Comparative Assessment of Blended and Fumigated Ethanol in an Agriculture Diesel Engine

Transcription

1 Petrotech October-3 November 21, New Delhi, India Paper ID : 2115 Comparative Assessment of Blended and Fumigated Ethanol in an Agriculture Diesel Engine Naveen Kumar* 1, Hari Singh Rathour 2 1 Professor, Mechanical Engineering Department, Delhi Technological University, New Delhi, India, 2 ME student, Mechanical Engineering Department, Delhi Technological University, New Delhi, India, naveenkumardce@gmail.com Abstract The increasing industrialization and motorization of the world has lead to a steep rise in the demand of petroleum-based fuels which are limited and highly concentrated in certain regions of the world. These fuels are also causing environmental degradation which is resulting into changed weather pattern all over the world. The renewable alternative fuels to substitute these fuels have been under extensive research since last century. Ethanol, a potential renewable alternative to petroleum derived fuels has successfully been used as substitute to gasoline world over; however, its use as diesel engine fuel is under extensive research across the globe. The present study was undertaken to evaluate and compare the effects of ethanol fumigation and ethanol diesel fuel blends on performance and emission characteristics of an agriculture diesel engine. Ethanol fumigation was achieved by using a simple carburetor whereas ethanol diesel blend was prepared by inline mixing using a static mixer. 1%, 2% and 3% ethanol was supplemented in diesel using both the techniques. The series of test were conducted using each of the above mentioned techniques to evaluate the potential suitability of both the techniques and make comparative assessment. The brake thermal efficiency showed an upward trend on ethanol substitution than diesel fuel operation. This may be mainly due to increase in the ignition delay upon ethanol substitution which results in release of rapid rate of energy reducing the heat loss from the engine as there is not enough time for heat rejection. Exhaust temperature, in general, were found lower for ethanol based fuel than diesel as large amount of latent heat absorbed by combustion chamber to evaporate ethanol and thus exhaust temperature decreases. The CO, HC emissions were found to increase with ethanol substitution as compared to base line data with diesel. The fumigation showed lower increase in these emissions as compared to blending. The NO x emissions were found lower for ethanol based fuels than the diesel fuel. The smoke opacity was found lower for both blended and fumigated ethanol as the engine was running leaner, with the combustion being now assisted by the presence of the fuel-bound oxygen of the ethanol even in locally rich zones. 1. Introduction All over the world, engine manufacturer are making stride to develop diesel engines with high thermal efficiency and specific power output and keep the engine emission within the norms which are now a days becoming more and more stringent. Biofuels derived from agricultural products (oxygenated by nature), may not only offer benefits in terms of exhaust emissions, but also reduce the world s dependence on petroleum imports. Despite having advantages such as the reductions of soot, carbon monoxide (CO) and unburned hydrocarbon (HC) emissions, ethanol still cannot be used extensively due to technology, economical and regional considerations. Ethanol has been extensively used as a SI Engine fuel, however, ethanol can also be used in CI engines [Rahimi et.al, Lapuert et. al].ethanol (C 2 H 5 OH) is a pure substance whereas diesel fuel is composed of C3 C25 hydrocarbon, and has wider transitional properties. Ethanol contains an oxygen atom and can be viewed as a partially oxidized hydrocarbon. Ethanol is completely miscible with water and may cause the blended fuel to contain water, resulting in the corrosion of the mechanical components, particularly made from aluminum, brass, and copper. Ethanol can react with most rubber and create jam in the fuel pipe. Therefore, it is advised to use fluorocarbon rubber as a replacement for natural rubber. The auto-ignition temperature of ethanol is higher than that of diesel fuel, which makes it safer for transportation and storage. On the other hand, ethanol has a much lower flash point than that of diesel fuel, a major disadvantage with respect to safety [Corkwell et. al, Rackopoulos et. al]. 1

