RU2540029C1 - Method for corrected feeding of combustible biogas in gas diesel engine of power plant - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention proposes a method of corrected feeding of combustible gas to working cylinders of a gas diesel engine, in which gaseous fuel is fed through an inlet system of the diesel engine and its inlet valves to working cylinders; with that, an ignition batch of diesel fuel is sprayed with injectors to the working cylinders of the gas diesel engine, and combustible gas feeding is corrected depending on combustible gas composition. Correction of combustible gas - biogas feeding as per percentage content of methane in biogas is performed as per an indirect evaluation of methane content by means of measurements of content of carbon dioxide in biogas at the inlet of the inlet gas diesel engine system and/or temperature of waste gases at the gas diesel engine outlet.

EFFECT: improving accurate correction of feeding of biogas and increasing a share of replacement of liquid oil fuel with gaseous fuel and limiting the temperature of waste gases at the level specific for operation on biogas with low content of methane in it.

3 cl, 5 dwg, 3 tbl

Description

Technical field

The invention relates to the field of operation of engines operating simultaneously on several types of compression ignition fuel, the main fuel being gaseous, and in particular, to methods for supplying gas diesel engines operating as part of biogas power plants, in particular diesel generator sets generating variable electricity.

State of the art

A known method for correcting the ignition dose of diesel fuel in diesel engines operating on a gas-diesel process, in accordance with which with increasing speed and load increase the dose of ignition fuel. Moreover, the ignition dose of diesel fuel is kept constant when the engine is running on the regulatory characteristic in the speed range from nominal to minimum and increase when the engine is running on the external speed characteristic. This ensures a reduction in diesel fuel consumption and an improvement in the quality of the engine due to the correction of the ignition dose of diesel fuel with the help of a regular corrector for the direct-acting speed controller (RF patent No. 2182249, IPC F02D 19/10, published on 05/10/2002).

The disadvantage of this method of supplying combustible gas to the cylinders of a gas diesel engine is the inability to accurately meter the supply of combustible gas, taking into account the composition and calorific value of the supplied gaseous fuel.

Another analogue is the method of supplying combustible gas to the working cylinders of a gas diesel engine, which consists in the fact that gaseous fuel is supplied through the intake system of the diesel engine and its intake valves to the working cylinders, wherein the ignition dose of diesel fuel is injected into the working cylinders of the diesel engine by the mechanism for supplying ignition doses of liquid fuel, associated with the regulator of the gas diesel (RF patent No. 2319846, IPC F02D 19/10, publ. 20.03.2008).

The disadvantage of this method of supplying combustible gas to the cylinders of a diesel engine of a power plant is the inability to accurately dispense a supply of combustible gas, taking into account the composition and calorific value of the supplied gaseous fuel. This, on the one hand, does not allow for the maximum replacement of liquid petroleum fuel with gaseous fuel, and on the other hand, it does not allow for precise limitation of the temperature of the exhaust gases at the required level, which entails an increase in the thermal tension of the parts of the combustion chamber of the diesel engine and its exhaust system and reduces reliability of their work and resource.

The closest to the proposed method for the adjustable supply of combustible gas to the working cylinders of a gas-diesel engine of a power plant can be recognized as a method for supplying combustible gas to the working cylinders of a gas-diesel engine, which consists in supplying gaseous fuel - associated petroleum gas (APG) through the diesel inlet system and its inlet valves to working cylinders, while the ignition dose of diesel fuel (diesel fuel) is injected into the working cylinders of the diesel engine by the mechanism for supplying ignition doses of liquid fuel associated with the gas regulator spruce, and the supply of APG is adjusted depending on its composition (RF patent No. 2465472, IPC F02D 19/08, publ. 02.27.2012). At the same time, the adjustment of the supply of APG is carried out according to a computer program using information, including from sensors of the dielectric parameters of substances - dielcometers, which the authors call sensors for monitoring the composition of APG and liquid fuel. Almost any diesel engine can be adapted for using APG, as structural differences in its various models are insignificant.

