Study on emission fuzzy control of ether dimethyl-diesel engine by Avl-fire

Abstract

In this study, the combination of fuel injection parameters and SCR was used to test the material emitted from DME engine combustion under different cylinder conditions by Avl-fire. In order to study the effect of injection pressure and injection time and SCR on engine emissions, the effect of injection DME on engine combustion emissions under the condition that the injection pressure changes continuously from 20 mpa-73 mpa and the injection time from BTDC to ATDC is 15° to ATDC. The study found that when the injection pressure around 38 MPa, NO_X, CO and HC emissions of engine exhaust can satisfy the VI emissions requirements; When the injection time within 3.5° BTDC to 3.5° between ATDC, NO_X, CO and HC emissions of engine exhaust can satisfy the VI emissions requirements; When affected by complex working conditions and environment, the production of NO_X will increase. At this point, with the combination of SCR, the maximum conversion rate of NO_X in the exhaust can reach nearly 79%. Through Fuzzy Logic Toolbox of MATLAB/Simulink (Fuzzy Logic Toolbox) engine emissions of Fuzzy inference system (FIS), then it is introduced into the Fuzzy Logic Controller (Fuzzy Logic Controller) in emission control, the simulation results show that under the condition of Fuzzy control, engine NOX emissions of nitrogen oxides, carbon monoxide, CO and HC hydrocarbons under the VI standard 8.9%, 4.0% and 5.0%, so as to improve the diesel car of environmental protection.

Keywords

Injection pressure injection time exhaust gas SCR fuzzy control

1 Introduction

Published “on the ecological environment of released national pollutant discharge standard” heavy diesel emission limits and measurement methods (stage 6) in China “(GB17691-2018) of notice” (hereinafter referred to as the “country VI”), announced that since July 1, 2021, all production, import, sales, and registration of heavy duty diesel vehicles shall comply with this standard requirements, see Table 1.

Table 1
VI standards with WHEC and WHSC

Experiment CO(mg/kwh) HC(mg/kwh) NOX(mg/kwh) NH₃(mg/kwh) PM(mg/kwh) PN(mg/kwh)

WHSC 1500 130 400 10 10 8.0×10¹¹

WHTC 4000 160 460 10 10 6.0×10¹¹

Experiment	CO(mg/kwh)	HC(mg/kwh)	NOX(mg/kwh)	NH₃(mg/kwh)	PM(mg/kwh)	PN(mg/kwh)
WHSC	1500	130	400	10	10	8.0×10¹¹
WHTC	4000	160	460	10	10	6.0×10¹¹

China VI emissions standards compared with the V, nitrogen oxide (NOx) and particulate matter (PM) emission limit value increased by 77% and 67%, respectively, to increase the number of particles (PN) emissions limit; On engine exhaust gas detection test methods at the same time also has changed dramatically, VI to countries in our country are European steady-state cycle (ESC) and the European transient cycle (ETC), the country VI emissions have adopted more representative world unified steady circulation (WHSC) and the world (WHTC) transient cycle.

According to the Ministry of Public Security, the number of cars on the road nationwide reached 260 million by the end of 2019, an increase of 21.22 million or 8.83 percent over the end of 2018. Diesel engine has the characteristics of high thermal efficiency and low energy consumption and has been widely used in the field of internal combustion engine industry and transportation system.

At present, research institutions and scholars at home and abroad have carried out researches on the special physicochemical properties of dimethyl ether, and proved the high efficiency and low pollution combustion characteristics of dimethyl ether engine. Wang Long et al. from Qingdao University in Shandong province found that the combustion rate of the mixed fuel increased with the increase of the amount of dimethyl ether mixed in the gasoline engine, and the emission of harmful gases, especially the amount of carbon smoke, decreased sharply [1]. AVL of Austria conducted experiments on the combustion of dimethyl ether on diesel engines and found that dimethyl ether can achieve ultra-low emission and gentle combustion, with almost zero carbon smoke emission and low combustion noise [2, 3].

