CN1584540A - Method and apparatus for on-line measuring vehicle petrol engine exhaust recirculating rate - Google Patents

Abstract

A method for on-line measuring waste gas recirculation ratio of vehicle gasoline engine includes executing DC bias voltage forward direction in between spark plug and electrode to change ion directional movement to be ion current; sending it to monolithic computer for sampling and recording after isolating, filtering and amplifying; measuring out waste gas recirculation ratio based on linear coorelation of recirculation ratio to peak value and peak value area. A device for realizing the method is also disclosed by the present invention.

Description

Method and device for online measuring exhaust gas recirculation rate of gasoline engine for vehicle

Technical Field

The invention relates to a method and a device for measuring the exhaust gas recirculation rate of a gasoline engine for a vehicle

Background

With the increase of vehicles and the increase of environmental pollution, the emission requirements of engines are becoming more and more strict. The Europe II and Europe III standards are about to be adopted in China. These stringent standards mean that emissions must be reduced from the engine itself. Combined with three-way catalytic conversion and other methods, Exhaust Gas Recirculation (EGR) cools part of exhaust Gas and introduces the cooled exhaust Gas into a combustion chamber, so that HC and CO emission can be reduced, and NO can be reduced_xAnd (5) discharging. However, too high an EGR rate results in unstable combustion and too little to achieve emission reduction. Due to lack of on-lineThe means of measuring the EGR rate in real time cannot realize the closed-loop control of the EGR rate.

The hydrocarbon fuel produces ions when burning, and the ions form ion current with certain intensity after being applied with proper voltage, and the current magnitude reflects the characteristics of the burning process. The ion concentration is detected by a spark plug or an ion current sensor disposed in the engine, so that the combustion characteristics are known.

Disclosure of Invention

The invention aims to provide an on-line measurement device and an on-line measurement device for the exhaust gas recirculation rate of a gasoline engine for a vehicle by utilizing the relationship between the ion current of an engine spark plug and the exhaust gas recirculation rate.

The measuring method comprises the following steps: 1. after a spark plug in a cylinder of the gasoline engine for the vehicle is ignited, ions are generated when the carbon-hydrogen fuel is combusted; 2. the direct current bias voltage is positively applied between the electrodes of the spark plug to make the ions move directionally into ion current; 3. then the sample is sent to a computer for sampling and recording after passing through an isolation circuit, a filter circuit and an amplifying circuit; 4. the waste gas recirculation rate obtained by theoretical derivation and experimental verification has obvious linear staring relevance with the ion current peak value and the ion current peak area which determine the ion current waveform; 5. the ion current of the spark plug is utilized to measure the exhaust gas recirculation rate of the gasoline engine for the vehicle on line.

Ions generated in the cylinder originate from two parts: chemical reaction ionization and thermal ionization. The former is mainly various free radicals generated in the chemical reaction process during combustion, and is mainly CHO⁺And H₃O⁺Wherein CHO⁺And quickly generate H₃O⁺Thus H in the final product₃O⁺Mainly comprises the following steps. The peak concentration of chemically reactive ions is located during the flame propagation period. The relevant reactions are:

the latter is ion generated by the destruction of chemical bond in reactant due to heat released rapidly by combustion, mainly NO⁺The corresponding peak and the in-cylinder pressure, i.e. around 15 degrees after top dead center, are reflected as:

the resulting ion concentration can be calculated from the chemical reaction equilibrium constants:

$\left[{\mathrm{CHO}}^{+}\right]=\frac{k_1\left[\mathrm{CH}\right]\left[O\right]}{k_2\left[H_{2}O\right]}$

$\left[H_3{O}^{+}\right]=\frac{k_2\left[\mathrm{CH}{O}^{+}\right]\left[H_{2}O\right]}{k_3\left[e^{-}\right]}=\frac{k_1\left[\mathrm{CH}\right]\left[O\right]}{k_3\left[e^{-}\right]}$

and the positive ion product is H during the flame propagation period₃O⁺Predominantly, i.e. [ H]₃O⁺]≈[e^-]Thus, therefore, it is

$\left[H_3{O}^{+}\right]\≈(\frac{k_1\left[\mathrm{CH}\right]\left[O\right]}{k_3}{)}^{1/2}...\left(5\right)$

As can be seen from the above formula, after EGR is introduced in the flame propagation period, the concentration of CH and O is reduced simultaneously, the reduction amplitude is in linear relation with the EGR rate, and therefore the concentration of positive ions in the final product is also in linear relation with the EGR rate.

In the later stage of flame propagation, the thermal ionization process is mainly used. Intuitively, the fact that the exhaust gas introduced after EGR increases the heat capacity of the gas in the cylinder means that the temperature change due to the same amount of heat absorbed by the mixture is smaller than that without EGR. The reaction rate of the thermal ionization reaction (4) decreases, the concentration of generated ions decreases, and the corresponding ion current decreases. But from the experimental results, the ion concentration variation in this portion is small relative to the flame propagation period. Therefore, the relationship between the ion current and the EGR rate in the flame propagation period is mainly analyzed later.

