Claims:We Claim:

1. A diesel exhaust fluid system (10) for determining a concentration of diesel exhaust fluid, comprising:
a diesel exhaust fluid tank (105) adapted to contain diesel exhaust fluid; and
a level sensor (110) mounted in the diesel exhaust fluid tank (105), the level sensor (110) adapted to sense a level of the diesel exhaust fluid in the tank (105);
characterized by:
a pressure sensor (115) mounted at a bottom (120) of the diesel exhaust fluid tank (105), the pressure sensor (115) adapted to sense pressure exerted by the diesel exhaust fluid contained in the tank (105).

2. A method (20) of determining a concentration of a diesel exhaust fluid in a diesel exhaust fluid tank (105) of a diesel exhaust fluid system (10), the method (20) comprising:
sensing (205) a pressure exerted by the diesel exhaust fluid contained in the tank (105), by a pressure sensor (115) mounted at a bottom (120) of the diesel exhaust fluid tank (105);
sensing (210) a level of the diesel exhaust fluid in the tank (105), by a level sensor (110) mounted in the diesel exhaust fluid tank (105);
determining (215) a density of the diesel exhaust fluid by a control unit (130), based on the sensed pressure of the diesel exhaust fluid and the sensed level of the diesel exhaust fluid; and
determining (220) a concentration of the diesel exhaust fluid by the control unit (130), based on the determined density of the diesel exhaust fluid.
, Description:FIELD OF THE INVENTION
[0001] This invention relates to a diesel exhaust fluid system and a method of determining a concentration of the diesel exhaust fluid.

BACKGROUND OF THE INVENTION
[0002] Selective catalytic reduction (SCR) systems are used in exhaust lines of diesel vehicle to reduce NOx emissions in the exhaust. SCR systems involve usage of diesel exhaust fluid (DEF) to reduce the NOx to nitrogen and water which is released harmlessly into the atmosphere. Diesel exhaust fluids are also called SCR reagents. The most common tradename of diesel exhaust fluid is AdBlue. DEF is a solution of urea in water. Once the DEF is dosed in the SCR module, the urea vaporizes into ammonia and the ammonia reacts with the NOx gases to form nitrogen and water. The concentration of urea in the DEF is important for efficient reduction of NOx. Therefore, it is imperative to maintain the concentration or quality of urea in the DEF. Consequently, constant monitoring of DEF quality is required. US2012118059A teaches a system for determining a quality and/or depth of a fluid in a tank. The system includes a controller, one or more transducers, and a temperature sensor. A fixed distance transducer transmits a sound wave toward a fixed surface. A depth transducer transmits a sound wave which reflects off a surface of the fluid. The temperature sensor senses a temperature of the fluid in the tank and provides an indication of the temperature to the controller. The controller measures the elapsed time for the sound waves to travel between the fixed distance transducer and a fixed surface and the elapsed time for the sound waves to travel between the depth transducer and the surface of the fluid held within the container. Using the elapsed times and the temperature of the fluid, the controller is able to determine a quality and the depth of the fluid.

BRIEF DESCRIPTION OF DRAWINGS
[0003] Embodiments of this disclosure is explained in principle below with reference to the drawings. The drawings are:
[0004] FIGURE 1 shows a schematic arrangement of a diesel exhaust fluid system for determining a concentration of diesel exhaust fluid; and
[0005] FIGURE 2 shows method steps for determining a concentration of a diesel exhaust fluid.

