ANALYSIS OF ENGINE PERFORMANCE AND EMISSIONS UNDER DIFFERENT LOADS WHEN METHANOL IS INJECTED INTO TH

International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN(P): 2249–6890; ISSN(E): 2249–8001 Vol. 10, Issue 3, Jun 2020, 229–238 © TJPRC Pvt. Ltd.

ANALYSIS OF ENGINE PERFORMANCE AND EMISSIONS UNDER DIFFERENT LOADS WHEN METHANOL IS INJECTED INTO THE ENGINE CYLINDER THROUGH THE INTAKE DUCT AFTER THE INTERCOOLER CHANG CHUN XU1 & HAENG MUK CHO2 1

PhD Student, Division of Mechanical and Automotive Engineering, Kongju National University, Cheonan Daero, Seobuk-gu, Cheonan-si, Chungcheongnam-do, South Korea 2

Professor, Division of Mechanical and Automotive Engineering, Kongju National University, Cheonan Daero, Seobuk-gu, Cheonan-si, Chungcheongnam-do, South Korea

ABSTRACT During the study of the diesel-methanol dual fuel experiment by adding methanol fuel to the existing diesel engine, it was found from the experiment that with the addition of methanol, the NOx emissions were significantly reduced, and then HC and CO emissions were significantly higher than diesel with the addition of methanol. This experiment was performed to compare the analysis of engine combustion performance and exhaust emissions after the addition of methanol, and methanol dual fuels are burned under low, medium, and high load conditions, the experimental condition was set at 1400rpm, and output torque set at 100N.m, 200N.m, 300N.m to do this experiment analysis. The air mainly enters the air pipe from the air inlet in front of the intercooler, passes through the intercooler, and then enters the cylinder. However, due to the physical factors of the methanol that are not miscible with diesel, methanol is mainly in the front of the intercooler was performed. At the same time, it was found that NOx emissions were significantly lower than those in the pure diesel mode, which reduced engine power. The optimized fuel cost of the DMDF mode is greatly increased, and the

Original Article

including the engine's Braking Thermal Efficiency (BTE), BSFC, PRR, HRR and in-cylinder pressure, when the diesel

BTE will be higher than that of the pure diesel combustion mode.

KEYWORDS: DMDF, Intercooler, Injection Position, Diesel Engine & Performance

Received: Feb 28, 2020; Accepted: Mar 19, 2020; Published: Apr 30, 2020; Paper Id.: IJMPERDJUN202022

INTRODUCTION Diesel vehicles are widely used in the transportation and industry. In order to bring great benefits, environmentally and economically use of biodiesel fuel are considered for alternating diesel. Biodiesel and primary alcohols are the most accepted biofuels. Since the 20th century, the researchers have focused on developing a potential alternative feedstock for diesel engine due to depleting fossil fuel reserves and stringent emission norms in the world. Due to the combustion, high temperature causes the increase of NOx. The alcohols into diesel will be used which include ethanol and methanol etc. which can be produced by fermentation of sugarcane juice and other renewable resource such as biomass and waste products. Alcohol which has low heat value, low viscosity, high oxygen, low cetane number can cause higher delay ignition and shorter combustion duration. As alcohols have easy ignition and faster combustion properties, it makes higher cylinder pressure and its high temperature cause the emission of HC and CO to decreased level. Another reason is that the low cetane number cause the air fuel mixed, complete the reaction and lower cylinder temperature due to high latent heat value of evaporation and decrease of the NOx production.

Alcohols serves as a fuel additive through which port was injected before intercooler and injected into diesel engine

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cylinder. This is because the methanol cannot be mixed effectively with diesel. It has been stated that the viscosity and surface tension of the fuel blends with alcohol addition decreases with an improvement of atomization and an increase in oxygen content.

In order to add methanol for using diesel engines, it has two important options to be considered. Fuel properties will need to be improved when methanol is used to mix with diesel. The other aspect is that the used additional additives would improve fuel properties when the fuels premixed for injection direction, because the methanol is not effectively mixed with diesel. In this paper, the experiment will consider port injection. When methanol used in diesel engine due to its characteristics that longer ignition delay and low viscosity cause methanol/air mix complete, into cylinder make shorter combustion duration and make the lower cylinder temperature, therefore cause NOx production decrease.