The magnitude of the ionic current is related to the concentration of positive and negative ions near the spark plug electrode due to the presence of H as the positive ions in the reactants during the flame propagation period₃O⁺Mainly, so that the magnitude of the ion current is equal to [ H]₃O⁺]Proportional and thus also linearly proportional to the EGR rate.

The relationship between the ion current and the thermal ionization NO is deduced from the plasma theory and the combustion theory.

Under thermodynamic equilibrium conditions, the NO thermionic equation is as follows:

in the formula: e_i-ionization energy (9.25ev)

The single ionization equilibrium constant of NO thermionic dissociation can be calculated from the Saha equation (Saha' Eq):

$\frac{n_{e^{-}}{n}_{{\mathrm{NO}}^{+}}}{n_{\mathrm{NO}}}=2{\left(\frac{2\mathrm{\π}{m}_e\mathrm{KT}}{h^2}\right)}^{\frac{3}{2}}\frac{B_{{\mathrm{NO}}^{+}}}{B_{\mathrm{NO}}}\exp [-\frac{E_i}{\mathrm{KT}}]...\left(6\right)$

in the formula:

n_e--electron density 1/cm³.

n_NO+——NO⁺Ion density 1/cm³.

n_NO-NO molecule density 1/cm³.

m_eElectron mass 9.1095 x 10^-31Kg.

h-Planck constant 6.6262X 10^-34JS.

K-boltzmann constant 1.3807 × 10^-23J/K.

E_iIonization energy 9.25ev.

B_NO+——NO⁺The distribution function of the ions.

B_NO-NO molecule distribution function $(B_{\mathrm{NO}}=B_{N{O}^{+}}{)}^{\left[8\right]}.$

In single thermionic equilibrium:

$n_{e^{-}}=n_{N{O}^{+}}...\left(7\right)$

concentration of NO molecules before ionization

$n_{\mathrm{tot}}=n_{e^{-}}+n_{\mathrm{NO}}...\left(8\right)$

Introducing the concept of ionization degree α:

$\mathrm{\α}=n_{N{O}^{+}}/n_{\mathrm{tot}}...\left(9\right)$

thus:

$n_{N{O}^{+}}=\mathrm{\α}{n}_{\mathrm{tot}}...\left(10\right)$

$n_{e^{-}}=\mathrm{\α}{n}_{\mathrm{tot}}...\left(11\right)$

$n_{\mathrm{NO}}=(1-\mathrm{\α})n_{\mathrm{tot}}...\left(12\right)$

if the right side of formula (6) is n, then:

${\mathrm{\α}}^2=\frac{n}{n_{\mathrm{tot}}}\mathrm{\α}-\frac{n}{n_{\mathrm{tot}}}=0...\left(13\right)$

$\mathrm{\α}=\sqrt{\frac{n}{n_{\mathrm{tot}}}}$

(since α<1, $\frac{n}{n_{\mathrm{tot}}}\mathrm{\&alpha;}<<\frac{n}{n_{\mathrm{tot}}}$ ) (14)

after a certain voltage is applied to two electrodes of the spark plug, the electron mass is far less than NO⁺Mass of ion $(m_{{\mathrm{NO}}^{+}}/m_e\&ap;5.4\&times;{10}^4),$ Thus NO in the spark plug gap field⁺The ion migration velocity is much smaller than that of electrons, i.e. the essence of the spark plug ion current is that the electron movement rather than the ion movement causes^[5]。

The ionic current i of the spark plug can be obtained according to the definition of the current intensity as follows:

i＝αn_totev_e(15)

in the formula: v. of_eThe electron transfer velocity is related to the voltage applied across the spark plug gap and the spark plug electrode.

Let the spark plug electrode area be Scm²Then, the spark plug ion current I:

$I=\mathrm{is}=\mathrm{\&alpha;}{n}_{\mathrm{tot}}e{v}_{e}s$

$=\sqrt{\frac{n}{n_{\mathrm{tot}}}}{n}_{\mathrm{tot}}e{v}_{e}s=\sqrt{n}e{v}_{e}s\sqrt{n_{\mathrm{tot}}}...\left(16\right)$

i.e. the voltage (v) applied between the two poles of the spark plug in the same spark plug structure_eS is the same), the combustion temperature is the same (Same) the spark plug ion current is proportional to the square root of the concentration of the thermally ionized NO molecules before thermal ionization. Namely:

$I\&Proportional;\sqrt{n_{\mathrm{tot}}}$

from the above research results, it is known that the ion current is related to the concentration of thermally ionized NO, which is mainly determined by the EGR rate in EGR, and therefore, the ion current is related to the concentration of thermally ionized NO.

