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Exhaust filter regeneration regime method and apparatusRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, Methods, Anti-pollutionExhaust filter regeneration regime method and apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080000219, Exhaust filter regeneration regime method and apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to an exhaust filter regeneration regime, method and apparatus for example for use in a diesel engine exhaust stream. [0002] Such equipment is used in the removal of carbon monoxide, hydrocarbons and NOX pollutants and particulates made in exhaust systems. [0003] In known systems, soot removal is usually achieved most effectively through the use of a filter. Regenerated traps, such as CRTs (Continuously Regenerated Traps), work on the principle of retaining soot particles within a ceramic or silicone carbide filter often termed a diesel particulate filter (DPF), which collects the soot particles within porous walls of the honeycomb structure of the filter. The accumulation of this soot within the surface of the filter increases the backpressure of the filter, which then requires the filter to be regenerated. [0004] Regeneration is achieved when the exhaust temperature reaches above around 600.degree. C. at which point the component of the exhaust gas stream reacts with the soot creating an exothermic reaction, which increases the trap temperature as soot is oxidised and burnt away. The regeneration occurs at a lower temperature in the presence of a catalyst. [0005] The temperature of the exhaust gas and filter are critical to the regeneration process, which lead to various problems with the technology. For example, for certain engine duty cycles it is not possible to achieve an exhaust gas temperature which enables unassisted regeneration. [0006] It is known to reduce the regeneration temperature by introducing a catalyst component upstream of the filter, which reacts with the upstream exhaust gas to create an NO.sub.2 enriched atmosphere. This stimulates the regeneration burning process enabling regeneration temperatures to be reduced to around 380.degree. C. There are, however, cases where the engine duty cycle is such that exhaust stream temperature never exceeds the 380.degree. C. regeneration target temperature and, therefore, other approaches are required to assist with the regeneration. [0007] One known solution to this is set out in "Particulate Trap Technology for Light Duty Vehicles with a New Regeneration Strategy" Zikoridse et al, SAE Technical Papers Series No. 2000-01-1924, in which exhaust gas flows through a heating module having a convection section followed by a radiation section before entering a particulate trap to raise the trap temperature. Alternatively, it is known to provide additional heating local to the filter to increase the approach temperature to enable regeneration, or to rely on fuel born catalysts. Auxiliary heating has drawbacks, as it requires more complex links to the vehicle's onboard power system, which in some cases will not be sufficiently sized to cope with the additional load; this also adds expense and maintenance difficulties. Fuel born catalysts, on the other hand, achieve the same result, however, there are growing concerns regarding the further emissions which are produced during this regeneration process. [0008] Yet a further known solution is described in the presentation "Demonstration of the effectiveness of a NOX absorber and particle filter system on a light-duty diesel vehicle" McGill et al, Oakridge National Laboratory, presented at Windsor Workshop 2001, Windsor, Ontario. According to that presentation fuel can be injected into the exhaust stream allowing catalytic reformation. However, if fuel is injected at too high a rate, it will slip past the catalytic converter without reacting, producing unwanted emissions such as white smoke. [0009] Further problems can arise with the known systems; the regeneration regime is heavily dependent on temperature and hence on vehicle type and usage, for example vehicle duty cycle. Accordingly, before a soot filtration system can be fitted it is necessary to understand the engine's duty cycle to model the temperature profile of the exhaust gas to gain assurance that it will in fact regenerate the filter. This adds further problems because, for example, in a bus application the bus may have the temperature trending compiled on a motorway route where it is found to reach the correct regeneration temperatures. However, it may subsequently be assigned to an inner city route where exhaust temperatures are not sufficient for regeneration. Specifically, the best temperature across the catalytic converter can be achieved after a period of high engine load followed by a period of idle. Under these conditions the exhaust components are already hot and there is oxygen available to oxidise the fuel. However, if the idle period is extended such that the engine starts to cool, it is then more difficult to maintain the temperature of the front of the catalytic converter. In particular, under cool engine conditions, such as low duty cycle operation, the heat to vaporise the fuel is taken from the front of the catalytic converter. The vaporised fuel progresses further into the catalytic converter where it is oxidised. The resultant heat is conducted to the front of the catalytic converter which in turn is used to vaporise more fuel. A problem arises if too much fuel is injected, however as the front of the catalytic converter is quenched leading to the collapse of temperature rise. [0010] The invention is set out in the claims. [0011] As a result the invention allows implementation of the control strategy that is adaptable to multiple usages and duty cycles. [0012] Embodiments of the invention will be described, by way of example, with reference to drawings of which: [0013] FIG. 1 is a schematic block diagram showing an engine implementing an exhaust filter regeneration