DETAILED DESCRIPTION
[0006] FIGURE 1 shows a schematic arrangement of a diesel exhaust fluid (DEF) system 10 for determining a concentration of diesel exhaust fluid. The DEF system 10 comprises a DEF tank 105 adapted to contain diesel exhaust fluid. The DEF system 10 further comprises a level sensor 110 mounted in the DEF tank 105, the level sensor 110 adapted to sense a level of the DEF in the tank 105. The DEF system 10 also comprises a pressure sensor 115 mounted at a bottom 120 of the DEF tank 105, the pressure sensor 115 adapted to sense pressure exerted by the DEF contained in the tank 105. THE DEF system 10 further comprises DEF and the DEF tank 105 are known in the art. The pressure sensor 115 is mounted at the bottom 120 of the tank 105, as the pressure exerted by a column of fluid is measurable at the bottom of any vessel or container. The pressure sensor 115 can be any conventional sensor available. As an example, the pressure sensor 115 can be a wheatstone based pressure sensor.
[0007] In the arrangement of the system 10, the level sensor 110 can be a float based level sensor, which rises as the level of DEF in the tank rises. The position of the float corresponds to the level of the DEF in the tank 105. This is commonly understood in the art. The level sensor 110 can also be an ultrasonic based level sensor mounted at a top portion 125 of the tank 105. In FIGURE 1, the level sensor 110 is shown attached to the top portion 125 of the tank 105. This is just for the purposes of illustration and the level sensor 110 can be located in other locations of the tank 105 or on the surface of the DEF in the tank 105 also.
[0008] The level sensor 110 and the pressure sensor 115 are in communication with a control unit 130, for determining a concentration of the DEF in the DEF tank 105. The control unit 130 can be any micro controller based device that has computational capabilities.
[0009] The system 10 here is the diesel exhaust fluid system and comprises structural components as described above.
[0010] A method 20 for determining the concentration of the diesel exhaust fluid in the diesel exhaust fluid tank 105 of the diesel exhaust fluid system 10 is described below. FIGURE 2 shows method steps for determining the concentration of diesel exhaust fluid. The method 20 comprises a first step 205 of sensing a pressure exerted by the diesel exhaust fluid contained in the tank 105, by the pressure sensor 115 mounted at the bottom 120 of the DEF tank 105. The second step 210 is sensing the level of the DEF in the tank 105, by the level sensor 110 mounted in the DEF tank 105. The method 30 comprises a third step 215 of determining the density of the DEF by the control unit 130, based on the sensed pressure and sensed level of the DEF.
[0011] In the first step 205, the pressure exerted by the column of the DEF in the tank 105 is sensed by the pressure sensor 115. In the second step 210, the level of the DEF in the tank 105 is sensed by the level sensor 110. In the third step 215, the density of the DEF is determined by the control unit 130 based on the sensed pressure in step 205 and the sensed level in step 210. The density is determined with the below formula:

P = ?gh,

[0012] where,
a. P = pressure sensed by the pressure sensor 115,
b. g = gravity,
c. h = head or level sensed by the level sensor 110, and
d. ? = density of the diesel exhaust fluid.
[0013] For the purposes of explanation, the density of the DEF is based on the concentration of the DEF. As the urea solution and water have differing individual densities, the density of diesel exhaust fluid, which is a mixture of urea solution and water, depends on the concentration of the DEF. An example of DEF concentration can be 30% urea, 40% urea etc. For a given volume, a 30% urea in DEF will produce a different DEF density than a 40% urea in DEF, as the amount of urea in the 30% and the 40% solution will vary. This is understood by the person skilled in the art. Therefore, differing concentrations of the DEF can have differing mass per given volume (density), which changes the pressure measured by the pressure sensor 115. In other words, a 30% urea in DEF will exert a different pressure at the bottom 120 of the tank 105 than a 40% urea in DEF.
[0014] With the measured pressure and level, the density of the DEF can now be calculated by the control unit 130. For the fourth step 220, and from the above description, it is known that there is a correlation between the density value and the concentration of urea in DEF. Hence, the concentration of urea in DEF can be determined once the density of the DEF is calculated. As the concentration of urea in the DEF indicates the quality of DEF, the quality of the DEF can be determined.
[0015] The above system 10 and method 20 provides a cost-effective way of determining the quality of DEF, which can then be communicated to the driver or the user of the vehicle. As the components of the system 10 is contained in the tank 105, the system 10 also provides spatial efficiency when compared to conventional ways of measuring DEF quality.
[0016] The system 10 and method 20 can find applications in diesel vehicles.
[0017] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. Any modification in the embodiments are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.