GB2533099A - Method for providing heating to a diesel exhaust fluid (DEF) tank and diesel exhaust fluid (DEF) tank - Google Patents

Abstract

A diesel exhaust fluid (DEF) tank has a pump on or in the bottom thereof. A first resistive heating element 130 is associated with the pump, and a plurality of second resistive heating elements 140 is attached to the inner surface of a side wall of the tank. In a first aspect the pump is housed in a deepening in the bottom of the tank. A second aspect provides a method of heating the tank. The method comprises estimating the freezing conditions of the DEF in the tank using at least two sensors, a first sensor 110 close to the pump, and a second sensor 120 close to the inner surface of the side wall. If the first sensor detects frozen DEF, the first resistive heating element is operated. If the second sensor detects frozen DEF, the plurality of second resistive heating elements is operated. The DEF is typically urea which is decomposed to form ammonia for use in a selective catalytic reduction (SCR) catalyst.

Description

Method for Providing Heating to a Diesel Exhaust Fluid (DEF) Tank and Diesel Exhaust Fluid (DEF) Tank The present invention mainly relates to selective catalytic reduction (SCR) systems and more particularly to heating systems which provide effective heating to the selective catalytic reduction (SCR) system with heating power.

Selective Catalytic Reduction (SCR) is well known in the art which is an advanced active emissions control technology system used in diesel engines that injects a liquid reductant agent through a special catalyst into the exhaust stream of a diesel engine. The reductant is usually automotive-grade urea, otherwise known as Diesel Exhaust Fluid (DEF). The DEF sets off a chemical reaction that converts nitrogen oxides also referred to as NOx into diatomic nitrogen (N2) and water, natural components of the air we breathe, which is then expelled through the tailpipe.

Commercial selective catalytic reduction systems are typically found on large utility boilers, industrial boilers, and municipal solid waste boilers and have been shown to reduce NOx by 70-95%. More recent applications include diesel engines, such as those found on large ships, diesel locomotives, gas turbines, and automobiles, etc. Vehicles that use diesel fuels emits large amounts of nitrogen oxides or, more generally, NOx, etc. These emissions are harmful to the environment. In order to solve this, the automobiles with diesel engines are often equipped with a selective catalytic reduction (SCR) exhaust treatment system used to reduce the amount of nitrogen oxide (NOx) in the engine's exhaust.

Generally, the SCR systems of vehicle include a DEF delivery system that includes a DEF source, pump, and delivery mechanism. The DEF source can be a container or tank storing a DEF, such as, for example, urea solution or ammonium solution. The pump supplies DEF from the source to the delivery mechanism via a DEF line. The delivery mechanism, which typically is a DEF injector, delivers the DEF into an exhaust gas stream upstream of an SCR catalyst. In automotive applications, the DEF typically is urea, which is injected into exhaust before a catalyst, where it vaporizes and decomposes to form ammonia (NH3) and carbon dioxide (CO2). The NH3 is then used in conjunction with the SCR catalyst and converts the NOx to harmless nitrogen (N2) and water (H20). For proper operation, the temperature of the DEF stored in the DEF storage tank and pumped through the DEF line between the tank and delivery mechanism must be maintained above the freezing point of the DEF and below a maximum temperature of the DEF.

Some conventional DEF temperature control system uses engine coolant to heat DEF stored in the storage tank and line. Other conventional DEF temperature control systems employ electrical heaters instead of coolant to heat DEF in the storage tank and line.

One of the challenging problems is to make sure the DEF is available for the SCR system at cold start conditions. At extreme cold temperatures, the DEF will begin to freeze at -11C. At the start up of a vehicle under such low a mbient temperatures, a heating system is used to provide the heat required for melting the frozen DEF.

Document EP 2415986 Al discloses a method for selectively heating a reducing agent line of an SCR device during operation of an exhaust gas purification system of an internal combustion engine and a device for exhaust gas purification. This document mainly discloses about identifying the zones in which real time freezing of reducing agent is identified and heat energy is supplied for preventing freezing of the reducing agent, where the heat energy is supplied by an electrical heater.

