JP2017203403A - Combustion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rich combustion method that can eliminate a need of DOC for oil dilution by fuel and fuel decomposition, and to provide a combustion method in PM regeneration.SOLUTION: An exhaust gas aftertreatment device 20 including a NOx occlusion reduction type catalyst and a filter is connected to an exhaust system of an engine 10, where post injection is performed for at least one cylinder 11c of a plurality of cylinders of the engine 10 at a timing of 40-50° ATDC when conducting rich reduction by the NOx occlusion reduction type catalyst or PM regeneration of the filter.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a combustion method that performs rich combustion with rich air-fuel ratio at the time of rich reduction of LNT that purifies engine exhaust, and a combustion method that performs temperature increase by post injection during PM regeneration of DPF.

  As exhaust gas aftertreatment devices for diesel engines, DOC (Diesel Oxidation Catalyst), NOx storage reduction catalyst (LNT: Lean NOx Trap), DPF (Diesel Particulate Filter; filter), etc. are connected to the engine exhaust system. Thus, removing NOx and PM has been put into practical use.

  LNT is lean combustion with the air-fuel ratio in a lean state (normal combustion), and adsorbs or occludes NOx in the exhaust gas, and in rich combustion with the air-fuel ratio in a rich state, the adsorbed or occluded NOx is exhausted from the cylinder. It is reduced to harmless gas with HC, CO, etc. supplied inside. Further, the DPF collects PM in the exhaust gas, and when the amount of accumulated PM reaches a constant level, the DPF regenerates the DPF by supplying HC into the exhaust gas and burning the PM.

  Post injection that injects fuel near 120 ° ATDC (after top dead center) in the cylinder is used as HC supply means to the exhaust pipe for PM regeneration of DPF and rich reduction of LNT It has been. When HC is added to exhaust gas by in-cylinder post-injection, the post-injected fuel is decomposed into various HCs in the cylinder but partially mixed with engine oil to cause oil dilution.

  HC dosing to the exhaust pipe is also used to prevent oil dilution due to fuel generated in post injection. The fuel injected into the exhaust pipe is decomposed to some extent at the temperature in the exhaust pipe and converted to HC gas.

JP 2004-132262 A JP 2011-058440 A JP 2013-227899 A JP2013-136985A JP 2004-251188 A

  These post injections and exhaust pipe injections have the following problems.

  Since PM regeneration of DPF burns HC, DOC is required before DPF.

  In addition, LNT rich reduction requires DOC before LNT to reform HC to CO.

  In-cylinder post-injection at 120 ° ATDC has a problem that a part of the injected fuel is mixed with oil, resulting in fuel dilution of the oil.

  Exhaust pipe injection requires a certain amount of temperature and time for HC gasification. When gasification is incomplete and reaches the catalyst in the form of droplets, partial oxidation may occur and soot may be generated, resulting in catalyst clogging. Therefore, since a certain distance is required from the exhaust pipe injection valve to the catalyst, there are restrictions in layout. Therefore, when exhaust pipe injection is used, it is difficult to install the catalyst close to the engine such that the catalyst is disposed immediately below the exhaust pipe injection.

  Thus, both post injection and exhaust pipe injection, in which fuel is injected in the vicinity of 120 ° ATDC in the cylinder, is a concept of increasing the temperature by burning HC with DOC, and thus requires DOC. In the cylinder post-injection, part of the fuel traveled down the liner and dropped into the oil, resulting in fuel dilution of the oil. Exhaust pipe injection has been developed to avoid this, but there is a problem incompatible with the close layout of the catalyst.

  Accordingly, an object of the present invention is to solve at least one of the above-mentioned problems, and in particular, a rich that suppresses oil dilution by fuel, eliminates the need for DOC for fuel decomposition, and enables close arrangement. It is to provide a combustion method and a combustion method during PM regeneration.

  In order to achieve the above object, according to the present invention, an exhaust gas aftertreatment device including a NOx storage reduction catalyst and a filter is connected to an exhaust system of an engine to perform rich reduction of the NOx storage reduction catalyst or PM regeneration of the filter. In performing the combustion, post-injection is performed at a timing of 40-50 ° ATDC in at least one of the plurality of cylinders of the engine.

  In the present invention, when rich combustion or PM regeneration is performed, post-injection is performed on at least one cylinder at a timing of 40-50 ° ATDC, so that oil dilution by fuel is suppressed and DOC for fuel decomposition is reduced. It has an excellent effect of making it unnecessary and enabling close placement.

