JP2008025438A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device, improving regeneration efficiency of NOx storage reduction catalyst, and preventing degradation of fuel consumption. <P>SOLUTION: This exhaust emission control device includes: an NOx storage reduction catalyst 30 provided in the midway of an exhaust pipe 11 for circulating exhaust emission 9 from an engine 1; an oxidation catalyst 32 provided on the upstream side of the NOx storage reduction catalyst 30; a fuel-adding means 34 for adding fuel into the exhaust emission 9 on the upstream side from the oxidation catalyst 32; and a reduction agent-adding means 39 for adding a reduction agent into the exhaust emission 9 between the oxidation catalyst 32 and the NOx storage reduction catalyst 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device applied to an engine.

  Conventionally, exhaust purification is carried out with an exhaust purification catalyst installed in the middle of the exhaust pipe. As this type of exhaust purification catalyst, NOx in exhaust gas is oxidized when the exhaust air-fuel ratio is lean. NOx occlusion reduction catalyst which has the property of temporarily storing in the form of nitrate and decomposing and releasing NOx through the inclusion of unburned hydrocarbons and CO etc. when the oxygen concentration in the exhaust gas is reduced. It has been known.

  In this NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded. Therefore, the oxygen concentration of the exhaust gas that periodically flows into the NOx occlusion reduction catalyst is reduced. It is necessary to reduce and release NOx by decomposition.

  For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the oxygen concentration in the exhaust gas and unburned carbonization in the exhaust gas. Although it is possible to promote the decomposition and release of NOx by increasing reducing components such as hydrogen and CO, it is difficult to operate the engine at a rich air-fuel ratio when the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine. It is.

For this reason, fuel addition means is installed in the exhaust pipe upstream of the NOx storage reduction catalyst, and fuel (HC) is injected and added into the exhaust gas by the fuel addition means, so that this added fuel is used as a reducing agent. By reacting with O ₂ on the NOx storage reduction catalyst, the O ₂ concentration in the exhaust gas is lowered (see, for example, Patent Document 1).

  Even if the NOx occlusion reduction catalyst and the fuel addition means are provided, if the catalyst temperature is so low that the exhaust temperature falls below 200 ° C. due to running of the vehicle on the congested road, the fuel on the catalyst Since the oxidation reaction of NOx does not occur and the NOx storage reduction catalyst cannot be regenerated and controlled by adding fuel, it is considered to provide an oxidation catalyst upstream of the NOx storage reduction catalyst to increase the temperature by burning the fuel. .

  In the following, a specific description will be given of a diesel engine exhaust pipe provided with a NOx storage reduction catalyst, an oxidation catalyst, and fuel addition means.

  Here, the diesel engine will be described first. As shown in FIG. 9, the diesel engine 1 is provided with a turbocharger 2, and the intake air 4 guided from the air cleaner 3 is passed through the intake pipe 5 to the compressor of the turbocharger 2. The intake air 4 sent to 2a and pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7 so that the diesel engine 1 It is distributed to each cylinder 8 (FIG. 9 illustrates the case of inline 6 cylinders).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

  Further, the exhaust manifold 10 and the intake pipe 5 connected to the intake manifold 7 are connected by an EGR pipe 12, and a part of the exhaust gas 9 extracted from the exhaust manifold 10 is water-cooled EGR cooler 13 and EGR. The exhaust gas 9 is recirculated to the intake pipe 5 through the valve 14 and the combustion of the fuel in each cylinder 8 is suppressed by the exhaust gas 9 recirculated from the exhaust side to the intake side to lower the combustion temperature. Thus, the generation of NOx can be reduced.

  On the other hand, the NOx occlusion reduction catalyst 15 is provided in the middle of the exhaust pipe 11 via a casing 16, and an oxidation for increasing the temperature of the NOx occlusion reduction catalyst 15 is provided upstream of the NOx occlusion reduction catalyst 15 in the casing 16. A catalyst 17 is equipped.