With the increase of methanol substitution percent, the diesel consumption and engine power will be reduced. Then, BTE will be decreased at low load. Zang et al[10]. found that the BTE decreases with an increase in fumigation methanol at low load. But fumigation methanol can decrease NOx emissions. And Liu J et al[3]. found that increasing the methanol substitution percentage would reduce global mixture reactivity, which led to a late combustion phasing, a long combustion duration, and eventually excessive levels of unburned HC and CO emissions. Meanwhile, methanol has high latent heat feature that can reduce the ambient temperature in the intake duct and cylinder, and such phenomenon is more pronounced at high MSP. As the methanol has high latent heat properties, it may cause cold starting problem of diesel engine, and combustion in cylinder is unstable under low temperature which can lead to misfire of engine.

In DMDF engine, methanol fuel is injected into engine with air premixed mixture with air, the diesel is directly injected into the cylinder. The mixture fuel that methanol and air enter into each cylinder of engine though a long pipe of air inlet and ignited by diesel compression in cylinder. The important phenomenon can be found that the pulsating flow in the air inlet can affect the mass flow rate into engine.

As the methanol with air mixture into each cylinder different caused combustion difference, and then makes the engine performance harmfully. But, because engine turbocharged make the air into cylinder harder, it can decrease the effect with different combustion.

COMPOSITION OF EXPERIMENTAL EQUIPMENT The experimental data in this paper was obtained using the Yunei D30 inline 4-cylinder supercharged intercooled commonrail diesel engine of the School of Automotive Engineering, Hefei University of Technology. The engine specifications used in this experiment are shown in Table 1. Figure 1 shows the structure of the engine during the experiment. The engine achieves dual fuel injection. Air enters the intake pipe through the air filter (to ensure that the air entering the cylinder is clean). Air quickly enters the cylinder and is cooled by an intercooler before entering the cylinder. Methanol injection is added before the intercooler of the intake pipe, after the intercooler and before the common rail injection. Biodiesel can be mixed with diesel in any ratio, so diesel and biodiesel can be injected directly into the cylinder to achieve dual fuel injection.

These controllable injection conditions are controlled by a variable ECU. There are multiple air temperature and pressure sensors on the intake pipe, which collect the temperature and intake pressure of the incoming air and fuel. The sensor is connected to a data collection computer. The collected data is used for data analysis.

The properties of diesel, biodiesel and methanol are listed in Table 2. Diesel consumption is measured by the AVL735 fuel gauge, and methanol is controlled only by the methanol ECU to inject at multiple positions before and after Impact Factor (JCC): 8.8746

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the air intake and before the air intake. Cylinder Combustion exhaust gas is collected and analyzed by MEXA-584L exhaust gas analyzer and AVL filter paper collection analyzer produced by HORIBA for smoke and dust emission.

Table 1: Engine Description Engine Type D30 4 Cylinder in-line diesel engine Turbocharged inter-cooled Air intake form 4 Cylinder NO. Diesel Fuel 2.977L Displacement 115KW Maximum power output 3200rpm Speed Max Hp 156马力 400N.m Max Torque 1500-2700rpm Max torque speed Min fuel consumption for full load ＜208g/kW.h 95X105mm Bore X Stroke Valve train 4个

Figure 1: Structure of the Experimental Engine.