In diesel engines, high-pressure injection systems can reduce smoke emissions by improving fuel-air mixing and spray atomization [4 –6]. Wang et al. studied the effects of super higher injection on flame structure and soot formation, as well as the effects of using a microporous nozzle with a diameter of 0.08 mm in a constant volume cavity on flame structure and soot formation. They found that the jet flame from the microporous nozzle at high pressure produced less soot and reduced particle size. In their work, using 200 MPa and 300 mpa ultra-high injection pressure and micro-orifice nozzles has obvious effect on reducing soot in the spray flame [7, 8].

Nitrogen oxide (NOx) is easily produced when the combustion gas temperature in the engine combustion chamber exceeds 2000 K, because NOx production is a product of high temperature conditions. Therefore, in order to minimize NOx formation, it is necessary to reduce the maximum combustion chamber temperature. Dimethyl ether (DME) is an ideal alternative fuel that can be synthesized from a variety of non-fossil sources and has good ignition performance, with a cetane value higher than that of petroleum diesel, as shown in Table 2 [9]. Compared with traditional diesel, dimethyl ether has oxygen-containing molecular structure, high latent heat, and no C-C bond. Therefore, the use of dimethyl ether fuel can greatly reduce the formation and development of soot in the combustion process of engines [10 –12].

Table 2

Comparison of main physical and chemical properties of methyl ether and diesel engine

characteristic	DME	diesel
chemical formula	CH₃-O-CH₃	CxHy
boiling point	–24.9	180–360
molecular weight	46.07	190–220
liquid densityg/cm³	0.668	0.84
Saturated vapor pressure/MPa	0.51	—-
Low heating value(MJ/kg)	28.4	42.5
cetane number	55–66	40–55
oxygen(% weight)	34.8	0
A/F	9.0	14.6

Fuel combustion retardation period, intake oxygen content, combustion temperature, and combustion duration are the main factors that affect NOX formation during engine combustion [13, 14]. The injection system parameters directly affect the atomization and combustion characteristics of the engine, and finally affect the NOX emission of the dimethyl ether engine. In this paper, the test for WD615 diesel engine in a naturally aspirated engine converted into dimethyl ether engine, based on the optimized by supply of dimethyl ether, by optimizing the nozzle injection pressure, injection time and SCR in the exhaust pipe to reduce the harmful gas engine main (NOX, HC and CO) emissions of experimental research, to the VI emissions standards. At the same time, on the premise of ensuring the fuel economy and power performance of the dimethyl ether engine, it provides certain industrial reference for the study of the combustion emission method of the dimethyl ether engine.

This article uses FIRE software to research on Fuel Injection Parameters and SCR in DME Engine to implement of dimethyl ether engine exhaust gas.

2 Build the simulation model of WD615 diesel engine

2.1 Establishment of combustion chamber simulation model

Combustion chamber geometry precision of the engine number of finite element numerical simulation is more important, but in the combustion chamber geometry model process is influenced by various factors [5], and if all according to the shape of combustion chamber will have larger geometric error modeling and influence the finite element computation efficiency. Therefore, in order to reduce the influence in the modeling process, we usually ignore the gap between the cylinder wall and the piston to improve the calculation accuracy. Table 3 shows the parameters of the eccentric combustion chamber of WD615 diesel engine used in this paper [6]. The 3D model of the engine can be divided by the HyperMesh after the PROE is drawn. As shown in Fig. 1, the finite element grid diagram of the engine at a certain crankshaft Angle.

Table 3
The specifications of WD615 diesel engine

model form WD615 four-stroke, Six cylinder, supercharge, intercooling

Cylinder diameter 110 mm

pistion stroke 130 mm

Vst 7.98

compression ratio 18 : 1

Maximum torque/speed 980 N.m/1450 r/min

Maximum power/speed 178 KW/2000 r/min

model form	WD615 four-stroke, Six cylinder, supercharge, intercooling
Cylinder diameter	110 mm
pistion stroke	130 mm
Vst	7.98
compression ratio	18 : 1
Maximum torque/speed	980 N.m/1450 r/min
Maximum power/speed	178 KW/2000 r/min

Fig. 1

Finite element mesh diagram of a certain axle corner.