  A fuel addition means 19 connected to a fuel tank (not shown) by an addition fuel line 18 is provided on the inlet side of the oxidation catalyst 17 in the exhaust pipe 11, and the fuel addition means 19 is connected to the addition fuel line. The fuel in the fuel tank can be injected into the inlet side of the oxidation catalyst 17 through the electromagnetic valve 21 and the injection nozzle 22 by driving the additive fuel pump 20 installed in the middle of the engine 18.

  Further, temperature sensors 23 and 24 for detecting the exhaust gas temperature are provided on the entry side of the oxidation catalyst 17 and the exit side of the NOx storage reduction catalyst 15, and the temperature signals from the temperature sensors 23 and 24 are supplied to the control device 25. The addition of fuel is controlled in accordance with the exhaust temperature on the inlet side of the oxidation catalyst 17 and the exhaust temperature on the outlet side of the NOx storage reduction catalyst 15.

Thus, even when the temperature of the catalyst is such that the exhaust temperature falls below 200 ° C. due to traveling of the vehicle on a congested road, the fuel is added to the oxidation catalyst 17 by adding fuel as shown in FIGS. Thus, the temperature is increased by combustion, and oxygen is consumed, so that the regeneration control of the NOx storage reduction catalyst 15 is facilitated.
JP 2000-282850 A

  However, when the oxidation catalyst 17 is installed in the preceding stage of the NOx occlusion reduction catalyst 15 and the fuel is burned as described above, the inflow amount of the fuel as a reducing agent to the NOx occlusion reduction catalyst 15 is reduced as shown in FIG. There has been a problem that the regeneration efficiency of the NOx storage reduction catalyst 15 is lowered. Further, if excessive fuel is added in consideration of the combustion of fuel by the oxidation catalyst 17, there is a problem that fuel efficiency is remarkably deteriorated.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust purification device that improves the regeneration efficiency of the NOx storage reduction catalyst and prevents the deterioration of fuel consumption.

  The present invention relates to a NOx occlusion reduction catalyst equipped in the middle of an exhaust pipe through which exhaust gas from an engine flows, an oxidation catalyst equipped upstream of the NOx occlusion reduction catalyst, and an exhaust gas upstream of the oxidation catalyst. An exhaust emission control device comprising fuel addition means 19 for adding fuel to the gas, and reducing agent addition means for adding a reducing agent to the exhaust gas between the oxidation catalyst and the NOx storage reduction catalyst. , Related to

  In the present invention, the reducing agent addition means preferably uses a reducing agent as a fuel.

  Thus, in this way, even if the fuel is burned by the oxidation catalyst and the inflow amount of the fuel to the NOx storage oxidation catalyst is reduced, the reducing agent is directly added to the NOx storage reduction catalyst by the reducing agent addition means. In addition to improving the regeneration efficiency of the NOx storage reduction catalyst, it is possible to suppress the addition of excessive fuel from the fuel addition means and to prevent the deterioration of fuel consumption.

  Further, if the reducing agent addition means uses the reducing agent as fuel, the fuel added by the fuel addition means and the reducing agent added by the reducing agent addition means can be the same fuel and can be supplied from the same supply source. The addition amount of the agent can be easily calculated, the regeneration efficiency of the NOx storage reduction catalyst can be appropriately performed, and the manufacturing cost can be greatly reduced.

  According to the exhaust gas purification apparatus of the present invention described above, various excellent effects can be achieved in that the reducing agent addition means can improve the regeneration efficiency of the NOx occlusion reduction catalyst and prevent deterioration of fuel consumption.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIGS. 1-6 shows the 1st example of the form which implements this invention, and the part which attached | subjected the code | symbol same as FIG. 9 in the figure represents the same thing.

  As shown in FIG. 1, the exhaust purification apparatus of the first example of the embodiment of the present invention oxidizes NOx in the exhaust gas 9 in the middle of the exhaust pipe 11 through which the exhaust gas 9 circulates when the exhaust air-fuel ratio is lean. A NOx occlusion reduction catalyst 30 that is temporarily occluded in the form of nitrate and decomposes and releases NOx by the intervention of a reducing agent when the oxygen concentration in the exhaust gas 9 is lowered is provided via a casing 31.