Table 2: Characteristics of Diesel, Biodiesel and Methanol Properties Methanol Diesel 0.7866 0.829 Densty g/ml 65 187-343 Boiling point ℃ 136 15-25 octane 3.8 40-55 cetane 16 46 Energy density MJ/L 20.1 42.8 LHV MJ/Kg 1.2 0.23-0.60 Evaporation heat MJ/Kg -97 -40--34 ℃ 12 74 Cooling point ℃ 463 235 Autoignition temperature ℃ 0.5445*10-3 Viscosity Pa s

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TEST FUEL The diesel used in the test was commercial 0# diesel fuel, where the sulfur content in diesel is lesser than 10ppm. And, the diesel fuel was set inject into engine cylinder directly and the methanol bought from factory and used ECU controlled from intake port before intercooler injected methanol into cylinder of engine. During the experiments, diesel temperature was maintained at approximately 25℃ to rule out the effect of diesel temperature on the experimental results. And the methanol used was the chemical analysis methanol, and the purity is 99.99%. Methanol temperature was fixed at 25℃. Table 2 shows the methanol properties and the diesel properties.

EXHAUST EMISSIONS MEASUREMENT The gaseous emissions including CO, HC and NOx were measured by using a gas analyzer system from MEXA-584L, HORIBA. And the gaseous emissions were measuring in the exhaust emission system. Emissions analysis date is obtained from the measuring system. In the emission system, the method of gaseous emissions are different. Flame lionization detector analyzer was used to measure total hydrocarbon emissions. Infrared detector analyzer was used to measure CO 2 and CO emissions. Chemiluminescent detector analyzer was used to measure NOx emissions. Meanwhile, a smoke meter (AVL filter paper collection analyzer) was used for soot emissions measurements.

The cylinder pressure was measured with a pressure transducer mounted on the first engine cylinder head. A shaft encoder with 360 pulses per revolution was used, which supplies a resolution of 1 。crank angle. The pressure transducer was connected to a kistler K-box charger amplifier to get the digital signal, which was then passed to the K-box combustion analyzer for future processing. The cylinder pressure data was recorder as the average of 50 consecutive cycles of data.

TEST METHODS AND PROCEDURE During the experiments, investigation was done to find the effect of intake air temperature on performance and exhaust emissions of diesel methanol dual fuel engine at each methanol mass fraction flow into three positions, and with each experiment set the constant diesel injected pressure that 100Mpa 200Mpa, 300Mpa, and set injection timing constant. The engine was operated at constant engine speed such as 1400rpm and the methanol substitution ratio was set 0%，30%，40%, 50% for methanol injection without engine EGR system, and the MSR calculated the methanol mass fraction from the methanol tank was used to replace diesel fuel for combustion in the engine cylinder. At each test point, the period of operation was maintained for about 3minutes Based on the engine load and the mass consumption rate of diesel and methanol, the formula MSR is as follow shown： MSR=

𝑚𝐷𝑛𝑒𝑎𝑡 −𝑚𝐷𝑑𝑢𝑎𝑙 𝑚𝐷𝑛𝑒𝑎𝑡

∗ 100%

The term 𝑚𝐷𝑛𝑒𝑎𝑡 represents diesel fuel consumption when the engine was operated with neat diesel (kg/h), while 𝑚𝐷𝑑𝑢𝑎𝑙 represents the diesel fuel consumption when methanol injected (kg/h). Both of these data are measured by an AVL 735 fuel flow meter.

Comparison of changes in different Methanol Replacement Rates, BTE, HRR and Cylinder Pressure When the engine uses different fuels, its effective thermal efficiency can more effectively represent the fuel economy. Under different operating conditions, the effective thermal efficiency of the engine using the same fuel increases with the increase Impact Factor (JCC): 8.8746

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of the average effective pressure in the cylinder. The effective thermal efficiency of using methanol fuel has a significant increase over the effective thermal efficiency of diesel, as shown figure 3, but it has a significant increase with the increase of the speed cut back. This is mainly because of the fact that the oxygen contained in methanol can improve the combustion process of fuel oil, and its viscosity is low, it is easy to evaporate, and it improves the combustion efficiency. Relative to the use of different fuels, the effective fuel consumption rate decreases as the average pressure increases. At the same speed, the addition of methanol increases the fuel consumption, as shown in figure 1. As the speed increases, the fuel consumption also increases.

Figure 1: The Cylinder Pressure under different Loads (Low, High).

Figure 2: The BSFC under Different Loads.