2 Petrotech October-3 November 21, New Delhi, India Several techniques involving alcohol-diesel dual fuel operation can be adopted to substitute diesel by ethanol and the most common methods for achieving dual fuel operation are : Alcohol fumigation - the addition of alcohol to the intake air charge Alcohol-diesel fuel blend - using an emulsifier to mix the fuels to prevent separation or using inline mixing For both the techniques, lots of work has been done separately but no significant amount of work has been done for their comparative analysis. There is still uncertainty about which is superior of the above two methods. In the present work, experimental investigations were conducted to compare the two techniques namely fumigation and diesel-ethanol blends in a diesel engine. For preparing blends, Inline mixing by static mixer was used. Static mixing is a new technique which is used for inline mixing of ethanol in diesel in the running condition of the engine. For static mixing, a static mixer was used to avoid the necessity of an emulsifier and mechanical blending. 2. Experimental section Considering the wide application of a small capacity diesel engine which has great dominance in Indian agriculture sector, a similar type of engine was selected for the present study. The direct injection (DI) diesel engine used for this study has been manufactured by M/s Vimal and It was a single cylinder, naturally aspirated, four stroke, vertical, water-cooled engine. It had a provision of loading electrically since it was coupled with single phase alternator through flexible coupling. The schematic diagram of the test rig is shown in the Plate 1. The engine was started on diesel and subsequently changed to ethanol mode (fumigation or blending). Performance and emission characteristics of the engine were determined at different loading condition (%, 2% 4% 6% 8% and 1%). Readings were taken only when the engine reached steady state. Digital rpm sensor, ammeter, voltmeter, temperature indicator were used and the load was varied by changing the power output from the alternator which was connected to the load bank. Plate 1: Schematic Diagram of the Test Rig 3. Result and Discussion The present study was carried on a small capacity, agriculture diesel engine which was developed to run on 3 different modes of operations (Diesel, Ethanol-diesel blend by inline mixing and Ethanol fumigation). The main objective of the study was to evaluate the performance and emission characteristics for comparative assessment of utilization of blended and fumigated ethanol in diesel engine Brake Thermal Efficiency vs. BMEP Figure 1 shows the variation of brake thermal efficiency for both the techniques of introducing ethanol in diesel engine. The figure suggests improvement in the brake thermal efficiency with increase in ethanol substitution in both the techniques. The improvement was higher for fumigation. The peak thermal efficiency for blended ethanol is 27% at 3% blending, for fumigation it was 33.91% at 3% ethanol fumigation, and for diesel it was only 24%. This may be mainly due to increase in the ignition 2

3 Petrotech October-3 November 21, New Delhi, India delay upon ethanol substitution which results in release of rapid rate of energy reducing the heat loss from the engine as there is not enough time for heat rejection. 4 1% fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend 35 3 BTE(%) Figure 1: Brake Thermal Efficiency vs. BMEP 3.2. Brake Specific Energy Consumption vs. BMEP The brake specific energy consumption was taken as a parameter to compare the energy requirement for producing unit power in case of different test fuels. It is clear from figure 2 that for all techniques of introducing ethanol in engine, brake specific energy consumption is little higher than diesel at all loads. Since calorific value of ethanol is lower than diesel, the specific fuel consumption of the engine will increase resulting in increased specific energy consumption [Rakopoulos et. al, Ecklund et. al, Caroa et. al]. In case of fumigation at higher loads, specific energy consumption is lower than diesel and it may be because of better combustion in fumigation technique. 35 1% fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend 3 BSEC(M j / KWh) Figure 2: Brake Specific Energy Consumption vs. BMEP 3.3. Exhaust Gas Temperature vs. BMEP It is clear from figure 3 that exhaust gas temperature has increased as percentage of ethanol increases in ethanol-diesel blend. This is due to more fuel injected at higher load which leads to higher combustion temperature. As ethanol is an oxygenated fuel, more oxygen is available for combustion, which contributes to increased exhaust gas temperature during combustion. Howervr, latent heat of ethanol is much higher than diesel and for vaporization it takes more heat from combustion chamber and reduces the temperature [Rakopoulos (27) et. al, Caroa et. al]. During fumigation, exhaust temperatures is further lower than blended ethanol. In fumigation, evaporation of ethanol takes place in intake air and due to higher latent heat of evaporation of ethanol, it reduces the intake mixture temperature which in turn also reduces the exhaust temperature. The results obtained are in agreement with the findings of Chen et al. The reason may be for higher exhaust temperature of blend in comparison to fumigation is higher ignition delay of blended fuel which gives sudden combustion resulting increased temperature. 3

4 Petrotech October-3 November 21, New Delhi, India 25 1% fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend Exhaust temprature( C ) Figure 3: Exhaust Gas Temperature vs BMEP 3.4. NO x Emission vs. BMEP As engine load increases, NO x emission increases because more fuel would be injected into the cylinder and result in higher temperature. NO x formation is a temperature dependent phenomenon so NO x emission increases with load. It is clear from figure 4 that NO x emission initially at 1% blend increases in small amount and then starts decreasing. As elaborated previously in figure 3, exhaust temperature is maximum for 1% blend; and for 2% and 3% blends, it reduces. For fumigation it further reduces, due to dependency of NO x formation on temperature. The NO x emission was found maximum as1435 ppm for 1% ethanol blend and minimum 131 ppm for 3% fumigation % fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend 12 NOx(ppm) Figure 4. NO x Emission vs. BMEP 3.5. CO Emission vs. BMEP Figure 5 shows the comparison of the CO emissions for all the fuels at different engine load. As engine load increases, CO increases because at higher load the combustion occurs with rich fuel air ratio and for rich mixture CO emission increases due to poor combustion of charge. Figure 5 suggests that CO emission is maximum for neat diesel and as the percentage of ethanol in blend or fumigation is increased, CO level reduces. Ethanol has oxygen bonding which gives extra oxygen and engine running leaner than actual fuel air ratio [Rakopoulos (27) et. al, Caroa et. al]. In fumigation technique, the ignition is started by neat diesel and ethanol is burnt in combustion chamber by ignited flame which overcomes the ethanol larger ignition delay and results in complete combustion hence CO emission is minimum in fumigation. 4