However, dielcometers are quite complex, inaccurate and therefore rare sensors that are not commercially available. Therefore, the entire invention is a prototype rather so far has a narrow scientific, and not wide practical character.

In addition, the specificity of APG is a very small percentage of the presence of carbon dioxide CO ₂ in it, in contrast to biogas, where the content of CO _{2 on the} contrary is very significant and CO ₂ usually takes the second place in biogas after methane, and together they are methane and carbon dioxide As a rule, they occupy the overwhelming share of volume in biogas, since the remaining impurities in biogas occupy only units of volume percent. At the same time, CO ₂ sensors are well known and widespread with good characteristics in accuracy, reliability and cost.

Disclosure of invention

The technical task of the proposed method for the adjustable supply of combustible biogas to the working cylinders of a gas-diesel engine of a power plant is to increase the accuracy of adjusting the supply of combustible biogas and in this regard, increase the proportion of substitution of liquid petroleum fuel with gaseous fuel and limit the temperature of exhaust gases to a level typical for low biogas operation methane in it.

The technical result is achieved due to the fact that in the method of the adjustable supply of combustible gas to the working cylinders of the diesel engine, gaseous fuel is supplied through the intake system of the diesel engine and its intake valves to the working cylinders, while the ignition dose of diesel fuel is injected into the working cylinders of the diesel engine through nozzles by the ignition dose supply mechanism liquid fuel associated with the regulator of the diesel engine, and the flow of combustible gas is adjusted depending on the composition of the combustible gas. In this case, the adjustment of the supply of combustible gas - biogas by the percentage of methane in biogas is carried out by indirectly assessing the methane content by measuring the content of carbon dioxide (carbon dioxide) in biogas at the inlet to the gas-diesel inlet system and / or the temperature of the exhaust gases at the gas-diesel outlet.

In order to increase the share of liquid petroleum fuel replacement with gaseous fuel and limit the temperature of exhaust gases to a level typical for biogas with a low methane content, when using biogas with a methane content of at least 50%, increase the methane content in biogas for every 4 ... 5% the mass fraction of gaseous fuel by 4 ... 5% and, accordingly, reduce the share of the ignition dose of diesel fuel also by 4 ... 5%.

Additionally, to reduce the supply of the ignition dose of diesel fuel, combustible biogas supplied to the inlet system of the gas diesel is heated by 10 ... 12 degrees due to the heat of the exhaust gases while reducing the ignition dose of diesel fuel for every 4 ... 5% of such a decrease.

List of figures

Figure 1. A fuel supply system diagram for implementing the proposed method for supplying combustible biogas to the working cylinders of a gas-diesel engine of a power plant.

Figure 2. The dependence of the effective power N _e (a) and the effective efficiency η _e (b) of a diesel engine on the methane concentration in biogas C _CH4 at the modes of regulatory characteristics at various rotation frequencies n of the output shaft of the gas diesel engine.

Figure 3. The dependence of the effective diesel efficiency η _e on the load (effective power N _e ) and methane content in biogas C _CH4

Figure 4. Dependence of the temperature of the exhaust gas T _ОG on the methane content in C _CH4 biogas under the regime of regulatory characteristics at various rotational speeds n (a) and on the effective efficiency η _{e of the} gas diesel engine at constant methane concentrations in C _CH4 biogas and a change in the speed regime (b).

Figure 5. Change in the parameters of a gas-diesel engine with a change in the methane content in biogas C _CH4 .

The implementation of the invention

The method of supplying combustible gas to the cylinders of a gas-diesel engine of a power plant is carried out, for example, in a gas-diesel engine in Fig. 1.