2.2 Parameter setting

2.2.1 Calculate the time step

Studying the characteristics of dimethyl ether engine emissions can be through the establishment of the corresponding model, so we focus on researching two stroke which are work and discharge, the corresponding crank Angle is 348 ° CA To 708 ° CA [4]. The engine oil supply Angle is 348 ° CA, internal combustion engine soon after oil supply, so we will be 348 ° CA - 378 ° CA calculation step length is set to 0.05, 378 ° CA - 708 ° CA is set to 0.1 [7].

2.2.2 Boundary conditions

The effective area calculated by this model is the combustion chamber of the engine, while the combustion chamber is a closed system which is consisting of three boundary surfaces consisting of the cylinder head surface, the piston top surface and the cylinder wall surface. In this system of temperature boundary can be identified at the top of the cylinder head bottom and cylinder wall and piston temperature boundary are the three surface as the constant value, thus we can refer to the constant value experience in the following formula [8]: $T_{w 1} = 120 + 30 p_{e} + 273$ (1) $T_{w 2} = 100 + 7 p_{e} + 273$ (2) $T_{w 3} = 100 + 4 p_{e} + 273$ (3)

In the formula, Pe represents average effective pressure (bar). According to the above empirical formula, the final cylinder temperature of the wall surface is 470 K, the top of piston and cylinder head temperature is 570 K. The boundary data obtained from the calculation is entered into the boundary conditions of FIRE2013 [9].

2.2.3 Initial condition setting

The setting of boundary conditions and initial conditions has great influence on the final simulation result for the high speed combustion hybrid fuel engine. Assumption in the initial phase calculation, the initial temperature and pressure of the gas in the cylinder is uniform, pressure value by the experiment of the related equipment to measure, the initial temperature can be calculated according to the empirical formula: $T = 316 + 0.86 (T_{0} - 273)$ (4)

In the formula, T0 represents the temperature of the inlet.

The turbulence kinetic energy TKE at the initial time can be calculated according to the following formula [10]: $TKE = \frac{3}{2} \times u^{' 2}$ (5) $u^{'} = 0.7 \times C_{m}$ (6) $C_{m} = 2 \times h \times (\frac{n}{60})$ (7)

Where, u’ is the velocity of turbulence pulsation, and the unit is m/s; The average velocity of the piston is m/s. H is the stroke of the piston, the unit is m; N is the engine speed, the unit is r/min. According to Equation 5, the size of TLS (turbulent length) can be calculated [11]: $TLS = \frac{h_{v}}{2}$ (8)

Where, the hv unit is m, which represents the maximum valve lift. The calculation equation of the fuel injection amount of the engine is: $V_{b} = \frac{b_{e} P_{e} τ}{120 n ρ_{f} i} \times 10^{3}$ (9)

Among them, Pe is the power of the calibration power point, and the density of the dimethyl ether is the density of l, and I is the number of cylinder of diesel engine, the number of stroke of the diesel engine, and the fuel consumption rate of the calibration power point [12].

2.3 Calculation model selection

3 Simulation of emission characteristics and analysis

Liang Chen, of Beijing University of Technology, found that when the quality score of dimethyl ether was more than 25%, the dynamic performance of the engine decreases greatly at high speed and heavy load, resulting in a serious increase in NOx emissions. Therefore, the proportion of diesel mixed with dimethyl ether can’t be more than 25%. In order to further demonstrate the advantages of the combustion of dimethyl ether engine, this section selects four kinds of mixed fuels with a mixture ratio of 0%, 5%, 15% and 25% to study and analyze the emission characteristics.

3.1 The effect of dimethyl ether on diesel engine emissions

By AVL FIRE software simulation output graphics can see clearly in the mixing dimethyl ether in diesel combustion emissions in the instantaneous change rule. In this paper, we selected the engine speed n = 1400 r/min, BMEP = 0.5 MPa, NOx, and found HC and CO in the engine exhaust gas with dimethyl ether in diesel blending proportion change of emission characteristics.

