JPH04178550A - Thermal fuel property sensor - Google Patents

Abstract

PURPOSE:To conduct nature judgement with a large applicability by knowing the nature of fuel from a thermal material value which is a product of a coefficient of thermal conductivity and a specified power of a Prandtl number. CONSTITUTION:A heating resistor 1 coated with a platinum wire and a heating resistor 2, the output of which does not change with the speed of a fluid and differs with temperature are used to change the flow speed of fuel in more than two stages, and according to the flow speed ratio, a function expressed by a product of a coefficient of thermal conductivity of fule at a certain temperature and a Prandtl number raised to 0.2 power is obtained. On the basis of the function, the gasification rate of gasoline at that temperature is calculated, and a required quantity of fuel is decided in such a manner that combustion is performed at a preset fuel ratio to a desigated quantity of air to control a fuel injection equipment, Thus, the nature of fuel can be known from a thermal material value very close related to combustion, so that a sensor can be operated with a large applicability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection system for automobiles, and more particularly to a fuel injection system that can supply an appropriate amount of fuel depending on the properties, temperature, and pressure of the fuel.

[Conventional technology]

In the fuel injection system of an automobile, the technology of calculating the appropriate amount of fuel according to the operating condition of the engine by knowing the properties of the fuel is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 57-51920, There are methods that measure the refractive index of light using a glass rod and estimate the fuel properties from this refractive index.

However, the light refraction type fuel property sensor has problems such as attenuation of the light intensity of the light source as it is used, and deterioration of the detector over time due to impurities in the fuel, fine dust particles, etc.

Furthermore, the refractive index of the fuel cannot be said to have a clear correlation with the properties of the fuel that affect the state of combustion within the cylinder, that is, the vaporization rate and octane number of the fuel.1 For example, for gasoline mixed with alcohol, Its use was limited to measuring the mixing ratio of fuels with widely different properties. In addition, other fuel property sensor methods have been devised, such as infrared absorption type, capacitance type, and method for determining latent heat of vaporization.
When considering installation in automobiles, it is considered difficult to put these into practical use due to size, cost, etc.

On the other hand, regarding the measurement of thermal conductivity, which is an important clue for investigating the thermal properties of fluids, for example, Proceedings of the Japan Society of Mechanical Engineers, Vol.
There is a method using an unsteady thin wire heating method as described on page 277, which achieves high accuracy with simple measurement. However, this method requires energization for only a few seconds in order to remove the effects of natural convection, and it is desirable to keep the fluid stationary during this time, making it unsuitable for installation in automobiles etc. that involve vibrations and forced convection. . In addition, in order to perform measurements in a short time, it is necessary to reduce the heat capacity by setting the diameter of the heating thin wire to about 50 μm. Therefore, when used for a long period of time, the measurement accuracy may deteriorate due to dirt on the thin wire. There is a problem.

[Problem to be solved by the invention]

Among the above-mentioned conventional technologies, the photorefraction type fuel property sensor does not take into consideration the aging of the detector due to use and the validity of evaluating the thermal properties of fuel using the refractive index. There was a problem in that it was difficult to detect minute differences in thermophysical property values, such as determining the degree of gravity.

In addition, regarding the unsteady thin wire heating method, in order to accurately measure thermal conductivity, the diameter of the thin wire must be approximately 50 μm, and there are concerns that the thin wire will not change over time due to dirt, and that the fluid to be measured must be kept stationary for a certain period of time. There was a problem that it would not work.

The present invention achieves this by directly measuring the thermal conductivity and Prandtl number, which are the main physical property values related to fluid vaporization.
The aim is to obtain more accurate information about the fuel properties of gasoline under conditions where vibration and convection are present.

Furthermore, by specifying fuel properties, the aim is to determine a more appropriate amount of fuel to be supplied, thereby improving engine performance and reducing fuel consumption.

[Means to solve the problem]

In order to achieve the object 1E, the present invention provides a heating resistor 1 coated with platinum wire (hereinafter referred to as hot wire), and
Using a heating resistor 2 (hereinafter referred to as a cold wire) whose output does not change depending on the velocity of the fluid and whose output varies depending on the temperature, the fuel flow velocity is varied in two or more stages, and the heat conduction of the fuel at a certain temperature is determined from the ratio of the flow velocities. rate and Prandtl number of 0.2
Find the function expressed by the product of the product and calculate the vaporization rate of gasoline at that temperature based on this, and determine the required amount of fuel so that combustion will occur at the set air-fuel ratio for the given amount of air. , the fuel injection device is suppressed.