The installation comprises a shut-off valve 1, to which a biogas pipeline is connected from a cylinder with compressed biogas (not shown in Fig. 1), a biogas pressure reducer 2, a gas-diesel intake system 3 with a regulator — a gas supply valve 4, a biogas flow sensor 5 and a shut-off valve 6 placed in the inlet pipe 7 of the compressor 8 of the gas turbine pressurization system. The exhaust pipe 9 of the compressor through the charge-receiving receiver 10 and inlet valves 11 is in communication with the working cylinders 12 of the gas diesel 13 through the channels of the heater 14, equipped with a temperature controller with a biogas temperature sensor 15 and an actuator - an exhaust gas supply valve 16 to the heater 14, controlled from the electronic unit 17 The biogas is heated after the compressor due to the heat of the exhaust gases coming from the exhaust system 18 of the gas diesel 13 through the gas line 19 in which the valve 16 is located. The exhaust system 18 also includes exhaust valves 21 located in the caps 20, communicating the working cylinders 12 with the exhaust manifold 22.

The diesel fuel ignition dose supply subsystem includes a fuel oil ignition dose delivery mechanism 23 connected to a gas diesel regulator (actuator 24 for changing the ignition dose of liquid fuel) controlled from the electronic unit 17. For ignition of combustible biogas, the gas diesel 13 is equipped with nozzles 25 for supplying an ignition dose of liquid fuel with discharge pipelines 26.

The operation of the gaseous and liquid fuel supply system is carried out by the control unit 17, which receives information from the sensor 27 of carbon dioxide CO ₂ in biogas, the sensor 5 of the biogas flow sensor 29, the flow rate of the ignition dose of liquid fuel (position sensor of the metering body of the mechanism 23 of the supply of ignition doses of liquid fuel), biogas temperature sensor 15, exhaust gas temperature sensor 28. The control unit 17 generates control signals to the actuators - shut-off valve 6, the valve 16 for supplying exhaust gas to the heater 14, the actuator 24 for changing the supply of the ignition dose of liquid fuel.

The method is as follows.

The start of the gas diesel 13 is carried out through a diesel cycle with the supply of liquid fuel to the nozzles 25 through the discharge pipes 26. To switch to the gas diesel cycle, combustible biogas is supplied under pressure from a cylinder with compressed biogas (not shown in Fig. 1) through a shut-off valve 1, a pressure reducer 2 biogas, gas diesel inlet system 3 with valve 4, sensor 5 and shut-off valve 6 in the inlet pipe 7 of the compressor 8 of the gas turbine pressurization system.

Passing together with the air through the intake system 3 of the diesel engine, the blade apparatus and the diffuser of the compressor 8, the combustible biogas is mixed with air. In this case, a homogeneous gas-air mixture is formed, which, through the inlet valves 11 located in the caps 20, is directed to the working cylinders 12 of the gas-diesel engine 13. This gas-air mixture has insufficient self-ignition under the conditions of the gas-diesel working cylinders 12 (the self-ignition temperature of this mixture is significantly higher than the self-ignition temperature of the air mixture with the sprayed liquid diesel fuel).

Thus, a gas-diesel cycle is realized in which the specified mixture of combustible biogas with air is ignited by the ignition dose of diesel fuel injected into the working cylinders 12 of the diesel engine with nozzles 25 for supplying ignition doses of liquid fuel with injection pipelines 26 connecting nozzles 25 with the mechanism 23 for supplying ignition doses of liquid fuel associated with the actuator 24 changes the supply of the ignition dose of liquid fuel, controlled from the electronic unit 17.

If it is necessary to minimize the ignition dose of diesel fuel, it is possible to heat the mixture of combustible biogas with air. To this end, a heater 14 is installed in the compressor outlet pipe 9, having a temperature controller with a biogas temperature sensor 15 and an exhaust gas supply valve 16 to the heater 14, controlled from the electronic unit 17. The mixture of combustible biogas with air is heated to the required temperature through a charging receiver 10 and inlet valves 11 enters the working cylinders 12 of the diesel engine. In this case, the biogas is heated after the compressor due to the heat of the exhaust gases coming from the exhaust system 18 of the gas diesel 13 through the gas line 19 with a valve 16. The exhaust gases enter the exhaust system 18 through the exhaust valves 21 communicating the working cylinders 12 with the exhaust manifold 22.

