Influence of higher alcohols on the emissions of diesel engine operated with rape seed oil Dr. Ákos Bereczky, Tamás Laza 1 Department of Energy Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, 1111 Budapest, Mőegyetem rkp. 3. Abstract In the article we would like to introduce our research areas, which are running at the Department of Energy Engineering in the field of regenerative diesel fuels. We introduce the measuring system, which is based on an ASTM-CFR F5 cetane method diesel fuel-rating unit. In the course of measuring we analysed the influences of different alcohol rape seed oil mixtures (1 and 2 vol% 2- and 1-) to their burning processes. Introduction Because of the regulations of environmental protection and considerably high depending on import, Europe and our country have to take some footsteps in the field of regenerative fuels. One of the most important application areas of regenerative fuels is transport and decentralised energy producing, which would be more significant in the future. The fuels of internal combustion engines can be interchangeable with regenerative fuels. We investigated 6 alcohol rape seed oil mixture samples (2 samples 1- rape seed oil mixtures; 2 samples 2- rape seed oil mixtures) and the natural rape seed oil. In the article we introduce our measuring system and the results of measured emissions at the adjustment for diesel oil. Basics Overall CFR-F5 rating unit description The model CFR-F5 Cetane Method Diesel Fuel Rating Unit is a packaged version of the single cylinder, four-stroke cycle CFR Engine designed for compression-ignition testing of diesel fuel samples. The complete unit is known as the ASTM-CFR Engine and is marked by American Society for Testing and Materials and the Coordinating Fuel Research Committee [1]. A unique cylinder/cylinder head assembly with variable compression ratio and an indirect injection system assembles on the basic CFR-48D crankcase, which is mounted on a bedplate. The engine flywheel is belt connected to electronic synchronous-reluctance type motor acts to start the engine, and maintain constant engine speed [1][3]. Build of the test method engine The cylinder head incorporates a cylinder precombustion chamber (Fig. 1.) that is connected to the main combustion chamber by a turbulence passage. The injector nozzle sprays fuel into this chamber from one end while a variable compression plug controlled by a handwheel mechanism blocks the opposite end. This plug can be moved in and out of the pre-combustion chamber to cause changes in compression ratio with the engine operating. To the cetane measuring sample fuels and reference fuels are introduced to any of three fuel tanks critically mounted above the inlet port of an injection pump trough a selector-valve. The selected fuel is delivered from injection pump to the pre-combustion chamber of the engine trough an injector nozzle assembly. An adjustable timing device, integral with the injection pump, permits controlled variation of the time of injection. Detection of the time of injection and the start of combustion are sensed by electromagnetic pickups while two reference pickups sense the crankshaft position at prescribed points in the combustion cycle. Signals from these pickups are input to a Cetane Meter which digitally displays injection time (advance) and ignition delay in crank angle degrees. Engine inlet air temperature is established using an electric heater controlled by temperature control instrumentation. Electrical heater mounted under the engine crankcase and in the cylinder head jacket cooling system, maintains crankcase lubrication oil and cooling water temperature both when the unit is operating and when it is shut down [1]. The cetane number and the emissions of the mixtures during the cetane number measuring is published in [5]. The indicating, high speed data acquisition and emission measuring system We could investigate 3 channels in our measurement. The electric signal of the magnetostrictive pickup piezo crystal (Fig. 2.) and 1 Corresponding author: laza@energia.bme.hu European Combustion Meeting 29
