Heating control strategy of an exhaust gas aftertreatment system

Abstract

Heating control strategy of an exhaust gas aftertreatment system for a spark-ignition internal combustion engine (110), in which - the internal combustion engine includes a plurality of cylinders (125, 125'), each of which is equipped with a device for igniting the air / fuel mixture, and - the exhaust gas after-treatment system includes at least one oxidizing catalytic converter (280) and a selective catalytic reduction system (290) of exhaust gases, the control strategy including the following phases: - activating the control strategy, - if the temperature of the selective catalytic reduction system (290) of exhaust gases is equal to the target temperature, ending the control strategy, otherwise, if the temperature is lower than the target value, continuing the control strategy, - if the temperature of the oxidizing catalytic converter (280) is above a predetermined minimum threshold, continuing the control strategy, otherwise ending the control strategy, - if there is torque reserve available, continuing the control strategy, otherwise ending the control strategy, - deactivating the ignition device of at least one cylinder (125'), - increasing the load on the remaining cylinders (125) to deliver the required torque, - optimizing a maximum fuel injection into the deactivated cylinders to maximize an exothermic reaction through the oxidizing catalytic converter (280), - monitoring the temperature at the inlet and outlet of the oxidizing catalytic converter (280) to optimize fuel injection on at least one deactivated cylinder, with closed loop control, - monitoring the temperature of the selective catalytic reduction system (290) of exhaust gases and reactivating the control strategy.

Description

[0001] HEATING CONTROL STRATEGY OF AN EXHAUST GAS

[0002] AFTERTREATMENT SYSTEM

[0003] D E S C R I PTI O N

[0004] Technical field of the invention

[0005] The present invention relates to a heating control strategy of an exhaust gas aftertreatment system of an internal combustion engine. The method is particularly suitable for hydrogen-fueled internal combustion engines.

[0006] Background art

[0007] Motor vehicles typically operate by using an internal combustion engine to convert the energy in a fuel, such as gasoline or diesel, into mechanical energy to propel the motor vehicle and then provide motion to the vehicle's wheels. Unfortunately, fossil fuels are expensive and contribute to environmental pollution. Because of these drawbacks, increasing attention is being paid to reducing fuel consumption and pollutants emitted by automobiles and other highway vehicles.

[0008] To alleviate some of these drawbacks, hydrogen-fueled internal combustion engines have been proposed, but they require special measures to ensure proper operation.

[0009] In fact, although it is a carbon-free fuel and therefore does not produce emissions of unburned hydrocarbons (HC) and carbon monoxide (CO), the combustion of hydrogen (H2) generates a considerable amount of nitrogen oxides (NOx) during transient operations. Therefore, an exhaust gas after-treatment system (ATS) equipped with a selective catalytic reduction (SCR) system is required to meet the requirements for NOx tailpipe emissions during transient operations on vehicles for on-road and off-road applications.

[0010] Furthermore, to comply with the emission requirements during cold start emission cycles, it is necessary to reduce as much as possible the warm-up time of the after-treatment system, in particular the selective catalytic reduction system (SCR). On the contrary, the internal combustion engine powered by hydrogen has longer ATS warm-up times than a similar Diesel engine.

[0011] In fact, with the same calibration, a Diesel engine provides a higher thermal power to the ATS than the hydrogen engine, both at low and high loads, where the thermal power transmitted is proportional to the flow rate and temperature of the exhaust gases. The higher thermal power is obtained because the Diesel engine processes a higher flow rate of exhaust gases and, at high loads, has a more favorable air / fuel ratio A than the hydrogen engine.

[0012] The aftertreatment system warming strategy, in the case of spark ignition internal combustion engines, includes countermeasures such as ignition delay and air / fuel mixture enrichment. For a hydrogen-fueled internal combustion engine the same countermeasures do not bring benefits. In particular, as easily demonstrated experimentally, ignition delay increases the exhaust gas temperature but worsens the specific hydrogen consumption. Furthermore, mixture enrichment, if on one hand implies a large effect on the increase of exhaust gas temperature, on the other hand does not increase the total thermal power available to warm the ATS system, since the flow rate of the exhaust gases is reduced. Furthermore, mixture enrichment generates a huge increase in NOx production at the engine outlet and a strong deterioration of the specific fuel consumption.

[0013] There is therefore a need to define a heating control strategy for an exhaust gas aftertreatment system that is free from the above-mentioned drawbacks.