It is the schematic which shows one embodiment of this invention. In this invention, it is a figure which shows the fuel injection timing with respect to the crank angle at the time of performing rich combustion, and the change of a cylinder internal pressure and a heat release rate. In this invention, it is a figure which shows the opening / closing timing of the intake / exhaust valve | bulb at the time of performing rich combustion.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows an outline of a multi-cylinder diesel engine 10 when performing rich combustion and PM regeneration and an exhaust gas aftertreatment device 20 connected to an exhaust system of the engine 10 according to the present invention.

  In FIG. 1, a cylinder block 11 of the engine 10 is provided with a piston 14 that moves up and down connected to a crankshaft 12 and a connecting rod 13 for each cylinder 11c. The cylinder head 15 on the cylinder block 11 is provided with a fuel injector 16 for injecting fuel for each cylinder 11c, and an intake valve 17 and an exhaust valve 18. A glow plug 19 is provided in the vicinity of the fuel injector 16 for accelerating the ignition of fuel at the start.

  The fuel injector 16 is supplied with high-pressure fuel from a common rail (not shown), and the ECU (engine control unit) 30 controls the opening and closing of the fuel injector 16.

  The intake air to the engine 10 is boosted by the compressor of the turbocharger 22, passes through an intercooler (not shown) from the intake pipe 23, the intake air amount is adjusted by the intake throttle valve 25, and the intake manifold 26 passes through the intake valve 17. Then, the air is taken into the cylinder 11c. The exhaust from each cylinder 11c is exhausted to the exhaust manifold 27 via the exhaust valve 18, and then the turbocharger 22 turbo is driven through the exhaust pipe 28 as an exhaust system, and then the NOx storage reduction catalyst (LNT). It is introduced into an exhaust gas aftertreatment device 20 comprising a filter (DPF) or the like, where NOx and PM (particulate matter) in the exhaust gas are removed, and then exhausted to the atmosphere through an exhaust brake valve 29.

  A part of the exhaust gas from the exhaust manifold 27 is recirculated to the intake manifold 26 via an EGR pipe 31, an EGR cooler (not shown), and an EGR valve 32.

  The ECU 30 receives the detection value of the rotation sensor 34 that detects the rotation of the crankshaft 12 and the detection value of the λ sensor 35 provided in the exhaust pipe 28.

  The ECU 30 controls the fuel injector 16 based on the detection values of the rotation sensor 34 and the λ sensor 35 and other sensor information.

  In particular, the ECU 30 includes post injection means for performing in-cylinder post injection control during PM regeneration of the DPF or rich reduction of the LNT. The in-cylinder post injection by the post injection means is an estimated value when the PM accumulation amount in the DPF estimated based on the differential pressure before and after the DPF detected by a differential pressure sensor (not shown) reaches a set value or an estimated value. This is performed when the NOx occlusion amount in the LNT reaches a predetermined amount.

  At this time, the ECU 30 performs post injection at a crank angle of 40-50 ° of ATDC (after top dead center) of the piston 14 when performing post injection in at least one cylinder 11c among the plurality of cylinders 11c of the engine 10. .

  At this time, the ECU 30 closes the EGR valve 32 (EGR cut), reduces the opening of the intake throttle valve 25, reduces the intake amount based on the detection value of the λ sensor 35, and sets the injection timing by the fuel injector 16. Correct according to the intake air amount. At this time, it is preferable to correct the post-injection timing using the detection value of the rotation sensor 34 or the detection value of a cylinder pressure sensor (not shown).

  By post-injecting after the main combustion is completed with the intake air amount being small, the post-injected fuel burns in an atmosphere where the amount of oxygen in the cylinder is low and the temperature in the cylinder is low, resulting in a slow low-temperature combustion state. Soot and NOx emissions are suppressed, and carbon monoxide (CO) is mainly produced as an unburned gas component.

  As described above, rich combustion during PM regeneration or rich reduction becomes combustion in the expansion stroke, so most of the combustion energy becomes exhaust heat, the exhaust temperature rises, and the influence on torque is small. In other words, it becomes post-injection for raising the exhaust gas temperature and generating CO. The cylinders to be post-injected are not necessarily all cylinders, and only one cylinder or two cylinders are used, and the other cylinders can be normally controlled.