3.2 Influence of injection pressure

Figures 2 and 3 show the influence of continuous pressure changes between 20 MPa and 73 MPa on NOx emission of dimethyl ether engine under different cylinder pressures. It can be seen that with the reduction of the nozzle injection pressure, NOx emission in the tail gas is significantly reduced. When BMEP = 0.327 MPa, when the injection pressure Pinj, down from Pinj = 73 MPa = 20 MPa, NOx fell by 0.643 g/kWh, a drop of 77.3%, in the Pinj 38 MPa, or less NOx emissions of engine exhaust China VI emission standard of less than 450 mg/kWh; For BMEP = 0.654 MPa, when the injection pressure Pinj, down from Pinj = 73 MPa = 20 MPa, NOx fell by 0.768 g/kWh, a drop of 87.2%, in the Pinj acuities were 38.5 MPa, NOx emissions of engine exhaust conform to the VI two situations (WHSC and WHTC) emission standard of less than 450 mg/kWh. This is mainly due to the reduction of nozzle injection pressure, the increase of internal combustion retardation period of the engine, dimethyl ether combustion rate significantly delayed, the overall delay of the engine combustion, mixed gas combustion far away from the upper dead point, combustion capacity decline, the maximum combustion temperature in the engine cylinder significantly reduced, so NOx specific emissions significantly reduced.

Fig. 2

Relationship between NOx and injection pressure.

Fig. 3

Relationship between NOx and injection pressure.

Figures 4 and 5 show the influence of continuous pressure changes between 20 MPa and 73 MPa on CO and HC emissions in tail gas under different in-cylinder pressures of dimethyl ether engine. It can be seen that with the increase of the nozzle injection pressure, the CO emission in the tail gas decreased significantly. When BMEP = 0.327 mpa and BMEP = 0.654 mpa, when the injection pressure increased from Pinj = 20 MPa to Pinj = 73 MPa, the CO emissions from 20 MPa to 73 MPa showed a significant decrease, both by more than 50%. And under the background of two kinds of constant pressure, different from the burning of injection pressure CO emission were below 1500 mg/kWh, which conform the VI two situations (WHSC and WHTC) emissions to the requirement of CO. In addition, with the increase of nozzle injection pressure, HC emission in exhaust gas also decreases significantly. When BMEP = 0.327 mpa and BMEP = 0.654 mpa, when the injection pressure increased from Pinj = 20 MPa to Pinj = 73 MPa, the HC emissions from 20 MPa to 73 MPa also showed a significant decrease, both by more than 70%. And in BMEP = 0.327 MPa and Pinj acuity 38.2 MPa, HC emissions of less than 130 mg/kWh, accord with the VI two situations (WHSC and WHTC) emissions standards; In BMEP = 0.654 MPa and a Pinj 38 or MPa, HC emissions of less than 130 mg/kWh, accord with the VI two situations (WHSC and WHTC) emissions standards.

Fig. 4

Relationship between CO and injection pressure.

Fig. 5

Relationship between HC and injection pressure.

Figures 6 and 7 show the effect of SOI (Start of Injection) on NOx emission with different Injection times under different in-cylinder pressures. As for BMEP = 0.327 mpa, when the injection time was delayed from SOI = 12°CA BTDC (engine operating rough limit) to SOI = 7°CA ATDC (engine fire limit), the NOx emission decreased by 0.675 g/kWh or 78.6% during the continuous change stage. At BMEP = 0.654 mpa, when the injection time was delayed from SOI = 13.5°CA BTDC (engine operating roughness limit) to SOI = 9.2°CA ATDC (engine misfire limit), during the continuous change phase, the NOx ratio decreased by 1.03 g/kWh, or 78.9%. Through the two pictures we can find that when the SOI after 3.5 ° CA BTDC, which occurred before the fire limit, NOx emissions of engine exhaust conform to the VI two situations (WHSC and WHTC) emission standard of less than 450 mg/kWh.

Fig. 6

Relationship between NOx and injection time.