Further, document US 2011/0047966 discloses an apparatus for controlling the heating of diesel exhaust fluid (DEF) in a DEF delivery system. This document mainly discloses about DEF heating mechanism which includes a coolant based heating mechanism to heat DEF in the tank and an electric heater based mechanism to heat DEF in the lines.

Also, in Document EP 2226479 Al which discloses a method for melting a volume of a frozen fluid (F) located in a fluid tank of a motor vehicle wherein the motor vehicle makes available a predetermined maximum tapped supply power (V) which is converted into heat at least partially by a heating device with a number of heating elements arranged on or in the fluid tank and said heat is supplied to the volume. In order to melt the volume after a cold start of the motor vehicle the heating elements are operated consecutively individually or in groups, the whole heat output convertible into heat being introduced respectively in concentrated form by the operated heating element or the operated group of heating elements within a restricted range.

Presently, the existing set up uses a heating element inserted into the tank which melts the frozen DEF. By using this setup there is some time lag between the vehicle start up and the availability of DEF to the SCR system. The response time of the tank heating system to deliver adequate quantities of DEF depends on the initial temperature, mass of the frozen urea, heating system design, dimensions, etc. Therefore there is a need in the art for improved heating systems which provide effective heating to urea-based diesel exhaust fluid (DEF) with minimal heating power for reducing NOx emissions that function efficiently at low temperatures.

An aspect of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below.

Accordingly, the present invention provides a method for providing heating to Diesel Exhaust Fluid (DEF) tank, the method including the step of estimating the freezing conditions of Diesel Exhaust Fluid (DEF) in the SCR tank using at least two sensors, a first sensor and a second sensor. The first sensor is arranged in close proximity to a pump that is arranged on the bottom of the tank and the second sensor is positioned close to an inner side wall of the tank. lithe first sensor senses frozen DEF in the tank, a first resistive heating element associated with the pump and constantly in contact with DEF is operated or activated. If the second sensor senses frozen DEF in the tank a plurality of second resistive heating elements are operated or activated.

The invention also pertains to a Diesel Exhaust Fluid (DEF) tank having side walls and a bottom wall, wherein the bottom wall exhibits a deepening that houses a pump for pumping the DEF out of the tank, and wherein a first resistive heating element and a plurality of second resistive heating elements are provided within the tank, the first resistive heating element being associated with the pump and the plurality of second resistive heating elements being attached at the inner surface of a side wall of the tank.

Within the tank a first and a second sensor for sensing a frozen or solid state of the DEF within in the tank are provided. The first sensor may be attached to the pump or may be located with a distance of few centimeters or less to the pump. The first resistive heating element may be arranged within the pump. The second sensor may be located with a distance of few centimeters or less to a side wall of the tank or may be attached to the side wall of the tank. The plurality of second resistive heating elements are preferably heating tapes that are preferably attached at the inner surface of the tank side wall, especially at planes having an orientation corresponding to a longitudinal axis of the tank. Preferably three to ten, especially four to six heating tapes are provided as second heating elements, the heating tapes being arranged at preferably at least approximately equal distances from each other.

The first and second heating elements are preferably triggered by the sensors to provide uniform heating of the DEF thereby achieving effective heating with minimal heating power.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

FIG. 1 shows one exemplary embodiment of a DEF tank of a vehicle according the present invention.

FIG. 2 is a flow diagram showing principles of a method for providing effective heating to the DEF tank according to present invention.

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

In the following detailed description of various embodiments of the invention, numerous specific details are set forth in order to provide a thorough understanding of various aspects of one or more embodiments of the invention. However, one or more embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, procedures, and/or components have not been described in detail so as not to unnecessarily obscure aspects of embodiments of the invention.

FIG. 1 shows one exemplary embodiment of DEF tank. An only roughly indicated vehicle 100 includes one or more sensors. A first sensor (Si) 110 and a second sensor (S2) 120 are provided. The first sensor 110 is placed or arranged in close proximity to a DEF pump along with a main heater 130 and the second sensor 120 is placed or arranged in the close proximity to a side wall of the tank. The pump is situated in a deepening of the DEF tank. Preferably the deepening is located at the centre of the bottom of the tank. The first sensor 110 and the second sensor 120 may be volume fraction sensors for sensing the fluid level. Both the sensors Si and S2 can detect a frozen state of the Diesel Exhaust Fluid (DEF) in the tank.