[0014] Summary of the invention

[0015] In order to substantially solve the technical problems highlighted above, an object of the present invention is a heating control strategy of an exhaust gas after-treatment system of an internal combustion engine, the strategy being based on increasing the concentration of hydrogen in the exhaust by misfiring the hydrogen / air mixture trapped inside at least one cylinder of the internal combustion engine. This causes the accelerated heating of the exhaust gas selective catalytic reduction (SCR) system thanks to the exothermic process generated by the oxidation of hydrogen on an oxidation catalyst (OC) located upstream of the SCR catalyst. Therefore, according to the present invention, a heating control strategy of an exhaust gas aftertreatment system of an internal combustion engine is provided having the characteristics set forth in the independent claim, attached to the present description.

[0016] Further preferred and / or particularly advantageous embodiments of the invention are described according to the characteristics set forth in the attached dependent claims.

[0017] Brief description of the drawings The invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of its implementation, in which:

[0018] - figure 1 schematically illustrates an internal combustion engine to which the control strategy according to the present invention is applied, and

[0019] - figure 2 is a flow chart of the heating control strategy of an exhaust gas after-treatment system of the internal combustion engine of figure 1, according to a preferred embodiment of the present invention.

[0020] Detailed description

[0021] By way of example and not limitation, the heating control strategy of an exhaust gas aftertreatment system of an internal combustion engine will now be described with reference to the above figures. It should be noted that the control strategy is particularly suitable for internal combustion engines with spark ignition and fueled by hydrogen. However, the same strategy can also be used in the presence of other fuels, such as petrol or methane, in a way that is obvious to a technician in the sector.

[0022] An automotive system 100, as illustrated schematically in Figure 1 (in this figure, many known components have been omitted to lighten the figure), includes an internal combustion engine 110 having an engine block 120 defining at least one cylinder 125, 125' having a piston coupled to rotate a crankshaft. The cylinder head cooperates with the piston to define a combustion chamber. A mixture of fuel (preferably hydrogen) and air is disposed in the combustion chamber and ignited, resulting in combustion and expansion of the exhaust gases which causes the reciprocating motion of the piston. The fuel is supplied by at least one fuel injector and the air through at least one intake port. The ignition of the air / fuel mixture is controlled at the required time by an ignition device (spark plug). Each of the cylinders 125, 125' has at least two valves, operated by a camshaft that rotates in synchrony with the crankshaft. The valves selectively allow air to enter the combustion chamber from the intake port and alternately allow exhaust gases to exit through an exhaust port.

[0023] Air may be distributed to the air intake port(s) through an intake manifold 200. An air intake duct may supply air from the ambient environment to the intake manifold. In other embodiments, a throttle body may be provided to regulate the air flow into the manifold 200. In still other embodiments, a forced air system may be provided such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250. The rotation of the compressor 240 increases the pressure and temperature of the air in the manifold 200. An intercooler, disposed in the intake manifold, may reduce the temperature of the air. Turbine 250 rotates to receive exhaust gases from an exhaust manifold 225 which directs the exhaust gases out of the exhaust ports and through a series of vanes before expanding through turbine 250. The exhaust gases exit turbine 250 and are directed into an exhaust system 270.

[0024] The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust gas aftertreatment devices 280, 290. The aftertreatment devices may be any device configured to modify the composition of the exhaust gas. Some examples of aftertreatment devices include, but are not limited to, oxidizing catalytic (OC) converters 280. Other aftertreatment devices include selective catalytic reduction (SCR) systems 290. Other embodiments may include an exhaust gas recirculation (EGR) system coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system may include an EGR cooler to reduce the temperature of the exhaust gas in the EGR system. An EGR valve regulates a flow of exhaust gas into the EGR system.

[0025] The automotive system 100 may further include an electronic control unit (ECU) in communication with one or more sensors and / or devices associated with the internal combustion engine 110 and provided with a data carrier. The ECU may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the internal combustion engine 110. The sensors include, but are not limited to, a mass air flow and temperature sensor, a manifold pressure and temperature sensor, a combustion pressure sensor, coolant and oil level and temperature sensors, a fuel rail pressure sensor, a cam position sensor, a crank position sensor. In particular, the exhaust system 270 may include exhaust pressure and temperature sensors 300, 310, 320, nitrogen oxide concentration, air / fuel ratio sensors. Additionally, the ECU can generate output signals to various control devices that are designed to control the operation of the ICE 110, including, but not limited to, the fuel injectors, throttle body, and EGR valve.