Fig. 7

Relationship between NOx and injection time.

Figures 8 and 9 show the effect of SOI (Start of Injection) on CO and HC emissions with different Injection times. When SOI is pushed forward with the injection time, CO and HC emissions decrease significantly. But in terms of CO, both in BMEP = 0.327 MPa and BMEP = 0.654 MPa, in different injection time CO emission were below 1500 mg/kWh, conforms to the VI two situations (WHSC and WHTC) emissions to the requirement of CO. For HC, at BMEP = 0.327 mpa, when the injection time was delayed from SOI = 12°CA BTDC (engine operating roughness limit) to SOI = 7°CA ATDC (engine fire limit), the HC specific emissions decreased by 0.124 g/kWh or 83.1% during the continuous change in this stage. However, when BMEP = 0.654 mpa and the injection time was delayed from SOI = 13.5°CA BTDC (engine operating violent limit) to SOI = 9.2°CA ATDC (engine fire limit), the HC specific emissions decreased by 0.074 g/kWh or 80.4% during the continuous change in this stage. Through the two pictures we can find that when the SOI before 6.4 ° CA ATDC, the injection time from engine work before rough point check points on the first check point 3.5 ° CA after that time, the engine HC in the exhaust emission is less than 130 mg/kWh, accord with the VI two situations (WHSC and WHTC) emissions standards.

Fig. 8

Relationship between CO and injection time.

Fig. 9

Relationship between HC and injection time.

3.3 Influence of SCR

In this paper, SCR selected V205-TI02 catalytic converter to reduce NOx emission in engine exhaust pipe. The connection between SCR and engine is communicated by CAN bus. Urea in SCR is aqueous urea solution conforming to GB 29518-2013 standard.

Figure 10 shows the change of NOX conversion rate in engine exhaust pipe with the concentration of urea (NH3) ejected from SCR under normal operation of DME engine. It can be seen that with the increase of the injection concentration, NH3 gradually increases from 80 ppm to 140 ppm, and the NOX conversion rate in the engine exhaust pipe is improved to a certain extent. When working hours reached 12 S, the conversion rate increased to 78.7%. When used in conjunction with the front article said the injection time and injection pressure, the DME engine can be greatly reduced the amount of NOX in the exhaust pipe, can reduce the ECU of injection pressure and injection time on the accuracy of the requirements under the premise of meet the engine exhaust gas of NOX emissions in accordance with the VI two situations (WHSC and WHTC) emission standard of less than 450 mg/kWh.

Fig. 10

Relation between NH3 concentration and NOX conversion rate.

4 System control parameter optimization

4.1 Determine the objective function

Firstly, nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) were selected as the optimization objective parameters [9], and the optimization objective function was established as Formula (10), whose variables were the content of dimethyl ether in the mixture and the engine fuel injection advance Angle. $f (x) = min [ω_{1} m_{{NO}_{X}} + ω_{2} m_{CO} + ω_{3} m_{HC}]$ (10)

In the equation, ω₁ is the weighted coefficient of NOX mass in emissions, ω₂ is the weighted coefficient of CO mass in emissions, and ω₃ is the weighted coefficient of HC mass in emissions.

4.2 Determine the weighting coefficient

The Analytic Hierarchy Process is to determine the weighted coefficient by comparing the results of each evaluation index.

H_ab represents the comparative value of the importance degree between evaluation index A and evaluation index B. This method determines: if A and B are equally important, the value is 1; if A is more important than B, the value is 9.

The judgment matrix as shown in Table 4 can be constructed through the importance values of each evaluation index.

Table 4
Model name in FIRE

Name Choose the model name in FIRE

Engine combustion chamber model turbulence model k-ξ-f model

Fuel spray model WAVE discrete model

Evaporation model of mixed fuel Mufti-component model

combustion model ECFM-3Z flame model

NOx generation model Zeldov-ich model

Carbon smoke formation and oxidation model Lund Flamelet Model

Name	Choose the model name in FIRE
Engine combustion chamber model	turbulence model k-ξ-f model
Fuel spray model	WAVE discrete model
Evaporation model of mixed fuel	Mufti-component model
combustion model	ECFM-3Z flame model
NOx generation model	Zeldov-ich model
Carbon smoke formation and oxidation model	Lund Flamelet Model

VI according to vehicle emission standards in our country (countries), selection of nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) as the main index in the evaluation of vehicle emissions, environmental protection.

