Field of invention

The present invention relates to an apparatus for monitoring particles and especially to an apparatus as defined in the preamble of independent claim 1.

Description of the state of the art

Fine particles having diameter between 1 nm and 10 μητι are formed in many combustion processes. For various reasons these fine particles are measured. The fine particle measurements may be conducted because of their potential health effects and also for monitoring operation of combustion processes, such as operation of combustion engines, especially diesel engines. The above reasons there is need for reliable fine particle measurement apparatus.

One prior art method and apparatus for measuring fine particles is described in document WO2009109688 Al. In this prior art method clean, essentially particle free, gas is supplied into the apparatus and directed as a main flow via an inlet chamber to an ejector provided inside the apparatus. The clean gas is further ionized before and during supplying it into the inlet chamber. The ionized clean gas may be preferably fed to the ejector at a sonic or close to sonic speed. The ionizing of the clean gas may be carried out for example using a corona charger. The inlet chamber is further provided with a sample inlet arranged in fluid communication with a channel or a space comprising aerosol having fine particles. The clean gas flow and the ejector together cause suction to the sample inlet such that a sample aerosol flow is formed from the duct or the space to the inlet chamber. The sample aerosol flow is thus provided as a side flow to the ejector. The ionized clean gas charges the particles. The charged particles may be further conducted back to the duct or space containing the aerosol. The fine particles of the aerosol sample are thus monitored by monitoring the electrical charge carried by the electrically charged particles. Free ions may removed further be removed using an ion trap. In addition to the above mentioned fine particles industrial processes and combustion processes form usually also particles having particle diameter greater than 1 μπι, or greater than 2 μηη, 3 μηι, 5 μηι or even greater. These coarse particles having particle diameter greater than 1 μητι may be formed in small amounts in normal operation conditions, but especially in special operation conditions such as during start ups, shutdowns, malfunction conditions. The size distribution of the diesel engine exhaust particles generally shows three different modes: the nuclei mode consists of particles having a diameter of less than approximately 50 nm, the accumulation mode consists of particles having diameters between 50 nm and 1 pm and in the coarse mode the particle diameter is greater than 1 pm. A majority of the diesel engine exhaust particles is born after the exhaust gases escape from the exhaust pipe and these particles typically belong to the accumulation and nuclei mode.

One important demand for the fine particle monitoring apparatuses especially for on-board-diagnoses of diesel engines is small and compact construction. Furthermore, it is also preferable that these fine particle monitoring apparatuses may be operated long time periods without need for maintenance. In many applications, such as monitoring fine particles of combustion engines, it is further preferable that the monitoring apparatus may be operated continuously for conducting fine particle measurements in real-time. Certain apparatuses used for diesel engine emission measurements are not sufficiently robust to withstand forces or temperatures encountered by such apparatuses and certain apparatuses cannot accurately indicate the presence of particulate matter due to poor signal noise ratio. Accordingly, in view of the shortcomings of apparatuses of the prior art, there is a need for improved apparatuses for monitoring fine particles flowing within an exhaust gas stream.

Summary of the invention

The object of the present invention is to provide an apparatus so as to overcome the prior art disadvantages. The objects of the present invention are achieved with an apparatus according to the characterizing portion of claim 1. The preferred embodiments of the invention are disclosed in the dependent claims.

The apparatus of one embodiment of the present invention has following specifications:

- volumetric flow of the essentially clean air: 0.5 - 5 dm ³ /min at NTP

- measurement flow from the exhaust system: 1 - 10 dm ³ /min at NTP

- assembly thread: M29xl.5

- impact resistance: >30G

- operational range (for exhaust gas particle concentration): <25 mg/m ³ Brief description of the drawings

In the following, the invention will be described in more detail with reference to the appended principle drawing, in which

Fig. 1 shows an embodiment of the invented apparatus.

For the sake of clarity, the figures only show the details necessary for understanding the invention. The structures and details which are not necessary for understanding the invention and which are obvious for a person skilled in the art have been omitted from the figures in order to emphasize the characteristics of the invention.

Detailed description of preferred embodiments

Apparatus 1 comprises a housing including part 1 3 extending into the exhaust system 4 of a combustion engine. The apparatus 1 is attached and sealed 5 to the wall of the exhaust system 4, preferably to the wall of an exhaust pipe of a combustion engine. A particle measurement sensor 6 is placed inside the housing 2 and the housing 2 has an inlet hole 7 for providing a measurement flow to the sensor 6 and an outlet hole 10 for exiting the measurement flow. At least a fraction of the particles entering the sensor 6 is charged and the apparatus comprises means for measuring the electrical current carried by the charged particles. It is essential to the present invention that assembling the apparatus to the exhaust pipe only requires a single opening in the pipe and thus easy and non-expensive assembly is achieved. The coupling to the single opening in the exhaust pipe comprises an electrical coupling for providing power to the sensor, such as high voltage to the discharge device, such as a corona discharge device used to ionize the essentially clean gas flow, another electrical coupling for transmitting the electrical signal generated by the particle measurement sensor and gas coupling for providing essentially clean air to the sensor. These couplings are placed in the means 5 for attaching apparatus 1 to the exhaust system 4. The sensor preferably includes an ion trap 9 for removing ions not attached to particles. The sensor also preferably includes a venturi throat and particle ionizing chamber such as described in WO2009109688 Al.

The length of part 1 extending into the exhaust gas system is preferably less than or equal to 55 mm. The length of the part of apparatus 1 expanding outside the exhaust gas system wall is preferably 30-50 mm. Part 1 is preferably assembled into the exhaust gas system in such direction that the gas flowing in the exhaust pipe does not directly enter to the inlet hole in the housing. Although this is in contradiction to the isokinetic particle sampling well known to a person skilled in the art, it provides a beneficial effect as coarse particles in the exhaust gas flow tend not to enter the inlet hole. In one embodiment of the present invention the inlet hole is placed such that the housing wall effectively shadows the inlet hole and there is no line-of-sight route of particles into the inlet hole. This is especially a beneficial embodiment when the particle sensor comprises an essentially clean gas flow, such as described in WO2009109688 Al, which provides a pressure difference between the inlet hole and the exhaust pipe such that the pressure at the inlet hole is lower than the pressure in the exhaust pipe.

The embodiment of figure 1 shows a structure where the part 1 extending into the exhaust system comprises parts manufactured from sheet metal. In the preferred embodiment of the invention the essential parts of part 1 extending into the exhaust system are manufactured from sheet metal which provides a structure which can be easily manufactured and is non-expensive.. Especially the part of housing 1 inside the exhaust system, venturi throat and ion trap 9 are manufactured from sheet metal in the preferred embodiment of the invention.

It is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above-presented examples must not be interpreted as restrictive to the invention, but the embodiments of the invention can be freely varied within the scope of the inventive features presented in the claims herein below.