Coordination of the work of the considered subsystems is implemented by the control unit 17 based on the signals from the sensor 27 of carbon dioxide content of CO ₂ in biogas, sensor 5 of biogas consumption, sensor 29 of the flow rate of the ignition dose of liquid fuel, sensor 15 of the biogas temperature, sensor 28 of the exhaust gas temperature. Based on information from these sensors using the basic control algorithms embedded in the control unit 17, this unit acts on the actuators of the respective subsystems - shut-off valve 6 for supplying combustible biogas, valve 16 for supplying exhaust gases to the heater 14, actuator 24 for changing the ignition dose liquid fuel.

The analysis of combustible biogas obtained from various raw materials and biowaste at various biogas plants for subsequent use in various kinds of power plants, including gas-diesel equipment, showed that this biogas can contain various components, but they almost always have two main components: methane and carbon dioxide (dioxide or carbon dioxide), significant changes in the content of which in biogas, as a rule, are in antiphase due to the small volumetric amount of other components. This gives a practical opportunity, knowing the content of CO ₂ , by simple arithmetic to indirectly evaluate the content of CH ₄ . Typically, biogas has the following composition: methane CH ₄ - 50 ... 85% by volume, carbon dioxide CO ₂ - 10 ... 45%, respectively, hydrogen H ₂ - up to 1%, hydrogen sulfide H ₂ S - up to 1%, other impurities - about 3 % That is, biogas components in addition to CH ₄ and CO ₂ , as a rule, have a total volume of about 5%.

Thus, the methane content in biogas can be estimated by the content of CO ₂ . Carbon dioxide sensors for CO ₂ are used in gas analysis (in particular, in evaluating the exhaust gas composition of internal combustion engines). The use of such sensors makes it possible to increase the accuracy of correcting the supply of fuel gas, since the carbon dioxide content of CO ₂ in biogas can change more than four times (from 10 to 45%). As a result, with practically acceptable accuracy (~ 5%), knowing the CO ₂ content and taking 5% of impurities as a constant, we can estimate the volume content of CH ₄ in biogas as approximately (95% -% CO ₂ ).

The main combustible component of biogas is methane CH ₄ . Its content in biogas can range from 50 to 85%. Accordingly, the calorific value of biogas changes. An analysis of the experimental characteristics of the working processes of a gas-diesel engine showed that a change in the methane content in biogas leads to a significant change in the performance of a biogas-powered diesel engine. Studies were conducted on biogas with methane concentrations C _CH4 = 60.0, 72.8; 77.4 and 84.8%. The calorific value of biogas with different volumetric content of methane is shown in table 1.

Table 1 The calorific value of biogas at different contents of CH ₄ The methane content in biogas,% (vol.) 60.0 72.8 77.4 84.8 Lower calorific value, MJ / kg 18.52 22.47 24.01 26.17

Evaluation of the performance of a diesel engine using biogas as fuel was carried out using the results of experimental studies of a diesel engine 1 H 8/11 by Lister-Peter (DELTA series), some of the technical characteristics of which are presented in Table 2. This type of engine is widely used to drive pump and electric power plants.

table 2 The parameters of the diesel 1 H 8/11 Options Value engine's type Four stroke diesel Rated rotation speed n, min ^-1 1380 Rated power N _e , kW 4,5 Type of combustion chamber Semi-split piston combustion chamber Valve timing Valve Type Top Valve Supply system High pressure fuel pump with centrifugal regulator

Experimental studies of the diesel engine 1 H 8/11 were carried out on a stand equipped with the necessary measuring equipment. Data on the parameters of the diesel engine were digitally displayed on the control panel. The main modernization of the diesel engine was the equipment of a mixer built into the intake manifold of the engine. This made it possible to use the engine both in the basic version and in the gas-diesel version. In this regard, the details and design of the engine remained unchanged.