NO_X and CO are toxic gases, which will damage the respiratory system and even cause death when inhaled. Therefore, compared with HC, NO_X and CO are in a very important position. CO and NO_X are both toxic gases and of equal importance.

To sum up, the judgment matrix of each evaluation index in this paper is obtained, as shown in Table 6.

Table 5

Judgment Matrix

Comparison value	index 1	index 2	Index 3
index 1	1	h12	h13
index 2	1/h12	1	h23
index 3	1/h13	1/h23	1

Table 6

Judgment Matrix

Comparison value	NO_X	CO	HC
NO_X	1	1	9
CO	1	1	9
HC	1/9	1/9	1

According to the judgment matrix in Table 6, the weighted coefficient of each evaluation index is calculated according to the requirements of ahP:

Calculate the multiplication vector of judgment moment (Table 9) matrix row elements: $X_{m} = \prod_{n = 1}^{3} e_{mn}$ (11)

The calculated matrix Xm = [9,9,1/81].

Calculate the third square root vector Hm multiplied by the vector Xm according to the matrix Xm, $H_{m} = \sqrt[3]{X_{m}}$ (12)

Hm = [2.080,2.080,0.2311].

Compute the canonical vector of the vector Hm. $β = H_{m} / \sum_{i = 1}^{n} H_{i}$ (13)

As calculated β = [0.4737,0.4737,0.0526], the vector is the weight coefficient of each evaluation index. Therefore, according to the calculation results, the weighted coefficient of NOX is 0.4737, the weighted coefficient of carbon monoxide CO is 0.4737, and the weighted coefficient of hydrocarbon HC is 0.0526.

Verify the consistency of judgment matrix Consistency ratio: $CR \frac{λ_{max} - n}{RI (n - 1)} = \frac{\sum_{i = 1}^{n} \frac{(EH)_{i}}{n H_{i}} - n}{RI (n - 1)}$ (14)

Where, when n = 3, RI = 0.58, and CR = –1.753 < 0.1, the consistency test is passed.

4.3 Parameter optimization based on genetic algorithm

Based on the finite element simulation model and evaluation system established above, the genetic algorithm optimization program was written in MATLAB/Simulink with Formula (10) as the optimization objective function. The control parameters were selected as follows: population size: 80; Probability of variation: 0.06; Crossover probability: 0.70; Termination conditions: the evolutionary algebra is 200. The content of dimethyl ether in the mixture ranges from 10% to 60%.

Under typical working conditions (idle speed, low speed constant speed (30 km/h), medium speed constant speed (60 km/h), high speed constant speed (100 km/h), acceleration and deceleration), the content of dimethyl ether is optimized.

Table 7 and Table 8 show the optimal results of the proportion of dimethyl ether and the advance Angle of fuel injection under full load and no load in turn.

Table 7
Optimization Results of Full Load

Working condition dimethyl ether content (%)/ignition advance Angle (°CA)

Idle speed 43% /7°

constant speed slow 42% /8°

Medium speed uniform 37% /11°

The uniform 35% /12°

To speed up 27% /18°

Slow down 48% /5°

Working condition	dimethyl ether content (%)/ignition advance Angle (°CA)
Idle speed	43% /7°
constant speed slow	42% /8°
Medium speed uniform	37% /11°
The uniform	35% /12°
To speed up	27% /18°
Slow down	48% /5°

Table 8

Optimization Results of Road Load

Working condition	dimethyl ether content (%)/ignition advance Angle (°CA)
Idle speed	47% /6°
constant speed slow	45% /7°
Medium speed uniform	40% /9°
The uniform	37% /10°
To speed up	30% /15°
Slow down	49% /5°

5 System fuzzy control establishment

Neural network fuzzy control is developed on the basis of simulating the thinking process of human brain and the neural structure of human body. Its most prominent feature is the function of autonomous learning.