  In addition, an oxidation catalyst 32 that burns fuel and raises the temperature is provided in the front stage (upstream side) of the NOx storage reduction catalyst 30 in the casing 31.

  Here, the NOx occlusion reduction catalyst 30 may be the same as platinum / barium, alumina catalyst, iridium / platinum / barium / alumina catalyst already known as NOx occlusion reduction catalyst. In the example, the composition may specialize in the properties of NOx storage / release. The oxidation catalyst 32 may have a structure of a noble metal such as platinum, palladium, rhodium and a carrier such as alumina, zeolite, titania, silica, zirconia, etc. in a honeycomb structure such as stainless steel or cordierite.

  A fuel addition means 34 connected to a fuel tank (not shown) by an addition fuel line 33 is provided on the inlet side of the oxidation catalyst 32 in the exhaust pipe 11, and the fuel addition means 34 is connected to the addition fuel line. The fuel in the fuel tank can be injected into the inlet side of the oxidation catalyst 32 through the first electromagnetic valve 36 and the first injection nozzle 37 by driving the added fuel pump 35 provided in the middle of the engine 33.

  Further, a reducing agent addition means 39 connected between the oxidation catalyst 32 and the NOx occlusion reduction catalyst 30 in the exhaust pipe 11 by an addition reducing agent line 38 is provided with a reducing agent supply source (not shown). The reducing agent addition means 39 drives the additive reducing agent pump 40 installed in the middle of the additive reducing agent line 38 to supply the reducing agent in the additive reducing agent line 38 via the second solenoid valve 41 and the second injection nozzle 42. Injection can be performed between the outlet side of the oxidation catalyst 32 and the inlet side of the NOx storage reduction catalyst 30.

  Here, the supply source may be shared with the fuel tank of the fuel adding means 34 so that the reducing agent of the reducing agent adding means 39 is the same as the fuel of the fuel adding means 34. Further, the fuel tank is made common so that the fuel of the fuel adding means 34 and / or the reducing agent of the reducing agent adding means 39 is the same as the fuel injected from the fuel injection device 8a to each cylinder 8 of the diesel engine 1. Also good.

  A first temperature sensor 43 that detects the exhaust temperature is provided on the entry side of the oxidation catalyst 32, and a second temperature sensor 44 that detects the exhaust temperature is provided on the exit side of the NOx storage reduction catalyst 30. The first temperature sensor 43 and the second temperature sensor 44 are connected to a control device (control means) 45 to input a temperature signal.

  The control device 45 is connected to an accelerator sensor (load sensor) S1 for detecting the accelerator opening as a load of the diesel engine 1 and a rotation sensor S2 for detecting the rotational speed of the diesel engine 1, and from the accelerator sensor S1. The load signal and the rotation speed signal from the rotation sensor S2 are received, and the exhaust temperature on the inlet side of the oxidation catalyst 32, the exhaust temperature on the outlet side of the NOx storage reduction catalyst 30, the load and the rotation speed of the diesel engine 1 are determined. Accordingly, the addition of fuel by the fuel addition means 34 and the addition of the reducing agent by the reducing agent addition means 39 are controlled. As shown in FIG. 1, the control device 45 outputs a fuel injection signal for instructing the fuel injection timing and the injection amount toward the fuel injection device 8a for injecting fuel into each cylinder of the diesel engine 1. Also good.

  Hereinafter, the operation of the first example of the embodiment of the present invention will be described.

  When the fuel is added by the fuel addition means 34 as shown in FIG. 2 in a state where the temperature of the NOx occlusion reduction catalyst 30 is low such that the exhaust temperature falls below 200 ° C. due to traveling of the vehicle on the congested road, the oxidation catalyst 32 is added. Then, the temperature of the fuel is combusted to raise the temperature (FIG. 3), and at the same time, the reducing agent is added to the upstream side of the NOx storage reduction catalyst 30 by the reducing agent addition means 39 (FIG. 4). The inflow amount of the reducing agent is set to the optimum amount (FIG. 5).