The share of biogas in the fuel was set as high as possible, provided that the stability of the engine was maintained.

Tests of the engine were carried out at the characteristic load and speed modes of its operation. The results of the tests are summarized in table 3.

The data processing results of table 3 are presented in the form of graphs in figure 2, 3, 4, 5.

Figure 2. The dependence of the effective power N _e (a) and the effective efficiency η _e (b) of a diesel engine on the methane concentration in biogas C _CH4 at the regulatory characteristics at different rotational speeds n: 1 - n = 1380 min ^-1 ; 2 - n = 1420 min ^-1 ; 3 - n = 1500 min ^-1 ; 4 - n = 1620 min ^-1

Figure 3. The dependence of the effective diesel efficiency η _e on the load (effective power N _e ) and methane content in biogas. C _CH4 : 1 - work on diesel fuel; 2 - biogas operation with C _CH4 = 60.0%; 3 - C _CH4 = 72.8%; 4 - C _CH4 = 77.8%; 5 - C _CH4 = 84.8%

Figure 4. Dependence of the temperature of the exhaust gas Т _ОГ on the methane content in C _CH4 biogas at the regulatory characteristics at different rotational speeds n (a) and on the effective efficiency η _{e of a} diesel engine at constant methane concentrations in C _CH4 biogas and a change in the speed regime (b): a : 1 - n = 1380 min ^-1 ; 2 - n = 1420 min ^-1 ; 3 - n = 1500 min ^-1 ; 4 - n = 1620 min ^-1 ;

b: 1 - C _CH4 = 60.0%; 2 - C _CH4 = 72, S%; 3 - C _CH4 = 77.8%; 4 - C _CH4 = 84.8%.

Figure 5. Change in diesel parameters with a change in methane content in biogas C _CH4 :

N _e is the effective engine power; G _g - the proportion of substitution DT [%, mass.];

T _OG - temperature of the exhaust gases;

G _d - cyclic supply of diesel fuel;

G _g - cyclic feed of biogas

(solid lines - experiment, see table 3; dashed lines - recommended parameter values)

The main parameter characterizing the efficiency of the diesel engine is the effective efficiency η _e , which shows how fully the heat received during the combustion of a particular fuel is converted into mechanical work given to the consumer. Effective efficiency allows you to compare the parameters of engines running on different types of fuel.

Table 3 Dependence of diesel engine performance on methane concentration in biogas Speed n min ^-1 1620 1580 1560 1540 1520 1500 1480 1460 1420 1380 Power N _e [kW] at methane concentration in biogas C _CH4 [%, mass.] DT 0.58 1.46 1.82 2,30 2.78 3.25 3.52 3.82 4.28 4.42 C _CH4 = 60.0 0.58 1.26 1,69 1.86 2.23 2.73 3.20 3.42 3,50 3.62 C _CH4 = 72.8 0.59 1.16 1.28 1.73 2.26 2.79 3.12 3.26 3.73 4.12 C _CH4 = 77.8 0.59 1.18 1,52 1.76 2.29 2.82 3.20 3.33 3.81 4.23 C _CH4 = 84.8 0.59 1.18 1,53 1.74 2,30 2.84 3.12 3.37 3.84 4.34 The fraction of substitution of DT [%, mass.] At a methane concentration in biogas C _CH4 [%, mass.] DT 0 0 0 0 0 0 0 0 0 0 C _CH4 = 60.0 69.5 69.0 72.0 72,2 72.0 70.5 66.5 66.0 65.5 65,2 C _CH4 = 72.8 80.0 82.0 83.0 82.0 83.0 83.0 84.0 84.0 84.0 82.0 C _CH4 = 77.8 82.0 84.0 86.0 85.0 85.0 86.0 85.0 86.0 85.0 83.0 C _CH4 = 84.8 83.0 85.0 88.0 89.0 88.0 88.0 88.0 88.0 86.0 84.0 Effective efficiency η _e [%] at methane concentration in biogas C _CH4 [%, mass.] DT 12.6 15.8 17.5 21.1 22.9 25.6 26.1 26.8 27.9 27.9 C _CH4 = 60.0 15.6 24.1 30.9 34.3 36.5 39.0 39.3 40,0 40.1 41.2 C _CH4 = 72.8 16.9 24.4 25.6 28.7 32,5 35.1 38,2 39.6 39.9 40.1 C _CH4 = 77.8 17.0 25,2 27.3 29.1 31.1 36.8 38,4 39.5 38,4 37.8 C _CH4 = 84.8 16.1 26.2 26.9 29.1 30.8 33.8 35,2 36.6 36.7 35,4 Temperature of exhaust gas Т _ОГ [К] at methane concentration in biogas C _CH4 [%, mass.] C _CH4 = 60.0 572 595 612 632 652 682 722 732 753 773 C _CH4 = 72.8 593 603 643 703 723 743 773 793 833 863 C _CH4 = 77.8 594 633 653 683 733 753 783 813 843 853 C _CH4 = 84.8 550 613 621 648 681 737 763 802 854 897