regime in accordance with the present invention; [0014] FIG. 2 is a flow diagram demonstrating the steps implemented in the regeneration regime control strategy; [0015] FIG. 3 is a flow diagram demonstrating the steps implemented; [0016] FIG. 4 is a schematic block diagram showing a further improved approach to enhancing the regeneration regime; [0017] FIGS. 5a and 5b are views of the injector head of the present invention, and; [0018] FIG. 6 is a schematic view of the electric catalytic heating element. [0019] In overview, referring to FIG. 1 which shows in block diagram the principal components of an engine incorporating the system according to the invention. It will be seen that air is fed from inlet manifold 10 to an engine 12 from which through exhaust conduit 16a to a catalytic reducer 18 for reducing CO and HC. The reduced exhaust stream then passes via exhaust conduit 16b to a diesel particulate filter (DPF) 20 where particulate matter such as soot is removed from the exhaust stream and the exhaust stream passes through exhaust conduit 16c. [0020] A fuel injector 22 is mounted in the exhaust conduit 16a close to exhaust manifold 14. Alternatively the fuel injector 22 may be mounted directly in the exhaust manifold 14, to benefit from highest exhaust stream temperature. The fuel metered by the fuel injector 22 into the exhaust stream is oxidised by the catalytic converter 18 thus providing heat. The heat assists in raising the temperature of the DPF 20 to an appropriate level to allow combustion in conjunction with the oxygen present and beyond. As discussed in more detail below significant temperature increases up to the required level of approximately 550.degree. C., but more preferably temperatures of 650 to 700.degree. C. are available by this approach. Temperatures above this range can have the effect of damaging the catalytic converter. [0021] The system further includes a regeneration controller which can be separate from or part of an engine control unit ((ECU) 24 which controls the fuel injector 22 and also receives signals from sensors 26, 28, 30, 32, 34, 36, 38 and 40 as described in more detail below. Based on the sensed signals the ECU 24 implements a fuel injection strategy by fuel injector 22 to obtain the desired level of regeneration of DPF 20. In particular the sensed signals are used to determine when to switch fuel injection on and off and hence commence and terminate regeneration. Fuel injection start is triggered when the DPF is detected to exceed a predetermined particulate load and the relevant temperature conditions are detected for commencement of the catalytic reaction with the injected fuel in the catalytic converter 18. Similarly, fuel injection is terminated when the particulate load is detected to drop below a predetermined threshold or when the temperature conditions are detected as being insufficient to support regeneration. The particulate load is determined as a function of the pressure drop across the DPF 20 and mass flow through the engine and the temperature detected at the catalytic converter 18. The ECU 24 also controls the fuel injection regime via fuel injector 22 to ensure that an appropriate regeneration level is attained. In particular fuel injection is controlled as a function of the temperature of the catalytic converter 18 to avoid slippage of unburned fuel past the catalytic converter resulting in unwanted emissions in the form of white smoke, resulting from excessive injected fuel. [0022] As a result of this approach a method of regeneration is provided which is controlled entirely by on-board components requiring no operator involvement and which can be achieved for any operating vehicle's duty cycle. In particular it is achieved by artificially increasing the system operating temperature to above 550.degree. C. to ensure that soot is burnt off by virtue of the high pressure fuel injection regime providing an increased exhaust gas temperature downstream of the catalytic converter 18. As described in more detail below, fuel may be injected at high pressure (100 bar) or low pressure (2 bar) dependent on the operating conditions of the engine. [0023] The specific arrangement and strategies are discussed below together with further optimisations. [0024] Referring to FIG. 1 in more detail, the catalytic converter 18 comprises a high platinum load metal catalyst of a cordierite metal or silicon carbide material with mineral wash coat which is found to reduce CO and HC by up to 95%. The DPF 20 is a silicon carbide filter found to reduce mass particulate by 95% and nearly eliminate visible black smoke. The sensors comprise an inlet manifold absolute pressure (IM.sub.PA) sensor 26 and an inlet manifold absolute temperature (IM.sub.TA) sensor 28 provided on the inlet manifold 10. An engine speed (ES) sensor 30 is provided on the engine 12, or at the inlet manifold to measure cylinder inlet manifold pressure variation, which fluctuate each time the cylinder ports open hence representing engine speed. A temperature sensor 31 is provided for sensing the temperature of exhaust gas (T1) exiting the engine exhaust manifold 14 before the fuel injector 22, with a further temperature sensor 32 T.sub.CI on the entry face of the catalytic converter. A sensor 34 senses the temperature of gas at the exit face of the catalytic converter 18 (T.sub.CO). Sensor 36 senses the pressure at the inlet to the DPF 20 allowing the pressure drop (P.sub.DPF), with respect to atmospheric (i.e. pressure of the DPF outlet), across the DPF to be measured. Sensor 40 senses the temperature T.sub.DO of gas exiting the DPF 20. The sensors comprise elongate probes extending into the body of the component whose temperature is sensed. The sensors extend radially into the component such that the axial position of the sensor can be determined exactly. This is of importance, for example, when it is necessary to obtain the temperature at each axial end of a component. 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