The present invention relates to an exhaust gas measuring instrument using a mini-dilution tunnel to measure the amount of emission of various components in exhaust gas from an engine. The mini-dilution tunnel is arranged such that a part of exhaust gas is extracted from an exhaust pipe of the engine and introduced into the mini-dilution tunnel through a sampling tube and then diluted with air to lower the exhaust gas temperature.
A mini-dilution tunnel is used to measure the amount of emission of various components in exhaust gas from engines, particularly diesel engines. The mini-dilution tunnel lowers the temperature of extracted exhaust gas to 52xc2x0 C., for example, thereby creating a condition in which various components in the exhaust gas condense into particulate matter as a result of the lowering in temperature. An exhaust gas measuring instrument using a mini-dilution tunnel measures the concentration of exhaust gas components such as nitrogen oxides in a state approximately similar to that in a case where the exhaust gas is released into the atmosphere, and obtains the amount of emission of the exhaust gas components.
In an exhaust gas measuring method using a mini-dilution tunnel, the amount (weight) of emission of various components in exhaust gas from an engine is obtained in the form of the product of the concentration of various exhaust gas components obtained by analyzing the exhaust gas diluted in the mini-dilution tunnel, the flow rate of the diluted exhaust gas passing through the mini-dilution tunnel, the diluting ratio in the mini-dilution tunnel, and the flow rate split ratio, which is the ratio of the flow rate of exhaust gas passing through an exhaust pipe to the flow rate of exhaust gas introduced into a sampling tube.
It is essential to measure the amount of emission of various components in exhaust gas from an engine in each output or operation mode or the like accurately and with a minimal delay in time for the evaluation of the performance of the engine operated in various operation modes and for the judgment of the conformability to the emission regulations. An exhaust gas measuring instrument using a mini-dilution tunnel need not dilute the whole quantity of exhaust gas and is therefore capable of measuring the amount of emission of various components in exhaust gas by using a small-sized mini-dilution tunnel. Accordingly, the whole exhaust gas measuring instrument can be constructed in a compact structure.
However, the conventional exhaust gas measuring instrument using a mini-dilution tunnel was developed for the steady state operation mode of an engine, and it has a structure for measuring the concentration of exhaust gas components in the steady state. Because a long time is needed for the concentration to reach a stable state, the conventional exhaust gas measuring instrument cannot be used in the transient operation mode. In other words, the conventional exhaust gas measuring instrument using a mini-dilution tunnel cannot perform measurement of exhaust gas components in the transient operation mode because about 10 seconds is needed at 90% of response to a step input owing to the residence of exhaust gas in the sample tube and the delay in response of the detector.
An object of the present invention is to eliminate the disadvantages of the conventional exhaust gas measuring instrument and to provide a fast-response exhaust gas measuring instrument using a mini-dilution tunnel and capable of measuring the amount of various components in exhaust gas in the transient operation mode of an engine. A particular object of the present invention is to provide an exhaust gas measuring instrument in which a bypassed gas flow meter for measuring the exhaust gas flow rate in an exhaust pipe and an extracted gas flow meter for measuring the exhaust gas flow rate in a sampling tube are high response differential pressure type flow meters, respectively, so that it is possible to obtain a flow rate split ratio, which is the ratio of the exhaust gas flow rate in the exhaust pipe to the exhaust gas flow rate in the sampling tube in both the steady state and transient operation modes of the engine.
Another object of the present invention is to enable an even more accurate calibrated flow rate split ratio to be calculated in the exhaust gas measuring instrument using a mini-dilution tunnel by multiplying the flow rate split ratio obtained in the transient operation mode of the engine by a calibration coefficient. Other objects and advantages of the present invention will be made apparent in embodiments of the present invention, claims and drawings.
An exhaust gas measuring instrument according to the present invention has a mini-dilution tunnel in which a part of exhaust gas in an exhaust pipe of an engine is introduced through a sampling tube and diluted with air; a measuring means for measuring a specific component in the exhaust gas diluted in the mini-dilution tunnel; a high response differential pressure type extracted gas flow meter which measures the exhaust gas flow rate Qs in the sampling tube; a high response differential pressure type bypassed gas flow meter which measures the exhaust gas flow rate Qb in the exhaust pipe; and an arithmetic means for obtaining a flow rate split ratio R=Qb/Qs by dividing the exhaust gas flow rate in the exhaust pipe, which is obtained by the high response differential pressure type bypassed gas flow meter, by the exhaust gas flow rate in the sampling tube, which is obtained by the high response differential pressure type extracted gas flow meter.