When processing the results of experimental studies, the calculation of the effective efficiency η _{e of the} diesel engine was carried out taking into account the different calorific value of the fuels used in the expression:

$${\eta }_e=\frac{3,6N_e}{H_{U_{CM}}\left(G_{DT}+G_G\right)},$$

- теплота сгорания условной смеси подаваемого топлива, МДж/кг; N_e - эффективная мощность двигателя, кВт. Теплота сгорания смеси подаваемых в КС топлив определялась соотношением часовых расходов дизельного топлива G_ДТ и биогаза G_г [кг/ч] и их теплотворной способностью по соотношению:Where $$H_{U_{CM}}$$

- calorific value of a conventional mixture of supplied fuel, MJ / kg; N _e is the effective engine power, kW. The heat of combustion of the mixture supplied to the COP fuels was determined by the ratio of the hourly consumption of diesel fuel G _DT and biogas G _g [kg / h] and their calorific value according to the ratio:

$$H_{U_{CM}}=\frac{G_{DT}}{G_{\sum }}\cdot H_{U_{DT}}+\frac{G_G}{G_{\sum }}\cdot H_{U_G},$$

$$H_{U_{Г}}$$

- теплота сгорания соответственно дизельного топлива и биогаза, МДж/кг.Where $$H_{U_{DT}},$$

$$H_{U_G}$$

- calorific value, respectively, of diesel fuel and biogas, MJ / kg.

An increase in methane concentration of CH ₄ in biogas provides a higher value of the output power of the gas diesel. The most noticeable effect of the concentration of methane on the output power occurs at high loads (figure 2, a). So, at maximum load at a speed of n = 1380 min ^-1, an increase in methane concentration in biogas C _CH4 from 60.0 to 84.8% leads to an increase in maximum power _Ne from 3.6 to 4.3 kW (by 16 %). In the regime with a rotation speed n = 1420 min ^-1 and a load of about 90% of the full load, an increase in the methane concentration in biogas C _CH4 from 60.0 to 84.8% leads to an increase in power from 3.5 to 3.8 kW (by 8%). In the regime with a rotation speed of n = 1500 min ^-1 at a load of about 65% of the total increase in the concentration of methane C _CH4 from 60.0 to 84.8%, it is accompanied by an increase in power from 2.7 to 2.8 kW, i.e. by 3.6%. At low loads, a change in the concentration of methane in biogas does not significantly affect the effective performance of a diesel engine. Figure 2, b shows the effect of the concentration of methane in biogas C _CH4 on the effective efficiency of the diesel engine η _e in various modes of regulatory characteristics. As follows from the data presented, an increase in the methane concentration in biogas C _CH4 leads to a decrease in the effective efficiency η _e at high loads and does not have a noticeable effect on η _e at low loads. So in the regime with a rotational speed n = 1380 min ^-1 and a maximum load, an increase in the methane concentration in biogas C _CH4 from 60.0 to 84.8% leads to a decrease in the effective efficiency η _e from 41.2 to 35.4%. In the mode with a rotation speed n = 1420 min ^-1 and a load of about 90% of the total increase in the concentration of methane C _CH4 from 60.0 to 84.8%, the efficiency η _e decreases from 40.1 to 36.7%. At a rotation frequency of n = 1620 min ^-1 and a load of about 15% of the total increase in the concentration of methane C _CH4 from 60.0 to 84.8%, on the contrary, it leads to an increase in the efficiency η _e from 15.6 to 16.0%. The maximum values of the effective efficiency η _e are noted in the regimes with high and medium loads at rotational speeds n <1500 min ^-1 .