  Here, the amount of fuel added by the fuel adding means 34 is calculated by a predetermined function process or map process by the control device 45 according to the temperature of the exhaust gas 9, the load of the diesel engine 1 and the rotational speed. The addition amount of the reducing agent by the reducing agent addition means 39 is calculated by the controller 45 by a predetermined function process or map process according to the previous fuel addition quantity, the temperature of the exhaust gas 9, the load or the rotational speed of the diesel engine. The

  Thus, according to the first example of the embodiment, even if the fuel added by the fuel addition means 34 is burned by the oxidation catalyst 32 and the inflow amount of fuel to the NOx storage reduction catalyst 30 is reduced, the reducing agent addition Since the reducing agent is directly added to the NOx occlusion reduction catalyst 30 by the means 39, the regeneration efficiency of the NOx occlusion reduction catalyst 30 is improved and the addition of excessive fuel from the fuel addition means 34 is suppressed to prevent deterioration of fuel consumption. can do.

  Further, if the reducing agent adding means 39 uses the reducing agent as fuel, the fuel added by the fuel adding means 34 and the reducing agent added by the reducing agent adding means 39 can be made the same fuel and supplied from the same fuel tank. The addition amount of the fuel and the reducing agent can be easily calculated, the regeneration efficiency of the NOx storage reduction catalyst 30 can be appropriately performed, and the manufacturing cost can be greatly reduced.

  In fact, according to the results of experiments conducted by the present inventor, as shown in the graph of FIG. 6, in the example in which the reducing agent addition means 39 is provided in the embodiment, the NOx reduction rate (regeneration efficiency) is It is apparent that the exhaust purification device without the oxidation catalyst 32 is improved by about 10% or more, and the exhaust purification device with the oxidation catalyst 32 is also improved. The experimental conditions here are based on a predetermined examination mode.

  FIG. 7 shows a second example of the embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same parts.

  As shown in FIG. 7, the exhaust purification apparatus of the second example of the embodiment of the present invention includes a NOx occlusion reduction catalyst 30 equipped via a casing 50 in the middle of an exhaust pipe 11 through which exhaust gas 9 circulates, and NOx occlusion. The oxidation catalyst 32 is provided via another casing 51 so as to be positioned on the upstream side of the reduction catalyst 30. Here, the NOx storage reduction catalyst 30 and the oxidation catalyst 32 are substantially the same as in the first example.

  The exhaust pipe 11 is provided on the inlet side of the oxidation catalyst 32 with a fuel addition means 34 similar to that in the first example connected to the fuel tank (not shown) by the addition fuel line 33, and in the exhaust pipe 11. Between the oxidation catalyst 32 and the NOx occlusion reduction catalyst 30, there is provided a reducing agent addition means 39 similar to that in the first example connected to a reducing agent supply source (not shown) by an addition reducing agent line 38. Yes. Here, the supply source may be shared with the fuel tank of the fuel adding means 34 so that the reducing agent of the reducing agent adding means 39 is the same as the fuel of the fuel adding means 34. Further, the fuel tank is made common so that the fuel of the fuel adding means 34 and / or the reducing agent of the reducing agent adding means 39 is the same as the fuel injected from the fuel injection device 8a to each cylinder 8 of the diesel engine 1. Also good.

  A first temperature sensor 52 and a second temperature sensor 53 for detecting the exhaust temperature are provided on the entry side and the exit side of the oxidation catalyst 32, and on the entry side and the exit side of the NOx storage reduction catalyst 30, A third temperature sensor 54 and a fourth temperature sensor 55 for detecting the exhaust temperature are provided. The first temperature sensor 52, the second temperature sensor 53, the third temperature sensor 54, and the fourth temperature sensor 55 are controlled by a control device (control). Means) 56 is connected to input a temperature signal.

  The control device 56 is connected to the accelerator sensor (load sensor) S1 and the rotation sensor S2 as in the first example, and receives the load signal from the accelerator sensor S1 and the rotation speed signal from the rotation sensor S2. Depending on the exhaust temperature on both sides of the oxidation catalyst 32, the exhaust temperature on both sides of the NOx storage reduction catalyst 30, the situation of the diesel engine 1, the addition of fuel by the fuel addition means 34, and the reducing agent by the reducing agent addition means 39 The addition of is controlled.