  In the pre- (Pre) to main (Main) injection in the rich combustion and PM regeneration, the injection timing and the injection amount are adjusted to have the same heat generation timing with the same torque as in the normal operation. By doing so, torque fluctuations and changes in combustion temperature can be suppressed.

  In the present embodiment, auxiliary means are used to reliably burn the post-injected fuel in the cylinder under the above conditions. As this auxiliary means, it is conceivable to energize the glow plug 19 to assist ignition of the spray. Further, when the exhaust valve 18 has a variable valve mechanism, as shown in FIG. 3, a method (internal EGR) in which the exhaust valve 18 is temporarily opened during the intake period of the intake valve 17 and exhaust gas is taken into the cylinder 11c. ) To increase the in-cylinder temperature to assist the ignition of the post injection.

  FIG. 2 shows the cylinder with respect to the crank angle before and after the compression top dead center (TDC) during normal combustion (during lean combustion) when NOx is not being reduced by LNT and when NOx is being reduced (during NOx reduction). The fuel injection timing in the injector to the inside, and the change in heat generation rate and combustion pressure are shown.

  When the reduction is not performed, pilot injection is performed by the fuel injector before the compression top dead center as shown by the dotted line, and main injection is performed at the compression top dead center by the dotted line. As shown, the in-cylinder pressure rises, and the normal heat generation rate also rises instantaneously, which becomes the driving force of the engine.

  When NOx reduction is performed, pre-injection (85-55 ° TDC) and pilot injection (55-25 ° TDC) are performed by the fuel injector before the top dead center as shown by the solid line. Main injection (15 ° BTDC to 15 ° ATDC) is performed at the top dead center. At this time, since the intake air amount is controlled to be reduced, in-cylinder pressure and heat generation are shown as shown by the solid line. The rate of heat increase is small, and when 40 ° has passed from top dead center, post injection (40-50 ° ATDC) increases the heat generation rate in the cylinder just before exhaust, , HC gas can be supplied to the exhaust system and NOx rich reduction can be performed in the LNT.

  Thus, during rich reduction of LNT, HC can be supplied and CO can be generated, and this CO can be used as a reducing agent, so that a DOC for partial decomposition of HC can be eliminated.

  Further, since the exhaust gas temperature at the engine outlet can be raised during PM regeneration of the DPF, a DOC for raising the temperature by burning the post-injected fuel can be made unnecessary as in the prior art.

  As described above, since the DOC can be abolished, the cost merit is great. Moreover, since the exhaust gas temperature at the engine outlet can be raised during the rich reduction of LNT, the NOx reduction efficiency of LNT can be increased.

  As described above, in this embodiment, since the fuel is post-injected in the vicinity of 40-50 ° ATDC in the cylinder, most of the fuel is burned and gasified, so that the fuel is injected in the vicinity of the conventional 120 ° ATDC. Compared to post injection, oil dilution of oil can be reduced. Further, since exhaust pipe injection is not used, it is possible to place the catalyst close to the engine.

DESCRIPTION OF SYMBOLS 10 Engine 11c Cylinder 16 Fuel injector 20 Exhaust gas aftertreatment apparatus 28 Exhaust pipe

Claims (5)

  An exhaust gas aftertreatment device having a NOx storage reduction catalyst and a filter is connected to the exhaust system of the engine, and when performing rich reduction of the NOx storage reduction catalyst or PM regeneration of the filter, A combustion method comprising post-injecting at a timing of 40-50 ° ATDC in at least one cylinder.   When performing post-injection at the timing of 40-50 ° ATDC, the EGR valve is closed, the opening of the intake throttle valve is reduced to reduce the intake amount, and the exhaust gas temperature rises and CO is generated in the cylinder. The combustion method according to claim 1.   3. The internal EGR is performed by temporarily opening an exhaust valve and performing internal EGR during an intake period of at least one cylinder performing the post injection when performing the post injection at a timing of 40-50 ° ATDC. Combustion method.   The combustion method according to any one of claims 1 to 3, wherein when the post injection is performed at 40-50 ° ATDC, the glow plug is energized to raise the in-cylinder temperature.   An exhaust gas aftertreatment device including a NOx storage reduction catalyst and a filter is connected to an exhaust system of the engine, and a combustion apparatus for performing rich reduction of the NOx storage reduction catalyst or PM regeneration of the filter includes a plurality of the engines A combustion apparatus comprising post-injection means for performing post-injection at a timing of 40-50 ° ATDC in at least one of the cylinders.

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