Figure 3 shows the data on the effective efficiency of the gas η _e diesel engine for its operating conditions in the diesel and gas-diesel cycles at various concentrations of methane in biogas, C _CH4 . The supply of biogas to the combustion chamber (CC), with methane content C _CH4 = 60.0%, allows to increase the maximum value of the efficiency η _e from 27.9 to 41.2% (see figure 3, characteristics 1 and 2). But the specific effective fuel consumption when working on diesel fuel was lower by Δg _e = 50 (g / kW · h). This contradiction is explained by the low calorific value of biogas due to the presence of 40% non-combustible gases (in particular, CO ₂ ) in it and only 60% is accounted for by methane CH ₄ . A significant increase in the efficiency η _e when using biogas instead of diesel fuel is probably associated with a significant improvement in the mixture formation process, which is typical for small diesel engines with low injection pressure. The supply of biogas to the combustion chamber (CC) with a methane concentration C _CH4 = 72.8 allows you to raise the maximum value of the efficiency η _e from 27.9 to 40.1% (see Fig. 3, characteristics 1 and 3), with C _CH4 = 77.8% of the efficiency η _e increased to 37.8% (see figure 3, characteristics 1 and 4), and with C _CH4 = 84.8% - up to 37.8% (see figure 3, characteristics 1 and 5). The results of the studies confirm the existence of a dependence of diesel indicators on the concentration of methane in biogas C _CH4 . Therefore, there is a need to optimize the composition of biogas. With this optimization, the main engine performance should be taken into account, not allowing a transition beyond their limit values.

The main indicators include the effective efficiency of the diesel η _e and the temperature of the exhaust gases (exhaust) T _exhaust . The latter indicator is very important, since when the diesel is converted to biogas, the exhaust gas temperature can increase markedly. The characteristics of the effective efficiency of the diesel engine η _{e are} discussed above (see Fig. 2, b and 3), and the characteristics of the temperature of the exhaust gases T _{OG are} presented in Fig. 4. The data in Fig. 4, a indicate that with an increase in the load (with a decrease in the rotational speed n in the regimes of the regulatory characteristic), the exhaust gas temperature increases significantly and reaches the value of T _{exhaust gas} = 897 K (curve 1 in Fig. 4, and at C _CH4 = 84.8%).

Thus, when optimizing the biogas composition of the diesel under study, it is necessary to ensure maximum engine performance (maximum values of effective efficiency η _e ) under the restrictions imposed on the temperature of the exhaust gases T _OG . It should be noted that with an increase in the load (with a decrease in the rotational speed n in the regimes of the regulatory characteristic), the efficiency of the combustion process increases, which is accompanied by a simultaneous increase in the effective efficiency of the diesel engine η _e and the temperature of the exhaust _gas (ОГ) (Fig. 4, b). Moreover, if during the operation of the investigated engine in the diesel cycle (only on diesel fuel) the exhaust gas temperature limit reaches the level of T _ОГ = 800 К, then, as noted above, when the engine runs in the gas-diesel cycle (on biogas with an ignition dose of DT), the maximum exhaust gas temperature increases to T _OG = 897 K. This can lead to overheating of the components of the diesel engine and, in the first place, its exhaust valves and engine failure. Therefore, a contradiction arises between the desire to increase the effective efficiency of the diesel η _e and the need to limit the temperature of the exhaust _gas .