Neural network fuzzy control only needs to input the known input and the corresponding result into the controller, and the network will get the corresponding result through self-learning.

The combination of neural network and fuzzy control will greatly reduce the work of designers [12, 13].

To better improve the dimethyl ether - diesel engine under different working conditions, meet the VI (a) the ability of emissions standards, this article is based on the optimization results in section 3.4 above, using the neural network fuzzy control method on the ignition advance Angle (°CA) and dimethyl ether content two parameters to control, design adapted to the WD615 model of dimethyl ether - diesel engine neural network fuzzy controller, and verify that the control effect.

5.1 Design of Sugeno fuzzy controller

The optimizing results was what the engine under different load, full load and no load and different speed conditions (idle speed at a constant speed at a constant speed, medium speed at a constant speed, low speed, high speed, acceleration and deceleration) the optimization of the input and output data obtained under study, incorporating the 12 groups of test data after the combination in the form of matrix in the software shall be kept in the workspace for calls. T-S fuzzy controller with double input and single output of engine emission system is established in Matlab/Simulink, in which the combination algorithm takes the product, the disjunction algorithm takes the sum, and the clearness algorithm takes the weighted average.

T-s type fuzzy controller through the “edit” food is boring and a kind of adaptive neural network inference (Anfis), the training data for import, at the same time, the amount of input fuzzy subset number all choose 5, using gaussian membership function, output using linear model, the final will be generated with a fuzzy control rules of article 25 of the initial FIS, the system model structure is shown in Fig. 11.

Fig. 11

Anfis Structure of T-S Fuzzy Interference System.

On the basis of initial FIS, the data of ignition advance Angle and mixture concentration loading are trained by mixing method, and the system can automatically adjust the distribution of membership function.

The training number was set as 50 times, and the training error of ignition advance Angle displayed after the training was 0.27782, and the training error of mixture concentration was 0.44432. At this time, the t-S fuzzy inference engine suitable for dimethyl ether - diesel engine is designed. Open the membership function editor to see the distribution of the final ignition advance Angle and the mixture concentration, as shown in Fig. 12.

Fig. 12

Membership Function Distributions of Two Inputs of Spark Advance Angle and Mixture Gas Concentration.

5.2 Verification of control effect

Under mixed working conditions (idle speed, low speed uniform, medium speed uniform, high speed uniform, acceleration and deceleration), the controller designed in this paper is simulated and verified, and the simulation results are shown in Table 9.

Table 9
Simulation Result

Load M_NOX/ g/km M_CO/g/km M_HC/g/km

Full load 0.02 0.15 0.01

No load 0.03 0.17 0.03

Load	M_NOX/ g/km	M_CO/g/km	M_HC/g/km
Full load	0.02	0.15	0.01
No load	0.03	0.17	0.03

According to the optimization results in Table 9, after the optimization control of the content of dimethyl ether and the fuel injection advance Angle, the engine emission was greatly improved compared with that before the optimization control. The mass of NO_X per kilometer was reduced by at least 96.7%, and the mass of HC per kilometer was reduced by at least 94.4%.

Compared with China VI emission standards, NO_X quality below standard 8.9% per kilometer, CO quality below standard 4.0% per kilometer, HC quality below standard 5.0% per kilometer, the optimized dimethyl ether-diesel engine completely conform to the requirements of the countries VI emissions.