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Figure 3: The BTE under Different Loads.

There is a relationship between the maximum pressure increase rate and the maximum heat release rate and the substitution rate of methanol to diesel under different operating conditions. At a speed of 1400 rpm, the maximum pressure increase rate and the maximum heat release rate increase with the increase of the methanol replacement rate. And the increase trend is obvious under heavy load. Because the flame retardation period becomes longer as the methanol content increases, the premixed combustion increases to increase the maximum heat release rate and the maximum pressure increase rate. At 1400 rpm, the maximum heat release rate and the maximum pressure increase rate increase significantly with the increase of methanol to diesel replacement rate. At high load, the maximum heat release rate increases significantly and the maximum pressure increase rate slightly increases shown figure 1 and figure 4. With the addition of methanol, the ignition is delayed and the combustion period is prolonged, and the viscosity of methanol is low, and the diffusion and evaporation speed is fast, which results in the rapid combustion speed, as shown in figure 4.

Due to the rapid evaporation of methanol and the lower viscosity, the fuel injection atomization effect of the fuel is improved. The physical and chemical characteristics of low calorific value of methanol and high latent heat of evaporation may cause the first peak to be lower than the heat release curve of diesel corresponding peak. In the first stage, the fuel preinjection corresponding to the exotherm lasts for a short time. After that, due to the low viscosity and high evaporation rate of methanol, the heat release curve is higher than that of diesel.

Figure 4: The Heat Release rate under Different Loads (Low, High).

During the second exothermic period caused by subsequent fuel injection, after the diesel is added with methanol, Impact Factor (JCC): 8.8746

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the time for the rapid exothermic start will be delayed, mainly due to the lower cetane number of methanol, which causes the peak of the exothermic rate to gradually increase. Large, increased ignition delay puts more fuel in premixed combustion mode. However, the exothermic duration decreases as the blending ratio of methanol increases, because the high oxygen content of methanol improves the combustion process.

ENGINE PERFORMANCE ECONOMY COMPARISON In order to accurately compare the economics of the dual-fuel engine and the original diesel engine after the addition of methanol, the equivalent fuel consumption rate beq was quoted in the experiment. The equivalent fuel consumption rate is calculated from the energy of the fuel consumed to the consumption rate of pure diesel (g / KWh); 𝐻𝑑 ∗𝐺𝑑 +𝐻𝑚 ∗𝐺𝑚

𝑏𝑒𝑞 =

𝐻𝑑 ∗𝑃𝑒

*1000

Hd and Hm in the formula respectively represent the low heating value of diesel and alcohol, MJ / kg. Gd, Gc are the consumption of diesel and alcohol, kg / h. Pe is the engine power, Kw. From the comparison of equivalent fuel consumption rates, it is found that after methanol is added to the combustion, the equivalent fuel consumption rate of the engine is higher than that of diesel, and the maximum increase is 65%. From the figure 4, it can be concluded that the energy consumption rate of methanol combustion, the overall energy of the original diesel engine is relatively reduced.

Figure 4: Energy Economy Ratio under Different Loads.

Under low load, as the engine speed remains constant, as the replacement rate of methanol increases, the energyto-economic ratio also increases. The power of the engine remained unchanged during the experiment. Under low load conditions, as the methanol substitution ratio increased, as shown in the formula, the injection volume of methanol increased, and the resulting economic ratio also increased. On the other hand, the low calorific value of methanol and the high latent heat of vaporization result in a high degree of evaporation of methanol in the cylinder, so that the specific methanol cannot reach the energy required by the engine, so the amount of diesel will increase.

Under medium and high loads, there are fewer tendencies to change relative to relatively low loads. Although methanol will evaporate and contain high latent heat of vaporization, which will cause the temperature in the cylinder to

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decrease, the atomization characteristics of methanol can be ignored due to high load conditions. This relatively complements the combustion of diesel. Therefore, the amount of diesel injection will be relatively reduced. It makes the energy economy ratio relatively stable.

