine the reducing agent injection timing: After the exhaust or scavenging phase begins, when the cylinder temperature is lower than the auto-ignition point of ammonia (649°C), the ammonia injector injects ammonia into the cylinder to serve as the reducing agent for denitrification in the SCR system;

[0076] Step 10): Determine the ammonia injector continuous injection time T: T = M / q; or T = Mi / q;

[0077] T: Ammonia injector injection duration, s.

[0078] To prevent dry burning of ammonia injectors, in addition to using one or more cylinders to inject the reducing agent, a strategy is also implemented: periodically switching between different ammonia injectors within the same cylinder or rotating between ammonia injectors in other cylinders. The order in which ammonia injectors are switched between cylinders is the opposite of the engine ignition sequence.

Claims

1. A method for supplying reducing agent to an ammonia engine SCR system, characterized in that: The following steps are involved: Step 1): Based on the exhaust flow rate of ammonia engine, NO x Emission concentration, NH3 emission concentration, ammonia nitrogen ratio, calculate the reductant supply SCRnh3 required by the SCR system under various engine loads: SCRnh3=Mexh×(α×Vnox-Vnh3) / 1000000 / 1.293 / 22.4×17; Wherein, SCRnh3: the amount of reducing agent supplied to the SCR system, g / s; Mexh: engine exhaust flow, g / s; α: ammonia nitrogen ratio, α value is between 0.8 and 1.0; Vnox: NO x Emission concentration, ppm; Vnh3: NH3 emission concentration, ppm; Step 2): The ammonia injector must meet the ammonia fuel injection quantity requirement in the ammonia mode, and the ammonia injection quantity used as the SCR reductant is much smaller than the ammonia fuel injection quantity. Therefore, it is necessary to check whether the minimum continuous stable injection quantity Q of the ammonia injector can cover the reductant supply quantity M requirement per cylinder per working cycle; Step 3): If all the reducing agent required by the SCR system is supplied by a certain cylinder ammonia injector, calculate the reducing agent injection amount M of the cylinder per engine working cycle: M = SCRnh3 × 60 / V × N / 2; Where, N: number of engine strokes, 2 or 4; V: engine speed, rpm; M: Ammonia injection amount per working cycle of a cylinder of the engine, g; Step 4): If the reductant required by the SCR system is supplied by injection from all cylinder ammonia injectors, calculate the reductant injection amount Mi of each cylinder per working cycle of the engine: Mi=M / n; Wherein, Mi: the amount of ammonia injected per cylinder per working cycle of the engine, g; n: number of engine cylinders; Step 5): Determine the minimum continuous stable injection time t of the ammonia injector; Step 6): Determine the minimum continuous stable injection flow rate q of the ammonia injector; Step 7): Determine the minimum continuous stable injection amount Q of the ammonia injector: Q = q × t; Where, Q: minimum continuous stable injection amount of the injector, g; q: minimum continuous stable injection flow rate of ammonia injector, g / s; t: minimum continuous stable injection time of ammonia injector, s; Step 8): Control the state of injecting the reducing agent according to the minimum continuous stable injection amount Q of the ammonia injector: If Q>M, it means that the ammonia injector cannot meet the injection demand of the reducing agent supply amount M, and the ammonia injector cannot be used for the reducing agent injection of the SCR system; If Mi<Q≤M, it means that the ammonia injector can meet the requirement that the SCR reducing agent is all injected by one or several cylinders in each working cycle; then when the SCR is running, one or several cylinders can be fixed to inject the reducing agent; If Q≤Mi, it means that the ammonia injector can meet the requirement of the SCR reductant to be injected in each cylinder and each working cycle; then the reductant is injected in each cylinder and each working cycle when the SCR is running; Step 9): Determine the timing of reducing agent injection: After the exhaust or scavenging phase begins, when the cylinder temperature is lower than the auto-ignition point of ammonia, the ammonia injector injects ammonia into the cylinder to be used as a reducing agent for denitration of the SCR system; Step 10): Determine the continuous injection time T of the ammonia injector: T=M / q;or T=Mi / q; T: Ammonia injector injection duration, s.

2. The method for supplying reducing agent to an ammonia engine SCR system according to claim 1, characterized in that: The minimum continuous stable injection time t of the ammonia injector determined in step 5) is a factory setting.

3. The reducing agent supply method for an ammonia engine SCR system according to claim 1, characterized in that: The method for determining the minimum continuous stable injection flow rate q of the ammonia injector in step 6) is: Q = 1000A × (2P × ρ) ^ (1 / 2) Where A: effective flow area of ​​ammonia injector nozzle, m 2 , the value is factory setting; P: the difference between ammonia injection pressure and cylinder pressure, Pa; ρ: density of liquid ammonia, kg / m 3 .

4. The method for supplying reducing agent to an ammonia engine SCR system according to claim 1, characterized in that: The autoignition point in step 9) is 649°C.

5. The reducing agent supply method for an ammonia engine SCR system according to claim 1, characterized in that: In order to avoid the problem of dry burning of ammonia injectors, in addition to using one or several cylinders to inject the reducing agent, the following strategy is also adopted: replace different ammonia injectors in the same cylinder or the ammonia injectors of other cylinders to rotate the injection of reducing agent at regular intervals.

6. The method for supplying reducing agent to an ammonia engine SCR system according to claim 5, characterized in that: The switching sequence of the ammonia injectors between the cylinders is opposite to the engine ignition sequence.

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