  Hereinafter, the operation of the second example of the embodiment of the present invention will be described.

  When fuel is added by the fuel addition means 34 in a state where the temperature of the NOx occlusion reduction catalyst 30 such that the exhaust temperature falls below 200 ° C. due to traveling of a vehicle on a congested road is substantially the same as in the first example, Fuel is burned by the oxidation catalyst 32 and the temperature is raised. At the same time, a reducing agent is added to the upstream side of the NOx storage reduction catalyst 30 by the reducing agent addition means 39 to prevent a shortage of fuel for reduction with respect to the NO storage reduction catalyst.

  Here, the amount of fuel added by the fuel adding means 34 is calculated by a predetermined function process or map process by the control means in accordance with the temperature of the exhaust gas 9, the engine load and the rotational speed, and further, the reducing agent addition The amount of reducing agent added by the means 39 is calculated by predetermined function processing or map processing by the control means in accordance with the amount of fuel added in advance, the temperature of the exhaust gas 9, the engine load and the rotational speed.

  Thus, according to the second example of the embodiment, the same operational effects as the first example can be obtained. Further, since the first temperature sensor 52, the second temperature sensor 53, the third temperature sensor 54, and the fourth temperature sensor 55 are provided, the temperature state of the exhaust gas 9 is examined in detail, and the amount of fuel added and / or the reducing agent The addition amount is precisely controlled, and as a result, the regeneration efficiency of the NOx occlusion reduction catalyst 30 is further improved, and addition of excess fuel from the fuel addition means 34 is suppressed, so that deterioration of fuel consumption is suitably prevented. Can do.

  FIG. 8 shows a third example of the embodiment for carrying out the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same parts.

  The exhaust purification apparatus of the third example of the embodiment of the present invention includes a NOx occlusion reduction catalyst 30 equipped via a casing 50 in the middle of the exhaust pipe 11 through which the exhaust gas 9 flows, as shown in FIG. An oxidation catalyst 32 is provided on the upstream side of the NOx storage reduction catalyst 30 via another casing 51 so as to be close to the turbine 2b of the turbocharger 2. Here, the NOx storage reduction catalyst 30 and the oxidation catalyst 32 are substantially the same as in the first example.

  Then, in the middle of the exhaust pipe 11 a from the exhaust manifold 10 to the turbine 2 b of the turbocharger 2, a second fuel line 33 is connected to a fuel tank (not shown) so as to be positioned on the entry side of the oxidation catalyst 32. A fuel addition means 34 similar to that of the example is provided, and an addition reductant line is provided between the oxidation catalyst 32 and the NOx occlusion reduction catalyst 30 in the exhaust pipe 11 and a reductant supply source (not shown). The same reducing agent addition means 39 as that of the first example connected by 38 is provided. Here, the supply source may be shared with the fuel tank of the fuel adding means 34 so that the reducing agent of the reducing agent adding means 39 is the same as the fuel of the fuel adding means 34. Further, the fuel tank is made common so that the fuel of the fuel adding means 34 and / or the reducing agent of the reducing agent adding means 39 is the same as the fuel injected from the fuel injection device 8a to each cylinder 8 of the diesel engine 1. Also good.

  A first temperature sensor 52 and a second temperature sensor 53 for detecting the exhaust temperature are provided on the entry side and the exit side of the oxidation catalyst 32, and on the entry side and the exit side of the NOx storage reduction catalyst 30, A third temperature sensor 54 and a fourth temperature sensor 55 for detecting the exhaust temperature are provided. The first temperature sensor 52, the second temperature sensor 53, the third temperature sensor 54, and the fourth temperature sensor 55 are controlled by a control device (control). Means) 56 is connected to input a temperature signal.