The specially designed device for implementing the method comprises a spark plug and a distributor which are connected, wherein the spark plug is connected with 2 resistors and a power supply in parallel, the 2 resistors and the power supply are sequentially connected, an isolating circuit, a filter circuit, an amplifying circuit and a single chip microcomputer are sequentially connected, and the isolating circuit is connected with the connection positions of the 2 resistors.

The invention realizes the closed-loop control of the EGR rate by utilizing the ion current in the spark plug to measure the EGR rate on line in real time so as to reduce NO_xThe emission of (2) ensures the combustion stability in the cylinder, and the price is low.

Drawings

FIG. 1 is a schematic circuit diagram of an ion current measuring device of the present invention;

FIG. 2 is a schematic illustration of ion current waveforms for different exhaust gas recirculation rates;

FIG. 3 is a schematic of exhaust gas recirculation rate versus peak ion current;

FIG. 4 is a graphical illustration of exhaust gas recirculation rate versus ion current peak area.

Detailed Description

Referring to fig. 1, the measuring device specially designed for implementing the measuring method is that a resistor R1, a resistor R2 and a power supply E which are connected in sequence are connected with the connection part of a spark plug 1 and a distributor 2 of a vehicle gasoline engine cylinder and are connected with the spark plug 1 in parallel; the connecting part of the resistors R1 and R2 is connected with an isolating circuit 3, a filter circuit 4, an amplifying circuit 5 and a singlechip 6 which are connected in sequence, wherein, the direct current bias voltage of 200-500V is positively added between the electrodes of the spark plug 1 and is sent to the singlechip for sampling and recording after isolation, filtering and amplification. The sampling frequency is 10 KHz. The EGR rate of the test engine is controlled by a linear proportional valve driven by a stepping motor, and the opening degree of the EGR rate is determined by the PWM output of the singlechip. Under the condition that other conditions are unchanged, the EGR rate (6 working conditions such as 0, 5%, 10%, 15%, 20%, 25% and the like) is changed, and after the engine runs stably, the ion current waveform of 100 cycles is continuously measured (the signal is recorded according to sampling time during measurement and finally converted into the corresponding crank angle).

Fig. 2 is a waveform of ion current at different EGR rates, the uppermost curve being ion current output at an EGR rate of 0, and the lowermost curve being ion current output at an EGR rate of 25%.

The EGR rate is related to the ion concentration during the flame propagation period, and the corresponding ion current waveform during the flame propagation period (i.e. before and after the first peak of the ion current appears) is summarized as two parameters: the magnitude of the peak and the corresponding peak area (i.e., the area of the ion current signal between crank angle-20 to +10 degrees and time axis). The analysis used a mean of 100 cycles due to fluctuations between combustion cycles.

Fig. 3 and 4 show the relationship between the ion current peak value and peak area and the EGR rate for different EGR (0, 5%, 10%, 15%, 20%, 25%). The calculation shows that the linear correlation coefficient of the EGR rate and the ion current peak value is 0.9872, and the correlation coefficient of the EGR rate and the ion current peak area is 0.9923. Therefore, in the range of the EGR rate of 0 to 25%, it can be considered that the ion current peak value and the peak area are linearly related to the EGR rate. That is, it can be seen that EGR has a significant linear dependence on the magnitude of the ion current peak and the corresponding peak area. Therefore, the EGR rate can be measured on line by using the ion current, and the EGR closed-loop control is realized. In order to reduce the measurement error, a Kalman filter may be used to reduce the influence of the measurement error and random noise in a specific application.

Claims (2)

1. The method for measuring the exhaust gas recirculation rate of the gasoline engine for the vehicle on line comprises the following steps:

1) after a spark plug in a cylinder of the gasoline engine for the vehicle is ignited, ions are generated when the carbon-hydrogen fuel is combusted;

2) the direct current bias voltage is positively applied between the electrodes of the spark plug to make the ions move directionally into ion current;

3) then the sample is sent to a singlechip for sampling record after passing through an isolation circuit, a filter circuit and an amplifying circuit;

4) according to theoretical derivation and experimental verification, the obtained exhaust gas recirculation rate has an obvious linear relation with the ion current peak value and the ion current peak area which determine the ion current waveform;

5) the ion current of the spark plug is used for measuring the exhaust gas recirculation rate of the automobile on line.

2. Device specially designed for implementing claim 1, comprising a spark plug (1) and a distributor (2) connected, characterizedin that: the spark plug is characterized in that resistors (R1 and R2) and a power supply (E) which are connected in sequence are connected in parallel to the spark plug (1), an isolating circuit (3), a filter circuit (4), an amplifying circuit (5) and a single chip microcomputer (6) which are connected in sequence are arranged, and the isolating circuit (3) is connected with the connection parts of the resistors (R1 and R2).

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