[0026] The new heating control strategy of an exhaust gas aftertreatment system of an internal combustion engine, according to the present invention, has as its objective the reduction of the heating times, in particular, of the exhaust gas selective catalytic reduction system 290. The idea behind the invention originates from the consideration that a Diesel engine provides a higher thermal power to the exhaust gas aftertreatment system (ATS) than the hydrogen engine. It is therefore possible to calculate an exhaust gas temperature difference (hydrogen engine vs. Diesel engine) necessary to have the same thermal power.

[0027] This thermal power can be obtained by having a controlled level of hydrogen available which is oxidized in the oxidizing catalytic converter 280. The controlled level of hydrogen is obtained, by means of the control strategy, by deactivating the ignition devices of one or more cylinders 125' and therefore the respective combustion. The hydrogen injected into these cylinders, therefore, does not burn and is transferred directly into the exhaust system 270.

[0028] In this way, countermeasures such as ignition delay and enrichment of the air / fuel mixture can be avoided which, as already mentioned, imply an increase in nitrogen oxides (NOx) and, in the case of engines powered by petrol or methane, secondary emissions (unburned hydrocarbons). On the contrary, since there is no enrichment of the mixture, a reduction in fuel consumption is also obtained.

[0029] Depending on the engine operating point, the maximum required temperature difference across the oxidizing catalytic converter is about 250°C at low loads and decreases to 0°C for high load and high speed.

[0030] To achieve the maximum required exothermic reaction with respect to the oxidizing catalytic converter, the maximum amount of hydrogen required is about 3% of the total amount of hydrogen, as confirmed by experimental data.

[0031] Therefore, and with particular reference to figure 2, the control strategy according to the present invention is based on the following steps:

[0032] - activate the strategy S100,

[0033] - perform a first check SI 10: is the temperature of the selective catalytic reduction system 290 of the exhaust gas the target one? If yes, terminate the control strategy S190, otherwise, if the temperature is lower than the target value, continue the control strategy,

[0034] - perform a second check S120: is the temperature of the oxidizing catalytic converter 280 above a predetermined minimum threshold? If not, terminate S190 the control strategy, otherwise continue the control strategy,

[0035] - perform a third check S130: is there torque reserve available? If not, terminate S190 the control strategy, otherwise continue the control strategy,

[0036] - deactivate S140 the ignition device of at least one 125' cylinder. The number of 125' cylinders on which to deactivate the ignition must be calibrated experimentally. Advantageously, the deactivated 125' cylinders will vary periodically over time, i.e. they will not always be the same, to avoid excessive cooling of specific cylinders,

[0037] - increase S150 the load on the remaining 125' cylinders to deliver the required torque,

[0038] - optimize S160 the maximum injection of fuel, e.g. hydrogen, into the deactivated cylinders to maximize the exothermic reaction through the oxidizing catalytic converter 280. Of course, the strategy must comply with the safety and protection requirements of the entire exhaust gas after- treatment system and therefore the exhaust gas temperature, due to the exothermic reaction, must not exceed a predetermined maximum temperature threshold,

[0039] - monitor S170 the temperature at the inlet and outlet of the oxidizing catalytic converter 280 to optimize S160 the injection of fuel, for example hydrogen, on the at least one deactivated cylinder, with closed- loop control (as illustrated in figure 2),

[0040] - monitor S180 the temperature at the SCR of the exhaust gas selective catalytic reduction system 290 and reactivate S100 the control strategy.

[0041] Advantageously, at the end of the control strategy it is advisable to run, in the cylinders where the ignition devices have been deactivated, an adequate number of cycles without fuel injections and combustions to avoid combustion anomalies once the normal ignition and combustion mode has been restored.

[0042] Therefore, this control strategy is dedicated to reducing the warmup times of an exhaust gas aftertreatment system which preferably comprises at least one oxidizing catalytic converter 280 and an exhaust gas selective catalytic reduction system 290. In addition to substantially reducing the warm-up time of the exhaust gas selective catalytic reduction system 290, this control strategy allows for lower fuel consumption compared to traditional strategies (ignition delay, air / fuel mixture enrichment).

[0043] Therefore, the control strategy according to the present invention consists in increasing the concentration of hydrogen at the exhaust by deactivating the ignition of the air / hydrogen mixture trapped inside a cylinder.