the injector pintle transducer get to the SSH (Simultan Sample and Holding) A/D card. using chemiluminescent principle), CO/CO 2 (by IR principled system), THC (by H-FID principled system) and smoke (by AVL-415). The emissions were measured by Horiba Mexa-812 F. The analysed sample or the calibration gases go through the electromagnetic valves and then pass to the sample-preparating unit. Fig. 1. CFR F-5 Diesel combustion chamber assembly Fig. 2. The installed piezo crystal in the precombustion chamber For the interest of accuracy of the measurement is started by the encoder on crank axis (124 signal/round). Our results are saved in ASCII code, in simple format of numbers and letters (txt file). It is easily processable by a simple spreadsheet program. The indicating system can be seen in the Fig. 3. During the investigations wide measuring ranged, up-to-dated, good qualified emission measuring system was used. The measured emission parameters were NO/NO 2 /NO x (by system 2-1- Diesel oil Rape seed oil* Density [g/cm 3 ],785,898 82-845,92 Molar mass [g/mol] 6,1 74,1 Melting point [ C] -88,5-89,3 Boiling point [ C] 82,4 117,7 Flare up point [ C] 11,7 29 24-3 -18 282-338 >55 881-5 +5 >35 LHV [MJ/kg] 3 32 44 37 ~27 Self-ignition temp [ C] 456 345 254-285 ~35 Table 1: The physical parameters of the used alcohols. * The results depends on year, hybrid ect. Fig. 3. The structure of indicating system 4 Measured alcohols 2- (iso). It is the lowest secondary alcohol. It has mildly sweet smell. Field of application of 2- is like as an antifreeze component in screen cleaner liquids, cosmetic industry etc. Butanol. It is a higher alcohol with four carbon atomic nucleus. The has four isomers 1. It has typical smell; it is a clear liquid. The higher alcohols can be produced by biological degradation, with fermentation (for example ), or by indirect hidradization from CO and H 2 in synthetic way with carbon-hydrogen distillation. In the table 1., the relevant parameters of higher alcohols, rape seed oil and diesel oil are summarized. Measuring During the Cetane number rating the fuel flow rate (13 millilitres per minute) and the time of fuel injection (13 crank angle degrees before top dead center) are constant. The iignition delay is 13 crank angle degrees which means combustion occurs 13 degrees after injection of fuel into the combustion chamber). During the measurement of blends, the consumption remained 13 ml/minute, but due to
different viscosity, evaporation properties and cetane number there were changes in the preinjection angle and in the ignition delay. Results and discussion Figure 4 shows the pressure change characteristics of rape seed oil and 1- blends, and also diesel oil for comparison. Figure 5 shows the pressure change characteristics of rape seed oil and 2- blends, and of diesel oil, for comparison. 5 45 4 Rape seed oil 1% 1-2% 1- Diesel oil 35 3 Pressure [bar] 25 2 15 1 5 3 32 34 36 38 4 42 44 46 Crank angle [ ] Figure 4. Measured pressure in case of rape seed oil 1- mixtures and diesel oil 5 45 4 Rape seed oil 1% 2-2% 2- Diesel oil 35 3 Pressure [bar] 25 2 15 1 5 3 32 34 36 38 4 42 44 46 Crank angle [ ] Figure 5. Measured pressure in case of rape seed oil 2- mixtures and diesel oil
Figures indicate that when operated with diesel oil, the pressure drastically, steeply increases at 36. The reason of that is: due to cetane ranking unit settings, combustion starts at the upper dead point. In the other cases, due to the different properties of the fuel, combustion does not start at the upper dead point, but only afterwards (the preinjection changed during the measurement, the engine was configured for diesel oil). The pressure increment clearly indicates that in case of pure RSO the pressure starts rising earlier. That is caused by the evaporation of alcohol which cools the combustion field, increases the ignition delay, and decreases the flame propagation speed and the cetane number. It can be also observed that the peak pressure is positioned later. This can also be explained by the evaporation of alcohol. From the point of view of NO x formation, the length of the combustion curve and the proportion of kinetic and diffuse phases are important. Figure 6 shows that adding increases the amount of NO x, while adding decreases it. The reasons can be the followings (their exact determination is subject to future work): the kinetic phase is more intense in case of, the speed of heat production is higher, resulting in higher average temperature, which is beneficial for NO x formation. In case of, the kinetic phase is prolonged, and this has a reduction effect on NOx formation. It also needs to be taken into account that even though the fuel consumption was 13 ml/minute throughout the measurement, the calorific value so the introduced heat amount was the highest at rape seed oil, and decreased continuously with higher alcohol content. (See Table 1.) 