The exhaust gas measuring instrument according to the present invention further has a means for obtaining a calibration coefficient k of the flow rate split ratio, and a means for obtaining a calibrated flow rate split ratio kxc2x7R by multiplying the flow rate split ratio by the calibration coefficient. The means for obtaining the calibration coefficient k has a measuring means for measuring the concentration Db of a specific substance in the exhaust gas in the exhaust pipe during a transient operation of the engine; a means for obtaining the whole quantity Qbxc2x7Db of the specific substance in the exhaust pipe by multiplying the exhaust gas flow rate Qb in the exhaust pipe by the concentration of the specific substance in the exhaust gas in the exhaust pipe; a means for measuring the diluted exhaust gas flow rate Qt in the mini-dilution tunnel; a measuring means for measuring the concentration Dt of the specific substance in the exhaust gas diluted in the mini-dilution tunnel; a means for obtaining the whole quantity Qtxc2x7Dt of the specific substance in the mini-dilution tunnel by multiplying the diluted exhaust gas flow rate in the mini-dilution tunnel by the concentration of the specific substance in the exhaust gas diluted in the mini-dilution tunnel; and a means for calculating the concentration split ratio Rc=(Qbxc2x7Db)/(Qtxc2x7Dt) by dividing the whole quantity of the specific substance in the exhaust pipe by the whole quantity of the specific substance in the mini-dilution tunnel. The calibration coefficient k is obtained by dividing the concentration split ratio Rc by the flow rate split ratio R.
The measuring instrument according to the present invention preferably has the following arrangements.
(1) The specific substance is nitrogen oxides.
(2) The high response differential pressure type extracted gas flow meter has a sample orifice installed in the sampling tube and obtains the exhaust gas flow rate Qs in the sampling tube on the basis of a pressure difference between two sides of the sample orifice produced by the exhaust gas passing through the sample orifice.
(3) The high response differential pressure type extracted gas flow meter has first and second pressure-receiving pistons and a transducer placed between the two pressure-receiving pistons to convert a pressure into an electric signal. The pressure on one side of the sample orifice and the pressure on the other side of the sample orifice are applied to the first and second pressure-receiving pistons, respectively, whereby a pressure difference at the sample orifice is converted into an electric signal.
(4) The high response differential pressure type extracted gas flow meter has first and second bellows and a resistant-wire strain gauge which converts deformation of a plate spring, which is placed between the two bellows, into an electric signal. The pressure on one side of the sample orifice and the pressure on the other side of the sample orifice are applied to the first and second bellows, respectively, whereby a pressure difference at the sample orifice is converted into an electric signal.
(5) The high response differential pressure type bypassed gas flow meter has a bypass orifice installed in the exhaust pipe and obtains the exhaust gas flow rate Qb in the exhaust pipe on the basis of a pressure difference between two sides of the bypass orifice produced by the exhaust gas passing through the bypass orifice.
(6) The high response differential pressure type bypassed gas flow meter has first and second pressure-receiving pistons and a transducer placed between the two pressure-receiving pistons to convert a pressure into an electric signal. The pressure on one side of the bypass orifice and the pressure on the other side of the bypass orifice are applied to the first and second pressure-receiving pistons, respectively, whereby a pressure difference at the by pass orifice is converted into an electric signal.
(7) The high response differential pressure type bypassed gas flow meter has first and second bellows and a resistant-wire strain gauge which converts deformation of a plate spring, which is placed between the two bellows, into an electric signal. The pressure on one side of the bypass orifice and the pressure on the other side of the bypass orifice are applied to the first and second bellows, respectively, whereby a pressure difference at the bypass orifice is converted into an electric signal.
(8) The bypassed gas flow meter measures the exhaust gas flow rate Qb in the exhaust pipe as the sum of the intake air quantity and the fuel flow rate.
(9) The bypassed gas flow meter, which measures the exhaust gas flow rate in the exhaust pipe, measures the flow rate of exhaust gas remaining after a part of exhaust gas has been extracted through the sampling tube.
(10) The mini-dilution tunnel has an air pump which supplies air into the mini-dilution tunnel, and a blower which discharges the exhaust gas diluted in the mini-dilution tunnel.
(11) The blower is rotated at a constant speed, and the number of revolutions of the air pump is controlled, whereby the flow rate split ratio R is feedback-controlled.