[0044] Deactivating the ignition of at least one cylinder allows to obtain unburned hydrogen at the oxidizing catalytic converter 280, where it oxidizes generating heat. The generated heat is transmitted to the exhaust gas selective catalytic reduction system 290, for its rapid heating.

[0045] The amount of unburned hydrogen is proportional to the target temperature difference to be achieved across the oxidizing catalytic converter 280.

[0046] The control of the temperature at the outlet of the oxidizing catalytic converter 280 is implemented by calculating a required misfire rate: in other words, the percentage between a number of misfire events X compared to the number of combustion cycles Y as a function of the load per cylinder pair.

[0047] The missing torque as a function of the misfire rate is calculated and managed correctly with respect to the requested torque: if the torque demand increases, the maximum misfire rate decreases. It should be noted that, in this condition, also the required misfire rate would be reduced due to the higher exhaust gas temperature and their equally higher flow rate.

[0048] Advantageously, this control strategy can be used in combination with an additional control strategy based on a delay in the ignition of the ignition devices.

[0049] In conclusion, the present control strategy allows to achieve several advantages: - reduced and compliant warm-up times of the exhaust gas after- treatment system of an internal combustion engine, preferably fueled with hydrogen;

[0050] - low emissions of nitrogen oxides during cold start; - optimization of fuel consumption during cold start;

[0051] - greater robustness against combustion anomalies that could arise using the known strategy of ignition delay, in case of excessive delays.

[0052] In addition to the embodiment of the invention, as described above, it is to be understood that numerous other variations exist. It is also to be understood that such embodiments are exemplary only and do not limit the scope of the invention, its applications, or its possible configurations. Conversely, while the above description enables the skilled craftsman to carry out the present invention at least according to one exemplary embodiment thereof, it should be understood that many variations of the described components are possible without departing from the scope of the invention, as defined in the appended claims, which are construed literally and / or according to their legal equivalents.

Claims

C LA I M S1. Heating control strategy of an exhaust gas aftertreatment system for a spark-ignition internal combustion engine (110), in which- the internal combustion engine includes a plurality of cylinders (125, 125'), each of which is equipped with a device for igniting the a ir / fuel mixture, and- the exhaust gas after-treatment system includes at least one oxidizing catalytic converter (280) and a selective catalytic reduction system (290) of exhaust gases, the control strategy including the following phases:- activating the control strategy,- if the temperature of the selective catalytic reduction system (290) of exhaust gases is equal to the target temperature, ending the control strategy, otherwise, if the temperature is lower than the target value, continuing the control strategy,- if the temperature of the oxidizing catalytic converter (280) is above a predetermined minimum threshold, continuing the control strategy, otherwise ending the control strategy,- if there is torque reserve available, continuing the control strategy, otherwise ending the control strategy,- deactivating the ignition device of at least one cylinder (125'),- increasing the load on the remaining cylinders (125) to deliver the required torque,- optimizing a maximum fuel injection into the deactivated cylinders to maximize an exothermic reaction through the oxidizing catalytic converter (280),- monitoring the temperature at the inlet and outlet of the oxidizing catalytic converter (280) to optimize fuel injection on at least one deactivated cylinder, with closed loop control,- monitoring the temperature of the selective catalytic reduction system (290) of exhaust gases and reactivating the control strategy.

2. Control strategy according to claim 1, wherein the fuel is hydrogen.

3. Control strategy according to claim 1 or 2, wherein the cylinders (125') on which the ignition device is deactivated change over time.

4. Control strategy according to any of the preceding claims, wherein the temperature of the exhaust gases, due to the exothermic reaction, does not exceed a predetermined maximum temperature threshold.

5. Control strategy according to any of the preceding claims, wherein, at the end of the control strategy itself, a plurality of cycles without fuel injections and combustions are carried out in the cylinders in which the ignition devices have been deactivated.

6. Control strategy according to any of the preceding claims, wherein, the control of the temperature at the outlet of the oxidizing catalytic converter (280) is implemented by calculating a percentage of misfire events (X) with respect to a number of combustion cycles (Y) depending on the load over a pair of cylinders.

7. The control strategy according to claim 6, wherein if the torque demand increases, the percentage of misfire events (X) relative to a number of combustion cycles (Y) decreases.

8. Control strategy according to any of the preceding claims, suitable for use in combination with a further control strategy based on an ignition delay of the ignition devices.

Images