EXPERIMENTAL RESULTS AND DISCUSSIONS HC Emission Characteristics The high vaporization latent heat and low cetane number of methanol and diesel caused the temperature in the cylinder to decrease, and the ignitability of the combustion became worse, and even partial quenching occurred. In addition, the volatility of methanol makes the lean flameout area of the outer edge of the fuel injection larger. The combined effect of the two causes an increase in HC emissions. The place where there is a significant phenomenon is mainly in the area of low load, and the effects of excessive leanness and quenching are relatively large, which promotes HC emissions to be more obvious.

Therefore, the main reason for the increase in HC emissions after a diesel engine is mixed with methanol and diesel is that methanol is easily evaporated after the methanol is dissolved in the diesel, and the amount of the lean mixture may increase at the periphery of the diesel fuel bundle. The incomplete fuel combustion causes the engine exhaust increased HC emissions.

Figure 5: The HC Emissions under Different Loads.

CO Emission Characteristics The engine's CO emissions initially decrease and then increase, as the load increases. Under light load, the CO emissions of diesel engines when burning different fuels decrease from high to low methanol replacement rates. When burning methanol and diesel under low load, the CO emissions are higher, mainly because the high vaporization latent heat of methanol under low load causes the engine cylinder temperature to become lower, which increases the lean flameout zone. At this time, the air-fuel ratio of the engine is compared. Large, but the oxygen advantage of methanol does not play a role. These factors are not conducive to the continued oxidation of CO, which increases CO emissions.

Under high load, the temperature in the engine cylinder is higher, the air-fuel ratio becomes smaller, and the advantages of methanol containing oxygen are demonstrated, which compensates for the lack of high vaporization latent heat of methanol, improves diesel combustion, and reduces CO emissions. However, compared with diesel engines, due to the high oxygen content of the methanol molecules, the mixture is always in a state of high oxygen-rich combustion, resulting in a reduction in CO emissions.

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Figure 6: The CO Emissions under Different Loads.

NOx Emission Characteristics Under the condition of low road, the NOx emissions has shown increase when engine constant with 100 N.m, because the energy economy is high with 100N.m during engine operation conditions, cause the diesel injection higher than methanol as reference in figure 4. The combustion in the cylinder during the start makes the methanol physical characteristics lower than medium and high loads. The NOx emissions are higher than 200N.m and 300N.m with different MSR of methanol. The NOx increases with an increase of MSR methanol.

In the medium load area, with methanol injection position, and amount of methanol burned increases, and the NOx emission generally decreases significantly see figure 7. This is because the main factors affecting NOx generation are high temperature, oxygen-enriched, and high-temperature duration. Methanol is injected into the engine intake port at medium loads. As the methanol through port cause the evaporation of the methanol, the intake air temperature decreases. This reason cause the combustion temperature gradually reduced, so that the NOx emissions are reduced.

Under the condition of large load, because of the low boiling point, low viscosity of methanol, and the incompatibility with diesel, it will appear a "micro explosion" during the combustion process. While improving the combustion, it will make the explosion pressure and temperature in the cylinder has increased, which has caused the increase of NOx emissions, but it is still smaller than that of pure diesel. Therefore, in the combined combustion process, low and medium loads are more effective in reducing NOx emissions.

Figure 7: The NOx Emissions under Different Loads. www.tjprc.org

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CONCLUSIONS Compared with the original diesel engine, the combined combustion and alcohol injection engine has a certain improvement in CO emissions, and the improvement effect under high load conditions is better than that under low load conditions; Compared with the original diesel engine, the combined combustion alcohol injection engine has a certain improvement in HC emissions. The experimental results are similar to those obtained by CO. The improvement effect under high load conditions is better than that under low load conditions; Compared with the original diesel engine, the combined combustion and alcohol injection engine has a certain improvement in NOx emissions, but the effect on NOx emissions during low load periods is increasing with the increase of the methanol substitution ratio because the diesel economy is relatively high. The experimental results can be found that the improvement effect of medium load conditions is better than high and low load conditions.

ACKNOWLEDGMENT This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (NRF-2019R1A2C1010557).

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