[Effect]

In this thermal fuel property sensor, a hot wire and a cold wire are placed in a fuel flow path, and the flow rate of fuel flowing through this flow path is varied in two stages using means such as a valve or a bypass. At this time, if the input power is controlled so that the difference Tw - Ti between the temperature Tw of the hot wire and the temperature Ti of the flow becomes equal, the amount of heat Q taken away from the hot wire is determined by the thermal conductivity of the fuel, the number of plants, the flow rate, It is a function of kinematic viscosity.

Here, if the flow rate ratio n is known, terms related to the flow rate and kinematic viscosity can be eliminated from the two equations with different flow rates regarding the heat balance of the hot wire, and the terms related to the thermal conductivity of the fuel and the Prandtl number can be Find the function. From this, it calculates the rate at which the fuel injected into the intake pipe from the fuel injection device vaporizes and combusts effectively, and injects the amount of fuel commensurate with the amount of air taken into the engine. Furthermore, depending on the fuel properties, the fuel injection timing and ignition timing are controlled to achieve better vaporization.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The fuel flow path is divided into a main flow pipe 6 and a bypass pipe 7, and hot wires 1' and 1 and cold wires 2' and 2 are installed respectively. The fuel flow velocity in each pipe is V2 y
Even if the total flow rate, that is, the value of V□+v2 changes, the ratio of vl and v2 is almost determined by the minimum cross-sectional area of each flow path, and will hardly change. Therefore, if this ratio is n, then V2:Hy, (n>1) (1) The hot wire 1 and the cold wire 2 in the bypass section are
It is connected to a fixed resistor 3 and a variable resistor 4 to form a Wheatstone bridge. Although omitted due to space limitations, the hot wire 1' and cold wire 2' in the main flow section are omitted.
It is also connected to a very similar Wheatstone Bridge. If the resistance values of 1 to 4 are represented by symbols R□ to R4 (Ω), then if R4 is varied so that this circuit satisfies the relationship 1 R4, the current flowing through the galvanometer becomes O.

On the other hand, if the amount of heat taken from hot wire 1, that is, the power consumption of hot wire 1 is Q(W), and the current at this time is I, then Q□=I, "R1=(A+B mouth)(T knee) Tf)・
...(3) However, T1. Ti are the temperatures of the hot wire 1 and the fuel, respectively. Further, A and B are constants determined by the thermal conductivity, Prandtl number, kinematic viscosity, and temperature of the fuel fluid, and are given by when the fluid is a liquid. However, λ: Thermal conductivity of the fluid (W/mK) d: Diameter of the hot wire (m) Pr: Prandtl number of the fluid: Kinematic viscosity of the fluid (m2/s) Q: Length of the hot wire (m) It is.

Furthermore, in the same way for the main flow part, Iz"R4'
=Q2'=(A+B,/""i) (T2-T,)・
...The relationship (5) holds true. Here, I2. Q2. ``T2 are the current flowing through the main hot wire, the power consumption in the hot wire, and the temperature of the hot wire, respectively.
1' is the resistance value of the hot wire. Here, (3
), (5), the electrical input is adjusted so that the temperature of each hot wire is equal. That is,
T2=T-work, R1=R2', and the following relationship is obtained: (6).

On the other hand, if the resistance value of the hot wire when the temperature resistance coefficient of the hot wire is α flow temperature TI is Rx, then Rw=Rz
(1+(!(T1-Tt))αR7 (6) From equations (7) and (1), and from equation (8), B and v can be eliminated by making the two equations simultaneous.

That is, from equations (4) and (9), ...(main) In the above equation ((r)), α2g is a quantity determined by the shape and material of the hot wire, and n is the amount determined by the shape and material of the hot wire, as described above, It is determined by the ratio of the minimum cross-sectional area of the flow path, so
In the end, Io, I2. R□.