  The control device 56 is connected to the accelerator sensor (load sensor) S1 and the rotation sensor S2 as in the first example, and receives the load signal from the accelerator sensor S1 and the rotation speed signal from the rotation sensor S2. Depending on the exhaust temperature on both sides of the oxidation catalyst 32, the exhaust temperature on both sides of the NOx storage reduction catalyst 30, the situation of the diesel engine 1, the addition of fuel by the fuel addition means 34, and the reducing agent by the reducing agent addition means 39 The addition of is controlled.

  Hereinafter, the operation of the third example of the embodiment of the present invention will be described.

  When fuel is added by the fuel addition means 34 in a state where the temperature of the NOx occlusion reduction catalyst 30 such that the exhaust temperature falls below 200 ° C. due to traveling of a vehicle on a congested road is substantially the same as in the first example, Fuel is burned by the oxidation catalyst 32 and the temperature is raised. At the same time, a reducing agent is added to the upstream side of the NOx storage reduction catalyst 30 by the reducing agent addition means 39 to prevent a shortage of fuel for reduction with respect to the NO storage reduction catalyst.

  Here, the amount of fuel added by the fuel adding means 34 is calculated by a predetermined function process or map process by the control means in accordance with the temperature of the exhaust gas 9, the engine load and the rotational speed, and further, the reducing agent addition The addition amount of the reducing agent by the means 39 is calculated by a predetermined function process or map process by the control means in accordance with the fuel addition quantity, the temperature of the exhaust gas 9, the engine load and the rotational speed.

  Thus, according to the third example of the embodiment, the same operational effects as the first example and the second example can be obtained. Further, since the fuel addition means 34 is located upstream of the turbine 2b of the turbocharger 2, the fuel is evenly diffused by the turbine 2b, the excessive fuel addition from the fuel addition means 34 is suppressed, and the fuel consumption is deteriorated. Can be suitably prevented.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and the configuration of the fuel addition means and the reducing agent addition means is particularly limited as long as the fuel and the reducing agent can be added appropriately. However, the reducing agent is preferably the same as the fuel of the fuel adding means, but it may be a separate line, and other various modifications can be made without departing from the scope of the present invention. is there.

It is the schematic which shows the 1st example of the form which implements this invention. It is the schematic which shows the state which added the fuel to the upstream of the oxidation catalyst from the fuel addition means. It is the schematic which shows the state which a fuel burns with an oxidation catalyst and heats up. It is the schematic which shows the state which added the reducing agent to the upstream of the NOx storage reduction catalyst from the reducing agent addition means. It is the schematic which shows the state which has ensured sufficient reducing agent for the NOx storage reduction catalyst. It is a graph which shows the comparison of NOx reduction rate. It is the schematic which shows the 2nd example of the form which implements this invention. It is the schematic which shows the 3rd example of the embodiment which implements this invention. 1 is a schematic view showing a conventional exhaust purification device provided with a NOx storage reduction catalyst, an oxidation catalyst, and fuel addition means. It is the schematic which shows the state which added the fuel to the upstream of the oxidation catalyst from the fuel addition means. It is the schematic which shows the state which a fuel burns with an oxidation catalyst and heats up. It is the schematic which shows the state in which fuel is insufficient with a NOx storage reduction catalyst by combustion of the fuel with an oxidation catalyst.

Explanation of symbols

1 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 9 Exhaust gas 11 Exhaust pipe 11a Exhaust pipe 30 NOx occlusion reduction catalyst 32 NOx occlusion oxidation catalyst 32 Oxidation catalyst 34 Fuel addition means 39 Reductant addition means

Claims (2)

  NOx occlusion reduction catalyst installed in the middle of an exhaust pipe through which exhaust gas from the engine circulates, an oxidation catalyst installed upstream from the NOx occlusion reduction catalyst, and fuel in exhaust gas upstream from the oxidation catalyst An exhaust emission control device comprising: a fuel addition means for adding a reducing agent; and a reducing agent addition means for adding a reducing agent to the exhaust gas between the oxidation catalyst and the NOx storage reduction catalyst.   2. The exhaust emission control device according to claim 1, wherein the reducing agent adding means uses a reducing agent as fuel.

Images