5 Petrotech October-3 November 21, New Delhi, India 4 1% fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend CO(%) Figure 5: CO Emission vs BMEP 3.6. HC Emission vs. BMEP The main reason of increased HC emission is poor combustion of fuel and flame quenching. It is clear from figure 6 that HC emission is maximum in case of diesel (at higher load) and reduces as percentage of ethanol increases in ethanol-diesel blend. Up to 2% ethanol in blend, HC emission decreases but it is increases slightly for 3%. Since oxygen content in ethanol help in better combustion thus reduces the HC emission. However, as the percentage of ethanol is increased, the HC emission increases because ethanol has higher heat of vaporization (latent heat) and for vaporization, it takes heat from the combustion chamber. Thus, the temperature of combustion chamber is reduced and possibility of flame quenching increases. Due to flame quenching, end charge of combustion chamber are not burnt properly and results in increased HC emission (as in case of 3% emulsion) [Corkwell et. al, Rakopoulos (27) et. al, Ecklund et. al, Caroa et. al]. 3 1% fumigation 2% fumigation 3% fumigation diesel 1% blend 2% blend 3% blend 25 2 HC(ppm) Figure 6: HC Emission vs. BMEP 3.7. Smoke opacity vs. BMEP Figure 7 shows the smoke opacity for the neat diesel, ethanol-diesel blends and fumigation technique. It can be observed from the figure that the smoke opacity on ethanol diesel fuel blends and fumigated ethanol is significantly lower than diesel, with the reduction being higher for higher percentage of ethanol in the blend or fumigation. This may be attributed to the engine running overall leaner, with the combustion being now assisted by the presence of the fuel-bound oxygen of the ethanol even in locally rich zones. 5

6 Petrotech October-3 November 21, New Delhi, India 1% fumigation 2% fumigation 3% fumigation 1% blend 12 2% blend diesel 3% blend 1 Smoke Opacity (%) Figure 7: Smoke Opacity vs. BMEP 4. Conclusion This work was undertaken to study and compare the effects of ethanol fumigation and ethanol-diesel blends on the performance and emissions characteristics of an agriculture diesel engine. Ethanol fumigation was achieved by using a simple carburetor and ethanol diesel blend was prepared by inline mixing. From the investigation carried out, it was found that CO emission is lower for ethanol diesel blend and fumigation as compared to neat diesel. As the percentage of ethanol is increased, CO emission is further reduced. The reduction is higher in ethanol fumigation as compared to ethanol diesel blend. During fumigation technique, HC emission is higher than ethanol diesel blends. With increasing the percentage of ethanol in fumigation, HC emissions were found to increase. Up to 2% ethanol in ethanol diesel blend, HC emission decrease but for 3% ethanol it increased slightly. NO x emission is higher for blended ethanol as compared to fumigated ethanol. For lower percentage of ethanol in blend, NO x emission is little higher than diesel. NO x emission decreases as percentage of ethanol increases in fumigation and NO x emissions were minimum for fumigation. Smoke emitted by the ethanol diesel fuel blends and fumigated ethanol is significantly lower than diesel operation. But for higher percentage of fumigation, smoke opacity was found to increase. For 2% fumigated ethanol, smoke opacity was minimum. It was observed that for all ethanol-diesel fuel blends, the brake thermal efficiency was slightly higher than diesel. Exhaust temperature decreases continuously as percentage of ethanol increases in ethanol diesel blend. For fumigation, exhaust temperature is lower as compared to blend. Exhaust temperature is minimum for 3% fumigation. References CD Rakopoulos, KA Antonopoulos, DC Rakopoulos, DT Hountalas. Multi-zone modeling of combustion and emissions formation in a DI Diesel engine operating on ethanol diesel fuel blends. Energy Conversion and Management 49(28) CD Rakopoulos, KA Antonopoulos, DC Rakopoulos. Experimental heat release analysis and emissions of a HSDI diesel engine fueled with ethanol diesel fuel blends. Energy 32 (27) EE Ecklund, RL Bechtold, TJ Timbario, PW McCallum. State-of-the-art report on the use of alcohols in diesel engines. SAE Paper no ; Hadi Rahimi, Barat Ghobadian, Talal Yusaf, Gholamhasan Najafi, Mahdi Khatamifar. Diesterol: An environment-friendly IC engine fuel. Renewable Energy 34 (29) Hu Chen, Jianxin Wang, Shijin Shuai, Wenmiao Chen, Study of oxygenated biomass fuel blends on a diesel engine Fuel 87 (28) KC Corkwell, MM Jackson, DT Daly. Review of exhaust emissions of compression ignition engines operating on E Diesel fuel blends. SAE Paper no ; 23. Magın Lapuert, Octavio Armas, Jose M. Herreros. Emissions from a diesel bioethanol blend in an automotive diesel engine. Fuel, 87(28) P. Satge de Caroa, Z. Moulounguia, G. Vaitilingomb, J.Ch. Bergec. Interest of combining an additive with diesel ethanol blends for use in diesel engines. Fuel 8 (21)