By measuring R8, the product λPr0·2 of the thermal conductivity λ and the Prandtl number Pr to the 0.2 power can be determined. These currents and resistance values are measured by the measuring device shown in FIG. 1 and input to the arithmetic device. The calculation device calculates the formula (*), and the fuel property λPr
'・2 is output.

In addition, by making the cold wire 2 the same material and length as the hot wire, this resistance value is regarded as Ro,
The output value is corrected based on the fuel temperature.

In this embodiment, there are two fuel flow paths, a main flow path and a bypass path, and each flow path has a hot wire, a cold wire, a control circuit including a Wheatstone bridge, and a measuring device, for a total of two flow paths. For example, hot wires 1 and 1' in FIG. 1, cold wire 2
If 2' and 2' are configured to be switched by switches, the parts below the measuring device can be shared.

In addition, by using only one set of equipment below the hot wire, the flow rate of fuel flowing through the flow path can be controlled by valves, etc. It is also possible to have a structure that can be switched between two stages. Furthermore, although the present invention has been described as a method for detecting fuel properties of automobiles,
Not only for automobile fuel, but also for general gases and liquids.
λPr' in consideration of temperature 2. Furthermore, it can be used to measure thermal conductivity.

FIG. 2 is an example of an electronic fuel injection system using a thermal fuel property sensor. The control unit 5 controls the output from the fuel property sensor 1, the engine cooling water temperature, 2. Intake temperature 3. Obtain information on the engine speed 4 and determine the rate at which the supplied fuel vaporizes and contributes to effective combustion under the current engine operating conditions. The amount of fuel is increased or decreased to achieve a preset air-fuel ratio. Also, based on the output from the fuel property sensor, the time required to vaporize the fuel and the combustion state are predicted, and in order to increase the vaporization efficiency and perform more effective combustion, the fuel injection timing and ignition timing can be adjusted. control.

〔Effect of the invention〕

According to the present invention, the properties of a fuel can be determined by the product of the thermal conductivity of the fuel and the Prandtl number to the 0.2 power, which is a thermophysical property value closely related to combustion. This has the effect of widening the scope of application. Also,
Since the structure and principle are simple, it also has the effect of being highly economical. Furthermore, when this is applied to a fuel injection system, it has the effect of increasing combustion efficiency, improving engine output, lowering fuel consumption rate, and purifying exhaust gas.

[Brief explanation of the drawing]

Fig. 1 is a main circuit diagram of a thermal fuel property sensor, Fig. 2 is a block diagram of an electronic fuel injection system using a thermal fuel property sensor, and Fig. 2a shows that #! FIG. 2C is a diagram showing an example of controlling the injection timing based on fuel properties, FIG. 2C is a diagram showing an example of controlling the ignition timing. 1.1'...Hot wire made of thin platinum wire, etc., whose heat radiation amount changes depending on the fuel flow rate and applied voltage, 2゜2'・
・・Cold wire whose heat radiation amount changes only depending on the applied voltage. Figure 1 Figure 2 C

Claims (1)

[Scope of Claims] 1. A thermal fuel property sensor in an automobile fuel injection system, characterized in that the property of the fuel is evaluated by a function of the thermal conductivity of the fuel. 2. The thermal type fuel property sensor according to claim 1, wherein the measuring part is provided in the fuel passage bypass part, and the fuel flow rate flowing through the bypass part is switched in two or more stages. Fuel property sensor. 3. The thermal fuel property sensor according to claim 2, wherein the measuring portions are provided at two or more locations, a main flow portion of the fuel flow path and a bypass flow path portion. 4. The fuel injection system according to claim 1, which includes a heat generating resistor 1 whose heat radiation amount changes depending on the fuel temperature and fuel flow, and a heat generating resistor 2 whose heat radiation is influenced only by the fuel temperature. A thermal fuel property sensor characterized by being able to compensate for the effects of changes in physical property values due to temperature changes. 5. The fuel injection system according to claim 1, comprising means for detecting the temperature of the fuel and means for correcting the influence of changes in physical property values due to changes in the temperature of the fuel, and the system comprises means for detecting the temperature of the fuel, and means for correcting the influence of changes in physical property values due to changes in the temperature of the fuel, and the system is configured to detect the temperature of the fuel based on the output of the thermal fuel property sensor. A fuel injection system that adjusts the amount of fuel supplied, its injection timing, and ignition timing so that combustion conditions are optimized.