6 Conclusion

Using AVL-FIRE software on a modified diesel engine to study the emission characteristics of DME engines with different injection time (15°BTDC-10°ATDC) and different injection pressure (20 mpa –73 MPa) combined with SCR under two BMEPs (0.327 MPa and 0.654 MPa). For the conditions studied, the experimental results are summarized as follows:

With the increase of injection pressure (20 MPa –73 MPa), NOx emission in DME engine combustion shows an increasing trend. When BMEP = 0.327 MPa and BMEP = 0.654 MPa, injection pressure and MPa or less when the engine NOx emissions meet China VI emission requirements. With the increase of injection pressure (20 MPa –73 MPa), CO and HC emissions in DME engine combustion showed a downward trend. When BMEP = 0.327 MPa and BMEP = 0.654 MPa, CO emissions of all conform to the requirements of the countries VI standards; When BMEP = 0.327 MPa and BMEP = 0.654 MPa, the injection pressure acuity 38.2 MPa when engine HC emissions meet China VI emission requirements.

With the increase of injection time (15°BTDC-10°ATDC), NOx emission in DME engine combustion shows a downward trend. When BMEP = 0.327 MPa and BMEP = 0.654 MPa, the injection time in front of the check point on 3.5 ° C (BTDC) to occur before the fire limit engine NOx emissions meet China VI emission requirements. With the increase of injection time (15°BTDC-10°ATDC), CO and HC emissions in DME engine combustion showed an increasing trend. When BMEP = 0.327 MPa and BMEP = 0.654 MPa, CO emissions of all conform to the requirements of the countries VI standards; When BMEP = 0.327 MPa and BMEP = 0.654 MPa, the injection time from the engine working before check point on rough point after the first check point 3.5 ° CA ATDC) engine HC emissions during this time of the China VI emission requirements.

When SCR is involved in the exhaust pipe, NOX can be effectively transformed in the exhaust, but it is limited by the exhaust temperature and the concentration of urea (NH3) ejected in the SCR. The higher the urea concentration in SCR, the higher the professional efficiency of NOX increases with the extension of time, with a maximum conversion rate of nearly 79%.

Under typical conditions (idle speed at a constant speed at a constant speed, medium speed at a constant speed, low speed, high speed, acceleration and deceleration), through the genetic algorithm to the content of dimethyl ether and fuel injection advance Angle is optimized, compared before and after optimization, NOX emissions by 8.9% below VI standards, CO emissions 4.0% below VI standards, HC emissions 5.0% below VI standards, vehicle emissions, environmental protection.

References

Lim

O.T.

and Iida

, A study on the spray and engine combustion characteristics of diesel–dimethyl ether fuel blends, Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering229(6) (2015).

Tikani

, Vahdati

and iaei-Rad

, Two-Mode Operation Engine Mount Design for Automotive Applications, Shock and Vibration19(6) (2010).

Zhang

, Zhang

and Bayat

, Research on the Field Dynamic Balance Technologies for Large Diesel Engine Crankshaft System, Shock and Vibration2017 (2017).

, Shi

, Wang

, Cong

, Su

and Yu

, Investigation on performance of a spark-ignition engine fueled with dimethyl ether and gasoline mixtures under idle and stoichiometric conditions, Energy126 (2017).

Chen

, Wang

H.-tao

and Wang

, Different Oxygen Levels of Dimethyl Ether Combustion Influence Numerical Simulation, Procedia Engineering31 (2012).

Bai

, Ma

, Zhang

, Ying

and Fang

, Process simulation of dimethyl ether synthesis via methanol vapor phase dehydration, Polish Journal of Chemical Technology15(2) (2013).

Fuest

, Barlow

R.S.

, Chen

J.-Y.

and Dreizler

, Raman/Rayleigh scattering and CO-LIF measurements in laminar and turbulent jet flames of dimethyl ether, Combustion and Flame159(8) (2012).

Matzen

and Demirel

, Methanol and dimethyll ether from renewable hydrogen and carbon dioxide: Alternative fuels production and life-cycle assessment, Journal of Cleaner Production139 (2016).

Hosseini

S.Y.

and Nikou

M.R.K.

, Synthesis and Characterization of Different γ-Al2O3 Nanocatalysts for Methanol Dehydration to Dimethyl Ether, International Journal of Chemical Reactor Engineering10(1) (2012).

10.

Sezer

İ.

, Thermodynamic, performance and emission investigation of a diesel engine running on dimethyl ether and diethyl ether, International Journal of Thermal Sciences50(8) (2011).

11.