4 35 3 smoke formation and burnout. In case of, higher alcohol content results higher smoke emission. This can also be explained by the temperature drop caused by the evaporation of alcohol; and by the fact that in case of the prolonged kinetic phase gives time for the generated smoke to burn out. In case of 1% 2-, part of the smoke is able to burn out in the diffuse phase after a fast kinetic phase; while in case of 2% 2- the temperature may drop so much that it s not in favour of the smoke burnout. Smoke [FSN],8,7,6,5,4,3,2,1 Rape seed oil RSO + 1% 1- RSO + 2% 1- RSO + 1% 2- RSO + 2% 2- Figure 7. Measured Smoke-emission in case of Figure 8 summarizes the insufficient carbohydrate emission of rape seed oil and rape seed oil-alcohol blends. Results show that in engines equipped with cetane ranking unit and calibrated for diesel oil, alcohol increases the THC emission, and the reactions get frozen due to the prolonged combustion. This can also be caused by the decreased combustion temperature. At 2% alcohol content there is no significant difference in the measured THC emission of the two alcohol types. 35 Nox [ppm] 25 2 15 1 5 THC [ppm] 3 25 2 15 Rape seed oil RSO + 1% 1- RSO + 2% 1- RSO + 1% 2- RSO + 2% 2-1 5 Figure 6. Measured NO x -emission in case of Rape seed oil RSO + 1% 1- RSO + 2% 1- RSO + 1% 2- RSO + 2% 2- Figure 7 depicts the smoke emission. Observations show that the emission is lower than one of the rape seed oil in all other cases (alcohol burns with nearly smoke-free flame). The process of smoke emission can be departed into two phases: Figure 8. Measured THC-emission in case of Figure 9 shows the measured CO emission. Results indicate that alcohol increases the CO
emission. The rationale behind can be, once again the decreasing combustion temperature (reactions get frozen). The observation that at higher alcohol content the amount of CO in the smoke increases also confirms this. It s also visible that the effect of the alcohol type on the amount of emitted CO is neglectable. Periodica Politechnica ser. Mech. Eng. Vol. 5, No. 1, pp. 11-29, HU ISSN 324-651 (26),14,12,1 CO [V%],8,6,4,2 Rape seed oil RSO + 1% 1- RSO + 2% 1- RSO + 1% 2- RSO + 2% 2- Figure 9. Measured CO-emission in case of Conclusions Based on the measurement, it can be concluded that rape seed oil and rape seed oil alcohol blends can also be combusted in cetane ranking unit enabled engines calibrated for diesel oil. Measurements show that alcohol decreases the smoke emission of rape seed oil, but blending rape seed oil with 2% alcohol significantly increases THC and CO emission. NO x emission increases in case of 2- and decreases in case of 1-. Acknowledgements The authors gratefully acknowledge the support of the Hungarian Scientific Research Fund Programmes (OTKA) project No. D 48678 entitled Investigation of Combustion Properties of Renewable Energy Sources. References [1] Waukesha Engine Division: CFR F-5 Cetane Method Diesel Fuel Rating Unit Operation & Maintance, First Edition Dresser Industries, Inc., Wisconsin, USA, 1995. [2] Dr. Jenı Hancsók: Korszerő motor- és sugárhajtómő üzemanyagok II., Dízelgázolajok, Veszprémi Egyetemi Kiadó, Veszprém, 1999. [3] ASTM: Annual Book of ASTM Standards, Section 5, Petroleum Products, Lubricants, and Fossil Fuels, vol.: 5.4, Philadelphia, USA, 1991. [4] Richard Stone: Internal Combustion Engines Second Edtion. Society of Automotive Engineers, Inc., Warrendale, USA, 1994. [5] Laza, Kecskés, Bereczky, Penninger: Examination of burning process of regenerative liquid fuel and alcohol mixtures in diesel engine.