The analysis of the data of Figs. 4, a, b shows that the limitation of the exhaust gas temperature at the level of TOG = 800 K, typical for a base diesel engine, is achieved only when using biogas with a methane content of _CH4 = 60.0%. When using biogas with methane content C _CH4 = 72.8; 77.8 and 84.8% of this restriction is not provided.

When using biogas with different methane content, it is necessary to limit the temperature of the exhaust gases at a level characteristic of biogas with a low methane content. To do this, it is proposed, when changing the methane content in combustible biofuel, to reduce the ignition dose of diesel fuel by 4 ... 5% for every 4 ... 5% increase in the mass content of methane in biogas (in the diesel engine considered above, from 0.010 to 0.005 g / cycle when changing the methane content in combustible biofuels from 60 to 85%, see figure 5). In this case, the mass cyclic supply of combustible biogas should increase by 4 ... 5% with an increase in the mass content of methane in biogas by 4 ... 5% (in the diesel engine considered above, from 0.020 to 0.023 g / cycle with a change in the methane content in combustible biofuel from 60 to 85 %, see figure 5). Such a change in the cyclic supply of combustible biogas and the ignition dose of diesel fuel will ensure that the exhaust gas temperature remains constant at a level typical for biogas with a low methane content (in the diesel engine under consideration - at a level of 773 K, see figure 5). The indicated values of the ignition doses of diesel fuel are selected from the conditions for ensuring stable ignition of the working mixture. Lower values of ignition doses of diesel fuel do not allow the stable operation of a gas-diesel engine. But in this case, it can be provided by heating the combustible biogas supplied to the working cylinders of the diesel engine. Moreover, the heating of combustible gas is carried out in a heater installed after the compressor, due to the heat of the exhaust gases. An analysis of the experimental characteristics of a number of gas-diesel engines showed that biogas heating in the heater was 10 ... 12 degrees. allows you to reduce the ignition dose of diesel fuel by 4 ... 5% without compromising the flammability of the working mixture.

The proposed method can be widely used in such industries as transport and agricultural engine building, shipbuilding, small energy, etc. The application description contains sufficient information on how to use the proposed method to achieve the positive effect indicated in the technical result. The experimental data presented in the application description confirm the attainability of the technical result and once again prove the possibility of practical use of the proposed method for supplying combustible biogas to the working cylinders of a gas-diesel engine of a power plant. This suggests that the proposed method meets the criterion of "Industrial applicability".

Claims (3)

1. The method of correcting the supply of combustible gas to the working cylinders of a gas diesel, in which gaseous fuel is supplied through the inlet system of the gas diesel and its inlet valves to the working cylinders, wherein the ignition dose of diesel fuel is injected into the working cylinders of the gas diesel by nozzles connected to the mechanism for supplying ignition doses of liquid fuel associated with the regulator of the gas diesel, and the flow of combustible gas is adjusted depending on the composition of the combustible gas, characterized in that the adjustment of the flow of combustible gas - biogas according to percentage set the contents of methane in the biogas is carried out in an indirect evaluation of the content of methane by measuring the content of carbon dioxide in the biogas at the entrance into the inlet gas diesel engine system and / or exhaust gas temperature at the outlet of a gas diesel. 2. The method according to claim 1, characterized in that when using biogas with a methane content of at least 50%, increasing the methane content in biogas for every 4 ... 5% increases the mass fraction of gaseous fuel by 4 ... 5% and, accordingly, reduces the proportion of the ignition dose diesel fuel also by 4 ... 5%. 3. The method according to claim 1 or 2, characterized in that the combustible biogas supplied to the intake system of the gas diesel is heated by 10 ... 12 degrees due to the heat of the exhaust gases with a decrease in the ignition dose of diesel fuel for every 4 ... 5% of such a decrease.

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