The sensors Si and S2are arranged at predetermined positions (cylindrical coordinates Z1, R1; Z2, R2 with respect to the vertical Z-axis of the tank) within the DEF tank. The second sensor 120 is located at a higher level than the first sensor 110. Preferably the second sensor 120 is located at approximately half of the tank height. Further, a number of electrical heating tapes are provided as auxiliary heating elements 140. Here five heating tapes 140 are attached at the inner surface of the DEF tank wall at planes having an orientation corresponding to the longitudinal axis of the tank. The heating tapes 140 cover the bottom of the tank and the side walls at least up to a height at which DEF can be filled up. In an operation, to ensure that DEF can be pumped off the tank even at cold ambient condition where the DEF may freeze, the main heater 130 which is attached to the pump and/or the auxiliary heating elements 140 are operated conditionally depending on whether the one sensor (Si) or both sensors (Si and S2) detect frozen DEF.

FIG. 2 is a flow diagram showing a method for providing effective heating to a DEF tank according to one embodiment of the present invention. At step 210, the method initiates the Estimation of freezing conditions of Diesel Exhaust Fluid (DEF) in the DEF tank using the at least two sensors 51, S2 located in the tank at coordinates R1, Z1 and R2, Z2 respectively. The first sensor is positioned on a pump of the tank and the second sensor is positioned on a side wall of the tank. The sensors estimate the freezing condition of Diesel Exhaust Fluid (DEF) in the DEF tank respectively check the solid state of the DEF, where the first sensor 110 and the second sensor 120 are volume fraction sensors.

At step 220, the method determines whether the first sensor 110 has sensed frozen DEF in the tank. If so, at step 230 the method activates a first resistive heating element 130 to an "ON" state or holds it in the "ON" state with the help of the first sensor, the first resistive main heating element 130 is arranged with the pump and constantly in contact with DEF. If the first sensor has not sensed any frozen state of the fluid, the method puts or leaves the first resistive heating 110 element in the ''OFF" state (step 240).

The method then determines at step 250 whether the second sensor 120 has sensed frozen DEF in the tank. If so, the second sensor 120 activates the second heating elements to an "ON" state or holds them in the "ON" state at step 260. If the second sensor has not sensed any frozen state of the fluid, the method puts or leaves the second auxiliary resistive heating 110 elements in the "OFF" state (step 270).

Preferably, the first sensor 110 and the second sensor 120 are activated simultaneously if both sensors sense DEF in the frozen state. Preferably the first sensor 110 is checked first and then the second sensor 120 is checked.

The plurality of second resistive heating elements is attached at the inner surface of the tank wall at planes having an orientation corresponding to the longitudinal axis of the tank. The first resistive heating element is the main heater and the plurality of second resistive heating elements is auxiliary heating elements. The auxiliary heating elements are electrical heating tapes. The first resistive heating element and the second resistive heating element are triggered conditionally to provide uniform heating, whether the first sensor or the second sensor or both have detect the frozen DEF to achieve effective heating with minimal heating power.

The method then moves to step 280, where the first and the second sensor are checked whether they detect both DEF in the frozen state. If so, the method continues with step 220. If both sensors do not detect DEF in the frozen state, the first, main heating element is turned off as well as the second, auxiliary heating elements.

In the present method, primarily, the heat is sustained within the DEF tank i.e. optimal heating in such a way that more melt pool is available for spray, secondly refreezing is prevented and thirdly less power input is required by the main heater for melting. Further, the method effectively heats the system. Furthermore, the present method resolves the problem of non-uniform heating thus helping the pump to perform better. Moreover, the present method avoids the use of antifreeze components with SCR.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. Although a preferred embodiment of the present invention has been illustrated and described, other changes will occur to those skilled in the art. It is therefore intended that the scope of the present invention is to be limited only by the scope of the appended claims.